Catalytic Synthesis and Characterization of Biodegradable ...

Catalytic Synthesis and Characterization of 

Biodegradable Polyesters and 

Their Radical Block Copolymers 

生分解性ポリエステルおよびそのラジカル 

ブロック共重合体の触媒的合成と特性 

A Thesis 

Presented to 

Waseda University 

July 2010 

Xiuli Zhuang 

庄秀丽

Promoter: Prof. Dr. Hiroyuki Nishide 

Referees: Prof. Dr. Kuniki Kino 

Prof. Dr. Timothy E. Long 

Assoc. Prof. Dr. Kenichi Oyaizu

Preface 

Biodegradable polyesters have attracted great attentions to be developed as the environment 

friendly materials and biomedical materials due to their excellent biodegradable and biocompatible 

properties. Two main tasks, i.e. controlled synthesis and functionalization of polyesters, have 

emerged in order to obtain the polyesters with tunable properties for biomedical applications. Great 

advances have been achieved by virtue of the recent progresses on the controlled living 

polymerizations and polyesters functionalities. However, efforts still remained on the synthesis of 

polyesters with more controllable structures and smart properties. 

In this thesis, the author has provided two strategies to synthesize biodegradable polyesters by 

using a series of newly synthesized cobalt-Schiff-base complexes. Controlled synthesis of 

polylactide (PLA)-analogues polyesters are expected based on the studies on the catalyst’s activity 

and polymerization mechanism. Moreover, functionality of PLA by incorporating with stable 

TEMPO radical-substituted polymers has also been synthesized and investigated for the biomedical 

applications in tissue engineering and bioimaing. Chapter 1 reviews on biodegradable polyesters, 

electro-active polymers and radical polymers, plus their applications in biomedical fields. Chapter 2 

describes the synthesis of a series of cobalt-Schiff-base catalysts for alternative copolymerization of 

racemic propylene oxide and carbon dioxide. Chapter 3 describes the application of 

cobalt-Schiff-base catalysts in ring-opening polymerization of lactic acid-O-NCA (LCA) monomer 

to synthesize PLA. Chapter 4 describes the synthesis and bio-valuations of TEMPO-contained 

PLA-PTAm random copolymers. Chapter 5 deals with the controlled synthesis of block copolymers 

bearing radical polymer segments by RAFT polymerization method and their biomedical 

applications. Chapter 6 deals with the synthesis of amphphilic di- and tri-block copolymers 

containing stable TEMPO radical segment and their untiliting as EPR bioimaging probes. Chapter 7 

concludes this thesis and proposes the perspective of the controlled synthesis, functionalization and 

biomedical applications of polyesters. 

III 

Xiuli Zhuang

Preface 

Catalytic Synthesis and Characterization of 

Biodegradable Polyesters and 

Their Radical Block Copolymers 

生分解性ポリエステルおよびそのラジカル 

ブロック共重合体の触媒的合成と特性 

Contents 

Chapter 1 Polymerization and Applications of Biodegradable Polyesters 

1.1 Introduction …..2 

1.2 Copolymer of Epoxide and Carbon Dioxide …..2 

1.3 Polylactide …11 

1.4 Others Biodegradable Polyesters …15 

1.5 Electroactive Polymers …18 

1.6 Radical Polymers …39 

References …49 

Chapter 2 Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes 

and Their Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide 

2.1 Introduction …60 

2.2 Synthesis and Characterization of L-Co III -dnp Complexes …60 

2.3 Copolymerization of CO2 and rac-PO …63 

2.4 Electrochemistry of Cobalt(III) Complexes …66 

2.5 Conclusions …68 

2.6 Experimental Section …68 


IV

Chapter 3 Polymerization of Lactic O-Carboxylic Anhydride using Organometallic 

Catalysts 


3.2 Polymerization of LacOCA using Co(III) Complexes with 

Schiff Base Ligands …77 

3.3 Polymerization of LacOCA using Tin(II) or Al(III) Based Complexes …79 

3.4 Characterization of the Obtained PLA …80 




Chapter 4 Synthesis of Lactide-Grafted Poly(TEMPO-acrylamide) and its 

Electrochemical Property and Biocompatibility 


4.2 Synthesis of PTAm-g-PLA …87 

4.3 Electrochemical Properties …90 

4.4 Thermal Properties …92 

4.5 Phase Separation Behavior of PTAm-g-PLA …92 

4.6 Cytotoxicity of PTAm-g-PLA …93 

4.7 Cell Adhesion and Spreading …94 




Chapter 5 Synthesis of Triblock Copolymers of TEMPO-Acrylamide and Lactate by 

RAFT Polymerization 

5.1 Inroduction ..102 

5.2 Synthesis of Triblock Copolymer ..103 

5.3 Thermal Properties ..105 

V

5.4 Cytotoxicity and Biocompatibility of Copolymers ..106 

5.5 Electrospun of Copolymers ..107 

5.6 Conclusions ..108 

5.7 Experimental Section ..108 

References ..110 

Chapter 6 Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, Lactate, 

and Ethyleneoxide 

6.1 Inroduction ..114 

6.2 Synthesis of MPEG-CPAD and MPEG-b-PLA-CPAD ..115 

6.3 Synthesis of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm ..116 

6.4 Micelles preparation and characterization ..119 

6.5 EPR study of the micelles in PBS containing ascorbic acid ..120 

6.6 Cytotoxicity assay ..121 

6.7 Conclusions ..122 

6.8 Experimental section ..123 

References ..126 

Chapter 7 Conclusion and Future Prospects 

7.1. Conclusion ..130 

7.2. Future Prospects ..132 

List of publications 

Acknowledgements 

VI

Chapter 1 

Polymerization and Applications of Biodegradable Polyesters 

1.1 Introduction 

1.2 Copolymer of Epoxide and Carbon Dioxide 

1.3 Polylactide 

1.4 Others Biodegradable Polyesters 

1.5 Electroactive Polymers 

1.6 Radical Polymers 

References

Chapter 1 


Biodegradable polyesters are one of the main types of biomaterials. Biodegradable 

polyesters like polyglycolide, polylactides, poly-ɛ-caprolactone, polycarbonates and their 

copolymers have found a wide range of applications, such as sutures, bone fracture fixation 

devices, drug controlled release carriers, tissue engineering scaffolds and green plastics as 

wrapping materials, disposal containers and fibers because of their biodegradability and 

biocompatibility. 1 In recent years, developments in tissue engineering, regenerative medicine, 

gene therapy, and controlled drug delivery have promoted the need of new properties of both 

biologically derived and synthetic biodegradable polyesters with biodegradability. 1 

Biodegradable polyesters with diverse special properties are needed for in vivo 

applications because of the diversity and complexity of in vivo environments. Although 

biologically derived biodegradable polymers possess good biocompatibility, synthetic 

polyesters have been becoming better alternatives for biomedical applications because of the 

following reasons: (1) chemical modifications for biologically derived biodegradable 

polymers are difficult; and (2) chemical modifications likely cause the denaturation of the 

bulk properties of the biologically derived biodegradable polymers. In contrary, numerous 

properties can be obtained for synthetic polyesters and further modifications are easy to be 

carried out for as-prepared synthetic biomaterials. 

1.2 Copolymer of Epoxide and Carbon Dioxide 

1.2.1 Introduction 

Because carbon dioxide (CO2) is an abundant, inexpensive, and nontoxic biorenewable 

resource, it is an attractive raw material for incorporation into important industrial processes. 

Eminent on the list of processes that are technologically viable is the use of CO2 as both a 

monomer and a solvent in the manufacturing of biodegradable copolymers, most notably, 

polycarbonates. This process is illustrated in Scheme 1.2.1 for the copolymerization of 

cyclohexene oxide and CO2 to afford poly(cyclohexene carbonate). As indicated in Scheme 

1.2.1, in general, this process is accompanied by the production of varying quantities of 

five-membered cyclic carbonates. There appears to be some confusion among members of the 

scientific community who object to referring to the use of CO2 as a raw material for 

generating useful chemicals as “green chemistry”. It has been apparent to most of us that the 

‐ 2 ‐

- 3 - 


small quantity of CO2 consumed in these processes is likely always to be a very small fraction 

of the total CO2 produced from fossil fuel combustion and other sources. Although this 

consumption would have a effect on global warming, its use is considered “green chemistry” 

in the context of providing more environmentally benign routes to producing chemicals 

otherwise made utilizing reagents detrimental to the environment. 

Scheme 1.2.1 

Both the monomeric and the polymeric products provided from the coupling of CO2 and 

epoxides have important industrial applications. Polycarbonates possess outstanding 

properties, which include strength, lightness, durability, high transparency, heat resistance, 

and good electrical insulation; in addition, they are easily processed and colored. 2 Hence, 

these materials have wide-scale uses in electronics, optical media, glazing and sheeting, the 

automotive industry, the medical and healthcare industry, and many other consumable goods. 

On the other hand, cyclic carbonates find numerous applicabilities, most importantly as high 

boiling and flash point solvents with low odor/toxicity in degreasing, paint stripping, and 

cleaning processes. 3 These monomeric compounds are also extensively employed as reactive 

intermediates. 

In 1969, Inoue and co-workers made the remarkable discovery that a mixture of ZnEt2 and 

H2O was active for catalyzing the alternating copolymerization of propyleneoxide (PO) and 

CO2, marking the advent of epoxide–CO2 coupling chemistry. 4, 5 An optimum 1:1 ratio of 

ZnEt2/H2O gave the best yields of methanol-insoluble PPC with an activity of 0.12 h -1 (mol of 

PO converted to polymer per mol Zn per h) at 80 o C and 20–50 atm CO2. On the basis of 

elemental analysis, the copolymer contained 88% carbonate linkages. Notably, a 1:1 mixture 

of ZnEt2 and MeOH did not generate an active catalytic species for polycarbonate synthesis. 

Following this initial lead, Inoue investigated the use of dihydric sources, including 

resorcinol, 6, 7 dicarboxylic acids, 8 and primary amines, 9 in mixtures with ZnEt2 for PO–CO2 

copolymerization. These systems showed TOFs of 0.17, 0.43, and 0.06 h -1 , respectively.

Chapter 1 

The next major breakthrough in the area of propylene oxide and CO2 copolymerization 

came with the uncovering of air-stable dicarboxylic acid derivatives of zinc by Soga and 

co-workers. 10 These catalysts were prepared by the reaction of zinc hydroxide or zinc oxide 

with dicarboxylic acids in toluene. Although the zinc glutarate analogue was found to be 

catalytically most active, producing significant quantities of polypropylene carbonate from 

propylene oxide and CO2, the percent of active zinc sites on this heterogeneous catalyst was 

quite low (

- 5 - 


in the presence of a quaternary organic salt or triphenylphosphine. At ambient temperature 

and a relatively high catalyst loading, reaction rates were slow, generally requiring 12-23 days 

and thereby affording rather low molecular weight polymers. Nevertheless, copolymers from 

ethylene oxide, propylene oxide, or cyclohexene oxide and carbon dioxide with very narrow 

molecular weight distributions (1.06-1.14) were isolated. Approximately a decade later, 

Kruper and Dellar investigated the use of (tpp)CrX complexes in the presence of 4-10 equiv 

of nitrogen donors, such as N-methylimidazole (N-MeIm) or (4-dimethylamino)pyridine 

(DMAP), for the coupling of a wide variety of epoxides and carbon dioxide to provide cyclic 

carbonates. 15 For example, propylene oxide readily afforded propylene carbonate at 50 bar of 

CO2 pressures with a TOF of 158 h -1 at 80 . Conversely, cyclohexene oxide and CO2 

yielded predominantly copolymer under similar reaction conditions. In more recent studies, 

Holmes and co-workers have reported the copolymerization of cyclohexene oxide and CO2 in 

the presence of a fluorinated (tpp)CrCl catalyst (Figure 1.2.2) along with a cocatalyst such as 

DMAP. 16 TOFs greater than 150 h -1 were observed for reactions performed at 110 in scCO2 

(225 bar) where the catalyst solubility is greatly enhanced over its (tpp)CrCl analogue, with 

the resulting copolymers having a high percentage of carbonate linkages (>97%) and narrow 

polydispersities (PDIs). The rapid advances currently being experienced in the 

copolymerization of cyclohexene oxide and carbon dioxide were fueled by Darensbourg’s 

development of a series of discrete zinc phenoxide derivatives as catalysts in 1995. 17 A 

typical bis(phenoxide)Zn(THF)2 complex (where THF = tetrahydrofuran) used in these 

studies is illustrated in Figure 1.2.3, where the steric bulk of the phenoxide ligands limits 

aggregate formation. 

Figure 1.2.2 Fluorinated porphyrin derivative of chromium(III) chloride. 

These catalysts were extremely effective for homopolymerizing epoxides to polyether;

Chapter 1 

hence, the CO2 content of the copolymer provided by this method was generally about 90% 

even though the reactions were carried out at high CO2 pressures. 18 The copolymerization 

processes were performed in the absence of an organic solvent at 55 bar CO2 pressure and 80 

. Bulk polymerization reactions were run over a 24 h period, providing minimum values of 

TOFs of about 10 h -1 with catalytic activity varying slightly as a function of the substituents 

on the phenoxide ligands. Although the coupling reaction of propylene oxide and CO2 

provided predominantly propylene carbonate at 80 , at 40 , the reaction selectivity 

switched mainly to copolymer formation. This temperature dependence of product selectivity 

is a general phenomenon observed for most catalyst systems investigated. Terpolymers with 

up to 20% propylene oxide content were produced from reaction mixtures of propylene 

oxide/cyclohexene oxide and carbon dioxide. More moisture-tolerant dimeric zinc derivatives 

(Figure 1.2.4) containing the less sterically encumbering 2,6-difluorophenoxide were also 

shown to be quite active for the copolymerization process. 19 

Figure 1.2.3 Monomeric zinc-bis(phenoxide) complex for the copolymerization of cyclohexene 

oxide and CO2. The phenoxide ligand is 2,6-diisopropylphenoxide. 

Figure 1.2.4 Dimeric zinc-bis(phenoxide) complex for the copolymerization of cyclohexene 

oxide and CO2. The phenoxide ligand is 2,6-difluorophenoxide. 

‐ 6 ‐

1.2.2 Aluminum Catalysts 

- 7 - 


In 1978, Inoue developed the first single-site catalysts for epoxide–CO2 copolymerization 

based on a tetraphenylporphyrin (tpp) ligand framework, 1a–d. 20 [(tpp)AlCl] (1a) and 

[(tpp)AlOMe] (1b) (Figure 1.2.5) were found to be living initiators for the 

homopolymerization of PO and lactones, including lactide, b-butyrolactone, and 

ɛ-caprolactone, as well as for the copolymerization of CO2 and epoxides and of PO and 

phthalic anhydrides. 21-23 1a and 1b reacted with PO to form poly(propylene oxide) (PPO) in a 

living polymerization with PDIs of 1.07–1.15. The chloride initiator ring-opened the least 

hindered C-O bond and generated a regioregular PPO. In addition, 1b copolymerized PO and 

CO2 at 20 o C and 8 atm CO2, giving PPC (Mn=3900 gmol -1 ; Mw/Mn=1.15) with 40% 

carbonate linkages over the course of 19 days. 23 Although molecular weights were low and 

reaction times were long, this reaction marked the first example of monodisperse 

polycarbonates having a narrow PDI. The low molecular weights of polymers produced 

by{(tpp)Al} catalysts suggest chain transfer, which supports Inoue’s proposal of an 

“immortal” type polymerization. 20 An immortal polymerization allows for multiple chains to 

propagate from one metal center, whereas a living polymerization grows only one chain per 

metal center. Protic sources facilitate chain swapping such that there are more polymer chains 

than active catalytic sites. Free chains are dormant, but continue to grow polymer when 

exchanged onto the active site. If the chain swapping is more rapid than propagation, polymer 

chains with narrow PDIs are produced. 

Figure 1.2.5 Aluminum and manganese porphyrins for the homopolymerization of epoxides and 

copolymerization of epoxides and CO2 (R=alkyl, oligomer of PPO). 

Recently, a salicylaldimine (salen)–aluminum complex, 2a, was found to be highly active

Chapter 1 

for the cyclization of EO and CO2 to ethylene carbonate (Figure 1.2.6). 24, 25 Lewis bases 

orquaternary ammonium salts, including pyridine, MeIm, and nBu4NX (X=Cl, Br, I), were 

utilized as cocatalysts, enhancing rates by up to a factor of five. At 110 o C and in scCO2 (ca. 

150 atm CO2), a 1:1 mixture of 2a/nBu4NBr catalyzed the conversion of EO to EC with a 

TOF of 2220 h -1 . Salen-chromium (2b) and -cobalt (2c) analogs also promoted cyclic-species 

formation showing rates of 2140 and 1320 h -1 , respectively. Darensbourg and co-workers 

have reported AlCl4 - -based complexes that exhibit TOFs up to 50 h -1 for the synthesis of 

propylene carbonate from PO and CO2. 26 

Figure 1.2.6 Salen catalyst systems (cocatalyst = tetrabutylammonium halide, pyridine, or MeIm) 

for the synthesis of ethylene carbonate. 

Aluminum complexes are indeed active for the copolymerization of epoxides and CO2; 

however, they are plagued by low activities and yield polycarbonates with high percentages of 

ether linkages. It appears that without additives, current aluminum catalysts do not cleanly 

generate alternating copolymer. Nevertheless, the “immortal” polymerization of [(tpp)AlX] 

compounds shows promise for the synthesis of a wealth of unique copolymers with varying 

levels of carbonate linkages provided the activities can be improved. 

1.2.3 Chromium Salen Catalysts 

Kruper and Dellar discovered that [(tpp)CrX] (Figure 1.2.7) in mixtures with 4–10 

equivalents of a Lewis-basic amine cocatalyst [such as MeIm or (4-dimethylamino)pyridine 

(DMAP)] are moderately active for the cyclization of epoxides and CO2. 27 A wide range of 

epoxides, including PO, trans-2-butene oxide, epichlorohydrin, CHO, and cyclopentene oxide 

(CPO), were rapidly converted to the corresponding cyclic carbonates. For instance, one of 

the (tpp)CrX and DMAP catalyzed CHC formation at 50 atm CO2 and 95 o C, exhibiting 

activities of 103 h -1 . In this case, PCHC was isolated as the major product. Following 

‐ 8 ‐

- 9 - 


thermolysis, a 95:5 ratio of trans and cis CHC was observed, suggesting the possibility of dual 

mechanisms. 

Figure 1.2.7 Chromium–porphyrin complexes for the coupling of epoxides and CO2. 

Jacobsen and co-workers found [(salen)CrCl] complexes to be highly active in the 

asymmetric ring opening of epoxides. 28 This elegant work has since led to many crucial 

discoveries in the coupling of epoxides with CO2; in fact the first report of 

(salen)chromiummediated epoxide–CO2 polymerization appeared in a 2000 patent by 

Jacobsen and co-workers. 29 Nguyen and Paddock reported highly active [(salen)CrCl]/DMAP 

based systems (Figure 1.2.8), for the cyclo-addition of CO2 and a variety of terminal aliphatic 

epoxides, including PO, epichlorohydrin, butadiene monoepoxide, and styrene oxide (SO). 30 

Figure 1.2.8 Salen–chromium and salen–cobalt complexes for the coupling of epoxides and CO2. 

Darensbourg and co-workers began efforts to uncover well-defined transition metal 

coordination complexes as catalysts for the coupling of CO2 and epoxides to selectively

Chapter 1 

provide polycarbonates. (Figure 1.2.9). 28 They use (Salen)M III X as a catalyst for the 

copolymerization of CO2 and cyclohexene oxide in the presence of N-MeIm. At 80 and 

58.5 bar CO2 pressure, (Salen)M III X alone copolymerized cyclohexene oxide and carbon 

dioxide to poly(cyclohexylenecarbonate), void of polyether linkages, with a TOF of 10.4 h-1. 

1.2.4 Lanthanide-Based Catalysts 

Figure 1.2.9. (Salen)M III X catalyst for epoxides ring opening. 

Yttrium, aluminum, rare-earth metals, and combinations of multiple metal reagents have 

shown activity for the copolymerization of epoxides and CO2. For example, PO–CO2 

copolymerization was effected by a rare-earth metal system comprised of yttrium 

tris[bis(2-ethylhexyl)phosphate], AliBu3, and glycerol. The PPC produced contained only 

10–30% carbonate linkages, although molecular weights of up to 476000 gmol -1 were 

achieved. 31 This system also exhibited activity for the alternating copolymerization of CO2 

with epichlorohydrin 32 and glycidyl ether monomers. 33 Other rare-earth metal systems 

consisted of yttrium carboxylates [Y(CO2CF3)3 or Y(CO2RC6H4)3 where R is H, OH, Me, or 

NO2], ZnEt2, and glycerine. 34-36 The alternating copolymerization of CO2 and PO yielded PPC 

with up to 98.5% carbonate linkages, turnover frequencies up to 2.5 h -1 , and molecular 

weights reaching 100 000 gmol -1 . CHO–CO2 copolymerization produced PCHC with 100% 

carbonate linkages, molecular weights of 19000–330000 gmol -1 , and Mw/Mn’s of 3.5–12.5. It 

must be noted that control experiments indicated that ZnEt2, but not Y(CO2CF3)3, was 

essential for polymerization. Finally, ternary catalysts composed of Nd(CO2CCl3)3, ZnEt2, 

and glycerol were also reported to copolymerize PO and CO2. 37 

‐ 10 ‐

1.3 Polylactide 

1.3.1 Introduction 

- 11 - 


Polylactide (PLA) is biodegradable, thermoplastic, aliphatic polyester derived from lactic 

acid, which is made from renewable resources, such as corn starch or sugarcanes. 38 PLA has 

similar mechanical properties to polyethylene terephthalate, but has a significantly lower 

maximum continuous use temperature. Poly(L-lactide) (PLLA) is the most important PLA. It 

is a semicrystalline polymer and has a crystallinity around 37%, a glass transition temperature 

~67 and a melting temperature ~180 . PLA can be processed like all other thermoplastic 

polymers with extrusion, injection molding, blow molding, or fiber spinning processes into 

various products. The products can be recycled after use either by remelting and processing 

the material a second time or they can be hydrolyzed into lactic acid, the basic chemical. The 

last possibility is to compost the polylactide to introduce it into the natural life cycle of all 

biomass, where it degrades into CO2 and water. PLA can be recycled following the traditional 

ways, composted like all other organic matter, and it will do no harm if burned in an 

incineration plant or introduced into a classical waste management system. PLA becomes of 

commercial interest in recent years, in light of its biodegradability. 

1.3.2 Synthesis of PLA 

Figure 1.3.1 synthesis of PLA by the polycondensation of lactic acid. 

PLA can be prepared by direct polycondensation of lactic acid (Figure 1.3.1), which is 

produced from the bacterial fermentation of corn starch or cane sugar. 39 However, it is usually 

difficult to obtain high molecular weight polymer by polycondensation. Because each 

polymerization reaction generates one molecule of water, the presence of which degrades the 

forming polymer chain and results in the generation of low molecular weight PLA. So water 

has to be removed during the polycondensation in order to generate PLA with high molecular 

weight. Yamaguchi et al. has reported the synthesis of high molecular weight PLA by using 

molecular sieve to dry water during direct polycondensation. 40 However long reaction times 

and high temperatures are required in lactic acid polycondensation. 41

Chapter 1 

Polylactide and poly(lactic acid) are same chemical product. PLA is used as abbreviation 

for both poly(lactic acid) and polylactide. Lactide is the cyclic dimer of lactic acid, which is 

produced by means of a combined process of oligomerization and cyclization of lactic acid. 

Ring-opening polymerization (ROP) of lactide (Figure 1.3.2) is a preferred route to prepare 

PLA because of the higher controllability of the polymerization. 42 Indeed, high 

molecular-weight PLA can be obtained by ROP of lactide. 43 Because one lactide molecule 

has the two chiral carbon atoms, three stereoisomers of lactide can be generated (L, L-, D, D-, 

and meso-lactide) (Figure 1.3.3). The 1:1 mixture of L, L-, and D, D-lactide is 

racemic-lactide (rac-LA). Since lactide monomer is chiral, the control of PLA 

stereochemistry is easily achieved by the polymerization of L, L-, D, D- and meso-lactide 

stereochemical forms. Modulation of the polymer stereochemistry leads to PLA with 

dramatically different properties. For example, PLLA is a semicrystalline polymer (Tg at 67 

, melting transition at 180 ), while poly(rac-lactide) is an amorphous material (Tg at 58 

). The degree of crystallinity of PLA decreases dramatically as the L,L- content decreases 

over narrow compositional range from 100 to 92%. The degree of crystallinity of PLA with 

85% L,L- content was amorphous. 44 

Figure 1.3.2 Synthesis of PLA by the ROP of lactide. 

O 

O 

O 

O 

L,L-lactide 

O 

O 

O 

‐ 12 ‐ 

O 

O 

O 

O 

O 

D,D-lactide meso-lactide 

Figure 1.3.3 Three stereoisomers of lactide. 

The driving force for the ROP of lactide is the ring strain of the monomer. As a 

polymerizable six-membered ring, the ring strain of lactide is modest. Therefore, high

- 13 - 


termperatures are usually required for the ROP of lactides. 45 Consequently, a polymerizable 

activated monomer of the lactide equivalent is highly desirable. 

5-Methyl-1,3-dioxolane-2,4-dione is a five-membered O-carboxyanhydride (LacOCA) 

derived from the lactic acid. It can be readily obtained by the reaction of lactate salt with 

diphosgene (Figure 1.3.4). 46 Bourissou et al. reported that the ROP of LacOCA proceeded in 

the presence of an organocatalyst, dimethylaminopyridine (DMAP) 47, 48 or lipase. 49 The ROP 

of LacOCA catalyzed by DMAP is well controllable. PLA with high molecular weight and 

narrow polydispersity index has been obtained under mild polymerization conditions. This 

indicates that the ROP of LacOCA is an alternative route to prepare PLA. 47 

Figure 1.3.4 Synthesis of LacOCA. 

1.3.3 Ring-opening polymerization of lactide and LacOCA 

Organometallic complexes are usually used as the catalyst of the ROP of lactide. For 

instance, stannous octoate, 45 alkylaluminum, aluminum alkoxides, 50-55 zinc alkyl, 56 calcium 

alkoxides, 57, 58 and strontium alkoxide 59 have been used as the catalyst/initiator for the ROP 

of lactides. Polymerization of lactide is usually assumed to proceed through a 

coordination-insertion mechanism. At first a complex between initiator and monomer is 

formed, followed by a rearrangement of the covalent bonds. The monomer is included in 

between the metal-oxygen bond of the initiator, cleaving the acyloxygen bond of the cyclic 

monomer, so that the metal is incorporated with an alkoxide bond into the growing chain 

(Figure 1.3.5). Among these complexes, stannous octoate [Sn(Oct)2] is most frequently used 

catalyst for the ROP of lactide because of its low toxicity and high thermal stability. The ROP 

reaction is carried out at ~120 ), because at the condition, transesterification reactions are 

virtually nonexistent, and retention of stereochemical purity during the conversion of 

monomer to polymer is exceptional (99% ). 60 Even though the mechanism of ROP of lactide 

with Sn(Oct)2 is not yet clearly established, it is widely accepted that the ring-opening 

polymerization is actually initiated from compounds containing hydroxyl groups such as

Chapter 1 

water and alcohols, which are either present in the lactide feed or can be added by demand. 

Although high molecular weight PLA can be obtained through the ROP of lactide, side 

reactions, such as intermolecular and intramolecular transesterification reactions exist and 

perturb the chain propagation, broaden the molecular weight distribution, and yield cyclic 

oligomers. Therefore, catalyst that has lower side reactions is desired. Indeed, aluminum 

based single-site complexes have shown excellent controllability for the solution 

52, 54, 61-67 

polymerization of lactide. 

Figure 1.3.5 ROP of lactide through a coordination-insertion mechanism. 

DMAP 47 and lipase 49 can be used as the catalysts for the ROP of LacOCA. The 

ring-opening reactions of LacOCA with alcohols are predicted to occur through the activation 

of the alcohol and with both the traditional stepwise mechanisms, which involve tetrahedral 

intermediates (Figure 1.3.6). Furthermore, DMAP is proposed to act as a bifunctional catalyst 

through its basic nitrogen center and an acidic ortho-hydrogen atom. 48 The ROP of LacOCA 

using DMAP as catalyst gives access to PLA of controlled molecular weights and low 

polydispersities under mild conditions (typically within a few minutes at room temperature 

with LacOCA). 47 Both lipase PS and Novozym 435 promote the ring-opening 

polymerization of LacOCA (Figure 1.3.7). Accordingly, PLA of relatively high molecular 

weights and low polydispersities are obtained in high yields within a few hours at 80 . 

Slight preference for L-lacOCA over D-lacOCA is observed, and with Novozym 435, the 

molecular weight of the obtained PLA can be controlled by varying the lipase loading. 

‐ 14 ‐

1.3.4 Application of PLA 

Figure 1.3.6 DMAP-catalyzed ROP of LacOCA. 

Figure 1.3.7 Liphase-catalyzed ROP of LacOCA. 

- 15 - 


Because PLA is biocompatible and bioresorbable, it can be used in a number of 

biomedical applications, such as suture, implants, fracture fixation, drug delivery, and tissue 

engineering. 68-70 Because PLA is biodegradable, it can also be employed in the preparation of 

bioplastic, useful for producing loose-fill packaging, compost bags, food packaging, 

disposable tableware, upholstery, disposable garments, awnings, feminine hygiene products, 

and nappies. As the depletion of petrochemical feedstocks draws near, PLA becomes an 

environmentally sustainable alternative to petrochemically-derived products because of the 

biodegradable characteristics and the renewable nature of its feedstock. 71 

1.4 Others Biodegradable Polyesters 

1.4.1 Poly(ε-caprolactone) 

Poly(ε-caprolactone) (PCL) is an aliphatic polyester composed of hexanoate repeat units. 

It has a low melting point of around 60 and a glass transition temperature of about -60 . 

The physical, thermal and mechanical properties of PCL depend on its molecular weight and 

its degree of crystallinity. It is a semicrystalline polymer with a degree of crystallinity which 

can reach 69%. PCL shows the rare property of being miscible with many other polymers, 

such as poly(vinyl chloride), poly(styrene–acrylonitrile), poly(acrylonitrile butadiene styrene), 

poly(bisphenol-A), polycarbonates, nitrocellulose and cellulose butyrate. It is also 

mechanically compatible with many other polymers, such as polyethylene, polypropylene, 

natural rubber, poly(vinyl acetate), and poly(ethylene–propylene) rubber. 72 PCL biodegrades 

within several months to several years, depending on the molecular weight, the degree of

Chapter 1 

crystallinity, and the conditions of degradation. 73-75 PCL is degraded by hydrolysis of its ester 

linkages in physiological conditions. Therefore PCL has been used in many fields such as 

scaffolds in tissue engineering, in long-term drug delivery systems, in microelectronics, as 

adhesives, and in packaging. 76-81 PCL has been approved by Food and Drug Administration 

(FDA) to be used in the human body as a drug delivery device, suture, or adhesion barrier. 

PCL can be synthesized by the polycondensation of hydroxycarboxylic acids. 82 But high 

molecular weight PCL is usually made by the ROP of ε-caprolactone (ε-CL) that is 

industrially produced from the oxidation of cyclohexanone by peracetic acid (Figure 1.4.1). 

Three different catalytic systems, including metal-based, enzymatic, and organic systems, can 

59, 83-85 

be used to catalyze the polymerization of ε-CL. 

1.4.2 Polyglycolide 

Figure 1.4.1 Preparation of poly(ε-caprolactone) 

Polyglycolide or polyglycolic acid (PGA) is a biodegradable, thermoplastic polymer and 

the simplest linear, aliphatic polyester. PGA has a glass transition temperature between 35-40 

and its melting point is reported to be in the range of 225-230 . The degree of 

crystallinity of PGA is around 45-55%. 86 High molecular weight PGA is insoluble in almost 

all common organic solvents. However PGA is soluble in highly fluorinated solvents like 

hexafluoroisopropanol and hexafluoroacetone sesquihydrate. PGA was used to develop the 

first synthetic absorbable suture with the tradename of Dexon by the Davis & Geck 

subsidiary of the American Cyanamid Corporation in 1962. 87 It is naturally degraded in the 

body by hydrolysis and is absorbed as water-soluble monomers, completed between 60 and 

90 days. PGA and its copolymers with lactic acid, ε-caprolactone, or trimethylene carbonate, 

are widely used as a material for the synthesis of absorbable sutures and are being evaluated 

in the biomedical field, such as implantable medical devices, tissue engineering or controlled 

drug delivery. 88 PGA can be prepared starting from glycolic acid by polycondensation or the 

ROP of glycolide. But the polycondensation yields a low molecular weight product. The most 

‐ 16 ‐

- 17 - 


common synthesis route to produce a high molecular weight PGA is ROP of "glycolide", the 

cyclic diester of glycolic acid (Figure 1.4.2). Glycolide can be prepared by heating low MW 

PGA under reduced pressure, collecting the diester by means of distillation. ROP of glycolide 

can be catalyzed using different catalysts, including antimony, zinc, tin, aluminum, calcium, 

and lanthanide compounds. Stannous octoate is the most commonly used catalyst, since it is 

high efficient and approved by the FDA as a food stabilizer. 89 

Figure 1.4.2 Ring-opening polymerization of glycolide to produce polyglycolide. 

1.4.3 Poly(lactide-co-glycolide) 

. Using the PGA and PLA properties as a starting point, it is possible to copolymerize the 

two monomers to extend the range of homopolymer properties. Copolymers of glycolide with 

lactide (PLGA) have been developed for medical device, tissue engineering and drug delivery 

applications. 90-92 It is important to note that there is not a linear relationship between the 

copolymer composition and the mechanical and degradation properties of the materials. For 

example, a copolymer of 50% glycolide and 50% D,L-lactide degrades faster than either 

homopolymer. 93 PLGA with 25-70% glycolide are amorphous due to the disruption of the 

regularity of the polymer chain by the other monomer. PLGA of 90% glycolide and 10% 

lactide was developed by Ethicon as an absorbable suture material under the trade name 

Vicryl. It absorbs within 3-4 months but has a slightly longer strength-retention time. 93 PLGA 

is produced by the copolymerization of lactide and glycolide under ring-opening 

polymerization catalyst (Figure 1.4.3). 

Figure 1.4.3 Synthesis of poly(lactide-co-glycolide).

Chapter 1 

1.4.4 Polyhydroxybutyrate 

Polyhydroxybutyrate (PHB) is a biodegradable thermoplastic polymer produced by 

micro-organisms. 94 The polymer is primarily a product of carbon assimilation and is 

employed by micro-organisms as a form of energy storage molecule to be metabolized when 

other common energy sources are not available. The poly(3-hydroxybutyrate) (P3HB) (Figure 

1.4.4) form of PHB is probably the most common type of polyhydroxyalkanoate. PHB has a 

melting point of 175 and glass transition temperature of 15 . The tensile strength is 40 

MPa, which is close to that of polypropylene. 95 PHB is water insoluble and relatively 

resistant to hydrolytic degradation, which differentiates PHB from most other currently 

available biodegradable plastics, such as PLA, PCL, and PGA, which are either water soluble 

or moisture sensitive. However ICI had developed the material to pilot plant stage in the 

1980s, but interest faded when it became clear that the cost of material was too high. 

1.5 Electroactive Polymers 

Figure 1.4.4 Chemical structure of poly(3-hydroxybutyrate). 

Recent advances in electroactive polymers have aroused more and more interests in their 

application as biomedical materials. These researches based on the theory that a multitude of 

cell functions, such as attachment, proliferation, migration, and differentiation could be 

modulated through electrical stimulation 96 , which have been demonstrated for a long time. 

Presently the electroactive polymers used are all conducting polymers, which have electrical 

and optical properties similar to inorganic semiconductors or metals. 97 Moreover, they also 

exhibit the unique properties as conventional polymers, including ease of synthesis and 

processing. These attractive properties have given these polymers a wide range of 

applications in the biological field, such as the matrix for tissue engineering or drug carrier 

for controlled release. 98, 99 Although there have been many conducting polymers discovered 

and characterized at the past 30 years, a small number of them have been developed for the 

‐ 18 ‐

- 19 - 


biomedical applications, including poly(pyrrole)s, polyanilines and polythiophenes. Thus, 

developing new type of electroactive polymers for biomedical application is still necessary 

both in theory and in practice. 

1.5.1 Introduction of Electroactive Polymers 

1.5.1.1 Poly(acetylene) 

Poly(acetylene) is the simplest conjugated polymer and historically the discovery of the 

metallike conductivity of poly(acetylene) doping triggered the explosion of the research to 

electroactive polymers (Figure 1.5.1A). Poly(acetylene) can exist in two isomeric forms: 

cis-transoid and trans-transoid, commonly called cis- and trans-poly(acetylene), respectively. 

The latter form being thermodynamically stable since cis to trans isomerization is irreversible. 

Polyacetylene is one of the most promising materials for applications in optoelectronics. 100 

The conductivity of this polymer after doping is equal to that of copper, and some forms of 

polyacetylene have record values of non-linear third-order optical susceptibility. Because it 

contains high concentrations of unsaturated sites which can be easily attacked by ozone and 

UV light, polyacetylene is very unstable to the environment. 101 The low stability of 

polyacetylene has been the major obstacle in the way of practical applications of this polymer. 

An effective approach to obtain stable poly(acetylene) without weakening its conductivity 

was blend poly(acetylene) with processable plastics. 

Figure 1.5.1 Structure of poly(acetylene) (A), polypyrrole (B) and poly(thiophene) (C).

Chapter 1 

1.5.1.2 Polypyrrole (PPy) 

Among conducting polymers, polypyrrole is especially promising for commercial 

applications because of its good environmental stability, facile synthesis, and higher 

conductivity than many other conducting polymers (Figure 1.5.1B). PPy can be easily 

prepared by either a chemical or electrochemical polymerization of pyrrole. However, the 

synthetically conductive PPy is insoluble and infusible. To improve the processibility, many 

approaches have been developed. For example, several kinds of soluble PPy have been 

synthesized, such as poly (3-alkylpyrrole) with an alkyl group equal to or greater than a butyl 

group. 102 Poly (3-alkylpyrrole) is easily soluble in common solvents or soluble in water when 

the substituents bear hydrophilic groups, such as –SOH3. However, poly (N-substituted 

pyrroles) has much lower conductivity due to greatly suppressed conjugation along the 

103, 104 

polymer chains by the substituents on nitrogen. 

1.5.1.3 Poly(thiophene) (PT) 

Like polypyrrole, poly(thiophene) is also an important poly(heterocyc1es) (Figure 1.5.1C). 

From a theoretical viewpoint, PT has been often considered as a model for the study of 

charge transport in conductive polymers with a nondegenerate ground state, while on the 

other hand, the high environmental stability of both its doped and undoped states has led to 

its wide applications. 105 PT is essentially prepared by means of two main routes: the chemical 

and the electrochemical syntheses. Although it is likely that chemical syntheses are the most 

adequate methods to prepare oligomers with defined structure, until now, the most 

extensively conjugated and most conductive PT have been prepared by electrochemical 

polymerization. Unsubstituted PT is conductive after doping, but is intractable and soluble 

only in solutions like mixtures of arsenic trifluoride and arsenic pentafluoride. 106 However, 

examples of organic-soluble PT were reported when it was substituted. Nickel-catalyzed 

Grignard cross-coupling was used to synthesize two soluble PTs, poly(3-butylthiophene) and 

poly(3-methylthiophene-co-3'-octylthiophene), which could be cast into films and doped with 

iodine to reach conductivities of 4 to 6 S/cm. 107 Hotta et al. synthesized 

poly(3-butylthiophene) and poly(3-hexylthiophene) electrochemically 108 , and characterized 

the polymers in solution and cast into films. 109 The soluble PATs demonstrated both 

thermochromism and solvatochromism in chloroform and 2,5-dimethyltetrahydrofuran. 110 

‐ 20 ‐

1.5.1.4 Polyaniline (PANi) 

- 21 - 


Polyaniline is an intrinsically conducting polymer consisting of phenyldiamine and 

quinodiimine units, the general formula can be shown as Figure 1.5.2. Polyaniline is widely 

studied due to its ease of synthesis, environmental stability, and simple doping/dedoping 

chemistry. The synthesis approaches of PANi were various but the most common method was 

based on mixing aqueous solutions of aniline hydrochloride and ammonium peroxydisulfate 

at room temperature, followed by the separation of PANi hydrochloride precipitate by 

filtration and drying. 111 Electrochemical synthesis is also a common alternative for preparing 

PANi, particularly because this synthetic procedure is relatively straightforward. It was found 

that the structure of PANi and its physical and chemical properties strongly dependent on 

their preparation and doping methods. Therefore, to explore new synthesis and doping 

method is necessary to expand the application extent of PANi. In recent years, a number of 

novel polymerization methods were developed, such as emulsion polymerization, 

microemulsion polymerization and template polymerization. 112 

Figure 1.5.2 Structure of polyaniline. 

1.5.2 Electroactive Polymers for Biomedical Applications 

Electroactive polymers have been widely applied in the microelectronics industry, 

including battery technology, light emitting, diodes photovoltaic devices, and electrochromic 

displays. 113 Based on the concept that cellular activities can be influenced by electricity, 

electroactive polymers were found to be unique in modulating of the cell adhesion, migration, 

DNA synthesis, and protein secretion. 114-118 Most of the researches focused on the tissues or 

cells which respond to electrical impulses, including nerve, muscle, bone, and cardiac cells. 

Besides the ability of transferring charge from a biochemical reaction, most of electroactive 

polymers such as PPy and PT are biocompatible, which is an important property of 

biomaterials. These unique characteristics made them useful in many biomedical applications, 

such as tissue engineering materials, biosensors, drug delivery devices and bioactuators.

Chapter 1 

1.5.2.1 Tissue engineering applications 

The electroactive polymer, being electrical stimulus responsive, has become the focus of 

research after the demonstration that electrical signals can regulate cell attachment, 

proliferation and differentiation. 96 Lots of efforts had been made to use the electroactive 

polymers to regulate the proliferation and differentiation of cells. And they had been widely 

used in biological systems due to the key advantage of facile control of the intensity and 

duration of stimulation. 

PPy was one of the first electroactive polymers studied for its effect on cells. And it has 

been demonstrated to support adhesion and growth of a number of different cell types. The 

investigation of biocompatibility of PPy was just the first step. Its most attractive property is 

electroactivity. 

Figure 1.5.3 Photomicrograph of endothelial cells cultured on fibronectin-coated PPy doped with 

p-toluene sulfonate (PPyTS) for 4 h: (A) PPy in native oxidized state and (B) PPyTs reduced by 

application of -0.5V for 4 h(Magnify: ×700). 116 

Some reports have shown the possibility of using PPy to modulate cellular response via 

electrical stimulation. Wong et al. assessed the suitability of electroactive polymers for 

sustaining cell growth and controlling cell function. 116 In their study, aortic endothelial cells 

were cultured on fibronectin (FN)-coated PPy films which were in different oxidation state 

(Figure 1.5.3). It was found that neutral state PPy caused cell rounding and a concomitant 

drop (~98%) in DNA synthesis, and the oxidation of PPy resulted in cell spreading. 

Interestingly, cell viability (>90%) and adhesion were very good on both oxidized and neutral 

PPy despite the change in cellular morphology. Schmidt et al. have also made great 

‐ 22 ‐

- 23 - 


contribution to the application of PPy in the biomedical field. They reported that electrical 

stimulation of PPy in its oxidized form can also be used to modulate cell function. 119 In their 

experiment, rat pheochromocytoma cell line (PC-12) cells on poly(styrene sulfonate) 

(PSS)-doped PPy films were found to exhibit a ~91% increase in median neurite length in the 

presence of a direct current lasted for 2 h (Figure 1.5.4). These studies demonstrate that the 

electrical stimulus can significantly enhance PC-12 neurite outgrowth and spreading. 

Moreover, the reason why PPy could enhance the cell extension was studied and they 

concluded that the electrical stimulation increases the adsorption of serum proteins, which 

help to improve the growth and proliferation of cells. Subsequently, Lakard et al., 120 George 

et al., 121 and several other groups investigated adhesion and proliferation of cell cultured 

different cell lines on PPy. 122-124 

Figure 1.5.4 PC-12 cell differentiation on poly(styrene sulfonate)-doped PPy films. (A) Cells 

grown for 48 h but not subjected to electrical stimulation are shown for comparison. (B) PC-12 

cells were grown on PPy for 24 h in the presence of nerve growth factor, then exposed to 

electrical stimulation (100 mV) across the polymer film. Images were acquired 24 h after 

stimulation. Scale bar = 100 μm. 119 

The limitation of PPy as a favorable biomaterial is that it lacks biological activity. In order 

to endow it bioactivity, many biomolecules, such as adenosine 5'-triphosphate (ATP) 125-127 

and nerve growth factor (NGF) 128 were entrap in PPy. The introduction of biologically active 

molecules endows the material new properties. Thus, the resulted materials can modulate the 

growth of different cell types simply by varying the biomolecules. For example, Collier et al.

Chapter 1 

synthesized hyaluronic acid (HA)-doped PPy and explored its tissue engineering 

applications. 129 In vivo studies showed that the introducing of HA into PPy films improved the 

biocompatibility of PPy and promoted the vascularization. 

It should be noted that both conductivity and the film surface are often greatly changed 

when biologically active molecules are used as dopants. 129, 130 For example, the morphology 

and conductivity of polypyrrole-based films with different dopants were systematically 

studied. It was concluded that larger biomolecule dopants can significantly decrease 

conductivity and affect more obviously on morphology compared to small dopants. However, 

the exact effects of particular dopants are not very predictable (Figure 1.5.5). 

Figure 1.5.5 Morphology of thick PPy films as assessed using scanning electron microscopy 

(SEM) (top) and corresponding cyclic voltammograms (CVs), indicating electrical activity of the 

materials (bottom). (A) PPyCl. (B) PPy doped with poly(vinyl sulfate). (C) PPy doped with 

dermatan sulfate. (D) PPy doped with collagen (inset: thin film of collagen-doped PPy). A narrow 

‐ 24 ‐

- 25 - 


CV spectrum correlates to decreased electroactivity. Scale bars are 100 μm. 130 

PPy can not be further covalently modified due to there are no functional pendent or 

terminal groups on its chain. This limitation can be overcome by doping with polymers 

having functional groups. A good example of this technique is conducted by Song et al. In 

their report, PPy was doped with poly(glutamic acid) (PGlu), which has pendent carboxylic 

acid groups could further react with amino of polylysine and/or laminin. Dorsal root ganglion 

(DRG) neurons were observed to preferentially adhere to and extend neurites on the PPy 

surfaces modified with polylysine and/or laminin (Figure 1.5.6). 130 

Figure 1.5.6 Phase contrast and fluorescence images of DRGs adhered to the surface of pPy-X, 

where X = 1. pLys, 2. Lmn, and 3. pLys-Lmn. Cell nuclei were labeled with DAPI (blue 

florescence). All images were taken at 10× magnification and the 200 μm scale bar applies to all 

images shown. 130 

PPy is not biodegradable in nature and many works were carried out to blend it with 

biodegradable polymeric materials to obtain partially absorbable materials. For example, PPy 

nanoparticle was blended with PLA to fabricate a composite which is both biodegradable and 

conductive. 117 Altering the content of PPy in the composites will result in the changes of both

Chapter 1 

parameters. Moreover, the morphology of the composites will also be changed with different 

PPy content (Figure 1.5.7). The fibroblasts exhibited improved attaching and growth on the 

PPy nanoparticle-PLA composites membranes under the simulated of current compared to 

that cultured without simulation. The composites provided a new way to design electroactive, 

biocompatible and biodegradable materials with simple blending approach. 

Figure 1.5.7 SEM images of the surface of PPy nanoparticle-PLA composite membranes with 

various PPy content: (A) 5%, (B) 7%, (C) 9%, and (D) 17%. 117 

Many cells, especially nerve cell, have filaceous parts which will exhibit different 

topography. And the topography of culture substrate will influence the growth and 

differentiation of these cells. Some studies have explored the effect of surface topography of 

electroactive materials on cell culture. For instance, patterning of 1 and 2 μm wide PPyPSS 

microchannels can be fabricated using electron beam lithography. 131 Then the embryonic 

hippocampal neurons were seeded on this matrix and found to polarize (i.e., define an axon) 

faster, exhibiting a two-fold increase in the number of cells with axons compared to cells 

cultured on unmodified PPyPSS (Figure 1.5.8). For instance, patterning of 1 and 2 μm wide 

PPyPSS microchannels can be fabricated using electron beam lithography. 131 Then the 

embryonic hippocampal neurons were seeded on this matrix and found to polarize (i.e., define 

an axon) faster, exhibiting a two-fold increase in the number of cells with axons compared to 

cells cultured on unmodified PPyPSS (Figure 1.5.8). 

‐ 26 ‐

- 27 - 


Figure 1.5.8 Patterning of PPy to create microchannels for contact guidance of neurons. 

Phase-contrast (left) and fluorescence (right) photomicrographs of hippocampal neurons on PPy. 

(A, B) Cells cultured on 2 mm wide and 200nm deep PPy microchannels. (C, D) Cells cultured on 

unmodified PPy. The green labeling (Alexa 488) corresponds to Tau-1 (axonal marker) 

immunostaining. Cells polarized (i.e., established a single axon) more readily on microchannels 

than on unmodified PPy. Scale bar = 20 μm. Images are at the same magnification. 131 

PANi was another conductive polymer that had been explored for applications as novel 

intelligent scaffolds for cardiac and/or neuronal tissue engineering. As compared to PPy, the 

investigation of PANi as biomaterials developed more slowly. However, it is attracting more 

and more attentions due to the profound understanding on its electrical properties. For 

example, Mattioli-Belmonte et al. first demonstrated that PANi was biocompatible in vitro 

and in long term animal studies in vivo. 132 Later, Wei et al. reported that PANi films 

functionalized with the bioactive lamimin-derived adhesion peptide YIGSR (Tyr-Ile-Gly 

Ser-Arg) exhibited significant enhanced PC-12 cell attachment and differentiation. 133

Chapter 1 

Figure 1.5.9 (A) SEM image of PANi-gelatin blend fibers with ratio 45:55. Original 

magnification is 5000×. (B) Morphology of H9c2 myoblast cells at 20 h post-seeding on 45:55 

PANi-gelatin blend fiber. Staining is for nuclei-bisbenzimide and actin cytoskeletonphalloidin; 

fibers autofluoresce. Original magnification is 400×. (C) SEM images of H9c2 cells cultured on 

45:55 PANI-gelatin blend fibers. 134 

Despite the progress of PNAi in tissue engineering application, there was still a lot of work 

to do to improve their poor solubility, the poor polymer-cell interaction and biodegradability. 

Therefore, it is necessary to design novel electroactive polymers with good solubility, 

biocompatibility and biodegradability for the tissue engineering application. For example, 

polyanline was blended with natural polymers such as collagen and gelatin or covalently 

grafted with oligopeptides such as Ty-Ile-Gly-Ser-Arg (YIGSR) to improve its polymer-cell 

133, 134 

interaction (Figure 1.5.9). 

Figure 1.5.10 (A) Phase contrast images of PC-12 cell morphology of (a) TCP, (b) TCP with 

NGF, (c) ATQD-RGD,and (d) ATQD-RGD with NGF on day 10 (B)Neurite length distribution 

chart for ATQD-RGD substrates with and without NGF. 

‐ 28 ‐

- 29 - 


The solubility of polyaniline could be enhanced by covalently grafting side groups or 

polymers, such as poly(ethylene glycol), on the backbone of polyaniline. 135 Wei et al. 136 

demonstrated that the electroactive silsesquioxane precursor, 

N-(4-aminophenyl)-N'-(4'-(3-triethoxysilyl-propyl-ureido) phenyl-1,4- quinonenediimine) 

(ATQD), containing aniline trimer covalently modified by oligopeptide could be a kind of 

promising biomaterial for tissue engineering. The bioactive material, ATQD-RGD, supported 

PC-12 cell adhesion and proliferation, and stimulated spontaneous neuritogenesis in PC-12 

cells in the absence of neurotrophic growth factors (NGF), as shown in Figure 1.5.10. 

Figure 1.5.11 (A) Representational fluorescence micrographs of PC-12 cell for the substrates (a) 

TCPS (-) without electrical stimulation, (b) TCPS (+) exposed to electrical stimulation, (c) EM 

PLAAP (-) doped with CSA without electrical stimulation, (d) EM PLAAP (+) doped with CSA 

exposed to electrical stimulation on day 4. (B) The mean neurite length of PC-12 cells cultured 

on the substrates of EM PLAAP (-), TCPS (+), and EM PLAAP (+) on day 4. 136 

Based on the above works, Chen’s group did many works to expand the architecture of this 

kind of materials. They chose aniline oligomers (especially aniline pentamer with dicarboxyl 

end group (AP)) as electroactivity resource, which incorporated with degradable polymers, 

such as polylactide (PLA), poly(ε-caprolactone) (PCL) and natural biopolymer chitosan, to 

prepare new biodegradable electroactive biomaterials. 137-139 The introducing of PLA 

endowed the material with good electroactivity, solubility and biodegradability similar to 

pure PLA. In vitro cell evaluation showed that the electroactive copolymers could indeed 

promote the attachment and growth of rat C6 glioma cells. Moreover, in the comparison

Chapter 1 

experiments with and without applying electrical potentials, the dopped electroactive 

copolymers had the ability of improving the differentiation of PC-12 cells, as shown in Figure 

1.5.11. They also prepared a new kind of water-soluble electroactive polymer, aniline 

pentamer cross-linked chitosan. These new polymers showed good electroactivity even in 

aqueous solution. The MTT assay, cell adhesion test, and degradation assessment in the 

presence of enzyme confirmed that these polymers had good biocompatibility and 

biodegradability. The electroactive polymers can obviously improve the neuronal 

differentiation of PC-12 cells even without the extra electrical stimulation, as shown in 

Figure1.5.12. 

Figure 1.5.12 Visualization of PC-12 neurite outgrowth by micrographs for the substrates (A) 

without electroactivity (chitosan), (B) with electroactivity (aniline pentamer cross-linked 

chitosan) on day 5. 139 

A B 

As the study progressing, Chen et al. found that the oligomers without high conductivity 

and the polymers containing oligomers also showed improvement in the C6 cell 

differentiation in the absence of electrical stimulation, as shown in Figure 1.5.13. In the 

culture medium, the only difference from the electroactive polymers may be the exchange of 

the ion between the medium with polymer, and between the polymer with cells, which means 

the electroactivity changed the ion exchange between the cells and medium. 

‐ 30 ‐

- 31 - 


Figure 1.5.13 Visualization of C-6 outgrowth by micrographs in the culture medium (a), (b) in 

the presence of aniline pentamer cross-linked chitosan, (c) and (d) without aniline pentamer 

cross-linking chitosan. 

Besides the extensively investigated PPy and PANi, several electroactive polymers have 

been also studied, such as polythiophene (PT) and others. For example, a series of polymers 

composed of a PT backbone with oligosiloxane grafted to the b position of the thiophene 

rings was prepared. 140 All the polymers exhibited different conductivities after doped with 

iodine. However, the iodine is toxic to cells and the authors only investigated the 

biocompatibility of undoped polymers. The carbon-carbon bond of PT made it inherently 

nonbiodegradable. To overcome this drawback, some reports concentrated on the synthesis of 

biodegradable elcetroactive polymers containing heterocycles unit. For example, ester linkers 

were introduced to connect the conductive heterocycles (Figure. 1.5.14A). 96 The resulted 

polymer is conductive, and more importantly, it is biodegradable in the presence of esterases 

which made it be applicable in vivo. The conductivity of the polymer is mainly attributed to 

inter and intra “electron hopping” formed by the overlap of conjugated regions. However, the 

doping agent is also iodine. Despite this drawback, the undoped polymer was biocompatible 

in vitro. Nerve cells adhered to polymer film and readily expressed their nerve-like phenotype 

by extending neurites after one day (Figure 1.5.14B, left). After 8 days, significant cell 

proliferation was observed (Figure 1.5.14B, right). These data demonstrate that in addition to 

being non-toxic to cells in culture, this biodegradable electroactive polymer can also support 

cell attachment and proliferation. Subsequently, in vivo biocompatibility of this polymer was

Chapter 1 

characterized by subcutaneous implantation into rats for 14 and 29 days using FDA-approved 

PLGA as a control (Figure 1.5.14C). The results showed that inflammation around 

electroactive polymer is mild and similar to that seen with PLGA at 29 days. Thus, there 

appears to be no detectable toxic effect of the base material or its degraded products in vivo. 

Figure 1.5.14 (A) Chemical structures of biocompatible electroactive polymer. (B) Human 

neuroblastoma cells cultured in vitro on electroactive polymer films after 1 day (left) and s 8 days 

(right). Both images are at the same magnification. Scale bar = 100 μm. (C) Histological tissue 

sections (stained with hematoxylin and eosin) of Electroactive polymer (left) and PLGA (right) 

demonstrated comparably low inflammatory responses at 29 days. Both images are at the same 

magnification. Scale bar = 50 μm. 96 

1.5.2.2 Biosensor Applications 

Most of the electroactive polymers used for biosensors are conjugated polymers (CPs), 

which can couple analyte receptor interactions, as well as nonspecific interactions, into 

‐ 32 ‐

- 33 - 


observable responses. A key advantage of CP-based sensors is the potential of the CP to 

exhibit collective properties that are sensitive to very minor chemical or physical changes. 

The most important aspect of biosensor is how to combine the electrical component (i.e., CP) 

with the biological recognition components. An effective and widely used approach was to 

immobilize bioactive molecules in or on CPs. 141-143 

Physical adsorption is the simplest way to introduce bioactive molecules on CPs for 

biosensors. For example, glucose oxidase was directly adsorbed onto PPy for a biosensor 

which can detect glucose from concentrations of 2.5 to 30 mM using dimethylferrocene as an 

electron transfer mediator. 144 However, this method is not reliable because the amount of the 

absorbed compound is not repeatable and this immobilization is not stable. 145 An alternative 

way is to entrap the biomolecule into the polymers substrate. For example, poly(3, 

4-ethylenedioxythiophene) (PEDOT) exhibited a 5% shrinkage in thickness when it is rinsed 

with ethanol, which can be utilized to incorporate horseradish peroxidase. 146 Besides enzymes, 

this method has also been used for immobilization of antibodies and DNA. 147-149 Just like 

the absorption method, this approach also has some limitations such as denature of the 

proteins and the low accessibility of analytes to the sensing element. Moreover, entrapment 

methods need a high concentration of the biomolecule (~0.2-3.5 mg/mL), which is not 

suitable for industry application due to the higher cost. 

Compared to entrapment and absorption, affinity binding seemed to be more stable 

bonding techniques. The avidin-biotin complex was the most studied affinity binding pair due 

to the extremely specific and high-affinity interactions between biotin and the glycoprotein 

avidin (Ka = 1 × 10 15 mol -1 L). 150 This method requires the synthesis of biotinylated CPs 

firstly. For example, the pyrrole monomers was copolymerized with biotinylated hydrophilic 

pyrrole monomers with different PEG lengths as spacer arms to create the bonding site. 151 

And the amount of anchored avidin can be tuned by the biotin density or the length of the 

PEG spacer in the copolymer. There are also other affinity binding complexes that have been 

studied for the immobilization of DNA onto CP surfaces. For example, a unique intercalator 

(i.e., a molecule that inserts itself into double-stranded DNA)-based immobilization technique 

has been developed. 152 Target DNA strands are detected when they form DNA duplexes with 

labeled DNA probes and are subsequently immobilized by the affinity binding of the 

intercalator, which is covalently bound to PPy. And more importantly, the detection limits can 

lower to 1 pg/mL.

Chapter 1 

Covalent modification was another effective way to prepare stable detective component. 

Conducting copolymers containing covalently substituted monomers have been considered as 

an effective way to immobilize biomolecules. For example, copolymers of PPy and 

oligonucleotides bearing a pyrrole group have been reported for DNA sensors. 153, 154 An 

easier method is to prepare copolymers bearing functional groups such as amine or carboxylic 

acid groups, which can further react with biomolecules. Minett et al. designed an 

immunosensors for detecting Listeria monocytogenes by covalently binding the Listeria 

monoclonal antibody to a copolymer of carboxylic acid-functionalized PPy and regular 

PPy. 155, 156 In another example, N-Hydroxysuccinimide was introduced as a pendent group of 

the PT or PPy (Figure 1.5.15). 152, 157-159 This activated ester group can easily react with 

amines in proteins and other biomolecules under mild conditions to prepare detection 

materials. 

Figure 1.5.15 Immobilization of DNA on PPy derivatives with N-hydroxysuccinimide groups. 158 

Another conjugation method is the postpolymerization modification of CPs. For example, 

poly(acrylic acid) was grafted onto the unmodified PPy substrates by a photo-grafting method. 

The bonded carboxylic groups can be used for the subsequent immobilization of glucose 

oxidase. This method only altered the surface property of the substrate and did not change its 

bulk, which will not affect the conductivities of materials. 160 

Molecular imprinting technique is a novel method to precisely recognize molecules. A 

recent report provided a new approach for a biosensor. 161 The authors added caffeine during 

the electropolymerizing of PPy and subsequently the caffeine molecules were removed to 

‐ 34 ‐

- 35 - 


form their imprints, which are unique three-dimensional sites only selectively recognizing 

caffeine. Another novel biosensor technique is an indirect way. Le Floch et al. coated the 

aptamers covalently immobilized gold electrodes with ferrocene-modified PT. In this study, 

the bioactive aptamer is not immobilized directly to the CP; however, the CP still can act as 

an electrical transducer. 162 

1.5.3 Other Applications 

In addition to the tissue engineering, biosensors and probes, the electroactive polymers also 

have biological applications in other fields, such as drug delivery carrier, actuators, and 

antioxidants. The eleectroactive polymers exhibited a reversible redox property, which 

triggers adsorption or expulsion of ions leading to the volume change of materials. 163 Most of 

their applications in drug delivery and actuator are based on this electricity-responsive 

property. When they were used as drug delivery carriers, the incorporated biologically active 

proteins and drugs such as NGF, 128 dexamethasone, 98, 164 and heparin 165 can be controlled 

release through electrical stimulation. For example, Hodgson et al. reported an approach to 

entrap and electrically controlled release bovine serum albumin (BSA) and NGF from PPy 

doped with polyelectrolytes (e.g., dextran sulfate). 128 

Figure. 1.5.16 (A) Postpolymerization of PPy to incorporate aldehyde groups. (B) Covalent 

immobilization of PVA hydrogels containing heparin on PPy substrates. 165

Chapter 1 

The introduction of polyelectrolytes led to the materials being hydrophilic enough to swell 

in water, which allows the easy diffusion of entrapped protein. When the PPy was reduced by 

negative potential, the anions were quickly expulsed in less than one minute. The in vitro test 

demonstrated that the released NGF still retained activity. Generally the polymeric carriers 

will affect the entrapped protein’s folding and activity due to the strong hydrophobic nature 

of the polymer. However, this approach employed polyelectrolytes to increase the 

hydrophilicity of the materials, which had solved this problem in some extent. 

In another investigation, authors incorporated streptavidin into the PPy films doped with 

both biotin and dodecylbenzenesulfonate. Then the biotinylated NGF was immobilized to this 

film. When the film was electrically stimulated, NGF was exclusively released. The activity 

of the released protein was also confirmed in vitro. This method can be expanded to most of 

drugs that could be delivered through biotin-streptavidin strategy. 

Hydrogels have been studied for a long time as drug carrier. The release behaviors of 

“smart” hydrogels can be controlled by many stimuli, including pH, temperature, 

biomacromolecues and electrical stimulation. For example, PVA hydrogels were covalently 

immobilized onto aldehyde groups modified PPy films (Figure. 1.5.16). The heparin was 

loaded into the hydrogels and could be released through the diffusion without electrically 

stimulation. 165 When PPy was electrically stimulated, the release of heparin from the 

hydrogel was accelerated. Many factors were considered by the authors that could affect the 

results, such as changes in temperature, electrophoresis, changes in pH as a result of 

electrolysis, and the polyanionic nature of heparin. 

Besides the film, electroactive polymers can be fabricated into other shapes for drug 

delivery. For example, PEDOT nanotubes were synthesized on the electrospun PLGA fibers 

(~100 nm diameter) template (Figure. 1.5.17). 164 Then the PLGA loaded with dexamethasone 

was removed to produce PEDOT nanotubes encapsulating small molecules. The drug release 

of PEDOT nanotubes drug delivery system can be controlled by the electrical stimulation, 

probably as a consequence of expansion/reduction of polymer cavities induced by the 

expulsion of anions. 

‐ 36 ‐

- 37 - 


Figure. 1.5.17 (A) Electrospun PLGA fibers are loaded with drug (dexamethasone). (B) 

Degradation of PLGA fibers release the drug. (C) PEDOT is electropolymerized around PLGA 

fibers loaded with drug. (D) After degradation of PLGA fibers, PEDOT nanotubes are loaded 

with drug. (E) PEDOT nanotubes do not release drug in a neutral electrical condition. (F) PEDOT 

nanotubes release the drug upon external electrical stimulation with a positive voltage, which 

produces contraction of the nanotubes and the subsequent expulsion of the drug. (G) SEM image. 

Electropolymerized PEDOT nanotubes on the electrode site of an acute neural microelectrode 

after removing the PLGA core fibers. (H) Higher magnification of a single PEDOT nanotube on a 

neural microelectrode array. 164 

The volume change of electroactive polymers responding to electrical stimulation has also 

been explored to develop actuators as “artificial muscle” devices. For example, Otero et al. 

placed two layers of PPy in a triple layer arrangement separated by a non-conductive material, 

as illustrated in Figure. 1.5.18. 166, 167 When current applied across the two conductive films, 

one of the films is oxidized and the other is reduced. The oxidized film exhibited an inflow of 

dopant ions and an associated expansion, whereas the reduced film expels ions and shrinks. 166, 

168 

The combined effect is changed into a mechanical force that bends the films, which has 

been compared to the mechanisms in natural muscles. In order to increase the 

electromechanical actuation of the materials, carbon nanotubes (CNTs) were blended with

Chapter 1 

PANI fibers. 169 These devices have promising biomedical applications as 

electrical-responsive actuators, such as micropumps and valves for labs-on-a-chip, 170 

steerable catheters for minimally invasive surgery, 171 blood vessel connectors (Figure. 

1.5.19), 172 and microvalves for urinary incontinence. 

Figure. 1.5.18 (A) When current is applied, the left PPy film acts as anode and swells by the 

entry of the hydrated counter ions. Simultaneously, the right film acts as cathode and contracts by 

the expulsion of the counter ions. These volume changes and the constant length of the 

non-conducting film promote the movement of the triple layer device. (B) By changing the 

direction of current the movement takes place in the opposite direction. 167 

Scavenging of free radicals is a protective response in biological system, which may afford 

against various diseases, such as cardio-vascular diseases and cancer. The potential role of 

PANi 129 as antioxidants in rubber mixes has already been considered, and the PANi was 

demonstrated to be efficient in slowing down the rate of oxidation. And recently the 

electroactive polymers were also used in biological applications. 173 These polymers such as 

PANi and PPy in their neutral form can eliminate 2 ~ 4 free radicals per monomer unit. The 

ability of these materials to scavenge free radicals is attributed to their oxidation activity and 

has no relationship with electrical stimulation. These materials have potential biomedical 

applications in tissues experiencing high oxidative stress. 

‐ 38 ‐

- 39 - 


Figure. 1.5.19 PPy blood vessel connector insertion surgery. (A, B) A PPy-Au bilayer device in 

the reduced state is curled into a roll that is inserted half-way into one of the ends of the severed 

blood vessel. (C, D) The other half of the device is inserted inside the other end of the vessel and 

the bilayer expands a few minutes after PPy is oxidized. The PPy tube holds the two parts of the 

blood vessel together during healing, which replaces sutures. The connector is non-thrombogenic 

and very thin to avoid restricting the space inside the blood vessel. 172 

Although many kinds of electroactive polymers (most of them are CPs) have been explored 

for biomedical application, little attentions have been paid on the biologically active radical 

polymers. Therefore, in this thesis we prepared novel TEMPO-contained electroacitve 

polymers and investigated the feasibility of them in biomedical application. This exploration 

was creative and important for developing novel electroacitve biomaterials. 

1.6 Radicals Polymers 

As a stable radical, 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) has applications 

throughout chemistry and biochemistry. For example, it was widely used as a radical trapping, 

as a spinning-labeled reagent in biological systems, as a reagent in organic synthesis, and as a 

mediator in controlled free radical polymerization. 174-177 TEMPO is prepared by the oxidation 

of 2,2,6,6-tetramethylpiperidine (TEMP). It was well known that the nitroxide free radicals 

could participate in one-electron redox reaction in acidic medium to yield relatively stable

Chapter 1 

diamagnetic products, hydroxypiperidines structure (NOH), and oxo-piperidinium cations 

(NO + ). Figure 1.6.1 shows such one-electron redox reactions of free nitric oxide derivatives. 

Figure 1.6.1 The one-electron redox reactions of nitroxide free radicals. 178 

Based on the redox properties of the nitroxyl radicals, polymers bearing stable radicals in 

the side chains, also known as radical polymers, have been extensively studied as redox 

resins which catalyze the oxidative and/or reductive reactions of organic compounds. For 

example, poly(acrylate)-combined TEMPOs were synthesized and studied as a catalytic 

reagent for the oxidation of alcohols into aldehydes and ketones. 179 The organic radical-based 

or metal-free redox reagents have been recently reexamined from the perspective of green or 

environmentally compatible chemical reaction processes. 

In addition to this chemistry application, the robust electron exchange between unpaired 

electrons in the polymer side chains suggests these radical polymers to be used for organic 

electronic or magnetic materials. However, it is not until recently that the applications have 

been intensively investigated for use in organic secondary battery or memory devices by our 

group. The large population of the radical redox sites along the polymer chain allows the 

effective redox gradient-deriven electron transport, which leads to organic batteries with large 

energy density. On the other hand, polymers with nitroxyl radicals also attracts significant 

interest to be as biomedical materials since the stable nitroxyl radials have been discovered to 

have similar functions as nitric oxide (NO•) which was presence in many bioprocess such as 

inflammation, blood clotting, blood pressure, neurotransmission, cardiovascular disorders and 

antimicrobial property. 180-182 Thus, emphasis of this part of introduction would focus on the 

radical polymers for organic electronic devices and biomedical applications. 

‐ 40 ‐

1.6.1 Radical Polymers for Organic Electronic Devices 

1.6.1.1 Organic Radical Batteries 

- 41 - 


Rechargeable secondary batteries are widely used in portable equipments. Li-ion battery 

represents the currently most popular usage. However, the application of metal-based 

electrodes has come up against some inherent disadvantages, such as limited raw-material 

resource and tedious waste process. Therefore, organic-based electrode-active materials have 

received more and more attentions. Over the past few years, we have focused on the 

development of polymer bearing densely populated unpaired electrons, such as nitroxides, 

phenoxyl and galvinoxyl, in the pendant per repeating unit and utility of them as 

electro-active or charge-storage material in a rechargeable device. 178, 183-190 The organic 

178, 183, 188 

radical battery composed of the radical polymer electrodes has several advantages: 

(1) a high charging and -discharging capacity (>100 mAh/g), ascribed to the stoichiometric 

redox of the radical moieties, (2) a high-charging and -discharging rate performance resulting 

from the rapid electron-transfer process of the radical species and from the amorphous state of 

the radical polymers, and (3) a long cycle life, often exceeding 1000 cycles, derived from the 

chemical stability of the radicals and from the amorphous electrode structure. 

A variety of polymer backbones have been employed by our group to bear the pendant 

radicals, such as poly(meth)arylates, polystyrene derivatives, polymer(vinyl ether)s, 

polyethers and poly(norbornene)s, and were depicted in Figure 1.6.2 and Figure 1.6.3. Radical 

polymers, most of time, were synthesized by conventional radical polymerizations, and an 

additional oxidation processes must be needed in this case. The unpaired electron density of 

the polymers was then measured by SQUID, revealing the presence of the radicals in each 

repeating unit. The versatile of the polymers backbones also have another advantage, i.e. the 

polymers allow to be conveniently placed on the surface of a current collector by a 

solution-based wet process such spin-coating method. When the polymer is placed on the 

surface of the current collector and equilibrated in electrolyte solution, charge propagation 

within the polymer layer is sufficiently accomplished, leading to high-density charge storage 

because the redox sites are so populated that electron self-exchange reactions are completed 

within a finite distance of the polymer layer. 189

Chapter 1 

Figure 1.6.2 Nitroxide radical polymers based on various backbones. 188 

Figure 1.6.3 n-Type radical polymers. 188 

Typical radical polymers such poly(2,2,6,6-tetramethypiperidinyloxyl-4-yl-methyarylate) 

(PTAM) is a “p-type” redox active materials in organic battery. In order to obtain totally 

organic radical battery, we have recently extensively explored the n-type redox-active radical 

polymers based on the molecular design (Figure 1.6.4). A representative combination is the 

PTAM as the cathode and the poly(galvinoxylstyrene) as the anode. 190 The radical density of 

each polymer was >0.9 unpaired electrons per monomer unit. Solutions of the radical 

polymers were coated as thin films on an ITO-PET substrate as the current collectors. The 

coated radical polymers were suitably modified via a cross-linking reaction to impede their 

dissolution into the electrolyte solution which causes self-discharging of the battery. A 

microporous separator film containing the electrolyte solution, such as ethylene carbonate 

‐ 42 ‐

- 43 - 


containing tetrabutylammonium chloride, was sandwiched between two radical polymer films 

coated on the current collectors, to fabricate the all-organic “radical battery”. 

Figure 1.6.4 Totally organic radical battery. 188 

Though the organic-based batteries composed of radical polymers pose considerable 

advantages over the Li-ion batteries, the flammable or ignition risk of the organic electrolytes 

in the devices emerged as the fundamental safety issue in the practical use. To overcome this 

problem, radical polymer poly(2,2,6,6-tetramethylpiperidinyloxyl-4-yl vinylether) (PTVE) 

with a hydrophilic polyvinylether backbone was synthesized and demonstrated 

charging-discharging operation in aqueous electrolyte. 186, 187 However, the PTVE based 

devices were limited by their long cycle operation due to the low polymer weight and 

insufficient hydrophilicity of the polymers. Thus, an alternative type of radical polymer, 

poly(2,2,6,6-tetramethylpiperidinyloxyl-4-yl acrylamide), was designed and synthesized as an 

electrode-active polymer for organic rechargeable device containing aqueous electrolyte. 191 

The device demonstrated a 1.2 V output voltage, exceeded 2000 charging-discharging cycles, 

and a high charging rate performance within 1 min. 

1.6.1.2 Organic Radical Memories 

Besides the organic-based batteries using radical polymers, the development of a similar 

charge-storage configuration has also been anticipated for a dry system in the absence of the 

electrolyte by sandwiching a dielectric material within the radical polymers. 192 The 

metal–insulator–metal diode-type structure of the radical memory (see Figure 1.6.5) is 

composed of the thin layers of a p-type radical polymer such as PTMA, poly(vinylidene 

difluoride) (PVDF) as the dielectric material, and an n-type radical polymer such as PGSt. 

These layers have been conveniently spin-coated onto an indium tin oxide (ITO)/glass 

electrode without intermixing. When an increasing voltage of 0 to –5V is applied, the state of

Chapter 1 

the device is switched to a low resistance near –4.5 V as the threshold voltage. The low 

resistance state is maintained during the reverse sweep of the voltage from –5 to +1.4 V. The 

low-resistance or ON state was observed for repeated sweeps, regardless of the sweep 

direction. When a bias of –1.5 V was applied, the device sharply switched to the 

high-resistance or OFF state again. In the hysteretic curve, the ON–OFF ratio amounted to 

four orders of magnitude. The retention cycles of the ON and OFF states under open-circuit 

conditions persisted for more than 10 4 times. Furthermore, each state survived for a month 

after the corresponding once-time-only pulse as well as consecutive pulses. 

The charge injection at the radical polymer/electrode interface and transport in the bulk of 

the radical polymer layer are dominated by the Schottky barrier and the Poole–Frenkel 

mechanism. In the ON state, charges are trapped at the radical polymer/PVDF interfaces, and 

induce accumulation of the opposite charge at the radical polymer/electrode interfaces and 

reduction the Schottky barriers, allowing charges to transfer across the radical 

polymer/electrode interfaces even at low voltages. 192 The SOMO levels of the p-type PTMA 

and the n-type PGSt are near 5.4 and 4.7 eV, respectively. 

Figure 1.6.5 p-type and n-type radical polymer-based memory architecture, and charge injection, 

transporting, and trapping configuration. 

The p-type layer accepts holes, and electrons are injected into the n-type layer. The 

injected holes and electrons are transported by the hopping mechanism, and are stored at the 

radical polymer/PVDF interfaces. Under open-circuit conditions, the trapped holes and 

electrons were nonvolatile due to charge trapping at the radical polymer/PVDF interfaces and 

to blocking of the charge transfer in the polymer layers having sufficient resistances. The 

asymmetric configuration of the electrodes with the different work functions allows 

‐ 44 ‐

initialization of the device by applying an inverse voltage. 

1.6.2 Radical Polymers for Biomedical Applications 

1.6.2.1 Nitric Oxide Release Systems 

- 45 - 


Nitric oxide (NO•) is a small but highly reactive free radical with expanding known 

biological activities. Its essential roles involve the regulatory agent for normal physiological 

activities and cytotoxic species in diseases and their treatments. There have been numerous 

examples of application of the nitric oxide on disease treatments, such as antiviral compounds, 

cancer treatment, anti-inflammatory drugs and other nitric oxide-related diseases treatment. 

However, the excess introduction of nitric oxide into body may induce significant adverse 

side effects like microvascular leakage, tissue damage in cystic fibrosis, septic shock, B-cell 

destruction, and possible mutagenic risk. 193 Therefore, it is very important to develop smart 

delivery vehicles for control release of the nitric oxide. 

Biodegradable polymers are known to be biocompatible and degradable in physiological 

conditions which have been widely utilized as drug delivery vehicles in the forms of matrices 

or nanoparticles. Accordingly, pioneered works by C. C. Chu and co-workers have reported to 

incorporate of stable nitric oxide radicals to either the chain end or backbone of the 

biodegradable polymers. 193-196 In such contributions, nitric oxide derivative, tampamine 

nitroxyl radical (4-amino-2,2,6,6-tetramethylpiperidine-1-oxy, TAM) have been chemically 

coupled with various biodegradable polymers such as polyglycolide (PGA), poly(acrylic 

acid/lactide/ε-caprolactone) (PBLCA) and poly(ester amide)s (PEAs). The biological 

activities of these TAM-incorporated polymers and the release kinetic of the TAM from the 

polymer matrices have also been evaluated. For example, the level of the retardation of 

smooth muscle cell (SMC) of the TAM-PGA was conducted in vitro cell culture (Figure 

1.6.6). The TAM-PGA was found to show profound retardation of the proliferation of SMC as 

similar with the TAM free nitroxyl radicals at concentration of 1 μg/mL. Thus, it appeared 

that the long PGA segments had no evidently interference on the biological functions of 

nitroxyl radicals incorporated. However, the incorporation of TAM into the polymer chain 

end have limitation in the TAM content in the polymer, improved strategies have also been 

proposed by the authors via conjugating the TAM to the backbone of the biodegradable 

polymers such as PBLCA and PEAs. 193, 194 Up to 8.32% (wt %) of the TAM content in

Chapter 1 

PBCLA could be achieved. Though the TAM content was improved, the release of TAM from 

the materials seen to be less effective even in the presence of hydrolysis lipase. Only less than 

10 % of the TAM was released after 6 days. In order to solve this issue, a more versatile 

method has been investigated recently. The TAM nitroxyl radicals were loaded in the 

biodegradable PEAs nanofiber membranes instead of chemical conjugation. 195 The payload 

of the TAM in the nanofiber could be tunable by pre-loading different amount of TAM and 

the release kinetic study revealed that the encapsulated TAM would be completely released 

from the membranes within 5 days. 

Figure 1.6.6 The effect of TAM-PGA on the proliferation of human smooth muscle. 196 

1.6.2.2 Magnetic Resonance Imaging (MRI) 

MRI allows noninvasive imaging of deep internal structure of the body and, is 

widespread use in clinical diagnostic of physiologic and pathologic changes of disease. For 

MRI, the paramagnetic species are needed to serve as the contrast agents to enhance the 

image contrast. The most commercially used MR contrast agents are the gadolinium chelates, 

such as gadolinium diethylenetriaminepentaacetic aicd (Gd-DTPA). However, these agents 

are non-selective distribution in tissues and have short resistant time in tumors. Nitroxyl 

radicals are only well-known for their electronic paramagnetic resonance (EPR) properties 

until 1984, the T1 contrast property was found. Afterward, MRI applications of the nitroxyl 

radicals have been extensively investigated owing to their chemical flexibility, feasible 

preparation and low toxicity as comparison with conventional gadolinium chelates. 

Unfortunately, there are two fetal flaws would emerge when applied the nitroxyl radical MRI 

reagents in vivo. One is the relatively low MR relaxivities, while the other is the 

‐ 46 ‐

- 47 - 


paramagnetic nitroxyl radical may be reduced to diamagnetic hydroxylamine with the loss of 

T1 MR relaxation in the internal reduction environment. 

Figure 1.6.7 illustration of HPS-TEMPO. 

To address the abovementioned issues, several strategies have been reported, including 

conjugation of nitroxyl radical compounds with dendritic/hyperbranched polymers or 

copolymerization with hydrophilic monomers. As an example, Winalski et al. 197 reported to 

find that the fourth-generation polypropylenimide-(DAB) and third-generation 

polyamidoamide-(PAMAM) dendrimer-linked nitroxides had greater relaxivity than 

Gd-DTPA and the selective enhance contrast were observed in healthy articular cartilage. The 

relaxivities of the compounds were found to increase as the increase of nitroxides that 

incorporated in the dendrimers. This result was also observed by Ghandehari et al. and Koga 

et al.. Koga and co-workers have synthesized a series of high water-soluble hyperbranched 

poly(styrene) (HPS) carrying stable TEMPO radicals (Figure 1.6.7). 198 The relaxivity 14 

mM -1 s -1 , which is comparable with commercial Gd-DTPA agent, could be obtained when 

high density of TEMPO radicals has been conjugated with the polymers. Studies by 

Ghandehari et al. 199 have been reported that N-(2-hydroxylpropyl)methacryamide (HPMA) 

copolymer-linked nitroxides were synthesized for potential MRI application. The HPMA 

monomer was firstly copolymerized with reactive MAGGONp monomer and then chemical 

link with the nitroxides was performed via reactive MAGGONp residues. The relaxicities of 

the copolymers bearing nitroxides were found to be linear dependent on the nitroxides 

content in the copolymers which is consistent with the previous report by Winalski et al.. 

Another strategy has also proposed by Gussoni and co-workers. 200 They have synthesized 

pH-sensitive poly(amidoamine)s containing TEMPO radicals in the backbone. Though the 

relaxicity was measured to be not too high, the polymers were found to be tendency to 

accumulate in the tumor for a sufficient time.

Chapter 1 

1.6.2.3 Electronic Paramagnetic Resonance (EPR) imaging 

Electron paramagnetic resonance imaging (EPRI) is one of the recent functional imaging 

modalities that can provide valuable in vivo physiological information, such as tissue redox 

status, pO2, pH, and microviscosity, based on variation of EPR spectral characteristics, i.e., 

intensity, linewidth, hyperfine splitting, and spectral shape of free radical probes. 201 EPR 

imaging (EPRI) can obtain 1D–3D spatial distribution of such spectral components using 

several combinations of magnetic field gradients. With the addition of appropriate 

paramagnetic probes, the sensitivity of EPR on a molar basis is about 700 times greater than 

that of NMR. For EPRI applications, the spins probes should be (1) chemically stable and 

water soluble in biological media; (2) have simple EPR spectrum at ambient temperature; (3) 

have pharmacological half-time of at least 10 min to permit the imaging; (4) be 

non-toxicity. 202 The most used species are nitroxides, such as TEMPO radicals, due to their 

excellent EPR effect. However, the small molecular species pose some limitations, such as 

non-selective accumulation in normal tissues, quickly renal clearance, and rapid reduce under 

the reduction environment in vivo. 203 To solve these issues, Nagasaki and co-workers have 

designed core–shell-type nanoparticles carrying stable radicals in the core (Figure 1.6.8). 204, 

205 

The nanoparticles showed intense EPR signals and could resist to reduction environment 

even at the presence of 3.5 mM ascorbic acid which suggested the promising use of these 

nanoparticles to be use as the EPR probes in vivo. Further studies of such nanoparticles 

applied in vivo have revealed that the RNPs had more sufficient long-term blood circulation 

compared to the TEMPOL free radicals and were of extremely low toxicity due to the 

confinement of the TEMPO moieties in the nanoparticle core. Especially, the RNPs were pH 

sensitive, the L-band EPR signal could be observed only at the pH value below 6. Therefore, 

the pH-sensitive RNPs demonstrated the promising use as the EPR probes for low pH 

circumstances in vivo. 

Figure 1.6.8 Illustration of the radical-containing nanoparticle. 204 

‐ 48 ‐

1.6.2.4 Others 

- 49 - 


Stimuli-responsive polymers have step critical improvement to be developed as the 

biomedical materials. There are various factors that have been discovered to induce 

responsive of the polymers such pH, temperature, light, electric/magnetic field, biological 

events and so on. 206 Due to one electron redox properties of the nitroxyl radicals, polymers 

bearing these compounds are expected to have the redox sensitivity that may find potential 

use as the biomedical materials. Yoshida and Tanaka have proposed the oxidation-induced 207 

and reduction-induced 208 micellization of a diblock copolymer containing stable nitroxyl 

radicals. Light scatting technology and UV-Vis absorbance were used to characterization of 

the reversible micellization induced by the redox systems which have been illustrated in the 

Figure 1.6.1. However, the stimuli-responsive systems the authors have studied were 

performed in organic solvent which is far beyond the applications as biomaterials. Therefore, 

further efforts should be needed to investigate the reversible self-assembly systems in the 

aqueous or physiological medium and thus applications in biomedical field could be found. 

Reference 

1. LS. Nair, L. C, Prog. Polym. Sci. 2007, 32, 762. 

2. D. J. Brunelle, M. R. Korn, Proceedings of Symposium of the American Chemical Society, 

March 2003, Washington, DC 2005, 281. 

3. J. H. Clements, Ind. Eng. Chem. Res 2003, 42, 663. 

4. S. Inoue, H. K., T. Tsuruta, J. Polym. Sci., Part B: Polym. Phys. 1969, 7, 287. 

5. S. Inoue, H. K., T. Tsuruta, Makromol. Chem 1969, 130, 210. 

6. M. Kobayashi, S. I., T. Tsuruta, Macromolecules 1971, 4, 658. 

7. M. Kobayashi, Y. L. T., T. Tsuruta, S. Inoue, Makromol.Chem 1973, 169, 69. 

8. M. Kobayashi, S. I., T. Tsuruta, J. Polym. Sci. Polym. Chem. Ed. 1973, 11, 2383. 

9. S. Inoue, M. K., H. Koinuma, T. Tsuruta, Makromol.Chem 1972, 155, 61. 

10. K. I. Soga, E.; Hattori, I., Polym. J. 1981, 13, 407. 

11. A. Rokicki, U.S. Patent 4,943,677, 1990. Products and Chemicals, Inc.; Arco Chemicals 

Co. 1990. 

12. D. J. S. Darensbourg, N. W.; Katsurao, T., J. Mol. Catal. A 1995, 104, L1. 

13. D. J. H. Darensbourg, M. W.; Reibenspies, J. H., Polyhedron 1996, 15, 2341.

Chapter 1 

14. T. I. Aida, M.; Inoue, S., Macromolecules 1986, 19, 8. 

15. W. J. D. Kruper, D. V., J. Org. Chem 1995, 60, 725. 

16. S. C. Mang, A. I.; M. E. Colclough, N. Chauhan, A. B. Holmes, Macromolecules 2000, 

33, 303. 

17. D. J. H. Darensbourg, M. W.; Reibenspies, J. H., Macromolecules 1995, 28, 7577. 

18. C. W. Koning, J. R.; R. Parton, B. Plum, Steeman, P.; Darensbourg, D. J.; Holtcamp, M. 

W.; Reibenspies, J. H., Polymer 2001, 42, 3995. 

19. D. J. W. Darensbourg, J. R.; J. C. Yarbrough, J. Am. Chem. Soc. 2000, 122, 12487. 

20. S. Inoue, J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 2861. 

21. N. Takeda, S. I., Makromol. Chem 1978, 179, 1377. 

22. T. Aida, S. I., Macromolecules 1981, 14, 1162. 

23. T. Aida, S. I., J. Am. Chem. Soc. 1983, 105, 1304. 

24. X. B. Lu, X. J. F., R. He,, Appl. Catal. A 2002, 234, 25. 

25. X. B. Lu, R. H., C. X. Bai,, J. Mol. Catal. A 2002, 186, 1. 

26. D. J. Darensbourg, E. L. M., M.W. Holtcamp, K. K.Klausmeyer, J. H. Reibenspies,, 

Inorg. Chem 1996, 35, 2682. 

27. W. J. Kruper, D. V. D., J. Org. Chem 1995, 60, 725. 

28. E. N.Jacobsen, Acc. Chem. Res 2000, 33, 421. 

29. E. N. Jacobsen, M. T., J. F. Larrow,, 2000, PCT Int. Appl.WO 00/09463. 

30. R. L. Paddock, S. T. N., J. Am. Chem. Soc. 2001, 123, 11498. 

31. X. H. Chen, Z. Q. S., Y. F. Zhang, Macromolecules 1991, 24, 5305. 

32. Z. Q. Shen, X. H. C., Y. F. Zhang, Macromol. Chem. Phys 1994, 195, 2003. 

33. J. T. Guo, X. Y. W., Y. S. Xu, J. W. Sun, J. Appl. Polym. Sci. 2003, 87, 2356. 

34. C. S. Tan, T. J. H., Macromolecules 1997, 30, 3147. 

35. T. J. Hsu, C. S. T., Polymer 2001, 42, 5143. 

36. Z. Quan, X. H. W., X. J. Zhao, F. S.Wang,, Polymer 2003, 44, 5605. 

37. B. Y. Liu, X. J. Z., X. H.Wang, F. S.Wang,, J. Polym. Sci., Part A: Polym. Chem. 2001, 

39, 2751. 

38. R. Auras, B. Harte, S. Selke, Macromol. Biosci. 2004, 4, 835. 

39. J. Zhang, P. Krishnamachari, J. Z. Lou, A. Shahbazi, In Proceedings of the 2007 National 

Conference on Environmental Science and Technology, Uzochukwu, G. A., Ed. Springer: 

New York, 2009; pp 3-8. 

‐ 50 ‐

- 51 - 


40. M. Ajioka, K. Enomoto, K. Suzuki, A. Yamaguchi, Bull. Chem. Soc. Jpn. 1995, 68, 2125. 

41. S. Jacobsen, P. H. Degee, H. G. Fritz, P. H. Dubois, R. Jerome, Polym. Eng. Sci. 1999, 39, 

1311. 

42. H. R. Kricheldorf, M. Berl, N. Scharnagl, Macromolecules 1988, 21, 286. 

43. G. Schwach, J. Coudane, R. Engel, M. Vert, J. Polym. Sci., Part A: Polym. Chem. 1997, 

35, 3431. 

44. M. S. Reeve, S. P. McCarthy, M. J. Downey, R. A. Gross, Macromolecules 1994, 27, 825. 

45. G. Schwach, J. Coudane, R. Engel, M. Vert, Biomaterials 2002, 23, 993. 

46. L. Tang, L. Deng, J. Am. Chem. Soc. 2002, 124, 2870. 

47. O. T. Du Boullay, E. Marchal, B. Martin-Vaca, F. P. Cossio, D. Bourissou, J. Am. Chem. 

Soc. 2006, 128, 16442. 

48. C. Bonduelle, B. Martin-Vaca, F. P. Cossio, D. Bourissou, Chem.-Eur. J. 2008, 14, 5304. 

49. C. Bonduelle, B. Martin-Vaca, D. Bourissou, Biomacromolecules 2009, 10, 3069. 

50. X. Pang, H. Z. Du, X. S. Chen, X. H. Wang, X. B. Jing, Chem. Eur. J. 2008, 14, 3126. 

51. H. Z. Du, X. Pang, H. Y. Yu, X. L. Zhuang, X. S. Chen, D. M. Cui, X. H. Wang, X. B. 

Jing, Macromolecules 2007, 40, 1904. 

52. Z. H. Tang, V. C. Gibson, Eur. Polym. J. 2007, 43, 150. 

53. X. Pang, H. Z. Du, X. S. Chen, X. L. Zhuang, D. M. Cui, X. B. Jing, J. Polym. Sci., Part 

A: Polym. Chem. 2005, 43, 6605. 

54. Z. H. Tang, Y. K. Yang, X. Pang, J. L. Hu, X. S. Chen, N. H. Hu, X. B. Jing, J. Appl. 

Polym. Sci. 2005, 98, 102 

55. A. Kowalski, A. Duda, S. Penczek, Macromolecules 1998, 31, 2114. 

56. B. M. Chamberlain, M. Cheng, D. R. Moore, T. M. Ovitt, E. B. Lobkovsky, G. W. Coates, 

J. Am. Chem. Soc. 2001, 123, 3229. 

57. L. H. Piao, Z. L. Dai, M. X. Deng, X. S. Chen, X. B. Jing, Polymer 2003, 44, 2025. 

58. Z. Y. Zhong, P. J. Dijkstra, C. Birg, M. Westerhausen, J. Feijen, Macromolecules 2001, 

34, 3863-3868. 

59. Z. H. Tang, X. S. Chen, Q. Z. Hang, X. C. Bian, L. X. Yang, L. H. Piao, X. B. Jing, J. 

Polym. Sci., Part A: Polym. Chem. 2003, 41, 1934. 

60. H. R. Kricheldorf, A. Serra, Polym. Bull. 1985, 14, 497. 

61. Z. Y. Zhong, P. J. Dijkstra, J. Feijen, Angew. Chem.Int. Edit. 2002, 41, 4510. 

62. Z. H. Tang, X. S. Chen, Y. K. Yang, X. Pang, J. R. Sun, X. F. Zhang, X. B. Jing, J. Polym.

Chapter 1 

Sci., Part A: Polym. Chem. 2004, 42, 5974. 

63. Z. H. Tang, X. S. Chen, X. Pang, Y. K. Yang, X. F. Zhang, X. B. Jing, 

Biomacromolecules 2004, 5, 965. 

64. N. Nomura, A. Akita, R. Ishii, M. Mizuno, J. Am. Chem. Soc. 2010, 132, 1750. 

65. M. J. Stanford, A. P. Dove, Chem. Soc. Rev. 2010, 39, 486. 

66. H. Z. Du, A. H. Velders, P. J. Dijkstra, J. R. Sun, Z. Y. Zhong, X. S. Chen, J. Feijen, 

Chem.Eur. J. 2009, 15, 9836. 

67. D. Pappalardo, L. Annunziata, C. Pellecchia, Macromolecules 2009, 42, 6056. 

68. K. J. L. Burg, S. Porter, J. F. Kellam, Biomaterials 2000, 21, 2347. 

69. J. P. Penning, H. Dijkstra, A. J. Pennings, Polymer 1993, 34, 942. 

70. R. Bodmeier, K. H. Oh, H. Chen, Int. J. Pharm. 1989, 51, 1. 

71. H. Ohara, U. Doi, M. Otsuka, H. Okuyama, S. Okada, Seibutsu-Kogaku Kaishi-J. Soc. 

Ferment. Bioeng. 2001, 79, 142. 

72. M. Labet, W. Thielemans, Chem. Soc. Rev. 2009, 38, 3484. 

73. I. Barakat, P. Dubois, R. Jerome, P. Teyssie, Macromolecules 1991, 24, 6542. 

74. D. Bratton, M. Brown, S. M. Howdle, Macromolecules 2005, 38, 1190. 

75. V. Bergeot, T. Tassaing, M. Besnard, F. Cansell, A. F. Mingotaud, J. Supercrit. Fluids 

2004, 28, 249. 

76. S. W. Lee, S. J. Heo, J. Y. Jang, J. Y. Jeong, S. H. Kim, S. A. Park, E. S. Jeon, J. W. Shin, 

Tissue Eng. Regen. Med. 2010, 7, 9. 

77. S. Martinez-Diaz, N. Garcia-Giralt, M. Lebourg, J. A. Gomez-Tejedor, G.Vila, E. Caceres, 

P. Benito, M. M. Pradas, X. Nogues, J. L. G. Ribelles, J. C. Monllau, Am. J. Sports Med. 

2010, 38, 509. 

78. P. F. McDonald, J. G. Lyons, L. M. Geever, C. L. Higginbotham, J. Mater. Sci. 2010, 45, 

1284-1292. 

79. M. A. Del Nobile, A. Conte, G. G. Buonocore, A. L. Incoronato, A. Massaro, O. Panza, J. 

Food Eng. 2009, 93, 1. 

80. P. Ferreira, J. F. J. Coelho, M. H. Gil, Int. J. Pharm. 2008, 352, 172. 

81. Y. Aoyagi, C. K. Leong, D. D. L. Chung, J. Electron. Mater. 2006, 35, 416. 

82. C. Braud, R. Devarieux, A. Atlan, C. Ducos, M. Vert, J. Chromatogr. B 1998, 706, 73. 

83. H. Dong, S. G. Cao, Z. Q. Li, S. P. Han, D. L. You, J. C. Shen, J. Polym. Sci., Part A: 

Polym. Chem. 1999, 37, 1265. 

‐ 52 ‐

- 53 - 


84. H. Dong, H. D. Wang, S. G. Cao, J. C. Shen, Biotechnol. Lett. 1998, 20, 905. 

85. Y. Shibasaki, H. Sanada, M. Yokoi, F. Sanda, T. Endo, Macromolecules 2000, 33, 4316. 

86. J. C. Middleton, A. J. Tipton, Medical Plastics and Biomaterials Mar 1998, 30. 

87. D. K. Gilding, A. M. Reed, Polymer 1979, 20, 1459. 

88. S. L. Ishaug-Riley, L. E. Okun, G. Prado, M. A. Applegate, A. Ratcliffe, Biomaterials 

1999, 20, 2245. 

89. B. J. O'Keefe, M. A. Hillmyer, W. B. Tolman, J. Chem. Soc.-Dalton Trans. 2001, 15, 

2215. 

90. J. Zhou, G. Romero, E. Rojas, S. Moya, L. Ma, C. Y. Gao, Macromol. Chem. Phys. 2010, 

211, 404. 

91. W. D. Dai, N. Kawazoe, X. T. Lin, J. Dong, G. P. Chen, Biomaterials 2010 31, 2141. 

92. U. Bhardwaj, R. Sura, F. Papadimitrakopoulos, D. J. Burgess, Int. J. Pharm. 2010, 384, 

78. 

93. R. A. Miller, J. M. Brady, D. E. Cutright, J. Biomed. Mater. Res. 1977, 11, (5), 711-719. 

94. C. Simon-Colin, G. Raguenes, J. Cozien, J. G. Guezennec, J. Appl. Microbiol. 2008, 104, 

1425-1432. 

95. S. M. F. Pereira, R. S. Rodriguez, J. G. C. Gomez, Materia 2008, 13, 1. 

96. T. J. Rivers, T. W. Hudson, C. E. Schmidt, Adv. Funct. Mater. 2002, 12, 33. 

97. A. J. Heeger, Synth. Met. 2001, 125, 23-42. 

98. R. Wadhwa, C. F. Lagenaur, X. T. Cui, J. Controlled Release 2006, 110, 531. 

99. E. G. Fine, R. F. Valentini, R. Bellamkonda, P. Aebischer, Biomaterials 1991, 12, 775. 

100. H. Shirakawa, Synth. Met. 2001, 125, 3. 

101. K. I. Lee, H. Jopson, Polym. Bull. 1983, 10, 105. 

102. J. Ruhe, T. A. Ezquerra, G. Wegner, Synth. Met. 1989, 28, C177. 

103. D. Stanke, M. L. Hallensleben, L. Toppare, Synth. Met. 1995, 72, 89. 

104. J. Hlavaty, V. Papez, L. Kavan, P. Krtil, Synth. Met. 1994, 66, 165. 

105. J. Roncali, Chem. Rev. 1992, 92, 711. 

106. E. W. Tsai, S. Basak, J. Ruiz, J. R. Reynolds, K. Rajeshwar, J. Electrochem. Soc. 1988, 

135, C392. 

107. R. L, Elsenbaumer, K. Y. Jen, R. Oboodi, Synth. Met. 1986, 15, 169. 

108. S. Hotta, Synth. Met. 1987, 22, 103. 

109. M. J. Winokur, D. Spiegel, Y. Kim, S. Hotta, A. J. Heeger, Synth. Met. 1989, 28, C419.

Chapter 1 

110. C. A. Sandstedt, R. D. Rieke, C. J. Eckhardt, Chem. Mater. 1995, 7, 1057. 

111. E. M. Genies, A. Boyle, M. Lapkowski, C. Tsintavis, Synth. Met. 1990, 36, 139. 

112. S. Bhadra, D. Khastgir, N. K. Singha, J. H. Lee, Prog. Polym. Sci. 2009, 34, 783. 

113. K. Gurunathan, A. V. Murugan, R. Marimuthu, U. P. Mulik, D. P. Amalnerkar, 

Mater.Chem.Phys. 1999, 61, 173. 

114. N. C. Foulds, C. R. Lowe, J. Chem. Soc. Far. Trans. I 1986, 82, 1259. 

115. M. Umana, J. Waller, Anal. Chem. 1986, 58, 2979. 

116. J. Y. Wong, R. Langer, D. E. Ingber, Proc. Natl. Acad. Sci. U. S. A. 1994, 91, 3201. 

117. G. X. Shi, M. Rouabhia, Z. X. Wang, L. H. Dao, Z. Zhang, Biomaterials 2004, 25, 2477. 

118. N. K. Guimard, N. Gomez, C. E. Schmidt, Prog. Poly. Sci. 2007, 32, 876. 

119. C. E. Schmidt, V. R. Shastri, J. P. Vacanti, R. Langer, Pro. Natl. Acad. Sci. U. S. A.1997, 

94, 8948. 

120. S. Lakard, G. Herlem, N. Valles-Villareal, G. Michel, A. Propper, T. Gharbi, B. Fahys, 

Biosens. Bioelectron. 2005, 20, 1946. 

121. P. M. George, A. W. Lyckman, D. A. LaVan, A. Hegde, Y. Leung, R. Avasare, C. Testa, P. 

M. Alexander, R. Langer, M. Sur, Biomaterials 2005, 26, 3511. 

122. Y. Wan, H. Wu, D. J. Wen, Macromol. Biosci. 2004, 4, 882. 

123. H. Castano, E. A. O'Rear, P. S. McFetridge, V. I. Sikavitsas, Macromol. Biosci. 2004, 4, 

785. 

124. X. P. Jiang, Y. Marois, A. Traore, D. Tessier, L. H. Dao, R. Guidoin, Z. Zhang, Tissue 

Engineering 2002, 8, 635. 

125. A. Boyle, E. Genies, M. Fouletier, J. Electroanal. Chem. 1990, 279, 179. 

126. M. Pyo, G. Maeder, R. T. Kennedy, J. R. Reynolds, J. Electroanal.l Chem. 1994, 368, 

329. 

127. M. Pyo, J. R. Reynolds, Chem. Mater. 1996, 8, 128. 

128. A. J. Hodgson, M. J. John, T. Campbell, A. Georgevich, S. Woodhouse, T. Aoki, N. 

Ogata, G. G. Wallace, In Smart Materials Technologies and Biomimetics-Smart 

Structures and Materials 1996, Crowson, A., Ed. 1996, 2716, 164. 

129. J. H. Collier, J. P. Camp, T. W. Hudson, C. E. Schmidt, J. Biomed. Mater. Res. 2000, 50, 

574. 

130. D. D. Ateh, P. Vadgama, H. A. Navsaria, Tissue Engineering 2006, 12, 645. 

131. N. Gomez, J. Y. Lee, J. D. Nickels, C. E. Schmidt, Adv. Funct. Mater. 2007, 17, 1645. 

‐ 54 ‐

- 55 - 


132. M. Mattioli-Belmonte, G. Giavaresi, G. Biagini, L. Virgili, M. Giacomini, M. Fini, F. 

Giantomassi, D. Natali, P. Torricelli, R. Giardino, Int. J. Artif. Organs 2003, 26, 1077. 

133. Y. Wei, P. I. Lelkes, A. G. MacDiarmid, E. Guterman, S. P. K. Cheng,; P. Bidez, 

Contemporary Topics in Advanced Polymer Science and Technology. Peking University 

Press: Beijing, 2004. 

134. M. Y. Li, Y. Guo, Y. Wei, A. G. MacDiarmid, P. I. Lelkes, Biomaterials 2006, 27, 2705. 

135. P. Wang, K. L. Tan, F. Zhang, E. T. Kang, K. G. Neoh, Chem. Mater. 2001, 13, 581. 

136. Y. Guo, M. Y. Li, A. Mylonakis, J. J. Han, A. G. MacDiarmid, X. S. Chen, P. I. Lelkes, Y. 

Wei, Biomacromolecules 2007, 8, 3025. 

137. L. H. Huang, J. Hu, L. Lang, X. Wang, P. B. Zhang, X. B. Jing, X. H. Wang, X. S. Chen, 

P. I. Lelkes, A. G. MacDiarmid, Y. Wei, Biomaterials 2007, 28, 1741. 

138. L. H. Huang, X. L. Zhuang, J. Hu, L. Lang, P. B. Zhang, Y. S. Wang, X. S. Chen, Y. Wei, 

X. B. Jing, Biomacromolecules 2008, 9, 850. 

139. J. Hu, L. H. Huang, X. L. Zhuang, P. B. Zhang, L. Lang, X. S. Chen, Y. Wei, X. B. Jing, 


140. M. Waugaman, B. Sannigrahi, P. McGeady, I. M. Khan, Eur. Polym. J. 2003, 39, 1405. 

141. M. Gerard, A. Chaubey, B. D. Malhotra, Biosens. Bioelectron. 2002, 17, 345. 

142. E. Bakker, M. Telting-Diaz, Anal. Chem. 2002, 74, 2781. 

143. S. Cosnier, Electroanalysis 2005, 17, 1701. 

144. E. Tamiya, I. Karube, S. Hattori, M. Suzuki, K. Yokoyama, Sens. Actuators. 1989, 18, 

297. 

145. T. Ahuja, I. A. Mir, D. Kumar, Rajesh, Biomaterials 2007, 28, 791. 

146. J. Chen, B. Winther-Jensen, C. Lynam, O. Ngamna, S, Moulton, W. M. Zhang, G. G. 

Wallace, Electrochem. Solid. State. Lett. 2006, 9, H68. 

147. M. I. Rodriguez, E. C. Alocilja, Ieee. Sens. J. 2005, 5, 733. 

148. M. Mir, I. Katakis, Anal. Bioanal. Chem. 2005, 381, 1033. 

149. X. H. Jiang, X. Q. Lin, Anal. Chim. Acta. 2005, 537, 145. 

150. M. Wilchek, E. A. Bayer, Anal. Biochem. 1988, 171, 1. 

151. L. M. T. Rodrigez, M. Billon, A. Roget, G. Bidan, J.Electroanal. Chem. 2002, 523, 70. 

152. S. Cosnier, R. E. Ionescu, S. Herrmann, L. Bouffier, M. Demeunynck, R. S. Marks, Anal. 

Chem. 2006, 78, 7054. 

153. T. Livache, A. Roget, E. Dejean, C. Barthet, G. Bidan, R. Teoule, Nucleic. Acids. Res.

Chapter 1 

1994, 22, 2915. 

154. N. Lassalle, A. Roget, T. Livache, P. Mailley, E. Vieil, Talanta 2001, 55, 993. 

155. A. I. Minett, J. N. Barisci, G. G. Wallace, React. Funct. Polym. 2002, 53, 217. 

156. A. I. Minett, J. N. Barisci, G. G. Wallace, Anal. Chim. Acta. 2003, 475, 37. 

157. M. Hiller, C. Kranz, J. Huber, P. Bauerle, W. Schuhmann, Adv. Mater. 1996, 8, 219. 

158. H. Korri-Youssoufi, B. Makrouf, Anal. Chim. Acta. 2002, 469, 85. 

159. M. Bera-Aberem, H. A. Ho, M. Leclerc, Tetrahedron 2004, 60, 11169. 

160. J. W. Lee, F. Serna, J. Nickels, C. E. Schmidt, Biomacromolecules 2006, 7, 1692. 

161. B. S. Ebarvia, S. Cabanilla, F. Sevilla, Talanta 2005, 66, 145. 

162. F. Le Floch, H. A. Ho, M. Leclerc, Anal. Chem. 2006, 78, 4727. 

163. A. A. Entezami, B. Massoumi, Iran. Polym. J. 2006, 15, 13. 

164. M. R. Abidian, D. H. Kim, D. C. Martin, Adv. Mater. 2006, 18, 405. 

165. Y. L. Li, K. G. Neoh, E. T. Kang, J. Biomed. Mater. Res., Part A 2005, 73A, 171. 

166. T. F. Otero, J. M. Sansinena, Bioelectrochem. Bioener. 1997, 42, 117. 

167. T. F. Otero, M. T. Cortes, Sens.Actuators. B Chem. 2003, 96, 152. 

168. M. R. Gandhi, P. Murray, G. M. Spinks, G. G. Wallace, Synth. Met. 1995, 73, 247. 

169. V. Mottaghitalab, B. B. Xi, G. M. Spinks, G. G. Wallace, Synth. Met. 2006, 156, 796. 

170. E. Smela, N. Gadegaard, Adv. Mater. 1999, 11, 953. 

171. L. M. Low, S. Seetharaman, K. Q. He, M. J. Madou, Sens. Actuators. B Chem. 2000, 67, 

149. 

172. E. Smela, Adv. Mater. 2003, 15, 481. 

173. O. Ouerghi, A. Touhami, N. Jaffrezic-Renault, C. Martelet, H. Ben Ouada, S. Cosnier, 

Bioelectrochemistry 2002, 56, 131. 

174. B. Fink, S. Dikalov, E. Bassenge, Free. Radical. Bio. Med. 2000, 28, 121. 

175. C. J. Hawker, A. W. Bosman, E. Harth, Chem. Rev. 2001, 101, 3661. 

176. Y. Katayama, N. Soh, M. Maeda, Chemphyschem 2001, 2, 655. 

177. R. A. Sheldon, I. W. C. E. Arends, Adv. Synth. Catal. 2004, 346, 1051. 

178. H. Nishide, T. Suga, Electrochim. Soc. Interface 2005, 14, 32. 

179. T. Osa, U. Akiba, I. Segawa, J. M. Bobbitt, Chem. Lett. 1988, 8, 1423. 

180. W. M. Xu, L. Z. Liu, M. Loizidou, M. Ahmed, I. G. Charles, Cell. Res. 2002, 12, 311. 

181. M. Valko, D. Leibfritz, J. Moncol, M. T. D. Cronin, M. Mazur, J. Telser, Int. J. Biochem. 

Cell. Biol. 2007, 39, 44. 

‐ 56 ‐

182. R. B. Weller, J. Invest. Dermatol. 2009, 129, 2335. 

183. H. Nishide, K. Oyaizu, Science 2008, 319, 737. 

- 57 - 


184. K. Oyaizu, Y. Ando, H. Konishi, H. Nishide, J. Am. Chem. Soc. 2008, 130, 14459. 

185. Y. Takahashi, N. Hayashi, K. Oyaizu, K. Honda, H. Nishide, Polym. J. 2008, 40, 763. 

186. K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Macromol. Chem. Phys. 2009, 210, 1989. 

187. K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 7, 836. 

188. H. Nishide, K. Koshika, K. Oyaizu, Pure. Appl.Chem. 2009, 81, 1961. 

189. K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 2339. 

190. T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 1627. 

191. K. Koshika, N. Chikushi, N. Sano, K. Oyaizu, H. Nishide, Green. Chem. 2010, To be 

published. 

192. Y. Yonekuta, K. Susuki, K. C. Oyaizu, K. J. Honda, H. Nishide, J. Am. Chem. Soc. 2007, 

129, 14128. 

193. M. D. Lang, C. C. Chu, J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 4214. 

194. G. Jokhadze, M. Machaidze, H. Panosyan, C. C. Chu, R. Katsarava, J. Biomater. Sci. 

Polym. Ed. 2007, 18, 411. 

195. L. Li, C. C. Chu, J. Biomater. Sci. Polym. Ed. 2009, 20, 341. 

196. C. C. Chu, "Polymeric Biomaterials" 2nd Edition 2002, Marcel Dekker, Inc. Chapter 5. 

197. C. S. Winalski, S. Shortkroff, R. V. Mulkern, E. Schneider, G. M. Rosen, Magn. Reson. 

Med. 2002, 48, 965. 

198. H. Hayashi, S. Karasawa, A. Tanaka, K. Odoi, K. Chikama, H. Kuribayashi, N. Koga, 

Magn. Reson. Chem. 2009, 47, 201. 

199. Y. Huang, A. J. Nan, G. M. Rosen, C. S. Winalski, E. Schneider, P. Tsai, H. Ghandehari, 

Macromol. Biosci. 2003, 3, 647. 

200. M. Gussoni, F. Greco, P. Ferruti, E. Ranucci, A. Ponti, L. Zetta, New. J. Chem. 2008, 32, 

323. 

201. K. I. Matsumoto, S. Subramanian, R. Murugesan, J. B. Mitchell, M. C. Krishna, 

Antioxid. Redox Signaling. 2007, 9, 1125. 

202. G. Yan, L. Peng, S. Q. Jian, L. Li, S. E. Bottle, Chin. Sci, Bull. 2008, 53, 3777. 

203. K. Saito, S. Kazama, H. Tanizawa, T. Ito, M. Tada, T. Ogata, H. Yoshioka, Biosci. 

Biotech. Biochem. 2001, 65, 787. 

204. T. Yoshitomi, D. Miyamoto, Y. Nagasaki, Biomacromolecules 2009.

Chapter 1 

205. T. Yoshitomi, R. Suzuki, T. Mamiya, H. Matsui, A. Hirayama, Y. Nagasaki, Bioconjug. 

Chem. 2009, 20, 1792. 

206. C. S. Xiao, H. Y. Tian, X. L. Zhuang, X. S. Chen, X. B. Jing, Sci. Chin. Ser. B Chem. 

2009, 52, 117. 

207. E. Yoshida, T. Tanaka, Colloid. Polym. Sci. 2006, 285, 135. 

208. E. Yoshida, T. Tanaka, Colloid. Polym. Sci. 2008, 286, 827. 

‐ 58 ‐

Chapter 2 

Synthesis and Electrochemistry of Schiff Base Cobalt(III) 

Complexes and Their Catalytic Activity for Copolymerization of 

Epoxide and Carbon Dioxide 


2.2 Synthesis and Characterization of L-Co III -dnp Complexes 

2.3 Copolymerization of CO2 and rac-PO 

2.4 Electrochemistry of Cobalt(III) Complexes 

2.5 Conclusions 

2.6 Experimental Section 

References

Chapter 2 


Polycarbonate is one of the important thermoplastic with a good heat resistance, excellent 

optical and electrical properties and the unique biodegradability. 1-2 The mechanical properties 

are predominated by the stereostructure of the regioselectivity of the linear carbonate linkage 

in the polycarbonate. The enantioselectivity of the polycarbonate, head-to-tail connectivity, 

and carbonate linkage are important factors to determine the thermal stability and the 

mechanical properties. The reactivity and enantioselectivity are mainly related to the type and 

chemical stereostructure of the catalyst system. Several efficient catalyst systems, such as zinc, 

aluminum, cadmium, manganese, cobalt, chromium and rare-earth-metal complexes, in 

combination with other reagents for the copolymerization of CO2 and alicyclic epoxides such 

as propylene oxide have been developed. 3-7 Recently, salen-type catalysts have become the 

focus of many groups. The chemical structures of the complexes as catalysts are related to the 

overall catalytic copolymerization performance of CO2 with an epoxide. 8 Transition metal 

Schiff-base complexes with N,N,O,O-tetradentate ligands have been extensively studied, 9-16 

because of their various applications 17-19 and importance in the area of coordination 

chemistry. 20 Cobalt(III) Schiff-base complexes are characterized by the asymmetric structure 

containing axial ligands, which are frequently labile, and exhibit high activities and yet a 

significant stability. 21 Especially, binary catalytic system of many forms of the 

(salen)Co(III)/Lewis base as catalysts is widely used in the fixation of CO2 with epoxide to 

form polycarbonates. 22-26 Recent studies have focused on how to improve the efficiency of the 

copolymerization and to enhance the catalytic activity of these complexes. 22, 24, 25, 27-30 In this 

chapter, we describe the electrochemical properties of several structurally related cobalt 

complexes and the X-ray crystal structure, which provided an important insight into the 

copolymerization mechanism of CO2 and propylene oxide catalyzed by these complexes. 

To elucidate factors that dominate the cobalt-catalyzed polymerization, a series of cobalt 

complexes as catalyst containing N,N,O,O-tetradentate Schiff bases were synthesized. These 

complexes were different in bridging lengths between the two nitrogen atoms in the Schiff 

base ligands. The modification of the electronic and steric environments by altering the 

substituents on the diimine-bridge of the salen ligand around the metal center significantly 

affected the catalytic activity for the poly(propylene carbonate) formation, which was 

successfully ascribed to the stability of the six-coordinate cobalt complex and the lability of 

the propagating polymer chain as the axial ligand. 

2.2 Synthesis and Characterization of L-CoIII-dnp Complexes 

2.2.1 Synthesis of the Ligands 

‐ 60 ‐

Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their 

Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide 

The Schiff base ligands were synthesized by the condensation of the corresponding 

diamine and 3,5-di-tert-butylsalicylaldehyde in a 1:2 molar ratio in methanol (Scheme 2.1). 

The ligands were further purified by recrystallization from ethanol. 

2.2.2 Synthesis of the Complexes 

The L-Co III -dnp complex was prepared by the reaction of cobalt acetate tetrahydrate and 

the ligand, followed by subsequent oxidation in the presence of 1 equiv. of 2,4-dinitrophenol 

and an excess amount of oxygen. The formation of the Schiff base ligand and their complexes 

have been confirmed by spectroscopic methods and X-ray diffraction experiments (vide infra). 

All the Schiff base complexes were stable at room temperature, and were soluble in 

methylene chloride, chloroform and DMSO. 

Scheme 2.1 Preparation of the L-Co III -dnp complexes. 

2.2.3 Complexes Structure Characterization 

The molecular structure of L 1 -Co III -dnp (Figure 2.1) revealed that the complex was 

monomeric with a six-coordinated central cobalt atom in the solid state. 

‐ 61 ‐

Chapter 2 

Figure 2.1 Crystal structure of the L 1 -Co III -dnp complex. 

The geometry around the cobalt atom was octahedral with an almost linear axial 

O(2)–Co(1)–O(4) bond angle of 177.52(7)º, and nearly perpendicular for O(1)–Co(1)–O(3), 

O(3)–Co(1)–N(2), N(2)–Co(1)–N(1) and N(1)–Co(1)–O(1) of 88.03(7)º, 94.96(8)º, 83.29(8)º, 

and 93.71(7)º, respectively, for the equatorial donor atoms. The Co(1) atom deviated from the 

N(1)N(2)O(1)O(3) least-squares plane by only 0.0276 Å, representing the nearly ideal 

octahedral arrangement. The distances from the Co atom to the O(1), O(2), O(3), O(4), N(1) 

and N(2) atoms were 1.8969(15), 1.8868(15), 1.8964(16), 1.9672(16), 1.8985(18) and 

1.902(18) Å, respectively (Table 2.1). Interestingly, the phenolate oxygen, O(3), is involved in 

the equatorial planed rather than the four donor atoms in the tetradentate Schiff-base ligand. 

Table 2.1 Selected bond distances and angles for L 1 -Co III -dnp. 

Bond Distance(Å) Bond Angle(º) Bond Angle(º) 

Co-N(1) 1.8985(18) O(1)-Co-O(2) 92.54(7) O(1)-Co-N(2) 176.99(7) 

Co-O(1) 1.8969(15) O(1)-Co-N(1) 93.71(7) O(2)-Co-N(1) 96.37(7) 

Co-O(3) 1.8964(16) N(2)-Co-N(1) 83.29(3) O(1)-Co-O(3) 88.03(7) 

Co-N(2) 1.9020(18) O(2)-Co-O(3) 86.58(6) N(2)-Co-O(3) 94.96(8) 

Co-O(2) 1.8868(15) N(1)-Co-O(3) 176.50(7) O(1)-Co-O(4) 87.41(7) 

Co-O(4) 1.9672(16) O(2)-Co-O(4) 177.52(7) N(2)-Co-O(4) 92.16(7) 

N(1)-Co-O(4) 86.11(7) O(3)-Co-O(4) 90.93(7) 

O(2)-Co-N(2) 88.03(7) 

The IR spectral data of the ligands and the complexes in Table 2.2 showed major bands 

around 1624 cm -1 assigned to the C=N stretching vibration (vC=N), and around 1610 cm -1 and 

1525 cm -1 assigned to the ring vibrations. The peaks around 1566 cm -1 and 1327 cm -1 were 

assigned to the stretching of the N=O bonds, and the peaks around 1252 cm -1 and 1063 cm -1 

‐ 62 ‐



were definitely assigned to the stretching of the C–O and C–N bonds, respectively. 31, 32 The 

spectra of the complexes revealed that these vibrations shifted to lower wave numbers 

compared to the corresponding bands observed for the free ligands, as a result of the decrease 

in bond order upon complexation. Also, the characteristic bands for the out-of-plane 

deforming, δOH, of the free ligands were absent in the case of the complexes, as a consequence 

of the involvement of the oxygen anion in the bonds with the cobalt atom. The formation of 

the cobalt–oxygen bonds led to major absorption bands around 571 cm -1 assigned to a vCo–O 

vibration. 33 The IR spectra clearly showed the formation of the complexes by the coordination 

33, 34 

of cobalt(III) to the phenolic oxygens and the C=N nitrogens. 

Table 2.2. Infrared spectroscopic data for L-Co III -dnp. 

Complex vCo–O vC–N vC–O vC=N vAr-ring vN=O 

L 1 -Co III -dnp 

L 2 -Co III -dnp 

571 1063 1252 1624 1610 1566 

1525 1327 

579 1065 1257 1626 1596 1331 

1521 1569 

L 3 -Co III -dnp 583 1056 1269 1625 1597 1555 

1525 1310 

L 4 -Co III -dnp 575 1061 1261 1625 1601 1568 

1522 1318 

The –OH proton signals in the 1 H NMR spectra of the free ligands (13.75, 13.58, 13.58, 

and 13.82 ppm for H2L 1 , H2L 2 , H2L 3 and H2L 4 , respectively) disappeared in the complexes 

indicating that the –OH group was deprotonated and bonded to the metal ion as an oxygen 

anion. One 2, 4-dinitrophenoxide counter ion was involved in each cobalt(III) complex to 

maintain electroneutrality. Comparing the 1 H NMR spectra of the free ligands with the 

complexes, the imine proton resonances of the ligands (8.29, 8.44, 8.34 and 8.40 ppm in H2L 1 , 

H2L 2 , H2L 3 and H2L 4 , respectively) 15 shifted to lower fields upon the complexation (8.62, 

9.01, 8.41 and 8.89 ppm, respectively), as a result of the deshielding effect. The data from the 

elemental analysis and ESI MS also confirmed the structures of the complexes. 

2.3 Copolymerization of CO2 and rac-PO 

2.3.1 Mechanism for CO2/rac-PO Copolymerization 

The molecular structure of L 1 -Co III -dnp clearly demonstrated that the cobalt(III) tends to 

form a six coordination complex, which strongly suggested that all of the relevant 

L-Co III -dnp complexes characterized by the axial 2,4-dinitrophenolate ligands were 

‐ 63 ‐

Chapter 2 

six-coordinated in the solid state. Furthermore, end group analysis of the obtained polymer 

suggested that the six-coordination arrangement was maintained even in solution, i.e., in the 

catalytic cycle. The isolated poly(carbonate) obtained by the L 1 -Co III -dnp/Bu4NBr catalyst 

was determined by the presence of a 2,4-dinitrophenoxyl moiety as the end group of the 

polymer chain (Figure 2.2). 

Figure 2.2 1 H NMR spectrum of the poly(carbonate) catalyzed by L 1 -Co III -dnp/ Bu4NBr (298K, 

(CD3)2SO, 500 MHz). The enlarged spectrum between 9.0 and 7.4 ppm indicated that the polymer 

ended with the 2,4-dinitrophenoxyl group. 

The good agreement of the number-averaged molecular weights based on the end-group 

analysis (Mn= 2.64 × 10 4 ) and that determined by the GPC experiment (Mn = 1.40 × 10 4 ) 

suggested the polymerization mechanism in which the monomer was inserted to the 

cobalt-oxygen bond of the propagating end, as shown in Scheme 2.2. 

Scheme 2.2 Proposed mechanism for CO2/rac-PO copolymerization using the 

L-Co III -dnp/Bu4NBr catalyst systems. 

‐ 64 ‐



The Lewis basic monomer coordinated to the metal center in the axial site transferred to 

the propagating metal-polymer chain, thereby labilizing the metal alkoxide bond and 

facilitating the insertion of CO2. 3, 15, 22-25 The rac-PO monomer might be first favorably 

inserted into the Co−OR bond of the Schiff base cobalt complexes, followed by the insertion 

of the CO2 monomer, as shown in Scheme 2.2. Subsequent alternating copolymerization of 

rac-PO and CO2 afforded the alternating repeating unit structure to yield the polycarbonate. 

The side reaction to yield the cyclic carbonate could take place through the backbiting 

degradation of the growing polymer-catalyst complex, which may lead to the lower polymer 

yield. A similar mechanism has been proposed by Nguyen and co-workers using cobalt (salen) 

and N, N-dimethylaminoquinoline for the copolymerization of CO2 and PO. 15 

2.3.2 Complex Structure and Polymerization 

The copolymerizations of CO2 and rac-PO catalyzed by the series of L-Co III -dnp/Bu4NBr 

catalysts were studied, and the results are summarized in Table 2.3. The diimine-bridge (X) 

between the two nitrogen atoms in the Schiff bases significantly affected the catalytic activity. 

With X being (R,R)-1,2-cyclohexanediamine (L 1 -Co III -dnp in Scheme 2.1), the highest 

catalytic activity with a turn-over frequency (TOF) of 245 h -1 was accomplished (Table 2.3). 

Under the same conditions, when X was replaced by ethylenediimine or (R, 

R)-1,2-diphenylethylenediimine, the catalytic frequency was reduced to 210 and 190 h -1 for 

the L 2 -Co III -dnp/Bu4NBr and the L 3 -Co III -dnp/Bu4NBr catalysts, respectively. When X was 

2,2-dimethyl-1,3-propylenediimine, the L 4 -Co III -dnp/Bu4NBr catalyst showed the lowest 

activity. The catalytic activity of these complexes for the alternating copolymerization of CO2 

and rac-PO was in the order of L 1 -Co III -dnp > L 2 -Co III -dnp > L 3 -Co III -dnp >> L 4 -Co III -dnp, 

which revealed that the diimine-bridges with the three carbon atoms led to a lower activity. 

One could anticipate that the degree of polarization and/or the strength of the Co–O bond for 

the axial coordination should influence the rate of the monomer insertion and thus should 

affect the rate of the propagation during the polymerization. Although attempts to obtain all 

the molecular structures of the L-Co III -dnp complexes were not successful, the nature of the 

Co–O bond has been successfully determined by electrochemical methods (vide infra). 

Table 2.3 The catalytic activity for the copolymerization of CO2/rac-PO using the L-Co III -dnp/Bu4NBr 

catalyst systems. a) 

Run Complex 

TOF 

(h –1 ) b) 

Selectivity 

(%PPC) c) 

Head-to-tail 

Linkages (%) d) 

‐ 65 ‐ 

Mn e) 

×10 4 

Mn f) 

×10 4 

1 L 1 -Co III -dnp 245 74 88 2.6 1.4 1.4 

PDI f) 

2 L 2 -Co III -dnp 210 60 71 1.4 1.1 1.3 

3 L 3 -Co III -dnp 190 75 82 4.0 2.6 1.2

Chapter 2 

4 L 4 -Co III -dnp 25 70 81 3.1 1.4 1.2 

a) 

The reaction was performed in neat rac-PO ([rac-PO]:[Co]:[Bu4NBr] = 1000:1:1, molar ratio) in a 100 

mL autoclave at 25 ºC with 2 MPa of CO2 for 2 h; b) Turnover frequency of rac-PO to products 

(polycarbonate and cyclic carbonate); c) Selectivity for PPC over PC as determined by 1 H NMR 

spectroscopy; d) Determined by 13 C NMR spectroscopy; e) Determined by 1 H NMR. f) Determined by GPC. 

2.4 Electrochemistry of Cobalt(III) Complexes 

The electrochemical data for the ligands and the L-Co III -dnp complexes were shown in 

Table 2.4, and the representative voltammograms were presented in Figures 2.3 and 2.4. All 

CV curves for the ligands were recorded in the potential range of -2.00 to 1.50 V. The 

voltammograms showed an irreversible oxidation peak at potentials between 1.08 and 1.20 V. 

These peaks were ascribed to the oxidation of the Schiff base ligands (Figure 2.3). For the 

L-Co III -dnp complexes, the potential sweeps were made from -1.20 to 1.50 V. It is considered 

that the nature of the cobalt(III) atom in the Schiff base complexes should dominate the 

catalytic activity for the copolymerization of the epoxide and carbon dioxide, which prompted 

us to pay close attention to the Co III + e - 

Co II redox potential. The redox couple of Co III 

+ e - 

Co II was observed for L 1 -Co III -dnp, L 2 -Co III -dnp, L 3 -Co III -dnp, and L 4 -Co III -dnp 

at E1/2 = 107, 134, 163, and 32 mV, respectively (Figure 2.4). The absence of any redox 

responses near 0 to 0.5 V in the metal-free ligands (Figure 2.3) allowed one to ascribe these 

quasi-reversible waves to the cobalt(II/III) redox couple. 

Figure 2.3 Cyclic voltammograms of 1 mM solutions of H2L in DMF containing 0.1 M 

NBu4ClO4 on a glassy carbon electrode (� 3.3 mm). Potential is shown in V vs. Ag/Ag + at the 

scan rate of 100mV s -1 . I: H2L 1 ; II: H2L 2 ; III: H2L 3 ; IV: H2L 4 . 

‐ 66 ‐



Figure 2.4. Cyclic voltammograms of 1 mM solutions of L-Co III -dnp in DMF 

containing 0.1 M NBu4ClO4 on a carbon electrode. Potential is shown in V vs. 

Ag/Ag + at the scan rate of 100 mV s -1 . I: L 1 -Co III -dnp; II: L 2 -Co III -dnp; III: 

L 3 -Co III -dnp; IV: L 4 -Co III -dnp. 

Co II for L-Co III -dnp (Table 2.4) revealed that the length 

and steric structures of the diimine-bridges between the two nitrogen atoms in the Schiff bases 

significantly affected the redox potential. These complexes had the same auxiliary ligand, 

2,4-dinitrophenolate, but different diimine-bridges. The gradual shift of E1/2 to negative 

potentials for the L 3 -Co III -dnp, L 2 -Co III -dnp, and L 1 -Co III -dnp complexes indicated that the 

election-donating character of the ligand increased in this order, stabilizing the axial Co–O 

(phenolate) bond in Figure 2.1, which is an advantage when forming the transition state 

(Scheme 2.2) and thus leads to a faster copolymerization of CO2 and PO. However, 

The E1/2 data of Co III + e - 

L 4 -Co III -dnp has the most negative E1/2 of 32 mV and yet the lowest activity for the 

copolymerization. It is believed that the diimine-bridges containing two carbon atoms and 

three carbon atoms leads to a square pyramidal (sqp) and a trigonal bipyramidal (tbp) 

geometry for the central five-coordinated metal atom, respectively. Thus, the low catalytic 

activity of L 4 -Co III -dnp during the copolymerization of CO2 and PO may be ascribed to the 

unfavorable tbp geometry of the central cobalt atom, which prevents Bu4NBr from 

coordinating with cobalt in an axial position opposite to the Co–O (phenolate) bond, leading 

to the decrease in the activity. The utilization of carbon dioxide (CO2) has received much 

attention because of its potential use as an abundant, economical and biorenewable resource 

and its weakening of global warming or the greenhouse effect. The copolymerization of CO2 

as the monomer with epoxide was firstly reported by Inoue et al. in the 1960s. 35 The 

combination of the X-ray crystallographic and electrochemical results in the present 

investigation provided important insights into the factors dominating the catalytic activity 

‐ 67 ‐

Chapter 2 

useful for designing a highly efficient catalytic system. 

Table 2.4 Cyclic voltammogram data for the transition between Co III + e - 

Complex Epc (mV) E1/2 (mV) ΔE ipa/ipc 

L 1 -Co III -dnp 32 107 150 0.64 

L 2 -Co III -dnp 84 134 99 0.83 

L 3 -Co III -dnp 52 163 221 0.82 

L 4 -Co III -dnp -71 32 206 0.78 

‐ 68 ‐ 

Co II of L-Co III -dnp. a) 

a) Determined using 1 mM solution of L-Co III -dnp in DMF in the presence of 0.1 M NBu4ClO4 at carbon 

electrode vs. Ag/Ag + at the scan rate of 100 mV s -1 . 


A series of Cobalt Schiff-base complexes were investigated as the catalyst for the 

alternating copolymerization of CO2 and rac-PO in the presence of Bu4NBr. The 

poly(propylene carbonate) (PPC) and cyclic propylene carbonate (PC) selectivity of the 

resultant copolymers were determined by modification of the length of the diimine bridges 

between the two nitrogen atoms in the ligands. The L 1 -Co III -dnp/Bu4NBr catalyst exhibited 

the highest activity, PPC/PC selectivity, and degree of head-to-tail linkages. The 

L 2 -Co III -dnp/Bu4NBr catalyst showed slightly lower head-to-tail linkages. For the dimine 

bridges containing three-carbon chains between the two nitrogen atoms in the Schiff bases, 

the corresponding L 4 -Co III -dnp complex displayed the lowest catalytic activity. Based on the 

electrochemical measurements, the half-wave potentials of the complexes were obtained and 

the catalytic activity of these complexes was compared. The higher stability for the axial 

group’s metal–O (phenolate) bond indicated the more negative E1/2 of the Co III + e - 

redox couple in the L-Co III -dnp complexes, and the higher catalytic activity for the 

copolymerization of PO and CO2. In the case of the cobalt complexes with more positive 

Co(II/III) potentials and lower electron density on the cobalt center, the end of propagating 

chain to the cobalt center was considered to determine the overall polymerization rate. 

However, the L 4 -Co III -dnp with the most negative E1/2 possessed the lowest catalytic activity, 

which may be due to the unfavorable trigonal bipyramidal geometry during the transition state, 

preventing the Lewis bases from bonding to the metal center. 

2.6 Experimental Part 

Materials 

All experiments involving air- and/or water-sensitive compounds were carried out using 

standard Schlenk techniques under a dry argon atmosphere. All solvents were purified by 

Co II



standard procedures before use. 

(R,R)-N,N�-(1,2-cyclohexene)bis(3,5-di-tert-butylsalicylideneimine) (H2L 1 ), 

N,N�-ethylenebis(3,5-di-tert-butylsalicylideneimine) (H2L 2 ), 

(R,R)-N,N�-(1,2-diphenylethylethylene)bis(3,5-di-tert-butylsalicylideneimine) (H2L 3 ), and 

N,N�-(2,2-dimethyl-1,3-propylene)bis(3,5-di-tert-butylsalicylideneimine) (H2L 4 ) were 

synthesized according to previously published procedures. 22, 30 All other reagents were 

commercially available, and were used as received. 

Instrumentation and Methods 

The NMR spectra were recorded by a Bruker AV 400M or a Bruker AV 500M instrument 

in CDCl3 or (CD3)2SO at room temperature. Tetramethylsilane was used as the internal 

standard. The FT-IR spectra were obtained using a Perkin-Elmer 2000 FT-IR spectrometer. 

The EIS-MS data were obtained using a Finnigan LCQ TM ion trap mass spectrometer. It was 

operated with the following parameters: positive ion and negative ion mode, the electrospray 

voltage at 4.5 kV, the capillary voltage at 20 V, the tube lens offset voltage at 15 V and the 

capillary temperature between 80─100 . High-purity nitrogen (N2) was used as the sheath 

gas, and its flow rate was 60 arbitrary units. The sample solutions were injected at 5 µL min -1 

via a syringe pump. The GPC measurements were performed by a Waters 410 GPC with THF 

as the eluent (flow rate: 1 ml min -1 at 25 ). Polystyrene was used as the internal standard. 

The cyclic voltammetry experiments were performed using the BAS 660C electrochemical 

system. The sample solutions typically contained 1 mM of the cobalt complex in DMF and 

tetrabutylammoium perchlorate (TBAP) (0.1 M) as the supporting electrolyte at room 

temperature. The cyclic voltammograms were obtained at the scan rate of 100 m V s −1 under 

a nitrogen atmosphere. The potential sweep ranges were between −2.00 and 1.50 V for the 

ligands and between −1.20 and 1.50 V for the cobalt complexes. 

A suitable crystal for the X-ray diffraction experiment was obtained by slow evaporation 

of a saturated toluene solution of L 1 -Co III -dnp at room temperature, which was carefully 

collected and mounted on a Bruker SMART APEX CCD diffractometer with 

graphite-monochromated Mo-Kα (λ = 0.71073Å) radiation at room temperature. The crystal 

structure was solved by the direct method. Refinement was carried out by the full matrix 

least-squares methods based on F 2 using the SHELXL-97 software package. 

Preparation of the Complexes 

(2,4-Dinitrophenolato)(R,R)-N,N�-(1,2-cyclohexene)bis(3,5-di-tert-butylsalicylideneimina 

to)]cobalt(III) (L1-CoIII-dnp): 

(R,R)-N,N�-1,2-Cyclohexenebis(3,5-di-tert-butylsalicylideneiminato)cobalt(II) (L 1 -Co II ) 

‐ 69 ‐

Chapter 2 

was first synthesized according to the method described in a previous report 29 with some 

modifications as follows. A solution of cobalt acetate tetrahydrate (0.75 g, 3.0 mmol) in 

methanol (200 mL) was added to a solution of the ligand, H2L 1 (1.81 g, 3.0 mmol), in CH2Cl2 

(20 mL) via a cannula under an atmosphere of argon. A brick-red precipitate was observed 

before all of the cobalt acetate solution was added. The residue on the wall of the reaction 

flask was rinsed with methanol (20 mL), and the collected mixture was allowed to stir for a 

further 15 min at room temperature, and then for 30 min at 0 . The solids were collected by 

filtration and rinsed with cold (0 ) methanol (3 × 50 mL) before drying at 60 in a vacuum 

for 24 h. The product L 1 -Co II was obtained in 95% yield. FT-IR (KBr): 1610 (s, C=N), 1595 

(s, Ar–ring), 1527 (s, Ar–ring), 1254 (s, C–O), 572 cm -1 (w, Co–O). ESI-MS: m/z = 603.6 

(C36H52N2O2Co) + . 

(2,4-Dinitrophenolato)(R,R)-N,N�-(1,2-cyclohexene)bis(3,5-di-tert-butylsalicylideneiminat 

o)]cobalt(III) (L 1 -Co III -dnp) was synthesized according to a method described in the 

literature with modifications as follows. 22, 29 To a stirred solution of L 1 -Co II (1.48 g, 2.0 mmol) 

in CH2Cl2 (150 mL), 2,4-dinitrophenol (0.368 g, 2.0 mmol, 1 equiv.) in CH2Cl2 (20 mL) was 

added. The solution was stirred under dry oxygen at room temperature for 60 min. The 

solvents were removed under vacuum to leave a crude dark solid in an approximately 100% 

yield. The residue was further rinsed with a mixture of diethyl ether and hexane, and then 

dried at 60 under vacuum for 24 h, yielding a dark needle-like crystal (1.47 g, 94%). FT-IR 

(KBr): 1624 (s, C=N), 1610 (s, Ar–ring), 1566 (w, N=O), 1525 (s, Ar–ring), 1327 (s, N=O), 

1252 (s, C–O), 1063 (w, C–N), 571 cm -1 (w, Co–O). C42H55N4O7Co (786.8): Calcd. C 64.11, 

H 7.05, N 7.12; Found C 64.01, H 7.01, N 6.94. ESI-MS: m/z = 786.3, (C42H55N4O7Co) + , 

603.5 (C36H52N2O2Co) + , 183.2 (C6H3N2O5) - . Crystal data for L 1 -Co III -dnp: C42H55CoN4O20, 

M = 786.83, Triclinic space group P 1. 

a = 11.2788(13) Å, b = 14.4552(17) Å, c = 14.5806(17) 

Å, � = 90.382(2), = 108.936(2), � = 111.141(2), V = 2076.5(4) Å 3 , Z = 2, Dcalcd = 1.258 g 

cm -3 , (Mo K ) = 0.466 mm -1 . The data were collected at 293 K. Of the 11165 reflections, 

7503 were unique (Rint = 0.017). The non-hydrogen atoms were anisotropically refined. The 

hydrogen atoms were geometrically positioned and refined as riding atoms. The final cycle of 

the full-matrix least-squares refinement converged with R = 0.0447 and Rw = 0.1040 based on 

6046 reflections with I > 2(I). 

(2,4-Dinitrophenolato)[N,N�-ethylenebis(3,5-di-tert-butylsalicylideneiminato)]cobalt(I 

II) (L 2 -Co III -dnp) was synthesized by a procedure similar to that of L 1 -Co III -dnp. Yield: 89%. 

IR (KBr): 1626 (s, C=N), 1596 (s, Ar–ring), 1569 (w, N=O), 1521 (s, Ar–ring), 1331 (s, N=O), 

1257 (s, C–O), 1065 (w, C–N), 583 cm -1 (w, Co–O). C38H49N4O7Co (732.8): Calcd. C 62.29, 

H 6.74, N 7.65; Found C 62.12, H 6.67, N 7.52. ESI-MS: m/z = 603.5 (C32H46N2O2Co) + , 

183.2 (C6H3N2O5) - . 

‐ 70 ‐



(2,4-Dinitrophenolato)[(R,R)-N,N�-1,2-diphenylethylenebis(3,5-di-tert-butylsalicylide 

neiminato)]cobalt(III) (L 3 -Co III -dnp) was synthesized by a method similar to that of 

L 1 -Co III -dnp. Yield: 90%. IR (KBr): 1625 (s, C=N), 1597 (s, Ar–ring), 1555 (w, N=O), 1525 

(s, Ar–ring), 1310 (s, N=O), 1269 (s, C–O), 1056 (w, C–N), 571 cm -1 (w, Co–O). 

C50H57N4O7Co (884.9): Calcd. C 67.86, H 6.49, N 6.33; Found C 66.05, H 6.34, N 5.97. 

ESI-MS: m/z = 883.8, (C50H57N4O7Co) + , 701.5 (C44H54N2O2Co) + , 183.2 (C6H3N2O5) - . 

(2,4-Dinitrophenolato)[N,N�-2,2-dimethyl-1,3-propylenebis(3,5-di-tert-butylsalicylide 

neiminato)]cobalt(III) (L 4 -Co III -dnp) was synthesized by a procedure similar to that of 

L 1 -Co III -dnp. Yield: 95%. IR (KBr): 1625 (s, C=N), 1601 (s, Ar–CH), 1568 (s, N=O), 1522 (s, 

Ar–ring), 1318 (s, N=O), 1261 (s, C–O), 1061 (w, C–N), 575 cm -1 (w, Co–O). C41H55N4CoO7 

(774.8): Calcd. C 63.55, H 7.15, N 7.23; Found C 63.39, H 7.06, N 7.14. ESI-MS: m/z = 

774.1 (C41H55N4O7Co) + , 591.4 (C35H52N2O2Co) + , 183.1 (C6H3N2O5) - . 

Typical Copolymerization Procedure 

A mixture of the cobalt complex(0.1 mmol) and tetra(n-butyl)ammonium bromide 

(Bu4NBr)(0.1 mmol) was dissolved in 3.5 mL of racemic propylene oxide (rac-PO) under a 

nitrogen atmosphere. The mixture was injected into a high pressure reactor equipped with a 

magnetic stirrer under a CO2 atmosphere. The reactor with a 2.5 MPa CO2 pressure was 

placed in an oil bath. The mixture was stirred at 40 for the allotted reaction time and then 

vented in a fume hood. A small aliquot of the polymerization mixture was sampled from the 

reactor for the 1 H NMR spectroscopic analysis. The remaining polymerization mixture was 

then dissolved in CH2Cl2, quenched with 5% HCl in methanol, and transferred to a 

pre-weighed vial. The product mixture was dried under vacuum to a constant weight. The 

crude yield was carefully determined after subtracting the catalyst weight. The product was 

then dissolved in CH2Cl2 and precipitated from methanol again. The polymer was collected 

by filtration and dried under vacuum to a constant weight. Analytical data for the typical 

product (with the L 1 -Co III -dnp catalyst) was as follows. IR (KBr): 1749 (s, C=O), 1609 (w, 

Ar-ring), 1580 (w, N=O), 1531 (w, Ar-ring), 1314 (s, N=O), 1235 cm -1 (s, C-O). 1 H NMR 

(500 MHz, CDCl3, ppm): = 1.24 (–CHCH3), 4.19 (–CH2CH–), 4.90 (–CH2CH–). 13 C NMR 

(400 MHz, CDCl3, ppm): = 16.1 (–CH3), 72.3 (–CH2–), 69.1 (–CH–), 154.1 (C=O) . 

References 

1. J. K. Lee, S. W. Park, J. W. Lee, M. R. Kim, Polym. Int. 2006, 55, 849. 

2. H. Sugimoto, S. Inoue, J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 5561. 

3. D. J. Darensbourg, R. M. Mackiewicz, A. L. Phelps, D. R. Billodeaux, Acc. Chem. Res. 

2004, 37, 836. 

4. M. Cheng, E. B. Lobkovsky, G. W. Coates, J. Am. Chem. Soc. 1998, 120, 11018. 

‐ 71 ‐

Chapter 2 

5. Z. L. Quan, X. H. Wang, X. J. Zhao, F. S. Wang, Polymer 2003, 44, 5605. 

6. D. M. Cui , M. Nishiura , O. Tardif , Z. M. Hou, Organometallics 2008, 27, 2428. 

7. L. P. Guo, C. M. Wang, W. J. Zhao, H. R. Li, W. L. Sun, Z. Q. Shen, Dalton. Trans. 2009, 

5406. 

8. X. B. Lu, L. Shi, Y. M. Wang, R. Zhang, Y. J. Zhang X. J. Peng, Z. C. Zhang, B. Li, J. Am. 

Chem. Soc. 2006 128, 1664. 

9. J. Vargas, J. Costamagna, R. Latorre, A. Alvardo, G. Mena, Coord. Chem. Rev. 1992, 119, 

67. 

10. M. D. Hobday, T. D. Smith, Coord. Chem. Rev. 1972, 9, 311. 

11. 11a. S. Yamada, Coord. Chem. Rev. 1999, 192, 537. 11b. R. D. Jones, D. A. Summerville, 

F. Basolo, Chem. Rev. 1979, 79, 139. 

12. A. Christensen, H. S. Jensen, V. McKee, C. J. McKenzie, M. Munch, Inorg. Chem. 1997, 

36, 6080. 

13. S. H. Rehaman, H. Chowdhury, D. Bose, R. Ghosh, C. H. Hung, B. K. Ghosh, Polyhedron 

2005, 24, 1755. 

14. H. J. Kim, W. Kim, A. J. Lough, B. M. Kim, J. Chin, J. Am. Chem. Soc. 2005, 127, 

16776. 

15. R. L. Paddock, S. T. Nguyen, Macromolecules 2005, 38, 6251. 

16. M. Fondo, N. Ocampo, A. M. Garcia-Deibe, M. Corbella, M. S. El Fallah, J. Cano, 

Sanmartin, M. R. Bermejo, Dalton. Trans. 2006, 7, 4905. 

17. A. Chaudhary, N. Bansal, A. Gajraj, R. V. Singh, J. Inorg. Biochem. 2003, 93, 393. 

18. M. R. Malachowski, B. T. Dorsey, M. J. Parker, M. E. Adams, R. S. Kelly, Polyhedron 

1998, 17, 1289. 

19. H. Z. Du, A. H. Velders, P. J. Dijkstra, Z. Y. Zhong, X. S. Chen, F. J. Jan, 

Macromolecules 2009, 42, 1058. 

20. S. Chandra, K. Gupta, Trans. Metal. Chem. 2002, 27, 196. 

21. A. Bottcher, T. Takeuchi, K. I. Hardcastle, T. J. Meade, H. B. Gray, Inorg. Chem. 1997, 

36, 2498. 

22. Y. Niu, W. Zhang, X. Pang, X. Chen, X. Zhuang, X. Jing. J. Polym. Sci., Part A: Polym. 

Chem. 2007, 45, 5050. 

23. G. W. Coates, D. R. Moore, Angew. Chem., Int. Ed. 2004, 43, 6618. 

24. D. J. Darensbourg, J. C. Yarbrough, J. Am. Chem. Soc. 2002, 124, 6335. 

25. D. J. Darensbourg, J. C. Yarbrough, C. Ortiz, C. Fang, J. Am. Chem. Soc. 2003, 125, 7586. 

26. R. Eberhardt, M. Allmendinger, B. Rieger, Macromol. Rapid. Commun. 2003, 24, 194. 

27. S. Chen, Z. Hua, Z. Fang, G. Qi, Polymer 2004, 45, 6519. 

28. 28a. Y. Liu, K. Huang, D. Peng, H. Wu, Polymer 2006, 47, 8453; 28b. L. Lu, K. Huang, J. 

Polym. Sci., Part. A: Polym. Chem. 2005, 43, 2468. 

‐ 72 ‐



29. S. E. Schaus, B. D. Brandes, J. F. Larrow, M. Tokunaga, K. B. Hansen, A. E. Gould, M. E. 

Furrow, E. N. Jacobsen, J. Am. Chem. Soc. 2002, 124, 1307. 

30. D. J. Darensbourg, R. M. Mackiewicz, J. L. Rodgers, C. Fang, D. R. Billodeaux, J. H. 

Reibenspies, Inorg. Chem. 2004, 43, 6024. 

31. T. Joseph, S. B. Halligudi, C. Satyanarayan, D. P. Sawant, S. Gopinathan, J. Mol. Catal. A: 

Chem. 2001, 168, 87. 

32. K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 

Part B, 5th ed., Wiley 1997. 

33. A. Ramachandraiah, P. Rao, M. Ramaiah, Indian J. Chem. A 1989, 28, 309. 

34. X. Tai, X. Yin, Q. Chen, M. Tan, Molecules 2003, 8, 439. 

35. S. Inoue, H. Koinuma, T. Tsuruta, J. Polym. Sci., Part B: Polym. Lett. 1969, 130, 210. 

‐ 73 ‐

Chapter 3 

Polymerization of Lactic O-Carboxylic Anhydride using 

Organometallic Catalysts 


3.2 Polymerization of LacOCA using Co(III) Complexes with Schiff Base Ligands 

3.3 Polymerization of LacOCA using Tin(II) or Al(III) Based Complexes 

3.4 Characterization of the Obtained PLA 



References

Chapter 3 


Poly(lactic acid) (PLA) has been receiving much attention as biodegradable materials in 

recent years. 1, 2 It has found many applications in the field of biomedical purposes, such as 

suture, drug delivery, and tissue engineering. 3-5 Because the starting material of PLA is 

agricultural products such as corn, PLA is an environmentally sustainable alternative to 

petrochemically-derived products. 6 It can be employed in the preparation of biodegradable 

plastics. PLA can be prepared by directly polycondensation of lactic acid. 7 However, it is 

usually difficult to obtain high molecular weight PLA by polycondensation. Currently, 

ring-opening polymerization (ROP) of lactide is a preferred route to prepare PLA because of 

the higher controllability of the polymerization. 1 Indeed, high molecular-weight PLA can be 

obtained by ROP. The driving force for the ROP of lactide is the ring strain of the monomer. 

As a polymerizable six-membered ring, the ring strain of lactides is modest. Therefore, high 

temperatures are usually required for the ROP of lactides. 8 Undesirable transesterification and 

racemization often take place in these cases, 1 which significantly reduce the mechanical 

properties of the corresponding PLA. Consequently, a polymerizable activated monomer of 

the lactide equivalent is highly desirable. 5-Methyl-1,3-dioxolane-2,4-dione is a 

five-membered O-carboxyanhydride (LacOCA) derived from the lactic acid (Figure 3.1). 

Figure 3.1 Polymerization of LacOCA. 

It can be readily obtained by the reaction of lactate salt with diphosgene. 9 Bourissou et al. 

reported that the ROP of LacOCA proceeded in the presence of an organocatalyst, 

dimethylaminopyridine (DMAP) 10, 11 or lipase. 12 The ROP of LacOCA catalyzed by DMAP is 

well controllable. PLA with high molecular weight and narrow polydispersity index has been 

obtained under mild polymerization conditions. This indicates that the ROP of LacOCA is an 

alternative route to prepare PLA. 10 Organometallic complexes have been widely used as 

catalysts in a variety of polymerization. For instance, stannous octoate, 8 alkylaluminum, 

aluminum alkoxides, 13-18 zinc alkyl, 19 calcium alkoxides, 20, 21 and strontium alkoxide 22 have 

been used as the catalyst/initiator for the ROP of lactides. However, to the best of our 

‐ 76 ‐

Polymerization of Lactic O‐Carboxylic Anhydride using Organometallic Catalysts 

knowledge, there has been no report on the ROP of LacOCA using organometallic complexes 

as catalysts. Considering the high toxicity of DMAP, it is important to explore the 

organometallic complexes as the catalyst of the ROP of LacOCA. We have focused on 

Co(III) complexes with Schiff base ligands as the versatile and highly active catalysts, based 

on their potential activities to catalyze many kinds of reactions including Baeyer-Villiger 

oxidation, 23 hydrolysis of epoxides, 24 cyclizations of dianhydro sugar alcohols, 25 and 

copolymerization of epoxides and carbon dioxide. 26 Tin(II) aliphatates 8 and Al(III) 

complexes with Schiff base ligands 27, 28 have also been reported as the conventional catalysts 

for the ROP of lactides (Figure 3.2). In this chapter, the ROP of LacOCA using Co(III) 

complexes with Schiff base ligands, Tin(II) aliphatates and Al(III) complexes with Schiff 

base ligands as catalysts were described in detail. 

Figure 3.2 Structures of Co(III) complexes with Schiff base ligands employed in this study. 

3.2 Polymerization of LacOCA using Co(III) Complexes with Schiff Base Ligands 

Polymerization of LacOCA using Co(III) complexes with Schiff base ligands were 

performed at 70°C in toluene. The results of the polymerization were listed in Table 3.1. 

Poly(lactic acid) (PLA) was obtained in all experiments using the Co(III) complexes with 

Schiff base ligands as the catalyst. When the monomer/initiator ratio was 100/1 (Table 3.1), 

the number average molecular weight (Mn) of PLA was in the range of 3.3 – 9.6×10 3 , and the 

‐ 77 ‐

Chapter 3 

polydispersity index (PDI) of PLA was in the range of 1.1–1.5. The Mn of the obtained PLA 

was low in all experiments except the Co(III)-c-(NO2)2 initiating system, which gave PLA 

with a high Mn (9.6×10 3 ). The molecular weight distribution of the product obtained with the 

Co(III)-c-(NO2)2 catalyst was relatively broad (PDI = 1.4). When the Co(III)-b-NO2/ i PrOH 

initiating system (where i PrOH was isopropanol) was employed, the Mn of PLA increased 

from 3.3×103 to 6.0×103 and the PDI broadened from 1.1 to 1.5 as the monomer/initiator 

ratio increased from 100/1 to 200/1 (Table 3.1, Entries 5 and 6). The Co(III)-b-NO2 initiating 

system without i PrOH also catalyzed the polymerization of LacOCA. Compared with the 

Co(III)-b-NO2/ i PrOH initiating system, the Mn of the resulting PLA using the Co(III)-b-NO2 

initiating system was slightly higher (Mn = 7.6×10 3 ). The molecular weight distribution of 

PLA was also broad (PDI = 1.4), which was similar to that of the Co(III)-b-NO2/ i PrOH 

initiating system. These demonstrated that the Co(III) complexes with Schiff base ligands 

acted as the catalysts for the ROP of LacOCA. The present ROP method somehow allowed 

the control of the molecular weight of PLA, but the molecular weight distribution was broad 

in most cases of the polymerization examined in this study, especially in longer 

polymerization time. The large polydispersity implies that the ROP may have been 

accompanied by undesired intra- and/or inter-transesterification reactions. 

Table 3.1 Polymerizations of LacOCA 

Entry Initiating system [M]/[I] Temp. 

‐ 78 ‐ 

/°C 

Time 

1 Co(III)-a-(NO2)2/ i PrOH 100/1 70 35 4.0 1.3 

2 Co(III)-b-(NO2)2/ i PrOH 100/1 70 35 4.3 1.2 

3 Co(III)-c-(NO2)2/ i PrOH 100/1 70 35 9.6 1.4 

4 Co(III)-a-NO2/ i PrOH 100/1 70 35 6.4 1.4 

5 Co(III)-b-NO2/ i PrOH 100/1 70 35 3.3 1.1 

6 Co(III)-b-NO2/ i PrOH 200/1 70 60 6.0 1.5 

/hr 

Mn 

/10 3 

PDI


7 Co(III)-b-NO2 200/1 70 60 7.6 1.4 

8 Co(III)-c-NO2/ i PrOH 100/1 70 35 3.6 1.2 

9 Stannous benzoate/ i PrOH 120/1 70 15 6.4 1.2 

10 Stannous benzoate 120/1 70 15 7.0 1.3 

11 Stannous octoate/ i PrOH 150/1 60 15 7.9 1.4 

12 (Cyclohexylsalen)AlEt/BnOH 150/1 70 11 N/A N/A 

13 (Dimethylsalen)AlEt/BnOH 150/1 70 11 N/A N/A 

i PrOH: isopropyl alcohol. BnOH: benzyl alcohol. 

3.3 Polymerization of LacOCA using Tin(II) or Al(III) Based Complexes 

Tin(II) and Al(III) complexes are also widely used as catalysts for the ROP of lactides. 

Based on the activity of the Co(III) complexes (vide supra), we decided to examine the ROP 

of LacOCA using these metal complexes with the similar (or identical) ligands as the 

catalysts. Stannous benzoate, stannous octate, (cyclohexylsalen)AlEt, and 

(dimethylpropylsalen)AlEt (Figure 3.3) were employed in this chapter. Both stannous 

benzoate and stannous octate were efficient catalysts for the ROP of LacOCA. When the 

stannous benzoate/ i PrOH initiating system was used as the catalyst and the monomer/initiator 

ratio was 120/1, the Mn and PDI of the obtained PLA were 6.4×10 3 and 1.2, respectively 

(Table 3.1, Entry 9). When the stannous benzoate initiating system was applied, the resulting 

Mn of 7.0×10 3 was slightly higher than that obtained with the benzoate/ i PrOH initiating 

system (Table 3.1, Entry 9). This result suggested that the addition of i PrOH was not effective 

to control the Mn of the product of the LacOCA polymerization when stannous benzoate was 

used as the catalyst, which was in contrast to the DMAP/alcohol mediated ROP of LacOCA 

10, 11 

where the alcohol was able to control the Mn of PLA. 

(Cyclohexylsalen)AlEt 29, 30 and (dimethylpropylsalen)AlEt 28 (Figure 3.3) are efficient Al 

based catalysts for the ROP of lactides. However, no polymer was isolated from the ROP of 

LacOCA using those catalysts (Table 3.1, Entries 12 and 13), which indicated that the 

‐ 79 ‐

Chapter 3 

aluminum based complexes were totally inactive for the ROP of LacOCA. 

3.4 Characterization of the Obtained PLA 

Figure 3.3 Structures of aluminum based complexes. 

The 1 H NMR spectrum of the obtained PLA was shown in Figure 3.4. The doublet peaks 

at 1.73 ppm was assigned to CH3 resonance of the polymer chain. The quartet peaks at 

5.15 ppm was attributed to that of the CHCH3 of PLA. 13 C NMR spectrum of the PLA was 

displayed in Figure 3.5. The signals at 169.5, 69.0 and 16.6 ppm corresponded to the carbon 

resonances of carbonyl, methine, and methyl groups of the PLA chain, respectively. These 

results were consistent with the reported NMR spectra of PLA, 28 which demonstrated that 

PLA was formed by the polymerization of LacOCA. The carbonyldioxy group was 

eliminated from the polymerization system by the liberation of carbon dioxide. 

8 6 4 2 0 

ppm 

Figure 3.4 1 H NMR spectrum of poly(lactic acid) from LacOCA. 

The DSC thermogram of the obtained PLA was shown in Figure 3.6. The glass transition 

‐ 80 ‐


temperature (Tg) of the corresponding PLA was 55 °C. This was in consistent with the 

reported data in a literature (Tg ~ 55 °C). 31 The melting point Tm of the PLA was 154 °C, 

which was lower than that for the poly(L-lactide) reported in the literature (Tm ~ 175 °C). 31 

TGA revealed that T5%, the temperature corresponding to 5% weight loss, was 231°C for the 

PLA produced by the LacOCA polymerization. This was lower than that of the previously 

reported poly(L-lactide) (T5% ~ 320 °C). 32 These lower characteristic thermal transition 

temperatures were ascribed to the relatively low molecular weights of the PLA produced by 

the LacOCA polymerization. Increasing the molecular weights by suppressing the proposed 

side reactions such as the transesterification by tuning the catalytic activity with a suitably 

designed ligand around the cobalt center will be the topics of our continuous research. 

200 150 100 50 0 

ppm 

Figure 3.5 13 C NMR spectrum of poly(lactic acid) from LacOCA. 

Heat flow (W/g) 

0.5 

0.0 

-0.5 

-1.0 

-1.5 

-2.0 

50 100 150 

Temperature ( o C) 

Figure 3.6. DSC thermogram of poly(lactic acid) (Table 3.1, Entry 3). 

‐ 81 ‐

Chapter 3 


Co(III) complexes with Schiff base ligands and Tin(II) alphatates were found to be the 

catalysts for the ROP of LacOCA to produce poly(lactic acid). Intra- and/or 

inter-transesterification were suggested to coincide with the polymerization, which resulted in 

a relatively large polydispersity. The carbonyldioxy group was eliminated from the 

polymerization system. The corresponding PLA showed similar Tg but lower T5% compared 

with PLA obtained from lactides, as a result of the lower molecular weights. Al(III) 

complexes with Schiff base ligands were not catalytically active for the polymerization of 

LacOCA. 


General Procedures 

LacOCA and Co(III) complexes with Schiff base ligands (Figure 3.2) were prepared 

according to the already published procedures. 33, 34 Toluene was dried by distillation over 

sodium under the protection of nitrogen. 1 H NMR spectra were recorded on Bruker AV 300 

MHz, Bruker AV 400 MHz or Bruker AV 600 MHz spectrometer in CDCl3 at 25ºC. Chemical 

shifts were referenced to tetramethylsilane (TMS) for the 1 H NMR measurement. Gel 

permeation chromatography (GPC) was performed in THF (Flow rate 1.00 ml/min at 35ºC) 

on a Waters 410 GPC. The columns were calibrated against polystyrene (PS) as the external 

standard. Differential scanning calorimetry (DSC) analyses were carried out at a heating rate 

of 10 °C/min on a Perkin Elmer Instruments DSC-7. 

Polymerization of LacOCA 

All of the procedures were carried out under the protection of dry argon. In a typical 

procedure, LacOCA (2.92 mmol, 0.34 g), 2-propanol (0.029 mmol, in 0.34 mL of toluene), 

Co(III)-c-(NO2)2 (0.029 mmol, 0.0258g), and toluene (5.5 mL) were added to a dried 

ampoule equipped with a magnetic stirrer bar. The initial concentration of LacOCA monomer 

in toluene was 0.5 mol/mL. The ampoule was placed in an oil bath at 70 °C. After 

polymerization, the polymer was dissolved in chloroform and isolated by precipitation into 

cold ethanol, which was collected by filtration and dried under vacuum at room temperature 

for 24h. 

‐ 82 ‐

References 


1. H. R. Kricheldorf, M. Berl, N. Scharnagl, Macromolecules 1988, 21, 286. 

2. C. G. Pitt, M. M. Gratzl, G. L. Kimmel, J. Surles, A. Schindler, Biomaterials 1981, 2, 

215. 

3. K. J. L. Burg, S. Porter, J. F. Kellam, Biomaterials 2000, 21, 2347. 

4. J. P. Penning, H. Dijkstra, A. J. Pennings, Polymer 1993, 34, 942. 

5. R. Bodmeier, K. H. Oh, Chen, H. Int. J. Pharm. 1989, 51, 1. 

6. H. Ohara, U. Doi, M. Otsuka, H. Okuyama, S. Okada, Seibutsu-Kogaku Kaishi-J. Soc. 

Ferment. Bioeng. 2001, 79, 142. 

7. J. Zhang, P. Krishnamachari, J. Z. Lou, A. Shahbazi, In Proceedings of the 2007 National 

Conference on Environmental Science and Technology, Uzochukwu, G. A., Ed. Springer: 

New York, 2009; pp 3-8. 

8. G. Schwach, J. Coudane, R. Engel, M. Vert, Biomaterials 2002, 23, 993. 

9. L. Tang, L. Deng, J. Am. Chem. Soc. 2002, 124, 2870. 

10. O. T. Du Boullay, E. Marchal, B. Martin-Vaca, F. P. Cossio, D. Bourissou, J. Am. Chem. 

Soc. 2006, 128, 16442. 

11. C. Bonduelle, B. Martin-Vaca, F. P. Cossio, D. Bourissou, Chem. Eur. J. 2008, 14, 5304. 

12. C. Bonduelle, B. Martin-Vaca, D. Bourissou, Biomacromolecules 2009, 10, 3069. 

13. X. Pang, H. Z. Du, X. S. Chen, X. H. Wang, X. B. Jing, Chem. Eur. J. 2008, 14, 3126. 

14. H. Z. Du, X. Pang, H. Y. Yu, X. L. Zhuang, X. S. Chen, D. M. Cui, X. H. Wang, X. B. 

Jing, Macromolecules 2007, 40, 1904. 

15. Z. H. Tang, V. C. Gibson, Eur. Polym. J. 2007, 43, 150. 

16. X. Pang, H. Z. Du, X. S. Chen, X. L. Zhuang, D. M. Cui, X. B. Jing, J. Polym. Sci., Part 

A: Polym. Chem. 2005, 43, 6605. 

17. Z. H. Tang, Y. K. Yang, X. Pang, J. L. Hu, X. S. Chen, N. H. Hu, X. B. Jing, J. Appl. 

Polym. Sci. 2005, 98, 102. 

18. A. Kowalski, A. Duda, S. Penczek, Macromolecules 1998, 31, 2114. 

19. B. M. Chamberlain, M. Cheng, D. R. Moore, T. M. Ovitt, E. B. Lobkovsky, G. W. Coates, 

J. Am. Chem. Soc. 2001, 123, 3229. 

20. L. H. Piao, Z. L. Dai, M. X. Deng, X. S. Chen, X. B. Jing, Polymer 2003, 44, 2025. 

21. Z. Y. Zhong, P. J. Dijkstra, C. Birg, M. Westerhausen, J. Feijen, Macromolecules 2001, 

34, 3863. 

‐ 83 ‐

Chapter 3 

22. Z. H. Tang, X. S. Chen, Q. Z. Hang, X. C. Bian, L. X. Yang, L. H. Piao, X. B. Jing, J. 

Polym. Sci., Part A: Polym. Chem. 2003, 41, 1934. 

23. T. Uchida, T. Katsuki, K. Ito, S. Akashi, A. Ishii, T. Kuroda, Helv. Chim. Acta 2002, 85, 

3078. 

24. S. D. Choi, G. J. Kim, Catal. Lett. 2004, 92, 35. 

25. T. Satoh, T. Imai, S. Umeda, K. Tsuda, H. Hashimoto, T. Kakuchi, Carbohydr. Res. 2005, 

340, 2677. 

26. W. M. Ren, Z. W. Liu, Y. Q. Wen, R. Zhang, X. B. Lu, J. Am. Chem. Soc. 2009, 131, 

11509. 

27. Z. H. Tang, X. S. Chen, Y. K. Yang, X. Pang, J. R. Sun, X. F. Zhang, X. B. Jing, J. Polym. 


28. Z. H. Tang, X. S. Chen, X. Pang, Y. K. Yang, X. F. Zhang, X. B. Jing, 


29. Z. Y. Zhong, P. J. Dijkstra, J. Feijen, J. Am. Chem. Soc. 2003, 125, 11291. 

30. Z. Y. Zhong, P. J. Dijkstra, J. Feijen, Angew. Chem.Int. Edit. 2002, 41, 4510. 

31. D. Garlotta, J. Polym. Environ. 2001, 9, 63. 

32. G. X. Chen, J. S. Yoon, Polym. Degrad. Stabil. 2005, 88, 206. 

33. Y. S. Niu, W. X. Zhang, H. C. Li, X. S. Chen, J. R. Sun, X. L. Zhuang, X. B. Jing, 

Polymer 2009, 50, 441. 

34. Y. S. Niu, W. X. Zhang, X. Pang, X. S. Chen, X. L. Zhuang, X. B. Jing, J. Polym. Sci., 

Part A: Polym. Chem. 2007, 45, 5050. 

‐ 84 ‐

Chapter 4 

Synthesis of Lactide-Grafted Poly(TEMPO-acrylamide) and its 

Electrochemical Property and Biocompatibility 


4.2 Synthesis of PTAm-g-PLA 

4.3 Electrochemical Properties 

4.4 Thermal Properties 

4.5 Phase Separation Behavior of PTAm-g-PLA 

4.6 Cytotoxicity of PTAm-g-PLA 

4.7 Cell Adhesion and Spreading 



References

Chapter 4 


Stimulus-responsive polymers show great potential application as new “smart” 

biomaterials. 1 The electroactive polymer, being electrical stimulus responsive, has attracted 

increasing attentions since it has been established that variety of cells, including many of 

fibroblasts, nerve cells and osteoblasts are sensitive to the electrical effects generated from 

the electrodes in vitro or in vivo. 2, 3 Besides, they had been widely used in biological systems 

due to the key advantage of facile control of the intensity and duration of stimulation. So far, 

polypyrrole (PPy) and polyaniline (PANi) are still the most widely used two kinds of 

electroactive materials in tissue engineering although the researches on them have lasted a 

long time. 4-7 More recently, there are some new electroactive polymers being developed, such 

as polythiophene (PT) and other types of conductive polymers. 8 However, there are still few 

examples attempting to explore the application of new electroactive materials in tissue 

engineering. 

In recent years, polymers with stable free radicals, known as radical polymers, have 

attracted more and more attention due to their potential applications as electron transport 

materials and organic ferromagnets. 9, 10 Radical polymers are readily oxidized and reduced 

electrochemically, which allowed the use in charge-storage applications for new-types of 

batteries. 11, 12 However, little attention has been paid to investigate the application of 

nitroxide radical-containing polymers in the field of biomedical materials. Chu et al. 

synthesized biodegradable nitroxide radical-containing polymers through the condensation of 

4-amino-2,2,6,6-tetramethylpiperidine-1-oxy and polyglycolide. This material showed 

profound retardation of the proliferation of smooth muscle cell in vitro. 13, 14 However, the 

hydrolytic degradation of PGA will lead to the release of nitroxide radicals which may have 

adverse side effects to the body. Using radical polymers as the source of stable radical is an 

alternative way to solve this problem. These polymers usually have non-biodegradable 

backbones which will avoid the release of radical agents after the degradation of the 

main-chain. PTAm and its analogs are typical radical polymers and mostly examined as the 

cathode materials. 15, 16 To the best of our knowledge, there has few work to investigate the 

biomedical application of the radical polymers such as PTAm. In this chapter, we 

copolymerized it with a biodegradable polylactide (PLA) macromonomer, to obtain a novel 

biologically active and biocompatible copolymer. PLA are well known as very important 

synthetic biodegradable materials. Due to its low immunogenicity, good biocompatibility and 

‐ 86 ‐

‐ 87 ‐ 

Synthesis of Lactide‐Grafted Poly(TEMPO‐acrylamide) and 

its Electrochemical Property and Biocompatibility 

excellent mechanical properties, they are widely used in pharmaceutical and other medical 

applications, such as sutures, implants for bone fixation, carriers in drug delivery, and 

temporary matrices or scaffolds in tissue engineering. 17-19 The incorporation of PLA fragment 

into PTAm will improve the biocompatibility of PTAm, and the resulting biomaterials will 

have promising application in tissue engineering. 

4.2 Synthesis of PTAm-g-PLA 

The synthetic route of PTAP-g-PLA was shown in Scheme 4.1. Firstly, double bond ended 

PLA was synthesized by the ring-opening polymerization of lactide initiated by HEMA. Then 

the macromonomer was copolymerized with 2,2,6,6-tetrametylpiperidine-4-yl acrylamide 

prepared by the reaction of 4-amino-2,2,6,6-tetrametylpiperidine with acryl chloride 

according to our previous method. 20 The resulted copolymer was oxidized by the peroxide to 

give PTAm-g-PLA. 

Scheme 4.1 Synthetic routes of PTAm-g-PLA. 

As shown in Figure 4.1A, the peaks around 6.13 and 5.58 ppm were assigned to the 

characteristic peaks of the double bond of HEMA, and the peak at 5.19 ppm was attributed to

Chapter 4 

the proton of methenyl groups in the lactide backbone. The molecular weight of PLA-HEMA 

was 3000, calculated from the integration area ratio of peaks 1 and 6 (Figure 4.1A). To 

prevent the possible polymerization of HEMA under the high temperature, hydroquinone was 

used as an inhibitor which was removed during the purification step of the polymeric product. 

After the copolymerization with the TAP monomer, the peak associated with the double bond 

disappeared, as shown in Figure 4.1B, which suggested the polymerization of PLA-HEMA. 

The structure of copolymer was also confirmed by 13 C NMR (Figure 4.2). 

Figure 4.1 1 H NMR of PLA-HEMA (A) and PTAP-g-PLA2 (B). 

Figure 4.2 13 C NMR spectra of PTAP (A), PTAP-g-PLA (B) and PLA-HEMA (C). 

The contents of PTAP in the copolymers were determined by the integration area ratio of 

the peaks at 5.19 and 4.19 ppm. It was noted that the peak at 4.19 ppm contained the 

resonance from the –CH2CH2- groups capped at the PLA chain end, so this part of integration 

‐ 88 ‐

‐ 89 ‐ 



was subtracted to determine the monomer composition (Figure 4.1B). The compositions of 

the copolymers evaluated by the 1 H NMR spectra were summarized in Table 4.1. All the 

copolymer had a relatively lower PLA content compared with the feeding ratio. Presumably 

the PLA-HEMA macromonomers had a relatively low reactive efficiency and only part of the 

macromonomers copolymerized with the 2,2,6,6-tetrametylpiperidine-4-yl acrylamide 

monomer. The low yield of the copolymerization can also be attributed to the low reactivity 

of the macromonomers. The GPC results showed that the molecular weight of the copolymers 

decreased as the PLA content increased, indicating that the introduction of the PLA lowered 

the reactivity of the propagating copolymer radical, making them more readily terminated 

during the polymerization. 

Sample 

Table 4.1 Feed and result compositions of copolymers. a 

PLA-HEMA/Monomer 

(w/w) 

Feed Result b 

Yield 

(%) 

Mn c PDI c 

Unpaired 

electron 

density 

(spin/g) d 

1 3 : 7 1 : 9.0 42.0 7.0 × 10 4 1.98 2.14 × 10 21 

2 5 : 5 1 : 4.3 32.5 3.9 × 10 4 2.03 1.64 × 10 21 

3 7 : 3 1 : 2.4 40.8 1.2 × 10 4 1.97 1.39 × 10 21 

a Reaction temperature was 85 o C and duration was 24 h;. b Calculated from 1 H NMR; c Determined from GPC in DMF. d 

Determined from SQUID after oxidation. 

TEMPO are generally prepared through the oxidation of 2,2,6,6-tetramethylpiperidine. 

Several oxidants, including hydrogen peroxide, peracids and lead(IV) oxide, can be used to 

obtain the nitrooxide radical. In this chapter, the oxidation of PTAP-g-PLA was accomplished 

in the presence of 3-chloroperoxybenzoic acid. The obtained PTAm-g-PLA was orange 

powder. 

To further investigate the oxidation reaction of copolymer, the FTIR spectra before and 

after the oxidation were obtained (Figure 4.3). The peak at 1359 cm -1 was obviously 

enhanced after the oxidation, which was assigned to the characteristic peak of the nitroxide 

radical. 21, 22 The peak at 1758 cm -1 (νCO) was characteristic peak of the PLA segment, which 

did not change after the oxidation. The peaks at 1653 cm -1 (νCO) and 1548 cm -1 (νCO-NH) were

Chapter 4 

attributed to the amide group. The GPC elution curve for PTAm-g-PLA gave a unimodal peak, 

which indicated that there was no undesired homopolymer residue in the final product. Based 

on these results, it was concluded that the PTAm-g-PLA copolymers were successfully 

prepared by this method. 

Figure 4.3 FTIR spectra of PTAP-g-PLA2 (A) and PTAm-g-PLA2 (B). 

4.3 Electrochemical Properties 

Based on the presence of the nitroxide radicals, the copolymers exhibited 

electrochemically reversible properties similar to that of TEMPO. The cyclic voltammogram 

(CV) of the copolymer at different scan rates were shown in Figure 4.4. The CV curves for 

the copolymer were recorded in the potential range of 0.00 to 1.30 V. The response revealed a 

highly reversible redox property at around 0.63 V vs. Ag/AgCl, which was assigned to the 

oxidation of the nitroxide to the corresponding oxoammonium cation. The redox potential 

(0.63 V vs. Ag/AgCl) was in good agreement with that of the PTAm homopolymer (0.68 V vs. 

Ag/AgCl). Moreover, the peak current is proportional to the sweep rate, suggesting a fast 

electron transfer process in the copolymer film. 

‐ 90 ‐

‐ 91 ‐ 



Figure 4.4 CV of the copolymer (PTAm-g-PLA2) at different scan rates in an aqueous 

electrolyte solution of 0.1 M NaBF4. 

The spin concentration of the copolymer was determined by magnetic measurement using 

a SQUID technique. As determined from the Curie plots and the values for saturated 

magnetization (Figure 4.5), the radical concentration of PTAm-g-PLA2 was 1.64×10 21 spin/g. 

As calculated from the ratio of the radical amount determined by SQUID to the precursors 

derived from the 1 H NMR spectra of PTAP-g-PLA, it can be found that more than 80% of the 

TAP units was oxidized. Considering that almost all of the piperidine units were oxidized in 

the PTAm homopolymer under the same experimental conditions, the PLA segment probably 

inhibited the oxidation of the piperidine unit to a small extent. 

Figure 4.5 Curie and χT (inset) vs. T plots for the radical copolymers obtained by SQUID measurements.

Chapter 4 


The DSC thermograms of the PTAm homopolymer, PLA-HEMA and PTAm-g-PLA2 were 

recorded and shown in Figure 4.6A. PTAm showed no thermal transition at temperatures 

above 20 o C. The melting temperature Tm of PLA-HEMA was low, around 133 o C, due to its 

low molecular weight. For PTAm-g-PLA copolymer, no Tg or Tm was observed in the tested 

temperature ranges, which may be ascribed to the low PLA content in the copolymer. The 

TGA curves of the PTAm homopolymer, PLA-HEMA and PTAm-g-PLA also demonstrated 

that the copolymers had similar thermal properties with that of PTAm (Figure 4.6B). 

Figure 4.6 (A) DSC traces of the PLA-HEMA, PTAm, and PTAm-g-PLA2 in second heating. (B) 

TGA curves of PLA-HEMA, PTAm, and PTAm-g-PLA. 

4.5 Phase Separation Behavior of PTAm-g-PLA 

The phase behavior of the PTAm-g-PLA copolymer is very important to its application. 

Therefore, the phase images of blend of PTAm and PLA, blend of PLA and PTAm-g-PLA2, 

PTAm-g-PLA2 and PTAm-g-PLA1 films cast from their chloroform solutions were examined 

by AFM (Figure 4.7). It was observed in Figure 4.7B and 4.7C that the film of copolymer 

exhibited two different phases. One was continuous and another phase was uniformly 

dispersed in the film. Considering the low PLA content in PTAm-g-PLA2 and PTAm-g-PLA1, 

it can be safely concluded that the continuous phase was PTAm. This unique phase behavior 

can probably be attributed to the immiscible nature of PTAm and PLA as shown in Figure 

4.7A. It had been demonstrated that the incorporation of two immiscible chains into one 

copolymer prevented the macro-phase separation of these incompatible materials, which can 

restrict the partition of the components to nanoscopic (1-100 nm) domains. 23 As shown in 

‐ 92 ‐

‐ 93 ‐ 



Figure 4.7D, the blend film of PLA and PTAm-g-PLA2 also exhibited phase separation but 

the dispersion of PLA was more uniform, indicating that PTAm-g-PLA acted as a 

compatibilizer which modified the PLA and PTAm interface. 

4.6 Cytotoxicity of PTAm-g-PLA 

To determine the cytotoxicity of the PTAm-g-PLA copolymer in comparison with PLA and 

PTAm, the MTT assay by the RSC96 cell line was conducted, and the results were shown in 

Figure 4.8. The copolymers exhibited similar cytocompatibility as compared to the PTAm 

homopolymer. This is mainly attributed to the reason that all the polymers tested are 

hydrophobic and no cytotoxic small organic molecules or polymers were dissolved during the 

extraction process. 

Figure 4.7 AFM Phase image: blend of PLA and PTAm with a weight ratio of 1:4 (A); 

PTAm-g-PLA2 (B), PTAm-g-PLA1(C), and blend of PLA and PTAm-g-PLA2 with a weight ratio 

of 1:4 (D).

Chapter 4 

Figure 4.8 MTT assay for the cytotoxicity of PLA-HEMA, PTAm and PTAm-g-PLA. Statistical 

significance: *p < 0.05 

4.7 Cell Adhesion and Spreading 

Biocompatibility is also a great concern for medical applications. The biocompatibility of 

PTAm-g-PLA copolymers was evaluated by observing adhesion and spreading of RSC96 

cells on copolymer films. Figure 4.9 showed the micrographs of RSC96 cells incubated for 

48 h on PLA, PTAm-g-PLA2 and PTAm films, respectively. After 48 h, almost all cells 

adhered to the PLA and PTAm-g-PLA2 films and got spread. The cells extended from 

original elliptical shape to the irregular polygonal shape. Moreover, the filopodias appeared 

on the surface of cells and networks were formed among cells. All the above observation 

demonstrated that the adhesion and spreading of RSC96 cells on the PTAm-g-PLA2 were 

good. On the pure PTAm film, the cells also adhered well but their shapes were still original 

elliptical shape, which showed the cells did not spread on the film. The cells are separated 

and few filopodias or networks were observed. After copolymerized with PLA, the 

copolymers had improved biocompatibility compared with PTAm, which were comparable 

with PLA, indicating great potential use in tissue engineering. 

‐ 94 ‐

‐ 95 ‐ 



Figure 4.9 Cell morphology of F-actin distribution in RSC96 cells incubated on cover-slip coated 

with PLA (A), PTAm-g-PLA (B) and PTAm (C). RSC96 cells were incubated for 48 h and stained 

for F-actin. Representative fluorescence microscopy photographs were shown here. 


Novel PTAm-g-PLA copolymers were successfully prepared by a PLA macromonomer 

approach. The obtained copolymer contained stable radical units which was biologically 

active. The copolymers were amorphous which were determined from DSC measurement due 

to the relatively low PLA content. The copolymer exhibited an improved biocompatibility 

compared to PTAm homopolymer, which indicated that it was a promising biomaterial for the 

tissue engineering. 


Materials and Methods 

4-Amino-2,2,6,6-tetramethylpiperidine (>97%, TCI), hydroquinone (sinopharm chemical 

reagent, >98%), 3-chloroperoxybenzonic acid (sinopharm chemical reagent, >85%) were 

used as received. Acryloyl chloride was purchased from Best Chemical (China) and purified 

by vacuum distillation. 2-Hydroxyethyl methacrylate (HEMA, 96%, Acros) was distilled 

under reduced pressure before use. L-Lactide (LA) was purchased from Purac and 

recrystallized in ethyl acetate three times. 2,2'-Azoisobutyronitrile (AIBN, Beijing Chemical 

Co., China) was recrystallized twice from methanol. All the organic solvents used were dried 

over CaH2 and distilled prior to use.

Chapter 4 

The 1 H NMR and 13 C NMR measurements were performed on Bruker DMX300 

spectrometer with tetramethylsilane (TMS) as an internal reference. FTIR spectra were 

measured on a Bruker Vertex 70 Fourier Transform Infrared spectrometer using the KBr disk 

method. Atomic force microscopy (AFM) images were acquired in a commercial 

SPA300HV/SPI3800N Probe Station, Seiko Instruments, Japan, in tapping mode. A silicon 

microcantilever (spring constant 2 N/m and resonance frequency ~ 70 kHz, Olympus, Japan) 

with an etched conical tip was used for scan. Silicon wafers were cleaned by a 30 min dip in 

fresh 1:1 H2SO4 (concentrated)/H2O2 (30%) solution. Subsequently, the acids were removed 

by a thorough rinse in Millipore water. Polymer thin films were obtained by spin-coating a 

copolymer chloroform solution onto silicon wafers. Magnetization and magnetic 

susceptibility of the powder polymer sample were measured using a Quantum Design 

MPMS-7 SQUID (superconducting quantum interference device) magnetometer. The 

magnetic susceptibility was measured from 10 to 300 K under a 1.0 T field. Cyclic 

voltammetry was performed using a normal potentiostat system (BAS Inc. ALS660B) with a 

conventional three-electrode cell under a dry argon atmosphere. A platinum disk, coiled 

platinum wire, and Ag/AgCl were used as the working, auxiliary and reference electrode, 

respectively. The cyclic voltammogram was measured in a dichloromethane solution in the 

presence of 0.1 M tetrabutylammonium tetrafluoroborate as the supporting electrolyte. The 

film of copolymer was 100 nm in thickness. The formal potential of the 

ferrocene/ferrocenium redox couple was 0.45 V vs the Ag/AgCl reference electrode. The 

GPC analysis was performed using TOSOH HLC-8220 with 0.1 M LiCl DMF as solvent. 

Synthesis of PLA-HEMA 

PLA-HEMA was easily prepared by the ring-opening polymerization of L-lactide in the 

presence of HEMA and stannous octoate (Sn(Oct)2). First, 0.48 g HEMA, 5.0 g L-lactide, 8 

mg hydroquinone, and 5 mg Sn(Oct)2 were added into a dried glass reactor already 

flame-dried and nitrogen-purged three times. After injection of 35 mL toluene, the reactor 

was sealed and maintained at 120 o C for 24 h. The product was precipitated with an excess of 

ethanol, purified by precipitating twice into ethanol from chloroform solution, to give a white 

product. Yield: 34%. 

Synthesis of PTAP-g-PLA 

Typically, 0.15 g PLA-HEMA and 0.35 g 2,2,6,6-tetrametylpiperidine-4-yl acrylamide 

‐ 96 ‐

‐ 97 ‐ 



(TAP) were added into a dried glass reactor already flame-dried and nitrogen-purged three 

times. After injection of 6 mL dioxane, 6 mg AIBN was added to the glass in glove box. Then 

the system was degassed by three freeze-vacuum-thaw cycles. Finally, the glass reactor was 

sealed under Ar atmosphere and then immersed in an oil bath at 85 o C under stirring. After 24 

h, the reaction solution was poured into excessive methanol. The homopolymer of 

PLA-HEMA was precipitated and filtered. The poly(2,2,6,6-tetrametylpiperidine-4-yl 

acrylamide)-g-polylactide (PTAP-g-PLA) was dispersed in the methanol solution and 

collected by evaporation of methanol under reduced pressure. Then the product was purified 

by precipitating twice into diethyl ether from chloroform solution, and eventually dried under 

vacuum at room temperature for 24 h. 

Synthesis of PTAm-g-PLA 

PTAP-g-PLA was added to an ice-cold solution of 3-chloroperoxybenzoic acid in THF and 

stirred for 3 h at room temperature. The weight ratio of PTAP to 3-chloroperoxybenzoic acid 

was 1:4. The polymer was solved in THF with oxidation progress. The solution was added 

dropwise to diethyl ether/hexane (1/1 v/v 200 ml). The precipitate was collected by filtration, 

and dried under reduced pressure for 12 h. Yield: 77%. 

Cytotoxicity assay 

The cytotoxicity of the various polymer complexes were assessed using the MTT assay. 

PTAm-g-PLA, PLA and PTAm were dispersed in DMEM medium (Dulbecco's Modified 

Eagle Medium) supplemented with 10% fetal calf serum (Gibco) in a humidified incubator at 

37 and 5% CO2, respectively. After 24 h, extracted solutions of polymers were diluted into 

different concentrations. RSC96 cells were seeded at 1.2 ×10 4 cells/well in 96-well plates and 

cultured for 24 h. Then the culture media were replaced by the extracted solutions and the 

plates were returned to the incubator for an additional 24 h. At the end of the experiments, 20 

μL of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) solution (5 

mg/mL) was added to each well. The plates were returned to the incubator. After 4 h, the 

MTT solutions were carefully removed from each well, and 200 mL DMSO was added to 

dissolve the MTT formazan crystals. The plate was incubated for an additional 10 min before 

the absorbance at 492nm was recorded by an ELISA microplate reader (Bio-Rad). The cell 

viability (%) was calculated according to the following equation:

Chapter 4 

Cell viability (%) = (Asample / Acontrol) × 100 (1) 

where Asample was the absorbance of the polymers extracted solutions treated cells and Acontrol 

was the absorbance of the untreated cells. Each experiment was done in triplicate and 

repeated a minimum of three times. 

Cell Adhesion and Spreading 

RSC96 cells (rat Schwann cell) were used to investigate the cell adhesion and viability of 

the several materials. The cells were cultured in cell culture flasks with DMEM medium 

supplemented with 10% fetal calf serum in a humidified incubator at 37 and 5% CO2. 

The PLA, PTAm-g-PLA2 and PTAm were dissolved in CHCl3 (10 mg/ml), and the 

solution was cast onto glass slides. The coated slides were treated under vacuum for 48 h to 

remove the trace of CHCl3, followed by sterilizing by ultraviolet radiation for 2 h. 

Approximately, 30,000 RSC96 cells were seeded on the cover-slip coated with PLA, 

PTAm-g-PLA, PTAm and allowed to grow for 48 hours at 37 o C/5% CO2. RSC96 cells were 

routinely grown in DMEM medium containing 10% FBS and antibiotics (100 U/mL 

penicillin, 100 μg/mL streptomycin). Subsequently, the cells were fixed in 3% 

paraformaldehyde in PBS pH 7.4 for 15 min at room temperature, and washed twice with ice 

cold PBS. In order to improve the penetration of the antibody, cells were incubated for 10 

min with PBS containing 0.25% Triton X-100. Cells were incubated with 1% BSA in PBST 

for 30 min to block unspecific binding of the antibodies. Cells were incubated in the diluted 

F-actin antibody (Abcam) in 1% BSA in PBST in a humidified chamber for 1 hour at room 

temperature. The solution was decanted and the cells were washed three times in PBS, 5 min 

each time. Cells were incubated with the goat polyclonal to Rabbit IgG conjugated with 

Rhodamine secondary antibody (Abcam) in 1% BSA for 1 hour at room temperature in dark. 

The secondary antibody solution was decanted and washed three times with PBS for 5 min 

each in dark. Cells were incubated on 1 μg/ml DAPI (Sigma) for 2 min and rinsed with PBS. 

The cells were observed with a Nikon Eclipse TE2000-U fluorescence microscope equipped 

with a DXM1200F digital camera. 

References 

1. E. S. Gil, S. A. Hudson, Prog. Polym. Sci. 2004, 29, 1173. 

2. E. G. Fine, R. F. Valentini, R. Bellamkonda, P. Aebischer, Biomaterials 1991, 12, 775. 

‐ 98 ‐

3. I. Giaever, C. R. Keese, Pro. Natl. Acad. Sci-Biol. 1984, 81, 3761. 

‐ 99 ‐ 



4. J. Y. Wong, R. Langer, D. E. Ingber, Proc. Natl. Acad. Sci. U.S.A 1994, 91, 3201. 

5. H. K. Song, B. Toste, K. Ahmann, D. Hoffman-Kim, G. T. R. Palmore, Biomaterials 2006, 

27, 473. 

6. M. Y. Li, Y. Guo, Y. Wei, A. G. MacDiarmid, P. I. Lelkes, Biomaterials 2006, 27, 2705. 

7. L. H. Huang, X. L. Zhuang, J. Hu, L. Lang, P. B. Zhang, Y. S. Wang, X. S. Chen, Y. Wei, X. 

B. Jing, Biomacromolecules 2008, 9, 850. 

8. M. Waugaman, B. Sannigrahi, P. McGeady, I. M. Khan, Eur. Polym. J. 2003, 39, 1405. 

9. M. Tanaka, S. Imai, T. Tanii, Y. Numao, N. Shimamoto, I. Ohdomari, H. Nishide, J. Polym. 


10. H. Oka, H. Kouno, H. Tanaka, J. Mater. Chem. 2007, 17, 1209. 

11. K. Nakahara, S. Iwasa, M. Satoh, Y. Morioka, J. Iriyama, M. Suguro, E. Hasegawa, Chem. 

Phys. Lett. 2002, 359, 351. 


13. M. D. Lang, C. C. Chu, J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 4214. 


15. H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004, 

50, 827. 

16. J. K. Kim, G. Cheruvally, J. W. Choi, J. H. Ahn, S. H. Lee, D. S. Choi, C. E. Song, Solid 

State Ionics 2007, 178, 1546. 

17. R. Bhardwaj, A. K. Mohanty, J. Biobased Mater. Bio. 2007, 1, 191. 

18. A. Duda, S. Penczek, Polimery 2003, 48, 16. 

19. R. Jain, N. H. Shah, A. W. Malick, C. T. Rhodes, Drug. Dev. Ind. Pharm. 1998, 24, 703. 

20. K. Koshika, Waseda University, 2009, PhD. Thesis. 

21. T. Endo, K. Takuma, T. Takata, C. Hirose, Macromolecules 1993, 26, 3227. 

22. T. Kurosaki, K. Wanlee, M. Okawara, J. Polym. Sci., Part A: Polym. Chem. 1972, 10, 

3295. 

23. M. W. Matsen, F. S. Bates, Macromolecules 1996, 29, 1091.

Chapter 5 

Synthesis of Triblock Copolymers of TEMPO-Acrylamide and 

Lactate by RAFT Polymerization 


5.2 Synthesis of Triblock Copolymer 


5.4 Cytotoxicity and Biocompatibility of Copolymers 

5.5 Electrospun of Copolymers 



References

Chapter 5 


Radical polymers bearing pendant 2,2,6,6-tetramethylpiperidin-1-oxy (TEMPO) groups 

have attracted increasing interest due to their unique characteristics associated with the 

unpaired electrons present in free radicals. Up to now, radical polymers have been found 

numerous potential applications such as catalyst for redox reaction, 1 one-dimensional 

throw-bond organic ferromagnets, 2 probe for in vivo electron paramagnetic resonance (EPR) 3 

and cathode material for bendable batteries. 4 In Chapter 4 we synthesized graft copolymers 

composed of poly(2,2,6,6-tetramethylpiperidine-1-oxyl-4-yl acrylamide) (PTAm) and 

polylactide (PLA) and preliminarily investigated their application in biomedical field. 

However, the graft copolymers did not possessed definite structure due to the random 

location of PLA on the PTAm backbone. Therefore, it is necessary to design block 

copolymers of PLA and PTAm with well-defined structure and controlled molecular weight. 

The block copolymer of PTAm and PLA should combine the electroactive property of radical 

polymers and biodegradable property of PLA together. 

In this chapter, well-defined triblock copolymers composed of a radical polymer, PTAm, 

and PLA were synthesized by combination of ring-opening polymerization (ROP) and 

reversible addition-fragmentation chain transfer (RAFT) polymerization methods. Compared 

to another controlled radical polymerization method, atom transfer radical polymerization 

(ATRP), RAFT appears more practical in terms of monomer selection and reaction 

conditions. 5-7 Moreover, RAFT technique requires fewer purification steps after the 

polymerization. 

The resulted copolymers were then electrospun into mats with varied morphology. 

Electro-spinning technique was originally developed to produce ultra-fine polymer fibers, and 

has recently re-emerged as a novel tool for generating micro- or nano-scale biopolymer 

scaffolds for tissue engineering. 8-10 The scaffolds fabricated by electro-spinning have highly 

porous microstructure with interconnected pores and an extremely large specific surface-area, 

which allow accommodation of a large number of cells and facilitate uniform distribution of 

cells and diffusion of oxygen and nutrients. We envisioned that this material could exhibit 

improved biocompatibility, biodegradability, solubility and processability. More importantly, 

it may have promising application as electroactive biomedical materials. 

‐ 102 ‐

5.2 Synthesis of Triblock Copolymer 

‐ 103 ‐ 

Synthesis of Triblock Copolymers of TEMPO‐Acrylamide 

and Lactate by RAFT Polymerization 

The schematic procedures of the synthesis of the PTAm-b-PLA-b-PTAm copolymer were 

shown in Scheme 1. The first step was to prepare PLA bearing two hydroxyl groups at each 

chain end. The molecular weight of the HO-PLA-OH can be determined from 1 H NMR as 

1.0×10 4 (Figure 1A). Then the CPAD, used as a chain transfer agent, was coupled onto the 

PLA chain ends via condensation reaction in the presence of DCC and DMAP. The 1 H NMR 

spectra of CPAD-PLA-CPAD showed signals at 7.4 – 7.9 ppm, corresponded to the resonance 

of the protons from the phenyl in the CPAD (Figure 1B). The PTAP-b-PLA-b-PTAP was 

synthesized by RAFT polymerization using CPAD-PLA-CPAD as macro-RAFT agent. The 

monomer, TAP, is not suitable for ATRP polymerization due to its pendant imine group, 

which may competitively complex with the copper and form species with lower catalytic 

activity. Therefore, we synthesized the block copolymer via RAFT polymerization. Finally, 

the PTAm-b-PLA-b-PTAm was obtained after the oxidation of PTAP-b-PLA-b-PTAP. 

Scheme 1. Synthetic route of PTAm-b-PLA-b-PTAm.

Chapter 5 

Figure 1. 1 H NMR spectra of HO-PLA-OH (A) and CPAD-PLA-CPAD (B). 

Figure 2 showed the 1 H NMR spectra of PTAm-b-PLA-b-PTAm triblock copolymers. All 

the resonances attributed to PLA and PTAm repeat units were detected, which clearly 

indicated the successful preparation of the triblock copolymers. The degree of polymerization 

of PTAm block can be calculated based on the integration of proton peak c at 4.19 ppm from 

piperidine and the proton peak a at 5.18 ppm of the methine in PLA. Triblock copolymers 

with different PTAm block length can be obtained by varying the monomer feed. The 

molecular weights of the copolymers are summarized in Table 1. The yields were higher than 

80%, indicating the reaction is more effective than that described in Chapter 4. The 

copolymers had low polydispersities, and the GPC profiles of the copolymers were all single 

and symmetrical peak. These implied that all the macromonomers have initiated the TAP 

monomers successfully and no homopolymerization occurred. 

Figure 2. 1 H NMR spectrum of PTAP-b-PLA-b-PTAP. 

‐ 104 ‐

Sample 

Table 1. Feed and result compositions of copolymers. 

CPAD-PLA-CPAD/Monomer 

(mol) 

Feed Result a 

‐ 105 ‐ 



Yield 

(%) 

PDI b 

TLT1 1 : 100 1 : 70 81.0 1.40 

TLT2 1 : 200 1 : 180 90.0 1.42 

a Calculated from 1 H NMR; b Determined from GPC in DMF. 

The cyclic voltammogram (CV) of the copolymer at different scan rates were shown in 

Figure 3. The CV curves also confirmed the success of the oxidation. 

Figure 3. CV of the copolymer (TLT1) at different scan rates in acetonitrile solution of 0.1 M 

tetrabutylammonium perchlorate. 


The typical DSC traces for PLA, TLT1, TLT2 and PTAm were collected in Figure 4A. The 

PLLA homopolymer has a Tm at 155.6 o C and a Tc at 97.4 o C, while TLT1 exhibits a Tm at 

160.0 o C and TLT2 exhibits no Tm or Tg in the test temperature range. These differences 

indicated that the physical properties of the PLA in the block copolymers were really 

different from those of homo-PLA. In the triblock copolymers, the PLA block was still 

crystalline, but its crystalline parameters changed much due to the restriction of the PTAm

Chapter 5 

blocks, which exhibiting no Tm or Tg in the test temperature range. Figure 4B showed the 

decomposition behaviors of PLA, TLT1, TLT2 and PTAm. PLA began to decompose at 200 

o C, which originating from the chain end, and lost all the weight at 300 o C. The 

decomposition temperature of PTAm occured at 50 o C and lasted to 500 o C. For TLT1 and 

TLT2, their thermo-decomposition behaviors were more similar to PTAm because the end 

hydroxyl groups of PLA were protected by the PTAm chains. 

Figure 4. (A) DSC traces of the PLA, PTAm, and TLT in second heating. (B) TGA curves of 

PLA, PTAm, and TLT. 

5.4 Cytotoxicity and Biocompatibility of Copolymers 

In the biomedical application, TLT copolymer should be non-toxic and able to support cell 

adhesion and growth. Like described in Chapter 4, the cytotoxicity and cell compatibility of 

the block copolymers were assessed in vitro. To better observe the shape of the adherent cells 

(particularly whether irregular polygonal or original elliptical), the samples were prepared by 

regular cell-staining method, i.e. staining separately with nucleus and F-actin. 

Figure 5. A: Phase contrast microscopy images of RSC96 cells after incubation on different 

polymer films for 48h. (1) PLA film, (2) PTAm film, (3) TLT1 film and (4) TLT2 film. Scale bar 

‐ 106 ‐

= 25 μm. B: MTT assay for the cytotoxicity of PLA, PTAm, TLT1 and TLT2. 

‐ 107 ‐ 



It can be seen from Figure 5A that cells exhibited original elliptical on PTAm film, while 

cells seeded on TLT films extended well as on PLA film. Considering the results shown in 

Figure 5B, it can be concluded that block copolymers had improved cell viability and were 

more suitable to support the proliferation of RSC96 cells compared to PTAm homopolymer 

in higher concentration. 

5.5 Electrospun of Copolymers 

It is known that the size and morphology of electrospun materials can be influenced either 

by the intrinsic properties of solutions such as viscosity, surface tension, and conductivity, or 

by the spinning parameters such as voltage, flow rate, and working distance. 11-14 In our study, 

all electro-spinnings were conducted with identical spinning parameters, so the size and 

morphology of the nanofibers were closely related to the intrinsic properties of the 

electro-spinning solutions. As shown in Figure 6, the morphologies of the TLT1 electrospun 

at various concentrations are quite different. It can be seen that at low concentration (10 wt%) 

TLT1 copolymers formed tyre-like shape. As the concentration increased to 20wt%,the 

copolymer was electrospun to connected microspheres. When the concentration reached to 30 

wt%, the resulted felt exhibited fibroid shape. The shape evolution of the polymers is mainly 

attributed to the viscosity difference. In the case of low viscosity solutions (Figure 6A and B), 

the jet breaks up into droplets, which also known as electrospraying. For high viscosity 

liquids (Figure 6C), the jet does not break up and formed continous fibers. 

Figure 6. SEM photograph of the electrospun TLT1 at concentration of 10 wt%(A), 20 wt% 

(B) and 30 wt% (C). (Scale bar: A and B = 50 μm, C = 5 μm)

Chapter 5 


Triblock copolymers composed of PLA and PTAm with well-defined structure was 

prepared by combination of ROP and RAFT methods. Since the living characteristics of the 

RAFT polymerization, the triblock copolymers could be obtained with well-defined structure 

and compositions, which was confirmed by the comparison of their yields and PDIs with that 

of graft copolymers synthesized in Chapter 4. Biological evaluation of the material showed 

that the material has good biocompatibility and low cytotoxicity. Electrospinning technology 

was then adopted to prepare the electro-active porous polymer matrices with relatively large 

surface area for biomedical applications. The morphology of electrospun copolymers is 

mainly attributed to the viscosity difference from tyre-like shape at lower concentration to 

fibroid shape at higher concentration. 


Materials 

Lactide was purchased from Purac, Holland. Stannous octoate (Sn(Oct)2, 95%) and 

1,4-butanediol (BDO) were purchased from Aldrich. 2, 2'-Azoisobutyronitrile (AIBN, Beijing 

Chemical Co., China) was recrystallized twice from methanol. 4-Cyanopentnoic acid 

dithiobenzoate (CPAD) was prepared as described in literature. 

4-Amino-2,2,6,6-tetramethylpiperidine (TCI, >97%) and Acrylyl chloride (Alfa Aesar, 96%) 

were used to prepare the 2,2,6,6-tetra-methylpiperidinyl acrylamide (TAP) monomer. 

N,N'-Dicyclohexylcarbodiimide (DCC, 99%) and 4-dimethylaminopyridine (DMAP, 98%) 

were purchased from Sigma Chemical Co. and used as received. All other reagents were used 

without further purification. 

Instrument 

1 H NMR spectra were recorded on Bruker AV 400 NMR spectrometer in CDCl3. Gel 

permeation chromatography was performed with a DMF eluent using a Tosoh HLC-8220 

instrument, and the molecular weight and polydispersity were calibrated with polystyrene 

standards. Scanning electron microscope (SEM) images were obtained by using an ESEM 

(Model XL 30 ESEM FEG from Micro FEI Philips). The specimens were mounted on metal 

stubs using a double-sided adhesive tape and vacuum coated with a platinum layer prior to 

examination. Samples for cyclic voltammetry were prepared by depositing thin LM PAP film 

‐ 108 ‐

‐ 109 ‐ 



on an indium tin oxide (ITO) electrode as working electrode and Ag/Ag + as reference 

electrode. Cyclic voltammograms were recorded on a CHI 630 potentiostat with different 

scanning rate. 

Synthesis of Hydroxyl-capped PLA 

After recrystallization in ethyl acetate for three times, lactide (1 mol) was added to a 

flame-dried and nitrogen-purged glass ampoule, into which a 150 mL toluene solution of 

BDO (7.2 mmol) and Sn(Oct)2 (0.3% of the BDO, mol/mol) was then transferred. The 

reaction vessel was immersed into a thermostatic oil bath maintained at 120 o C, under 

magnetic stirring for 24 h. The reaction product was precipitated into ethanol, filtered and 

dried at 40 o C in vacuum for 48 h. 

Synthesis of Macromolecular CTA: CPAD-PLA-CPAD 

Typically, PLA 5 g (0.5 mmol), CPAD 0.28 g (1mmol), DCC 0.42 g (2 mmol) and DMAP 

0.025 g (0.2 mmol) were dissolved in 20 mL anhydrous methylene chloride. The solution was 

stirred at room temperature for 48 hours. After filtration of the precipitate, the solution was 

poured into 200 mL cold ethyl ether, yielding pink precipitate. The pink precipitate was 

redissolved in methylene chloride and precipitated again in cold ethyl ether. After washing 

with additional two times with ethyl ether, the pink product CPAD-PLA-CPAD was finally 

obtained, Yield 92%. 

Synthesis of PTAm-b-PLA-b-PTAm 

Typically, 0.20 g CPAD-PLA-CPAD (0.02 mmol), 0.29 g (1.4 mmol) TAP monomer and 

1.6 mg AIBN (0.01 mmol) ware dissolved in 2 mL THF. The mixture was deaerated by 

applying three times freeze-pump-thaw cycle. Afterwards, the tube was immerged in 90 o C 

oil bath and stirred for 12 hours. After cooling to room temperature, the mixture was 

precipitate in cold ethyl ether. The slight pink precipitate was collected and washed twice 

with ethyl ether. The product was obtained after vacuum drying for 24 h with a yield of 81%. 

In order to obtain PTAm-b-PLA-b-PTAm, an oxidation step was needed. Typically, 110 mg of 

the aforementioned PTAP-b-PLA-b-PTAP dissolved in 5 mL THF and stirred in ice-cold bath, 

to which 500 mg of m-chloroperbenzoic acid (mCPBA) was added. The mixture was allowed 

to move to the room temperature and stirred for further 4 hours. The final product was 

obtained by precipitate the mixture into 120 mL ethyl ether/n-hexane (v/v, 1:1), Yield: 92%.

Chapter 5 

Cytotoxicity assay, Cell Adhesion and Spreading 

See Chapter 4, experimental section. 

Electrospinning Process 

Polymers (PLA, PTAm or PTAm-b-PLA-b-PTAm) were dissolved in dichloromethane to 

achieve a certain concentration. The solution was stirred for 48 h at ice water bath and then 

loaded into the spinner with a capillary outlet of 1 mm in diameter, which as an anode was 20 

cm apart from the grounded collecting drum. The voltage applied between the spinner outlet 

and the drum was 15 kV. The resulted mats were collected on an aluminum sheet fixed on the 

rotating drum for 3 h. Then the obtained product was dried in a vacuum oven for 24 h. 

Reference 

1. M. F. Semmelhack, C. R. Schmid, D. A. Cortes, C. S. Chou, J. Am. Chem. Soc. 1984, 106, 

3374. 

2. H. Nishide, T. Kaneko, Magnetic properties of organic material. Dekker: New York, 

1999. 

3. E. E. Voest, E. Vanfaassen, J. J. M. Marx, Free Radical Biol. Med. 1993, 15, 589. 

4. K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 7, 836. 

5. R. Barbey, L. Lavanant, D. Paripovic, N. Schuwer, C. Sugnaux, S. Tugulu, H. A. Klok, 

Chem. Rev. 2009, 109, 5437. 

6. A. Vora, K. Singh, D. C. Webster, Polymer 2009, 50, 2768. 

7. J. L. Zhu, X. Z. Zhang, H. Cheng, Y. Y. Li, Cheng, S. X.; Zhuo, R. X., J. Polym. Sci., 

Part A: Polym. Chem. 2007, 45, 5354. 

8. A. K. Ekaputra, Y. F. Zhou, S. M. Cool, D. W. Hutmacher, Tissue Engineering Part A 

2009, 15, 3779. 

9. X. L. Xu, X. S. Chen, A. X. Liu, Z. K. Hong, X. B. Jing, Eur. Polym. J. 2007, 43, 3187. 

10. Y. L. Hong, Y. A. Li, X. L. Zhuang, X. S. Chen, X. B. Jing, J. Biomed. Mater. Res. Part A 

2009, 89A, 345. 

11. M. Li, M. J. Mondrinos, M. R. Gandhi, F. K. Ko, A. S. Weiss, P. I. Lelkes, Biomaterials 

2005, 26, 5999. 

12. J. A. Matthews, G. E. Wnek, D. G. Simpson, G. L. Bowlin, Biomacromolecules 2002, 3, 

232. 

‐ 110 ‐

‐ 111 ‐ 



13. J. M. Deitzel, J. Kleinmeyer, D. Harris, N. C. Beck Tan, Polymer 2001, 42, 261. 

14. Y. J. Ryu, H. Y. Kim, K. H. Lee, H. C. Park, D. R. Lee, Eur. Polym. J. 2003, 39, 1883.

Chapter 6 

Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, 

6.1 Inroduction 

Lactate, and Ethyleneoxide 

6.2 Synthesis of MPEG-CPAD and MPEG-b-PLA-CPAD 

6.3 Synthesis of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm 

6.4 Micelles preparation and characterization 

6.5 EPR study of the micelles in PBS containing ascorbic acid 

6.6 Cytotoxicity assay 


6.8 Experimental section 

References

Chapter 6 


Since the discovery of nitroxyl radicals in 1956, there have been of continually profound 

interest in the synthesis and investigation of compounds containing nitroxyl free radicals. 

Applications such as spin-labeling/trapping, MR/ESR in vivo imaging, oxidation 

organocatalysts and mediating radical polymerization have emerged based on the unique 

physical, chemical and biological properties of the nitroxyl radicals. Polymers bearing stable 

nitroxyl radicals in the pendant, known as radical polymers, also have been investigated 

during past several decades initially for their potential reactivities, however, it is not until 

recently that the radical polymers was intensively investigated for organic electronic devices 

applications. A series of radical polymers have been synthesized and evaluated by our group 

as the electro-active materials for secondary batteries and organic memory devices. 1-4 

Aside from the electronic applications, radical polymers are also receiving increasing 

interest for the application as biomaterials due to nitroxyl radical which plays critical roles in 

various metabolic processes. C. C. Chu and co-workers are pioneers in this field by 

conjugating 2,2,6,6-tetramethylpiperidinyloxy (TEMPO) radicals with biodegradable 

polymers. The resultant TEMPO-functionalized polymers could be degraded in the 

physiological condition to release the TEMPO nitroxyl radicals, which may found potential 

use as the scaffold or surface coating for the cardiovascular tissue engineering, the 

macromolecular drugs for anticancer therapy and the wound dressing with improved healing 

and antimicrobial capability. 5-7 On the other hand, the magnetic resonance relaxivity and 

electron paramagnetic resonance (EPR) property have endowed the nitroxyl radical-contained 

materials with the potential application as bioimaging probes. Much attentions have been paid 

on the development of the nitroxyl radical-based magnetic resonance imaging (MRI) probes 

since they have lower toxicity in comparison with the commercially gadolinium derivatives 

agents. 8-10 However, the MR relaxivities of the nitroxyl radical is relatively lower. In order to 

solve this issue, several strategies such as copolymerization or attachment of nitroxyl radical 

compound to the water soluble hyperbranched polymer have been investigated. 11-14 Also, the 

nitroxyl radical compounds, such as TEMPO, are now being investigated as EPR probes 

applied in vivo because of the sensitivity of the EPR is much higher than that of MRI. 15-19 

However, the reducing environment in vivo, which could reduce or eliminate the EPR signal 

by reducing the nitroxyl radical, has brought a great obstacle to the application of these 

‐ 114 ‐

Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, Lactate, and Ethyleneoxide 

materials. It has been reported that the half-time of free TEMPO radical in the blood was 

about 15 s which was far from satisfactory for practical use. 20 

Therefore, our purpose is to develop a kind of polymeric deliver system that can carry 

stable nitroxyl radicals and resist to the reduction environment, which may find potential use 

as the EPR probe for bioimaging in vivo. For this study, amphiphilic triblock copolymer, 

consisting of a hydrophilic PEG segment, a hydrophobic PLA segment and a TEMPO 

radical-contained hydrophobic PTAm segment, was synthesized. An amphiphilic diblock 

copolymer only contains PEG and PTAm segments were also synthesized. Both of them can 

self-assemble into micelles in aqueous solution with radicals in the core and generate stable 

EPR signal. The stability of the micelles against reducing environment was also evaluated. 

6.2 Synthesis of MPEG-CPAD and MPEG-b-PLA-CPAD 

4-Cyanopentnoic acid dithiobenzoate (CPAD) was prepared as described in the literature 

26. 1 H NMR spectra with proton resonance absorption assignments was shown in Figure 6.1 

A. Then, the macromolecular chain transfer agents, MEPG-CPAD and MPEG-b-PLA-CPAD, 

were synthesized by chemical coupling the CPAD to the chain-end of MPEG and 

MPEG-b-PLA in the presence of DCC and DMAP, respectively. The structures of the 

obtained polymers were verified by 1 H NMR characterization as shown in Figure 6.1 with the 

presence of the proton resonance absorption peaks from CPAD. 

Figure 6.1 1 H NMR characterizations of (A) CPAD; (B) MPEG-CPAD; (C) MPEG-b-PLA-CPAD 

‐ 115 ‐

Chapter 6 

6.3 Synthesis of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm 

Controlled living radical polymerization such as nitroxide-mediated polymerization 

(NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation 

chain transfer (RAFT) polymerization have recently received great attention for their ability 

to synthesize polymer materials with controlled molecular weight, various functional groups 

and diverse architectures. We used RAFT technique to obtain the novel block copolymers in 

virtue of the convenient and effective RAFT polymerization towards TAP monomer. The 

preparation of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm precursor polymers were 

conducted in 1,4-dioxane/methanol mixture using MPEG-CPAD and MPEG-b-PLA-CPAD as 

the macromolecular chain transfer agent (CTA), respectively (Scheme 1 and Scheme 2). 

Scheme 6.1 Synthesis of macromolecular chain transfer agents (CTA). 

To better understand the polymerization process, the kinetic of the RAFT polymerization 

of TAP was studied and the results were shown in Figure 6.2. The polymerization could reach 

a high monomer conversion up to ~87% within 6 hours. The linear dependence of the 

molecular weight on the monomer conversion strongly indicated that the RAFT 

polymerization towards TAP monomer had living characters. However, the molecular weight 

distribution of the polymer was increased from 1.20 at 0 hour to 1.57 at 6 hour, and further to 

1.73 if the polymerization proceeded more than10 hours which may be assigned either to 

intermolecular chain transfer or possibly to cross-termination at the high monomer 

conversions. This feature has already been observed in most of the dithiobenzoate-mediated 

RAFT system. 

‐ 116 ‐


Scheme 6.2 Synthesis and self-assembly of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm 

Figure 6.2 RAFT polymerization of TAP monomer using MEPG-CPAD as the CTA. (A) 

Monomer conversion versus time; (B) Dependence of molecular weights and molecular weight 

distributions of the block copolymers on the monomer conversion. 

Based on the aforementioned study, we then conducted the preparation of the block 

copolymer for 8 hours in order to achieve high monomer conversion and meanwhile 

minimum side reactions which might induce broaden of the molecular weight distribution. 1 H 

NMR was used to study the structure of the precursor block copolymers. The spectra shown 

in Figure 6.3 clearly confirmed the structure of the block copolymers. The degree of 

polymerization was calculated to be 46 and 42 for MPEG-b-PTAm and 

MPEG-b-PLA-b-PTAm, respectively, based on the integration of proton peak c at 4.19 ppm 

from piperidine and the proton peak b at 3.64 ppm for the methylene in MPEG. The obtained 

precursor block copolymers were then oxidized by m-chloroperbenzoic acid to convert the 

N-H groups into nitroxyl radicals, leading to MPEG-b-PTAm and MPEG-b-PLA-b-PTAm 

block copolymers with nitroxyl radical-contained segment. 1 H NMR (data not shown) was 

‐ 117 ‐

Chapter 6 

used to characterize the resultant block copolymer, the disappearance of the resonance 

absorption from the protons in the PTAm segment indicated that the N-H groups had been 

oxidized into paramagnetic nitroxyl radicals that would induce no magnetic resonance 

absorption. The GPC results (Figure 6.4) also revealed the two obtained block copolymers 

with unimodel GPC traces, demonstrating the successful preparation of the block 

copolymers. 

Figure 6.3 

1 H NMR spectra of (A) MPEG-b-PTAm precursor polymer; (B) 

MPEG-b-PLA-b-PTAm precursor polymer. 

Figure 6.4 GPC traces of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm 

‐ 118 ‐

6.4 Micelles preparation and characterization 


The micelles were prepared by dialysis method. The weighted block copolymer was 

dissolved in THF and subsequently added dropwise into deionic water to form micelles 

aggregation. The mixtures were then dialyzed against deionic water to remove the residual 

THF. The obtained micelles solutions were diluted to a concentration of 1.0 mg.mL -1 . The 

average hydrodynamic diameters for MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles 

were characterized by DLS to be 48 nm and 58 nm (see Figure 6.5 C), respectively. The 

slightly increased size of the micelles prepared from MPEG-b-PLA-b-PTAm may be ascribed 

to the more hydrophobic molecular weight ratio of MPEG-b-PLA-b-PTAm compared to that 

of MPEG-b-PTAm. 21 TEM was also used to confirm the micelles structure of the two block 

copolymers as shown in Figure 6.5 A and B. Cyclic voltammograms of MPEG-b-PTAm and 

MPEG-b-PLA-b-PTAm micelles were also conducted in aqueous HCl solution at a scanning 

rate of 10 mV/min. The results showed in Figure 6.6 demonstrated that both of the micelles 

produced a reversible redox wave at around 0.7 V vs Ag/AgCl, indicating that the nitroxyl 

radicals had been successfully incorporated into the micelles. 

Figure 6.5 TEM and DLS characterizations of MPEG-b-PTAm micelles (A) and 

MPEG-b-PLA-b-PTAm micelles (B) 

‐ 119 ‐

Chapter 6 

Figure 6.6 Cyclic voltammograms of (A) MPEG-b-PTAm and (B) MPEG-b-PLA-b-PTAm 

micelles in 0.1 M HCl aqueous solution. 

6.5 EPR study of the micelles in PBS containing ascorbic acid 

It is known that a reducing environment is necessary for biological systems. The 

antioxidants such as ascorbic acid (Vc) and glutathione (GSH) are important to keep the 

redox status in living cells and exist in most of parts in vivo. Thus, we evaluated the reduction 

resistance of the micelles in the presence of antioxidants. Since the reduction of nitroxyl 

radical into hydroxylamine group by GSH is much slower than Vc and there is higher 

concentration of Vc in the blood stream, 22, 23 we selected antioxidant Vc for our study. The 

EPR measurements were conducted in the presence of Vc at concentration of 5.0 mM which 

is 50 times more than the concentration of Vc in the blood. 

As shown in Figure 6.7 A, the EPR signal decreased over time in PBS solution 

containing Vc, ascribing to the reduction of nitroxyl radicals. And the EPR signal pattern of 

both MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles were broad single, which is 

distinct from typical triplet signal of free TEMPOL radical in diluted solution, due to the 

spin-spin interaction of TEMPO in the side chains. 19, 24, 25 Furthermore, we observed that the 

EPR signal in aqueous media is broader than in chloroform, which is consisted with previous 

report. 18 These results indicated that the polymer segment containing nitroxyl radicals had 

been incorporated into micelles in aggregated state in the hydrophobic core. By virtue of the 

micelle structure, the nitroxyl radicals in the core could resist reduction for a longer time than 

free TEMPOL radical even in the presence of higher concentration of Vc (Figure 6.7 B). The 

half-life time for both MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles were about 8 

‐ 120 ‐


min, however, the time for free TEMPOL radical was less than 1 min. The prolonging time 

for both MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles in the reducing environment 

would endow the systems have the promising application as the stable EPR probes. 

Figure 6.7 (A) EPR spectra of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles in PBS 

containing 5.0 mM ascorbic acid over time; (B) Dependence of EPR signal intensity on the time. 

6.6 Cytotoxicity assay 

MTT cell toxicity assay was used to determine the cytoxicity of the synthesized block 

copolymers MEPG-b-PTAm and MPEG-b-PLA-b-PTAm. The results shown in Figure 6.8 

revealed that both MEPG-b-PTAm and MPEG-b-PLA-b-PTAm had as low cytotoxicity as the 

MPEG5K and MPEG-b-PLA. The good biocompatibility of the MEPG-b-PTAm and 

MPEG-b-PLA-b-PTAm, presumably ascribing to the hydrophiphic shell of the MPEG 

segment in aqueous solution, would make these materials suitable for applications in vivo. In 

‐ 121 ‐

Chapter 6 

vivo cytotoxicity was also determined by injecting the micelles solution into the kunming 

mice (ca. 17~23 g). 0.5 mL of micelles solution at concentrations of 2 mg/mL, 5mg/mL and 

15mg/ml were injected into the five kunming mice in each group. All the mice were observed 

to show no significant indisposed nor death during the 2 day’s observation, indicating the 

good in vivo biocompatibility of the micelles. 

Figure 6.8 MTT cell toxicity assay. B1: MPEG-b-PLA; B2: MPEG-b-PTAm; B3: MPEG-b-PLA-b-PTAm. 


Amphiphilic triblock copolymer containing stable nitroxyl radicals was successfully 

prepared by combination of ring-opening polymerization and RAFT technique. The RAFT 

polymerization towards TAP monomer was monitored to show living features by using 

MPEG-CPAD as the CTA. Amphiphilic diblock copolymer containing stable nitroxyl radicals 

but without PLA segment was also prepared for the control study. The block copolymer 

structures were confirmed by 1 H NMR and GPC characterization. Both of the copolymers can 

self-assemble into micelles in aqueous solution with nitroxyl radicals in the hydrophobic core. 

All the micelles prepared from either triblock or diblock copolymer can produce EPR signal 

and protect the free radicals from being reduced for a longer time as compared to the free 

TEMPOL radicals in the presence of high concentration Vc. Additionally, the micellar 

structure also endow the two materials with low cytotoxicity. Therefore, such micelles with 

stable free radicals in the core should be promising to be used as the EPR probe for in vivo 

imaging application. 

‐ 122 ‐

6.8 Experimental section 

Materials and methods 


2,2’-Azoisobutyronitrile (AIBN, Beijing Chemical Co., China) was recrystallized twice 

from methanol. Monomethoxy poly(ethylene glycol) (MPEG Mw=5000 Da), 

4-hydroxyl-TEMPO (TEMPOL, 97%) N,N'-Dicyclohexylcarbodiimide (DCC, 99%) and 

4-dimethylaminopyridine (DMAP, 98%) were purchased from Aldrich Chemical Co. and 

used as received. 4-Cyanopentnoic acid dithiobenzoate (CPAD) was prepared as described in 

the literature 21. 26 4-Amino-2,2,6,6-tetramethylpiperidine (TCI, >97%) and Acryloyl chloride 

(Alfa Aesar, 96%) were used without purification to prepare the 

2,2,6,6-tetramethylpiperidinyl acrylamide (TAP) monomer. 27 All other reagents were used 

without further purification. 

1 

H NMR spectra were recorded on Bruker AV 300 or Bruker AV 600 NMR spectrometer 

in CDCl3. Gel permeation chromatography was performed with 0.1 M LiCl DMF eluent using 

a Tosoh HLC-8220 instrument, and the molecular weight and polydispersity were calibrated 

with polystyrene standards. For kinetic study, gel permeation chromatography was performed 

with a Schamback SFD GmnH mGPC2000 instrument using 0.1 M LiCl DMF as the eluent at 

40 o C, and the molecular weight and polydispersity were calibrated with polystyrene 

standards. Dynamic light scattering (DLS) were determined by DAWN EOS 18 Angles Laser 

Light Scattering Instructment (Wyatt Technology). Transmission electron microscopy (TEM 

JEM-2010 electron microscope, JEOL, Japan) was also used to characterize the morphology 

of the micelles. Electron paramagnetic resonance (EPR) spectra were recorded on a 

JES-FA200 EPR spectrometer. 

Synthesis of Macromolecular CTA: MPEG-CPAD and MPEG-b-PLA-CPAD. 

Typically, MPEG5k 2.5 g (0.5 mmol), CPAD 0.28 g (1mmol) DCC 0.42 g (2 mmol) and 

DMAP 0.025 g (0.2 mmol) were dissolved in 20 mL anhydrous methylene chloride. The 

solution was stirred at room temperature for 48 hours. After filtration of the precipitate, the 

solution was poured into 200 mL cold ethyl ether, yielding pink precipitate. The pink 

precipitate was redissolved in methylene chloride and precipitated again in cold ethyl ether. 

After washing with additional two times with ethyl ether, the pink product MPEG-CPAD was 

finally obtained, yield 92%. The preparation of MPEG-b-PLA-CPAD was similar as 

MPEG-CPAD, yield 89%. The structure of the two macromolecular CTA was verified by 1 H 

‐ 123 ‐

Chapter 6 

NMR. Characterization of MPEG-CPAD: IR: � ~ (cm-1) 1737 (C=O) 1044 (C=S). 1 H NMR 

(300M, CDCl3, δ ppm): 7.89 7.57 7.40 (5H, CH×3 in benzene), 4.27 (2H, CH2OC(O)-), 3.64 

(CH2 in PEG), 3.38 (3H, CH3O-), 2.46~2.75 (4H, CH2×2 in CPAD), 1.94 (3H, CH3 in CPAD). 

Characterization of MPEG-b-PLA-CPAD: IR: � ~ (cm-1) 1755 (C=O) 1044 (C=S). 1 H NMR 

(300M, CDCl3, δ ppm): 7.88 7.57 7.40 (5H, CH×3 in benzene), 5.15 (CH in PLA), 4.26 (2H, 

CH2OC(O)-), 3.62 (CH2 in PEG), 3.36 (3H, CH3O-), 2.46~2.75 (4H, CH2×2 in CPAD), 1.95 

(3H, CH3 in CPAD). 

Synthesis of MPEG-b-poly(2,2,6,6-tetramethylpiperidinyloxy acrylamide) 

(PEG-b-PTAm). 

For kinetic study, 0.22 g MPEG-CPAD (0.042 mmol), 0.53 g TAP (2.5 mmol) and 3.4 mg 

AIBN (0.021 mmol) were dissolved in 8 mL 1,4-dioxane/methanol (v/v, 3:1). The mixture 

was deaerated by applying three times freeze-pump-thaw cycle. Afterwards, the tube was 

immerged in 90 o C oil bath. Samples were taken out at various time intervals and quenched 

immediately into liquid nitrogen. The freezing samples were lyophilized to gain pink powders 

under reduced pressure and then used for 1 H NMR analysis to determine the monomer 

conversions. Molecular weights and molecular weight distributions were determined by GPC 

after the oxidation of the samples by m-chloroperbenzoic acid (mCPBA) in THF. The 

detailed oxidation processes are as follow. 

For preparation of MPEG-b-PTAm, 0.10 g MPEG-CPAD (0.019 mmol), 0.25 g TAP 

monomer (1.2 mmol) and 1.6 mg AIBN (0.01 mmol) were dissolved in 4mL 

1,4-dioxane/methanol (v/v, 3:1). The mixture was deaerated by applying three times 

freeze-pump-thaw cycle. Afterwards, the tube was immerged in 90 o C oil bath and stirred for 

8 hours. After cooling to room temperature, the mixture was precipitated from cold ethyl 

ether. The slight pink precipitate was collected and washed twice with ethyl ether. The 

product was obtained after vacuum drying for 24 h with a yield of 81% (0.29 g). In order to 

gain MPEG-b-PTAm, an oxidation step was needed. Typically, 110 mg of the aforementioned 

product dissolved in 5 mL THF and stirred in ice-cold bath, to which 500 mg of mCPBA was 

added. The mixture was allowed to move to the room temperature and stirred for further 4 

hours. The final product was obtained by precipitating the mixture into 120 mL ethyl 

ether/n-hexane (v/v, 1:1), yield 92%. (Mn=25200, PDI=1.38 by GPC). 

‐ 124 ‐

Synthesis of MPEG-b-PLA-b-PTAm. 


0.56 g MPEG-b-PLA-CPAD (0.04 mmol), 0.50 g (2.4 mmol) TAP monomer and 3.3 mg 

AIBN (0.02 mmol) ware dissolved in 6mL 1,4-dioxane/methanol (9:1, v/v). The mixture was 

deaerated by applying three times freeze-pump-thaw cycle. Afterwards, the tube was 

immerged in 90 o C oil bath and stirred for 8 hours. After cooling to room temperature, the 

mixture was precipitate in cold ethyl ether. The pale pink precipitate was collected and 

washed twice with ethyl ether. The product was obtained after vacuum drying for 24 h with a 

yield of 79% (0.84 g). An additional oxidation procedure was also needed to gain the final 

product MPEG-b-PLA-b-PTAm in good yield. (Mn=32300, PDI=1.42 by GPC) 

Micelles preparation and characterization. 

The preparation procedures for the MPEG-b-PTAm and MPEG-b-PLA-b-PTAm micelles 

are the same. Typically, 50 mg of the block copolymer was firstly dissolved in 5 mL of THF 

and then added dropwise into 10 mL deionized water. The mixture was then transferred into a 

dialysis bag (molecular weight cut-off = 3500 Da) and dialyzed against deionized water for 

24h. Afterwards, the micelles solution was diluted to 50 mL with deioinized water. The final 

concentrations of the micelles were 1.0 mg mL -1 . The structure of the micelles was 

characterized by DLS and TEM. 

EPR study. 

To evaluate the stability of the nitroxyl radicals containing micelles in the reducing 

environment, EPR study of the micelles in PBS buffering solution containing ascorbic acid at 

high concentration was conducted. 0.5 mL of the prepared micelle solution (1.0 mg.mL -1 ) 

was mixed vigorously with 0.5 mL of PBS solution (pH 7.4, 0.2 M containing 10.0 mM 

ascorbic acid). The mixture was then transferred into capillary tube immediately for EPR 

measurement over time. The final concentrations of the micelle and the ascorbic acid were 

0.5 mg.mL -1 and 5.0 mM, respectively. The same assay was performed toward TEMPOL at 

concentration of 0.5 mg mL -1 in the same buffer as the control. 

Cytotoxicity assay. 

The cytotoxicity of the block copolymers were assessed using MTT method. Polymer 

samples were dispersed in DMEM medium (Dulbecco's Modified Eagle Medium) 

supplemented with 10% fetal calf serum (Gibco) in a humidified incubator at 37 and 5% 

‐ 125 ‐

Chapter 6 

CO2 for 24 h. RSC96 cells were seeded at 1.2 ×104 cells/well in 96-well plates and cultured 

for 24 h. Then the culture media were replaced by the polymer solutions at various diluted 

concentrations. After incubation for additional 24 h, 20 μL of 

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) solution (5 mg/mL) 

was added to each well. The plates were return to the incubator for a period of 4 h culture. 

The supernatant were then carefully removed from each well, and 200 μL DMSO was added 

to dissolve the MTT formazan crystals. The plate was incubated for an additional 10 min 

before the absorbance at 492 nm was recorded by an ELISA microplate reader (Bio-Rad). 

The cell viability (%) was calculated according to the following equation: 

Cell viability (%) = (Asample / Acontrol) × 100 (1) 

Where Asample was the absorbance of the polymers extracted solutions treated cells and 

Acontrol was the absorbance of the untreated cells. Each experiment was done in triplicate and 

repeated a minimum of three times. 

References 

1. H. Nishide, K. Koshika, K. Oyaizu, Pure Appl. Chem. 2009, 81, 1961. 


3. K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 2339. 

4. T. Suga, Y. J. Pu, K. Oyaizu, H. Nishide, Bull. Chem. Soc. of Jap. 2004, 77, (12), 

2203-2204. 

5. M. D. Lang, C. C. Chu, J. Polym. Sci. Part A: Polym. Chem. 2001, 39, 4214. 

6. G. Jokhadze, M. Machaidze, H. Panosyan, C. C. Chu, R. Katsarava, J. Biomater. Sci. 

Polym. Ed. 2007, 18, 411. 


8. Z. Zhelev, R. Bakalova, I. Aoki, K. Matsumoto, V. Gadjeva, K. Anzai, I. Kanno, Mol 

Pharm 2009, 6, 504. 

9. Z. Zhelev, R. Bakalova, I. Aoki, K. Matsumoto, V. Gadjeva, K. Anzai, I. Kanno, Chem. 

Commun. 2009, 1, 53. 

10. Z. Zhelev, R. Bakalova, I. Aoki, K. I. Matsumoto, V. Gadjeva, K. Anzai, I. Kanno, Mol. 

Pharmacol. 2009. 

11. C. S. Winalski, S. Shortkroff, R. V. Mulkern, E. Schneider, G. M. Rosen, Magn. Reson. 

‐ 126 ‐

Med. 2002, 48, 965. 


12. Y. Huang, A. J. Nan, G. M. Rosen, C. S. Winalski, E. Schneider, P. Tsai, H. Ghandehari, 

Macromol. Biosci. 2003, 3, 647. 

13. Y.Sato, H. Hayashi, M. Okazaki, M. Aso, S. Karasawa, S. Ueki, H. Suemune, N. Koga, 


14. H. Hayashi, S. Karasawa, A. Tanaka, K. Odoi, K. Chikama, H. Kuribayashi, N. Koga, 


15. L. J. Berliner, V. Khramtsov, H. Fujii, T. L. Clanton, Free Radic. Biol. Med. 2001, 30, 

489. 

16.G. L. He, Y. M. Deng, H. H. Li, P. Kuppusamy, J. L. Zweier, Magn. Reson. Med. 2002, 47, 

571. 

17. B. P. Soule, F. Hyodo, K. Matsumoto, N. L. Simone, J. A. Cook, M. C. Krishna, J. B. 

Mitchell, Free Radic. Biol. Med. 2007, 42, 1632. 

18. T. Yoshitomi, D. Miyamoto, Y. Nagasaki, Biomacromolecules 2009, 10, 569. 

19. T. Yoshitomi, R. Suzuki, T. Mamiya, H. Matsui, A. Hirayama, Y. Nagasaki, Bioconjug. 

Chem. 2009, 20, 1792. 

20. K. Takechi, H. Tamura, K. Yamaoka, H. Sakurai, Free Radic. Res. 1997, 26, 483. 

21. H. T. Duong, T. U. Ngayen, M. H. Stenzel, Polym. Chem. 2010, 1, 171. 

22. J. Fuchs, N. Groth, T. Herrling, G. Zimmer, Free Radic. Biol. Med. 1997, 22, 967. 

23. J. Trnka, F. H. Blaikie, R. A. J. Smith, Murphy, M. P., Free Radic. Biol. Med. 2008, 44, 

1406. 

24. E. Yoshida, T. Tanaka, Colloid Polym. Sci. 2006, 285, 135. 

25. E. Yoshida, T. Tanaka, Colloid Polym. Sci. 2008, 286, 827. 

26. Y. Mitsukami, M. S. Donovan, A. B. Lowe, C. L. McCormick, Macromolecules 2001, 34, 

2248. 

27. K. Koshika, Waseda University PhD. Thesis. 2009. 

‐ 127 ‐

Chapter 7 

Conclusion and Future Prospects 

7.1. Conclusion 

7.2. Future Prospects

Chapter 7 

7.1. Conclusion 

In this thesis, the author described the catalytic synthesis and characterization of 

biodegradable polyesters and their radical copolymers. In this chapter, the author has 

described the synthesis of biodegradable polyesters by using a series of newly synthesized 

cobalt-Schiff-base complexes catalysts. The catalyst activity, polymerization mechanism, 

functionality of PLA by incorporating with stable TEMPO radical-substituted polymers and 

important conclusions derived from this study are summarized. 

In chapter 1, the author summarized “copolymer of epoxide and carbon dioxide”, 

“polylactide”, “others biodegradable polyesters”, “electroactive polymers” and “radical 

polymers”, respectively. 

In chapter 2, a series of Cobalt Schiff-base complexes were investigated as the catalyst for 

the alternating copolymerization of CO2 and rac-PO in the presence of Bu4NBr. The 

poly(propylene carbonate) (PPC) and cyclic propylene carbonate (PC) selectivity of the 

resultant copolymers were determined by modification of the length of the diimine bridges 

between the two nitrogen atoms in the ligands. The L 1 -Co III -dnp/Bu4NBr catalyst exhibited 

the highest activity, PPC/PC selectivity, and degree of head-to-tail linkages. The 

L 2 -Co III -dnp/Bu4NBr catalyst showed slightly lower head-to-tail linkages. For the dimine 

bridges containing three-carbon chains between the two nitrogen atoms in the Schiff bases, 

the corresponding L 4 -Co III -dnp complex displayed the lowest catalytic activity. Based on the 

electrochemical measurements to determine the half-wave potentials of the complexes, the 

catalytic activity of these complexes was compared. The higher stability for the axial group’s 

metal–O (phenolate) bond reflected the more negative E1/2 of the Co III + e - 

‐ 130 ‐ 

Co II redox 

couple for the L-Co III -dnp complexes with the diimine-bridge composed of two carbon atoms, 

which led to the higher catalytic activity for the copolymerization of PO and CO2. In the case 

of the cobalt complexes with more positive Co(II/III) potentials and thus with a lower electron 

density on the cobalt center, the coordination of a labile propagating chain end to the cobalt 

center is considered to determine the overall polymerization rate. 

In chapter 3, Co(III) complexes with Schiff base ligands and Tin(II) alphatates, were used 

as catalysts for the ROP of LacOCA to produce poly(lactic acid). Intra- and/or 

inter-transesterification were suggested to coincide with the polymerization, which resulted in 

a relatively large polydispersity in molecular weights. The carbonyldioxy group was

‐ 131 ‐ 


eliminated from the polymerization system. The corresponding PLA showed similar Tg but 

lower T5% compared with PLA obtained from lactides, as a result of the lower molecular 

weights. Al(III) complexes with Schiff base ligands were not catalytically active for the 

polymerization of LacOCA. 

In Chapter 4, novel PTAm-g-PLA copolymers were successfully prepared by a PLA 

macromonomer approach. The obtained copolymer contained stable radical units which was 

biologically active. The copolymers were amorphous determined from DSC measurement 

due to the relatively low PLA content. The copolymer exhibited an improved 

biocompatibility compared to PTAm homopolymer. 

In chapter 5, Triblock copolymers composed of PLA and PTAm with well-defined 

structure was prepared by combination of ROP and RAFT methods. Biological evaluation of 

the material showed that the material has good biocompatibility and low cytotoxicity. 

Electrospinning technology was then adopted to prepare the electro-active porous polymer 

matrices with relatively large surface area for biomedical applications. 

In chapter 6, two kinds of amphiphilic block copolymers containing stable nitroxyl 

radicals were synthesized. The RAFT polymerization towards TAP monomer was monitored 

to show living features. The block copolymer structures were confirmed by 1 H-NMR and 

GPC characterization. Both of the copolymers can self-assemble into micelles in aqueous 

solution with nitroxyl radicals in the hydrophobic core. The micelles can produce EPR signal 

and protect the free radicals from being reduced for a longer time as compared to the free 

TEMPOL radicals in the presence of high concentration Vc. Additionally, the micelle 

structure also endow the materials with low cytotoxicity. Therefore, such micelles with stable 

free radicals in the core should be promising to be used as the EPR probe for in vivo imaging 

application.

Chapter 7 

7.2. Future Prospects 

Recent advances of the biomedical use of polyesters have been paid increasing attention 

on dealing with the interaction and communication between the materials and life systems, 

for which the materials are termed as bioactive materials. In order to obtain bioactive 

materials, some modifications towards polyesters are usually taken to achieve bioactive 

functionalities, including hydrophobicity-hydrophilicity, softness-hardness, charge-charge 

density, stimuli responsiveness, and biological functionality. In the past few years, some 

efforts have been made by our lab on the functionalization of PLA and their use in the 

biomedical fields. For example, copolymerization of lactide monomer with functionalized 

cyclic monomers leads to biodegradable polymers with reactive amino or carboxyl groups 

which are subsequently used for conjugation with bioactive molecules such as folate, RGD, 

sugars, antibody and drugs. Then, the use of these bio-functionalized materials in, such as 

tissue engineering scaffolds or smart drug delivery systems have also been investigated. 

Though great efforts have been made, there are still challenges in synthesis of biodegradable 

polyesters with precise and smart properties, such as improved cell adhesions and 

proliferation, precise targeting drug delivery and triggered release, promoted cell 

internalization and so on. Fortunately, by virtue of the recent development on the click 

chemistry and living radical polymerization technique (ATRP, RAFT et al.), it is possible for 

us to prepare polyesters with diverse structures and architectures, ie. different kinds of 

polymers (natural polymers, synthetic polyesters and free radical polymers) can be 

conjugated together and great amount of vinyl monomers can be used to bring additional 

properties to the polyesters. Thus, it is possible for us to prepare biomedical polymers with 

more profound and precise functions for specific biomedical use. 

A tentative effort has been made in this thesis on the synthesis of the biodegradable 

copolymers of PLA and TEMPO-contained PTAm through combination of ring-opening 

polymerization and RAFT living radical polymerization. The biocompatibility and potential 

biomedical use were also evaluated. However, it is reasonably attractive to make step further 

in the application of the TEMPO-based radical polymers in biomedical fields based on the 

unique electronic, magnetic and biological properties of the nitroxyl radicals. Tasks are still 

remained in the further investigation of these materials interaction and communication with 

cells through electronic transport or nitroxyl radical triggered signal pathway. Materials in the 

‐ 132 ‐

‐ 133 ‐ 


forms of solid film, nano/micro fibrous film, mesoporous scaffold or drug-eluting stent 

coating should be constructed and evaluated in the field including induced cell differentiation 

and proliferation, cell adhension or retardation, antibacterials and so on. Additionally, the MR 

and ESR properties of the TMEPO radical also endow the copolymers with promising use as 

the “soft” bioimaging probes in vivo. As shown in our chapter 6, the core-shell micellar 

structure was able to protect the TEMPO from being reduced by reductant in a relatively 

longer time as compared to the free TEMPO molecules and reduced cytotoxicity was also 

observed. However, the stability of the micelles in the blood stream is still the problem 

encountered. The further improved stability and MR or EPR signal intensity are now under 

investigation. One of the strategies is to prepare core cross-linked nanogels, which may 

significantly improve the stability of the nanoparticles. And the nanogels can also be produced 

with stimuli responsive monomers, so that the obtained nano-probe could generate different 

signals in response to diverse environment for applications in probing various inner parts in 

vivo.

List of Publications 

1. Xiuli Zhuang, Kenichi Oyaizu, Yongsheng Niu, Kenichiroh Koshika, Xuesi Chen, Hiroyuki 

Nishide, “Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their 

Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide” Macromol. Chem. 

Phys., 210, 669-676 (2009). 

2. Xiuli Zhuang, Han Zhang, Natsuru Chikushi, Changwen Zhao, Kenichi Oyaizu, Xuesi Chen, 

Hiroyuki Nishide, “Biodegradable and Electroactive TEMPO-Substituted Acrylamide/Lactide 

Copolymer” Macromol. Biosci., (2010) in press. 

3. Xiuli Zhuang, Chunsheng Xiao, Kenichi Oyaizu, Natsuru Chikushi, Xuesi Chen, Hiroyuki 

Nishide, “Synthesis of Amphiphilic Block Copolymers bearing Stable Nitroxyl Radicals” J. 

Polym. Sci., Part A: Polym. Chem.,, (2010), submitted. 

4. Xiuli Zhuang, Haiyang Yu, Zhaohui Tang, Kenichi Oyaizu, Hiroyuki Nishide, Xuesi Chen, 

“Polymerization of Lactic o-Carboxylic Anhydride Using Organometallic Catalysts” Cn. J. Polym. 

Sci., (2010), in press. 

5. Xiuli Zhuang, Han Zhang, Yu Wang, Changwen Zhao, Kenichi Oyaizu, Xuesi Chen, Hiroyuki 

Nishide, “Synthesis of Biodegradable and TEMPO-Substitute Triblock Copolymers by 

Combination of ROP and RAFT Polymerization Methods” Polymer, (2010), submitted. 

6. Changwen Zhao, Xiuli Zhuang, Pan He, Chunsheng Xiao, Chaoliang He, Jingru Sun, Xuesi Chen, 

Synthesis of Biodegradable Thermo- and pH-Responsive Hydrogels for Controlled Drug Release, 

Polymer, 50, 4308-4316 (2009) 

7. Zhaopei Guo, Yanhui Li, Huayu Tian, Zhuang Xiuli, Xuesi Chen, Xiabin Jing, Self-Assembly of 

Hyperbranched Multiarmed PEG-PEI-PLys(Z) Copolymer into Micelles, Rings, and Vesicles, 

Langmuir, 25, 9690-9696 (2009). 

8. Youliang Hong, Yanan Li, Zhuang Xiuli, Xuesi Chen, Xiabin Jing, Electrospinning of 

Multicomponent Ultrathin Fibrous Nonwovens for Semi-Occlusive Wound Dressings, J. Biomed. 

Mater. Res. A, 89A, 345-354 (2009). 

9. Jun Hu, Lihong Huang, Le Lang, Yadong Liu, Zhuang Xiuli, Xuesi Chen,Yen Wei, Xiabin Jing, 

The Study of Electroactive Block Copolymer Containing Aniline Pentamer Isolated from 

Different Solvents, J. Polym. Sci., Part A: Polym. Chem., 47, 1298-1307 (2009). 

10. Yongsheng Niu, Hongchun Li, Xuesi Chen, Wanxi Zhang, Zhuang Xiuli, Xiabin Jing, Alternating 

Copolymerization of Carbon Dioxide and Propylene Oxide Catalyzed by Cobalt Schiff Base 

Complex, Macromol. Chem. Phys., 210, 1224-1229 (2009). 

11. Yongsheng Niu, Wanxi Zhang, Hongchun Li, Xuesi Chen, Jingru Sun, Zhuang Xiuli, Xiabin Jing 

Carbon Dioxide/Propylene Oxide Coupling Reaction Catalyzed by Chromium Salen Complexes, 

Polymer, 50, 441-446 (2009). 

12. Chunsheng Xiao, Huayu Tian, Zhuang Xiuli, Xuesi Chen, Xiabin Jing, Recent Developments in 

Intelligent Biomedical Polymers, Sci. China Ser B., 52, 117-130 (2009).

13. Xuan Pang, Xuesi Chen, Xiuli Zhuang, Xiabin Jing, Crown-Like Macrocycle Zinc Complex 

Derived from β-Diketone Ligand for the Polymerization of rac-Lactide, J. Polym. Sci., Part A: 

Polym. Chem., 46, 643–649 (2008). 

14. Lihong Huang, Xiuli Zhuang, Jun Hu, Le Lang, Peibiao Zhang, Yu Wang, Xuesi Chen, Yen Wei, 

and Xiabin Jing, Synthesis of Biodegradable and Electroactive Multiblock Polylactide and 

Aniline Pentamer Copolymer for Tissue Engineering Applications, Biomacromolecules, 9, 

850-858 (2008). 

15. Jun Hu, Lihong Huang, Xiuli Zhuang, Xuesi Chen, Yen Wei, Xiabing Jing, New Oxidation State 

of Aniline Pentamer Observed in Water-Soluble Electroactive Oligoaniline-Chitosan Polymer, J. 

Polym. Sci., Part A: Polym. Chem.,46, 1124–1135 (2008). 

16. Lihong Huang, Jun Hu, Le Lang, Xiuli Zhuang, Xuesi Chen, Yen Wei, Xiabin Jing, 

“Sandglass’’-Shaped Self-Assembly of Coil–rod–coil Triblock Copolymer Containing Rigid 

Aniline-Pentamer, Macromol. Rapid Commun., 29, 1242–1247 (2008). 

17. Li Chen, Zhigang Xie, Xiuli Zhuang, Xuesi Chen, Xiabin Jing, Controlled Release of Urea 

Encapsulated by Starch-g-poly(L-lactide), Carbohyd. Polym., 72, 342–348 (2008). 

18. Chaoliang He, Changwen Zhao, Xinhua Guo, Zhaojun Guo, Xuesi Chen, Xiuli Zhuang, Shuying 

Liu, Xiabin Jing, Novel Temperature- and pH-Responsive Graft Copolymers Composed of 

Poly(L-glutamic acid) and Poly(N-isopropylacrylamide), J. Polym. Sci., Part A: Polym. Chem., 46, 

4140–4150 (2008). 

19. Chaoliang He, Changwen Zhao, Xuesi Chen, Zhaojun Guo, Xiuli Zhuang, Xiabin Jing, Novel 

pH- and Temperature-Responsive Block Copolymers with Tunable pH-Responsive Range, 

Macromol. Rapid. Commun., 29, 490–497 (2008). 

20. Li Chen , Xiuli Zhuang , Ge Sun , Xuesi Chen , XiabinJing, An Approach to Synthesize 

Poly(ethylene glycol)-b-poly(epsilon-caprolactone) with Terminal Amino Group via Schiff's Base 

as An Initiator, Cn. J. Polym. Sci., 26, 455-463 (2008). 

21. Xueyu Qiu, Yadong Han, Xiuli Zhuang, Xuesi Chen, Yuesheng Li, Xiabin Jing, Preparation of 

Nano-Hydroxyapatite/Poly(L-lactide) Biocomposite Microspheres, J. Nanopaticle Res., 9, 

901-908, (2007). 

22. Yongsheng Niu, Wanxi Zhang, Xuan Pang, Xuesi Chen, Xiuli Zhuang, Xiabin Jing, Alternating 

Copolymerization of Carbon Dioxide and Propylene Oxide Catalyzed by 

(R,R)-SalenCo(III)-(2,4-dinitrophenoxy) and Lewis-Basic Cocatalyst, J. Polym. Sci., Part A: 

Polym. Chem., 45, 5050-5056 ( 2007). 

23. Junli Hu, Yadong Han, Xiuli Zhuang, Xuesi Chen, Yuesheng Li, Xiabin Jing, Self-Assembly of a 

Polymer Pair Through Poly(lactide) Stereocomplexation, Nanotechnology, 18, 185607 (2007). 

24. Hongzhi Du, Xuan Pang, Haiyang Yu, Xiuli Zhuang, Xuesi Chen, Dongmei Cui, Xianhong Wang, 

Xiabin Jing, Polymerization of rac-Lactide Using Schiff Base Aluminum Catalysts: Structure, 

Activity, and Stereoselectivity, Macromolecules, 40, 1904-1913 (2007). 

25. Chaoliang He, Jingru Sun, Ting Zhao, Zhongkui Hong, Xiuli Zhuang, Xuesi Chen, Xiabin Jing,

Formation of a Unique Crystal Morphology for the Poly (ethylene glycol)-poly( -caprolactone) 

Diblock Copolymer, Biomacromolecules, 7, 252-258 (2006). 

26. Xuan Pang, Hongzhi Du, Xuesi Chen, Xiuli Zhuang, Dongmei Cui, Xiabin Jing, Aluminum 

Schiff Base Catalysts Derived from β-Diketone for the Stereoselective Polymerization of 

Racemic Lactides, J. Polym. Sci., Part A: Polym. Chem., 43, 6605-6612 (2005). 

27. Xiuling Xu, Xiuli Zhuang, Xuesi Chen, Xinri Wang, Lixin Yang, Xiabin Jing, Preparation of 

Core-Sheath Composite Nanofibers by Emulsion Electrospinning, Macromol. Rapid. Commun., 

27 (19), 1637-1642 (2006). 

28. Suobo Zhang, Xiuli Zhuang, Jifeng Zhang, Wenqi Chen, Juzheng Liu, Synthesis and Crystal 

Structure of [(2,4-C7H11)2LnC≡CC6H5]2 (Ln=Gd, Er), J. Organomet. Chem, 584, 135 (1999). 

29. Jizhu Jin, Xiuli Zhuang, Zhongsheng Jin, Wenqi Chen, Syntheses and Crystal Structure of 

(C8H8)Nd(C5H9C5H4)(THF)2 and [(C8H8)Gd(C5H9C5H4)(THF)2], J. Organomet. Chem., 490, C8 

(1995). 

30. Jusong Xia, Xiuli Zhuang, Zhongsheng Jin, Wenqi Chen, Synthesis and Crystal Structure of 

[(C8H8)3(C6H5CH2C5H4)Nd2K(THF)3], Polyhedron, 15 3399-3403 (1996). 

31. Xiuli Zhuang, Suobo Zhang, Ninghai Hu, Wenqi Chen, Syntheses and Crystal Structure of 

Bis(tetrahydrofurfurylcyclopentadieny) Ytterbium Chloride Chem. Res. Cn. Univ., 10, 254 

(1994). 

32. Suobo Zhang, Xiuli Zhuang, Gecheng Wei Wenqi Chen, Syntheses of 

(C4H7OCH2C5H4)2LnCl(Ln=Nd,Gd,Dy,Yb) and Crystal Structure of (C4H7OCH2C5H4)2DyCl, 

Polyhedron, 13, 2867 (1994).

Acknowledgments 

The present thesis is the collection of the studies which have been carried out under the 

direction of Prof. Dr. Hiroyuki Nishide, Department of Applied Chemistry in Waseda 

University, during the 2008-2010. The author expresses the greatest acknowledgement to 

Prof. Dr. Hiroyuki Nishide for his invaluable suggestion, discussion, and continuous 

encouragement throughout this work. 

The author also expresses her sincere gratitude to Prof. Dr. Xuesi Chen of Changchun 

Institute of Applied Chemistry, Chinese Academy of Sciences, and Assoc. Prof. Dr. 

Kenichi Oyaizu of Waseda University for their valuable advice and encouragement. 

The author wishes to thank Prof. Dr. Kuniki Kino of Waseda University and Timothy E. 

Long of Virginia Polytechnic Institute and State University for their efforts as members 

on judging committee for the doctoral thesis. 

The author expresses the special thanks to all active and energetic collaborators, Dr. 

Kenichiroh Koshika, Dr. Changwen Zhao, Mr. Han Zhang, Mr. Chunsheng Xiao, Dr. 

Yongsheng Niu, Mr. Natsuru Chikushi, Mr. Haiyang Yu, Mr. Naoki Sano for their strong 

assistance in the experimental work. 

The author deeply thanks Dr. Xuan Pang, Dr. Zhaohui Tang, Dr. Takeo Suga, Ms Shiori 

Furuyama, Ms Yu Zhang, Dr. Wihatmoko Waskitaji, Mr. Won-Song Choi, Dr. Fumiaki 

Kato, Dr. Takeshi Ibe, Mr. Satoshi Nakajima, and all members in Prof. Nishide’s 

laboratory in Waseda University and Prof. Chen’s laboratory in Changchun Institute of 

Applied Chemistry for their fruitful discussion and kind assistance. 

Finally, the author expresses her deepest gratitude heartily to her parents, her husband, 

and her son for their heartfelt supports. 

July, 2010 

Xiuli Zhuang

Catalytic Synthesis and Characterization of Biodegradable ...

Create successful ePaper yourself

Delete template?

Save as template?