Catalytic Synthesis and Characterization of Biodegradable ...

More documents

Recommendations

Info

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 - Polymerization and Applications of Biodegradable Polyesters 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
Page 1 and 2: Catalytic Synthesis and Characteriz
Page 3 and 4: Preface Biodegradable polyesters ha
Page 5 and 6: Chapter 3 Polymerization of Lactic
Page 7 and 8: Chapter 1 Polymerization and Applic
Page 9 and 10: - 3 - Polymerization and Applicatio
Page 13 and 14: 1.2.2 Aluminum Catalysts - 7 - Poly
Page 17: 1.3 Polylactide 1.3.1 Introduction
Page 21 and 22: 1.3.4 Application of PLA Figure 1.3
Page 23 and 24: - 17 - Polymerization and Applicati
Page 27 and 28: 1.5.1.4 Polyaniline (PANi) - 21 - P
Page 47 and 48: 1.6.1 Radical Polymers for Organic
Page 51 and 52: initialization of the device by app
Page 55 and 56: 1.6.2.4 Others - 49 - Polymerizatio
Page 63 and 64: 182. R. B. Weller, J. Invest. Derma
Page 65 and 66: Chapter 2 Synthesis and Electrochem
Page 67 and 68: Synthesis and Electrochemistry of S
Page 69 and 70:
Synthesis and Electrochemistry of S
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79:
Page 84 and 85:
Chapter 3 3.1 Introduction Poly(lac
Page 86 and 87:
Chapter 3 polydispersity index (PDI
Page 88 and 89:
Chapter 3 aluminum based complexes
Page 90 and 91:
Chapter 3 3.5 Conclusions Co(III) c
Page 92 and 93:
Chapter 3 22. Z. H. Tang, X. S. Che
Page 94 and 95:
Chapter 4 4.1 Introduction Stimulus
Page 96 and 97:
Chapter 4 the proton of methenyl gr
Page 98 and 99:
Chapter 4 attributed to the amide g
Page 100 and 101:
Chapter 4 4.4 Thermal Properties Th
Page 102 and 103:
Chapter 4 Figure 4.8 MTT assay for
Page 104 and 105:
Chapter 4 The 1 H NMR and 13 C NMR
Page 106 and 107:
Chapter 4 Cell viability (%) = (Asa
Page 109 and 110:
Chapter 5 Synthesis of Triblock Cop
Page 111 and 112:
5.2 Synthesis of Triblock Copolymer
Page 113 and 114:
Sample Table 1. Feed and result com
Page 115 and 116:
= 25 μm. B: MTT assay for the cyto
Page 117 and 118:
‐ 109 ‐ Synthesis of Triblock C
Page 119:
‐ 111 ‐ Synthesis of Triblock C
Page 124 and 125:
Chapter 6 6.1 Introduction Since th
Page 126 and 127:
Chapter 6 6.3 Synthesis of MPEG-b-P
Page 128 and 129:
Chapter 6 used to characterize the
Page 130 and 131:
Chapter 6 Figure 6.6 Cyclic voltamm
Page 132 and 133:
Chapter 6 vivo cytotoxicity was als
Page 134 and 135:
Chapter 6 NMR. Characterization of
Page 136 and 137:
Chapter 6 CO2 for 24 h. RSC96 cells
Page 141 and 142:
Chapter 7 Conclusion and Future Pro
Page 143 and 144:
‐ 131 ‐ Conclusion and Future P
Page 145 and 146:
‐ 133 ‐ Conclusion and Future P
Page 147 and 148:
13. Xuan Pang, Xuesi Chen, Xiuli Zh
Page 149:
Acknowledgments The present thesis
show all

Catalytic Synthesis and Characterization of Biodegradable ...

Create successful ePaper yourself

Delete template?

Save as template?