Catalytic Synthesis and Characterization of Biodegradable ...

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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 - Polymerization and Applications of Biodegradable Polyesters 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
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 11: - 5 - Polymerization and Applicatio
Page 15 and 16: - 9 - Polymerization and Applicatio
Page 17 and 18: 1.3 Polylactide 1.3.1 Introduction
Page 19 and 20: - 13 - Polymerization and Applicati
Page 21 and 22: 1.3.4 Application of PLA Figure 1.3
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
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182. R. B. Weller, J. Invest. Derma
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Chapter 2 Synthesis and Electrochem
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Synthesis and Electrochemistry of S
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Chapter 3 3.1 Introduction Poly(lac
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Chapter 3 polydispersity index (PDI
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Chapter 3 aluminum based complexes
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Chapter 3 3.5 Conclusions Co(III) c
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Chapter 3 22. Z. H. Tang, X. S. Che
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Chapter 4 4.1 Introduction Stimulus
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Chapter 4 the proton of methenyl gr
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Chapter 4 attributed to the amide g
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Chapter 4 4.4 Thermal Properties Th
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Chapter 4 Figure 4.8 MTT assay for
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Chapter 4 The 1 H NMR and 13 C NMR
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Chapter 4 Cell viability (%) = (Asa
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Chapter 5 Synthesis of Triblock Cop
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5.2 Synthesis of Triblock Copolymer
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Sample Table 1. Feed and result com
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= 25 μm. B: MTT assay for the cyto
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‐ 109 ‐ Synthesis of Triblock C
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‐ 111 ‐ Synthesis of Triblock C
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Chapter 6 6.1 Introduction Since th
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Chapter 6 6.3 Synthesis of MPEG-b-P
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Chapter 6 used to characterize the
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Chapter 6 Figure 6.6 Cyclic voltamm
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Chapter 6 vivo cytotoxicity was als
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Chapter 6 NMR. Characterization of
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Chapter 6 CO2 for 24 h. RSC96 cells
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Chapter 7 Conclusion and Future Pro
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‐ 131 ‐ Conclusion and Future P
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‐ 133 ‐ Conclusion and Future P
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13. Xuan Pang, Xuesi Chen, Xiuli Zh
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Acknowledgments The present thesis
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