Catalytic Synthesis and Characterization of Biodegradable ...

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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 ‐ Conclusion and Future Prospects 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.
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Catalytic Synthesis and Characteriz
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Preface Biodegradable polyesters ha
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Chapter 3 Polymerization of Lactic
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Chapter 1 Polymerization and Applic
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- 3 - Polymerization and Applicatio
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1.2.2 Aluminum Catalysts - 7 - Poly
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1.3 Polylactide 1.3.1 Introduction
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- 13 - Polymerization and Applicati
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1.3.4 Application of PLA Figure 1.3
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1.5.1.4 Polyaniline (PANi) - 21 - P
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1.6.1 Radical Polymers for Organic
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initialization of the device by app
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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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Page 94 and 95: Chapter 4 4.1 Introduction Stimulus
Page 96 and 97: Chapter 4 the proton of methenyl gr
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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
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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
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Page 147 and 148: 13. Xuan Pang, Xuesi Chen, Xiuli Zh
Page 149: Acknowledgments The present thesis
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