Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 1 1.1 Introduction 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 - Polymerization and Applications of Biodegradable Polyesters 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.
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: Chapter 1 Polymerization and Applic
Page 11 and 12: - 5 - Polymerization and Applicatio
Page 13 and 14: 1.2.2 Aluminum Catalysts - 7 - Poly
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
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- 53 - Polymerization and Applicati
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- 55 - Polymerization and Applicati
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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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