Catalytic Synthesis and Characterization of Biodegradable ...

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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 - Polymerization and Applications of Biodegradable Polyesters 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
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 and 18: 1.3 Polylactide 1.3.1 Introduction
Page 19: - 13 - Polymerization and Applicati
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
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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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