Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 1 for the cyclization of EO and CO2 to ethylene carbonate (Figure 1.2.6). 24, 25 Lewis bases orquaternary ammonium salts, including pyridine, MeIm, and nBu4NX (X=Cl, Br, I), were utilized as cocatalysts, enhancing rates by up to a factor of five. At 110 o C and in scCO2 (ca. 150 atm CO2), a 1:1 mixture of 2a/nBu4NBr catalyzed the conversion of EO to EC with a TOF of 2220 h -1 . Salen-chromium (2b) and -cobalt (2c) analogs also promoted cyclic-species formation showing rates of 2140 and 1320 h -1 , respectively. Darensbourg and co-workers have reported AlCl4 - -based complexes that exhibit TOFs up to 50 h -1 for the synthesis of propylene carbonate from PO and CO2. 26 Figure 1.2.6 Salen catalyst systems (cocatalyst = tetrabutylammonium halide, pyridine, or MeIm) for the synthesis of ethylene carbonate. Aluminum complexes are indeed active for the copolymerization of epoxides and CO2; however, they are plagued by low activities and yield polycarbonates with high percentages of ether linkages. It appears that without additives, current aluminum catalysts do not cleanly generate alternating copolymer. Nevertheless, the “immortal” polymerization of [(tpp)AlX] compounds shows promise for the synthesis of a wealth of unique copolymers with varying levels of carbonate linkages provided the activities can be improved. 1.2.3 Chromium Salen Catalysts Kruper and Dellar discovered that [(tpp)CrX] (Figure 1.2.7) in mixtures with 4–10 equivalents of a Lewis-basic amine cocatalyst [such as MeIm or (4-dimethylamino)pyridine (DMAP)] are moderately active for the cyclization of epoxides and CO2. 27 A wide range of epoxides, including PO, trans-2-butene oxide, epichlorohydrin, CHO, and cyclopentene oxide (CPO), were rapidly converted to the corresponding cyclic carbonates. For instance, one of the (tpp)CrX and DMAP catalyzed CHC formation at 50 atm CO2 and 95 o C, exhibiting activities of 103 h -1 . In this case, PCHC was isolated as the major product. Following ‐ 8 ‐
- 9 - Polymerization and Applications of Biodegradable Polyesters thermolysis, a 95:5 ratio of trans and cis CHC was observed, suggesting the possibility of dual mechanisms. Figure 1.2.7 Chromium–porphyrin complexes for the coupling of epoxides and CO2. Jacobsen and co-workers found [(salen)CrCl] complexes to be highly active in the asymmetric ring opening of epoxides. 28 This elegant work has since led to many crucial discoveries in the coupling of epoxides with CO2; in fact the first report of (salen)chromiummediated epoxide–CO2 polymerization appeared in a 2000 patent by Jacobsen and co-workers. 29 Nguyen and Paddock reported highly active [(salen)CrCl]/DMAP based systems (Figure 1.2.8), for the cyclo-addition of CO2 and a variety of terminal aliphatic epoxides, including PO, epichlorohydrin, butadiene monoepoxide, and styrene oxide (SO). 30 Figure 1.2.8 Salen–chromium and salen–cobalt complexes for the coupling of epoxides and CO2. Darensbourg and co-workers began efforts to uncover well-defined transition metal coordination complexes as catalysts for the coupling of CO2 and epoxides to selectively
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 and 12: - 5 - Polymerization and Applicatio
Page 13: 1.2.2 Aluminum Catalysts - 7 - Poly
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
Page 63 and 64: 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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