Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 2 six-coordinated in the solid state. Furthermore, end group analysis of the obtained polymer suggested that the six-coordination arrangement was maintained even in solution, i.e., in the catalytic cycle. The isolated poly(carbonate) obtained by the L 1 -Co III -dnp/Bu4NBr catalyst was determined by the presence of a 2,4-dinitrophenoxyl moiety as the end group of the polymer chain (Figure 2.2). Figure 2.2 1 H NMR spectrum of the poly(carbonate) catalyzed by L 1 -Co III -dnp/ Bu4NBr (298K, (CD3)2SO, 500 MHz). The enlarged spectrum between 9.0 and 7.4 ppm indicated that the polymer ended with the 2,4-dinitrophenoxyl group. The good agreement of the number-averaged molecular weights based on the end-group analysis (Mn= 2.64 × 10 4 ) and that determined by the GPC experiment (Mn = 1.40 × 10 4 ) suggested the polymerization mechanism in which the monomer was inserted to the cobalt-oxygen bond of the propagating end, as shown in Scheme 2.2. Scheme 2.2 Proposed mechanism for CO2/rac-PO copolymerization using the L-Co III -dnp/Bu4NBr catalyst systems. ‐ 64 ‐
Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide The Lewis basic monomer coordinated to the metal center in the axial site transferred to the propagating metal-polymer chain, thereby labilizing the metal alkoxide bond and facilitating the insertion of CO2. 3, 15, 22-25 The rac-PO monomer might be first favorably inserted into the Co−OR bond of the Schiff base cobalt complexes, followed by the insertion of the CO2 monomer, as shown in Scheme 2.2. Subsequent alternating copolymerization of rac-PO and CO2 afforded the alternating repeating unit structure to yield the polycarbonate. The side reaction to yield the cyclic carbonate could take place through the backbiting degradation of the growing polymer-catalyst complex, which may lead to the lower polymer yield. A similar mechanism has been proposed by Nguyen and co-workers using cobalt (salen) and N, N-dimethylaminoquinoline for the copolymerization of CO2 and PO. 15 2.3.2 Complex Structure and Polymerization The copolymerizations of CO2 and rac-PO catalyzed by the series of L-Co III -dnp/Bu4NBr catalysts were studied, and the results are summarized in Table 2.3. The diimine-bridge (X) between the two nitrogen atoms in the Schiff bases significantly affected the catalytic activity. With X being (R,R)-1,2-cyclohexanediamine (L 1 -Co III -dnp in Scheme 2.1), the highest catalytic activity with a turn-over frequency (TOF) of 245 h -1 was accomplished (Table 2.3). Under the same conditions, when X was replaced by ethylenediimine or (R, R)-1,2-diphenylethylenediimine, the catalytic frequency was reduced to 210 and 190 h -1 for the L 2 -Co III -dnp/Bu4NBr and the L 3 -Co III -dnp/Bu4NBr catalysts, respectively. When X was 2,2-dimethyl-1,3-propylenediimine, the L 4 -Co III -dnp/Bu4NBr catalyst showed the lowest activity. The catalytic activity of these complexes for the alternating copolymerization of CO2 and rac-PO was in the order of L 1 -Co III -dnp > L 2 -Co III -dnp > L 3 -Co III -dnp >> L 4 -Co III -dnp, which revealed that the diimine-bridges with the three carbon atoms led to a lower activity. One could anticipate that the degree of polarization and/or the strength of the Co–O bond for the axial coordination should influence the rate of the monomer insertion and thus should affect the rate of the propagation during the polymerization. Although attempts to obtain all the molecular structures of the L-Co III -dnp complexes were not successful, the nature of the Co–O bond has been successfully determined by electrochemical methods (vide infra). Table 2.3 The catalytic activity for the copolymerization of CO2/rac-PO using the L-Co III -dnp/Bu4NBr catalyst systems. a) Run Complex TOF (h –1 ) b) Selectivity (%PPC) c) Head-to-tail Linkages (%) d) ‐ 65 ‐ Mn e) ×10 4 Mn f) ×10 4 1 L 1 -Co III -dnp 245 74 88 2.6 1.4 1.4 PDI f) 2 L 2 -Co III -dnp 210 60 71 1.4 1.1 1.3 3 L 3 -Co III -dnp 190 75 82 4.0 2.6 1.2
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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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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
Page 65 and 66: Chapter 2 Synthesis and Electrochem
Page 67 and 68: Synthesis and Electrochemistry of S
Page 69: Synthesis and Electrochemistry of S
Page 79: Synthesis and Electrochemistry of S
Page 84 and 85: Chapter 3 3.1 Introduction Poly(lac
Page 86 and 87: Chapter 3 polydispersity index (PDI
Page 88 and 89: Chapter 3 aluminum based complexes
Page 90 and 91: Chapter 3 3.5 Conclusions Co(III) c
Page 92 and 93: Chapter 3 22. Z. H. Tang, X. S. Che
Page 94 and 95: Chapter 4 4.1 Introduction Stimulus
Page 96 and 97: Chapter 4 the proton of methenyl gr
Page 98 and 99: Chapter 4 attributed to the amide g
Page 100 and 101: Chapter 4 4.4 Thermal Properties Th
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
Page 106 and 107: Chapter 4 Cell viability (%) = (Asa
Page 109 and 110: Chapter 5 Synthesis of Triblock Cop
Page 111 and 112: 5.2 Synthesis of Triblock Copolymer
Page 113 and 114: Sample Table 1. Feed and result com
Page 115 and 116: = 25 μm. B: MTT assay for the cyto
Page 117 and 118: ‐ 109 ‐ Synthesis of Triblock C
Page 119: ‐ 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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