Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 2 4 L 4 -Co III -dnp 25 70 81 3.1 1.4 1.2 a) The reaction was performed in neat rac-PO ([rac-PO]:[Co]:[Bu4NBr] = 1000:1:1, molar ratio) in a 100 mL autoclave at 25 ºC with 2 MPa of CO2 for 2 h; b) Turnover frequency of rac-PO to products (polycarbonate and cyclic carbonate); c) Selectivity for PPC over PC as determined by 1 H NMR spectroscopy; d) Determined by 13 C NMR spectroscopy; e) Determined by 1 H NMR. f) Determined by GPC. 2.4 Electrochemistry of Cobalt(III) Complexes The electrochemical data for the ligands and the L-Co III -dnp complexes were shown in Table 2.4, and the representative voltammograms were presented in Figures 2.3 and 2.4. All CV curves for the ligands were recorded in the potential range of -2.00 to 1.50 V. The voltammograms showed an irreversible oxidation peak at potentials between 1.08 and 1.20 V. These peaks were ascribed to the oxidation of the Schiff base ligands (Figure 2.3). For the L-Co III -dnp complexes, the potential sweeps were made from -1.20 to 1.50 V. It is considered that the nature of the cobalt(III) atom in the Schiff base complexes should dominate the catalytic activity for the copolymerization of the epoxide and carbon dioxide, which prompted us to pay close attention to the Co III + e - Co II redox potential. The redox couple of Co III + e - Co II was observed for L 1 -Co III -dnp, L 2 -Co III -dnp, L 3 -Co III -dnp, and L 4 -Co III -dnp at E1/2 = 107, 134, 163, and 32 mV, respectively (Figure 2.4). The absence of any redox responses near 0 to 0.5 V in the metal-free ligands (Figure 2.3) allowed one to ascribe these quasi-reversible waves to the cobalt(II/III) redox couple. Figure 2.3 Cyclic voltammograms of 1 mM solutions of H2L in DMF containing 0.1 M NBu4ClO4 on a glassy carbon electrode (� 3.3 mm). Potential is shown in V vs. Ag/Ag + at the scan rate of 100mV s -1 . I: H2L 1 ; II: H2L 2 ; III: H2L 3 ; IV: H2L 4 . ‐ 66 ‐
Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide Figure 2.4. Cyclic voltammograms of 1 mM solutions of L-Co III -dnp in DMF containing 0.1 M NBu4ClO4 on a carbon electrode. Potential is shown in V vs. Ag/Ag + at the scan rate of 100 mV s -1 . I: L 1 -Co III -dnp; II: L 2 -Co III -dnp; III: L 3 -Co III -dnp; IV: L 4 -Co III -dnp. Co II for L-Co III -dnp (Table 2.4) revealed that the length and steric structures of the diimine-bridges between the two nitrogen atoms in the Schiff bases significantly affected the redox potential. These complexes had the same auxiliary ligand, 2,4-dinitrophenolate, but different diimine-bridges. The gradual shift of E1/2 to negative potentials for the L 3 -Co III -dnp, L 2 -Co III -dnp, and L 1 -Co III -dnp complexes indicated that the election-donating character of the ligand increased in this order, stabilizing the axial Co–O (phenolate) bond in Figure 2.1, which is an advantage when forming the transition state (Scheme 2.2) and thus leads to a faster copolymerization of CO2 and PO. However, The E1/2 data of Co III + e - L 4 -Co III -dnp has the most negative E1/2 of 32 mV and yet the lowest activity for the copolymerization. It is believed that the diimine-bridges containing two carbon atoms and three carbon atoms leads to a square pyramidal (sqp) and a trigonal bipyramidal (tbp) geometry for the central five-coordinated metal atom, respectively. Thus, the low catalytic activity of L 4 -Co III -dnp during the copolymerization of CO2 and PO may be ascribed to the unfavorable tbp geometry of the central cobalt atom, which prevents Bu4NBr from coordinating with cobalt in an axial position opposite to the Co–O (phenolate) bond, leading to the decrease in the activity. The utilization of carbon dioxide (CO2) has received much attention because of its potential use as an abundant, economical and biorenewable resource and its weakening of global warming or the greenhouse effect. The copolymerization of CO2 as the monomer with epoxide was firstly reported by Inoue et al. in the 1960s. 35 The combination of the X-ray crystallographic and electrochemical results in the present investigation provided important insights into the factors dominating the catalytic activity ‐ 67 ‐
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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
Page 21 and 22: 1.3.4 Application of PLA Figure 1.3
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Page 27 and 28: 1.5.1.4 Polyaniline (PANi) - 21 - P
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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 71: 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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