Catalytic Synthesis and Characterization of Biodegradable ...

More documents

Recommendations

Info

Chapter 2 useful for designing a highly efficient catalytic system. Table 2.4 Cyclic voltammogram data for the transition between Co III + e - Complex Epc (mV) E1/2 (mV) ΔE ipa/ipc L 1 -Co III -dnp 32 107 150 0.64 L 2 -Co III -dnp 84 134 99 0.83 L 3 -Co III -dnp 52 163 221 0.82 L 4 -Co III -dnp -71 32 206 0.78 ‐ 68 ‐ Co II of L-Co III -dnp. a) a) Determined using 1 mM solution of L-Co III -dnp in DMF in the presence of 0.1 M NBu4ClO4 at carbon electrode vs. Ag/Ag + at the scan rate of 100 mV s -1 . 2.5 Conclusions A series of Cobalt Schiff-base complexes were investigated as the catalyst for the alternating copolymerization of CO2 and rac-PO in the presence of Bu4NBr. The poly(propylene carbonate) (PPC) and cyclic propylene carbonate (PC) selectivity of the resultant copolymers were determined by modification of the length of the diimine bridges between the two nitrogen atoms in the ligands. The L 1 -Co III -dnp/Bu4NBr catalyst exhibited the highest activity, PPC/PC selectivity, and degree of head-to-tail linkages. The L 2 -Co III -dnp/Bu4NBr catalyst showed slightly lower head-to-tail linkages. For the dimine bridges containing three-carbon chains between the two nitrogen atoms in the Schiff bases, the corresponding L 4 -Co III -dnp complex displayed the lowest catalytic activity. Based on the electrochemical measurements, the half-wave potentials of the complexes were obtained and the catalytic activity of these complexes was compared. The higher stability for the axial group’s metal–O (phenolate) bond indicated the more negative E1/2 of the Co III + e - redox couple in the L-Co III -dnp complexes, and the higher catalytic activity for the copolymerization of PO and CO2. In the case of the cobalt complexes with more positive Co(II/III) potentials and lower electron density on the cobalt center, the end of propagating chain to the cobalt center was considered to determine the overall polymerization rate. However, the L 4 -Co III -dnp with the most negative E1/2 possessed the lowest catalytic activity, which may be due to the unfavorable trigonal bipyramidal geometry during the transition state, preventing the Lewis bases from bonding to the metal center. 2.6 Experimental Part Materials All experiments involving air- and/or water-sensitive compounds were carried out using standard Schlenk techniques under a dry argon atmosphere. All solvents were purified by Co II
Synthesis and Electrochemistry of Schiff Base Cobalt(III) Complexes and Their Catalytic Activity for Copolymerization of Epoxide and Carbon Dioxide standard procedures before use. (R,R)-N,N�-(1,2-cyclohexene)bis(3,5-di-tert-butylsalicylideneimine) (H2L 1 ), N,N�-ethylenebis(3,5-di-tert-butylsalicylideneimine) (H2L 2 ), (R,R)-N,N�-(1,2-diphenylethylethylene)bis(3,5-di-tert-butylsalicylideneimine) (H2L 3 ), and N,N�-(2,2-dimethyl-1,3-propylene)bis(3,5-di-tert-butylsalicylideneimine) (H2L 4 ) were synthesized according to previously published procedures. 22, 30 All other reagents were commercially available, and were used as received. Instrumentation and Methods The NMR spectra were recorded by a Bruker AV 400M or a Bruker AV 500M instrument in CDCl3 or (CD3)2SO at room temperature. Tetramethylsilane was used as the internal standard. The FT-IR spectra were obtained using a Perkin-Elmer 2000 FT-IR spectrometer. The EIS-MS data were obtained using a Finnigan LCQ TM ion trap mass spectrometer. It was operated with the following parameters: positive ion and negative ion mode, the electrospray voltage at 4.5 kV, the capillary voltage at 20 V, the tube lens offset voltage at 15 V and the capillary temperature between 80─100 . High-purity nitrogen (N2) was used as the sheath gas, and its flow rate was 60 arbitrary units. The sample solutions were injected at 5 µL min -1 via a syringe pump. The GPC measurements were performed by a Waters 410 GPC with THF as the eluent (flow rate: 1 ml min -1 at 25 ). Polystyrene was used as the internal standard. The cyclic voltammetry experiments were performed using the BAS 660C electrochemical system. The sample solutions typically contained 1 mM of the cobalt complex in DMF and tetrabutylammoium perchlorate (TBAP) (0.1 M) as the supporting electrolyte at room temperature. The cyclic voltammograms were obtained at the scan rate of 100 m V s −1 under a nitrogen atmosphere. The potential sweep ranges were between −2.00 and 1.50 V for the ligands and between −1.20 and 1.50 V for the cobalt complexes. A suitable crystal for the X-ray diffraction experiment was obtained by slow evaporation of a saturated toluene solution of L 1 -Co III -dnp at room temperature, which was carefully collected and mounted on a Bruker SMART APEX CCD diffractometer with graphite-monochromated Mo-Kα (λ = 0.71073Å) radiation at room temperature. The crystal structure was solved by the direct method. Refinement was carried out by the full matrix least-squares methods based on F 2 using the SHELXL-97 software package. Preparation of the Complexes (2,4-Dinitrophenolato)(R,R)-N,N�-(1,2-cyclohexene)bis(3,5-di-tert-butylsalicylideneimina to)]cobalt(III) (L1-CoIII-dnp): (R,R)-N,N�-1,2-Cyclohexenebis(3,5-di-tert-butylsalicylideneiminato)cobalt(II) (L 1 -Co II ) ‐ 69 ‐
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:
Page 13 and 14:
1.2.2 Aluminum Catalysts - 7 - Poly
Page 15 and 16:
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 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 73: 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
Page 124 and 125:
Chapter 6 6.1 Introduction Since th
Page 126 and 127:
Chapter 6 6.3 Synthesis of MPEG-b-P
Page 128 and 129:
Chapter 6 used to characterize the
Page 130 and 131:
Chapter 6 Figure 6.6 Cyclic voltamm
Page 132 and 133:
Chapter 6 vivo cytotoxicity was als
Page 134 and 135:
Chapter 6 NMR. Characterization of
Page 136 and 137:
Chapter 6 CO2 for 24 h. RSC96 cells
Page 141 and 142:
Chapter 7 Conclusion and Future Pro
Page 143 and 144:
‐ 131 ‐ Conclusion and Future P
Page 145 and 146:
‐ 133 ‐ Conclusion and Future P
Page 147 and 148:
13. Xuan Pang, Xuesi Chen, Xiuli Zh
Page 149:
Acknowledgments The present thesis
show all

Catalytic Synthesis and Characterization of Biodegradable ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?