Catalytic Synthesis and Characterization of Biodegradable ...

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Chapter 6 6.3 Synthesis of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm Controlled living radical polymerization such as nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization have recently received great attention for their ability to synthesize polymer materials with controlled molecular weight, various functional groups and diverse architectures. We used RAFT technique to obtain the novel block copolymers in virtue of the convenient and effective RAFT polymerization towards TAP monomer. The preparation of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm precursor polymers were conducted in 1,4-dioxane/methanol mixture using MPEG-CPAD and MPEG-b-PLA-CPAD as the macromolecular chain transfer agent (CTA), respectively (Scheme 1 and Scheme 2). Scheme 6.1 Synthesis of macromolecular chain transfer agents (CTA). To better understand the polymerization process, the kinetic of the RAFT polymerization of TAP was studied and the results were shown in Figure 6.2. The polymerization could reach a high monomer conversion up to ~87% within 6 hours. The linear dependence of the molecular weight on the monomer conversion strongly indicated that the RAFT polymerization towards TAP monomer had living characters. However, the molecular weight distribution of the polymer was increased from 1.20 at 0 hour to 1.57 at 6 hour, and further to 1.73 if the polymerization proceeded more than10 hours which may be assigned either to intermolecular chain transfer or possibly to cross-termination at the high monomer conversions. This feature has already been observed in most of the dithiobenzoate-mediated RAFT system. ‐ 116 ‐
Synthesis of Amphiphilic Triblock Copolymers of Acrylamide, Lactate, and Ethyleneoxide Scheme 6.2 Synthesis and self-assembly of MPEG-b-PTAm and MPEG-b-PLA-b-PTAm Figure 6.2 RAFT polymerization of TAP monomer using MEPG-CPAD as the CTA. (A) Monomer conversion versus time; (B) Dependence of molecular weights and molecular weight distributions of the block copolymers on the monomer conversion. Based on the aforementioned study, we then conducted the preparation of the block copolymer for 8 hours in order to achieve high monomer conversion and meanwhile minimum side reactions which might induce broaden of the molecular weight distribution. 1 H NMR was used to study the structure of the precursor block copolymers. The spectra shown in Figure 6.3 clearly confirmed the structure of the block copolymers. The degree of polymerization was calculated to be 46 and 42 for MPEG-b-PTAm and MPEG-b-PLA-b-PTAm, respectively, based on the integration of proton peak c at 4.19 ppm from piperidine and the proton peak b at 3.64 ppm for the methylene in MPEG. The obtained precursor block copolymers were then oxidized by m-chloroperbenzoic acid to convert the N-H groups into nitroxyl radicals, leading to MPEG-b-PTAm and MPEG-b-PLA-b-PTAm block copolymers with nitroxyl radical-contained segment. 1 H NMR (data not shown) was ‐ 117 ‐
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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
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1.3.4 Application of PLA Figure 1.3
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1.5.1.4 Polyaniline (PANi) - 21 - P
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1.6.1 Radical Polymers for Organic
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initialization of the device by app
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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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Page 84 and 85: Chapter 3 3.1 Introduction Poly(lac
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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
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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
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Page 115 and 116: = 25 μm. B: MTT assay for the cyto
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Page 149: Acknowledgments The present thesis
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