Chain Growth and Branch Structure Formation during Lipase-Catalyzed Synthesis of Aliphatic Polycarbonate Polyols

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• 作者：Chen Liu ; Zhaozhong Jiang ; John Decatur ; Wenchun Xie ; Richard A. Gross
• 刊名：Macromolecules
• 出版年：2011
• 出版时间：March 22, 2011
• 年：2011
• 卷：44
• 期：6
• 页码：1471-1479
• 全文大小：882K
• 年卷期：v.44,no.6(March 22, 2011)
• ISSN：1520-5835

文摘

This study explored Candida antarctica Lipase B (CALB)-catalyzed condensation reactions to prepare high-purity, metal-free, polycarbonate polyols. Terpolymerizations of diethyl carbonate (D) with 1,8-octanediol (O) and tris(hydroxymethyl)ethane (T) were performed in bulk at relatively low temperature (80 掳C) using a pressure-varied two-stage process to minimize evaporative loss of diethyl carbonate. NMR experiments of resulting polycarbonate polyols, including analysis of proton NMR resonances by COSY spectra and carbon-13 resonances by HSQC, HSQC-TOCSY, and HMBC spectra, allowed determination of copolymer composition as well as relative percentages of linear, terminal, and dendritic T-units. With D/O/T monomer feed ratio 3:0.9:0.1, the highest values of dendritic T-unit content (83%) and M_w (23鈥?00) by SEC-MALLS were attained. By decreasing D content in the monomer feed, the mol % of dendritic T-units in chains decreased to as low as 0%. By keeping the D/(O + T) ratio constant at 2.0 while increasing the ratio of O-to-T units from 9:1 to 7:3, dendritic T-unit content decreased from 51 to 28 mol %. At short reaction times (e.g., 4 h), highly functional linear terpolymers were formed. Increase in reaction time from 4 to 8, 12, 24, and 30 h resulted in increased dendritic unit content (0鈭?8%), M_w/M_n (1.5鈭?.6), and relative M_w (2100 to 39鈥?00). Thus, immobilized lipase-catalyzed synthesis of polyol polycarbonates successfully enabled control of critical polymer structural parameters without formation of a gel fraction or product discoloration.