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

Abstract

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 °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 Mw (23 900) 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...