Synthesis of Polycarbonate Polyols by Double-Metal Cyanide Catalyzed Copolymerization of Epoxide with Carbon Dioxide

A new type of polycarbonate (PC) polyol was prepared by copolymerization of carbon dioxide with cyclohexene oxide (CHO) using double-metal cyanide (DMC) catalysts. These heterogeneous DMC catalysts were prepared by reacting ZnCl₂ and K₃Co(CN)₆ in the presence of various complexing agents (CAs) such as 2-methoxyethyl acetate, 2-ethoxyethyl acetate (EEA), 2-butoxyethyl acetate, diethyl glycol monoethyl ether acetate, ethylene glycol diacetate, and 4-hydroxy-4-methyl-2-pentanone. The catalysts were intensively characterized by infrared and X-ray photoelectron spectroscopy and X-ray powder diffraction. All of the developed catalysts showed high activity and carbonate selectivity, with EEA as the most effective CA. The copolymerization behavior was investigated in detail by varying the amounts of catalyst, CHO, starter and solvent, the carbon dioxide pressure, temperature, and reaction time. The resultant PC polyols had a wide range of molecular weights and narrow polydispersity. Specifically, bifunctional PC polyols were obtained using bifunctional poly(propylene glycol) as a starter.