Carbon Dioxide/Epoxide Copolymerization via a Nanosized Zinc–Cobalt(III) Double Metal Cyanide Complex: Substituent Effects of Epoxides on Polycarbonate Selectivity, Regioselectivity and Glass Transition Temperatures

In this study, we describe the substituent effect of epoxides on CO2/epoxide copolymerization catalyzed by a nanosized zinc–cobalt(III) double metal cyanide complex [Zn–Co(III) DMCC]. The Zn–Co(III) DMCC catalyzed the copolymerization of CO2 with 11 epoxides with alkyl or aryl groups at 50–60 °C within 15 h. The reaction afforded various CO2/epoxide copolymers with high epoxide conversion efficiencies up to 100%. The alternating degree (FCO2) of the resulting copolymer was solely decided by the steric hindrance of the substituents of the epoxides regardless of their electron-donating or withdrawing properties. Substituents with large steric hindrances (2, 2-dimethyl, tert-butyl, cyclohexyl, decyl, and benzyl) led to highly alternating degrees (up to 100%). The regioselective CO2/epoxide copolymerization was dominated by the electron induction effect of the substituent. The electron-withdrawing substituent such as phenyl and benzyl induced regioselective ring-opening at the methine site of the epoxide. For CO2/isobutene oxide copolymerization, the regioselective reaction occurred at the methylene site of the isobutene oxide because of the strong electron-donating ability and steric hindrance of the two methyls of the isobutene oxide. The linear alkyl groups of the epoxides could not induce the regioselective reaction during copolymerization. The glass transition temperatures (Tgs) of the CO2/epoxide copolymers with linear alkyl substituent groups decreased from +6 to −38 °C with increasing alkyl length, but increased from 6 to 84 °C with increasing steric hindrance of the epoxide substituents. Thus, various CO2/epoxide copolymers with a wide Tg range from −38 to +84 °C were provided and could be applied as elastomers or plastics.