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.
DOI: 10.1021/ma5023742
Macromolecules 2015, 48, 536?544