Silica-Grafted Diethylzinc and a Silsesquioxane-Based Zinc Alkyl Complex as Catalysts for the Alternating Oxirane−Carbon Dioxide Copolymerization

Abstract

A novel zinc silsesquioxane complex ([(c-C 5 H 9 ) 7 Si 7 O 11 (OSiMePh 2 )] 2 Zn 4 Me 4 ( 1 )) has been used as a model compound for silica-grafted zinc catalysts in the copolymerization of cyclohexene oxide and CO 2 . Complex 1 exists as a dimer in the solid state and is moderately active in the copolymerization, and polycyclohexene carbonates have been obtained with a carbonate content of 79−98%. Polymerizations with ZnEt 2 -treated silica particles resulted in polymer particles with M̄ n and M̄ w values and carbonate contents comparable to those of the polymers obtained with 1 . It was further demonstrated that CO 2 consumption can be followed online by monitoring the decrease of system pressure during the reaction. CO 2 consumption has been interpreted in relation to both polycarbonate and cyclic carbonate formation. These measurements represent the intrinsic kinetics of this reaction, which appear to be directly related to CO 2 pressure.