Zinc-catalyzed copolymerization of carbon dioxide and propylene oxide

Abstract

The zinc-catalyzed copolymerization of carbon dioxide and propylene oxide, which is one of the promising reactions for the utilization of carbon dioxide, has been investigated from various aspects. Above all, considering that supercritical carbon dioxide has recently been paid attention in the field of extraction, separation, and reaction medium, its aptitude for both a reaction solvent and a reactant was examined in zinc glutarate-catalyzed reactions. As a result, it was proved that supercritical carbon dioxide was a suitable substitute for organic solvents in the copolymerization reactions. Great diffusivity of supercritical carbon dioxide into polymer segments was thought to promote carbon dioxide supply to the active sites of the zinc species and to afford alternating polycarbonate production. Low reaction temperature appeared to be advantageous to polycarbonate and cyclic carbonate formation. Apart from zinc glutarate catalyst whose detailed mechanistic studies were hard to perform due to its insolubility, some other zinc compounds were studied. A homogeneous catalyst, bis(ethyl fumarato)zinc, showed similar polycarbonate yield to zinc glutarate, and the method of the catalyst preparation affected its catalytic activity. Only a small amount of the catalyst was considered to be active in the copolymerization process even in the homogeneous systems. In the zinc dicarboxylate complexes, the carbon number between two carboxyl groups and the steric nature in the vicinity of the zinc atom might be important factors for the copolymerization catalysis.