Salen cobalt complexes in polycarbonate synthesis: bimodal versus unimodal molecular weight distribution

Abstract

The copolymerization of epoxides and carbon dioxide under the action of (salen)-cobalt(iii) complexes and ammonium or phosphonium salts often results in the formation of polycarbonates with a bimodal molecular weight distribution. A method was proposed for preparing poly(propylene carbonate) with a unimodal molecular weight distribution due to the use of coordinating additives: water and alcohols. Possible reasons for the observed effects and the polymerization mechanism are discussed.