Copolymerization and Terpolymerization of CO₂ and Epoxides Using a Soluble Zinc Crotonate Catalyst Precursor

A soluble catalyst precursor derived from the reaction of zinc bis(trimethylsilyl)amide, Zn[N(SiMe3)2]2, and crotonic acid has been found to be extremely active toward the copolymerization of cyclohexene oxide and carbon dioxide with turnover frequencies approaching 35 g/g of Zn/h at 80 °C. This catalyst precursor was also demonstrated to be an efficient terpolymerization catalyst when propylene oxide or styrene oxide was added to the cyclohexene oxide/CO2 feed. Extensive characterization of the metal complex proved difficult, but 31P NMR studies have shown that only 10% of the anticipated epoxide binding sites were available for catalysis. This suggests that the complex has several structures at its disposal, only one of which is conducive to copolymerization.