Perfectly Alternating Copolymerization of CO and Epoxides to Aliphatic Polyester Oligomers via Cooperative Organoboron–Cobalt Complexes

The carbonylative polymerization of epoxides provides a promising but challenging strategy to synthesize polyhydroxyalkanoates (PHAs) which are of high commercial value in the field of biomedical materials and engineering plastics. Herein, a suite of well-defined bifunctional organoboron–cobalt catalysts, featuring simple preparation, high yields, and low metal content, are exploited for the carbonylative polymerization of epoxides to PHA oligomers. The organoboron–cobalt-mediated carbonylative polymerization exhibits high polyester selectivity (over 95%, four epoxide examples), and the obtained PHAs have more than 99% ester linkages on the polymer main chain. Detailed investigations based on in situ reactIR and ¹H NMR analyses first found the concurrence of the direct alternating copolymerization of epoxides/CO, the ring expansion carbonylation of the epoxides to afford β-lactones, and the in situ homopolymerization of β-lactones under a single catalyst. This rare discovery provides a fundamentally different mechanism in the preparation of PHAs from CO/epoxides, extending the arsenal of catalytic systems that can copolymerize CO with epoxides.