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 H-1 NMR analyses first found the concurrence of the direct alternating copolymerization of epoxides/CO, the ring expansion carbonylation of the epoxides to afford beta-lactones, and the in situ homopolymerization of beta-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.

Automated summary

The carbonylative polymerization of epoxides using bifunctional organoboron-cobalt catalysts provides a promising strategy for synthesizing valuable PHA oligomers. The method demonstrates high polyester selectivity and a fundamentally different mechanism for the preparation of PHAs compared to traditional methods, extending the range of catalytic systems available for copolymerizing CO with epoxides.