Precision copolymerization of CO2 and epoxides enabled by organoboron catalysts

Copolymerization of CO2 and epoxides is an industrially relevant means to alleviate anthropogenic carbon emissions and non-degradable plastic pollution. Despite recent advances, few studies have focused on controlling the enchainment of ether and carbonate segments, a process that determines the performance of the material. Here we report precise control of the enchainment of ether and carbonate segments by using a series of well-defined dinuclear organoboron catalysts. By altering the catalyst structure and optimizing reaction conditions, the alternating carbonate content in the propylene oxide/CO2 copolymer is finely regulated over a wide range of 3.0-95.2%, and the polyether content is arbitrarily varied between <0.1% and 97.0%. A unique microstructure, the -ABB- linkage, is identified by NMR spectroscopy, hydrolysis-derivatization experiments and single-crystal X-ray diffraction. Density functional theory calculations indicate that the -ABB- microstructure originates from a regioselectivity-directed copolymerization process. By analysis of the crystal structures of four catalysts and their catalytic performance, we quantified a correlation between dinuclear organoboron catalyst structure and sequence selectivity (-AB-, -ABB- and -AB(n)-, n >= 3) in propylene oxide/CO2 copolymerization, which should enable new catalyst design for this sustainable transformation.