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 -ABn-, n ≥ 3) in propylene oxide/CO2 copolymerization, which should enable new catalyst design for this sustainable transformation. Controlling the enchainment of ether and carbonate segments during copolymerization of CO2 and epoxides is rarely possible. Now, precise control of enchainment is realized by tuning the structure of an organoboron catalyst and the reaction conditions. Mechanistic and computational studies probe the origin of the unique ABB microstructure of the polymer.