The role of hydroxyl groups in poly(ionic liquid)s on CO2 cycloaddition with epoxides in the view of catalytic kinetics

Abstract

The cycloaddition of CO₂ and epoxides can produce high-value cyclic carbonates. This study developed a series of hydroxyl functional imidazolium-based poly(ionic liquid)s (PILs) by copolymerization of ionic liquids ([HeVIM]Br or [BVIM]Br), 4-vinylphenol, and divinylbenzene. The as-synthesized PILs were investigated as catalysts for the cycloaddition of CO₂ with epichlorohydrin, and higher catalytic activity was observed over PILs with the cooperative activation effect between imidazolium and hydroxyl groups. The optimized PILs could achieve a 92.9% yield of cyclic carbonate in 2 h at 1.0 MPa CO₂ and 393 K, and a considerable cyclic carbonate formation rate of 1.7–2.8 h⁻¹ at ambient reaction conditions (0.5 MPa CO₂ and 303 K). Kinetic experiments and theoretical calculations indicate that the presence of a hydrogen bond network lowers the energy barrier of the ring-opening step in CO₂ cycloaddition, further facilitating the CO₂ conversion over imidazolium groups.