Tailoring hypercrosslinked ionic polymers with high ionic density for rapid conversion of CO2 into cyclic carbonates at low pressure

Abstract

Designing and preparing hypercrosslinked ionic polymers (HIPs) with high ionic density for CO2 conversion is a significant challenge in materials science. Herein, the simple Friedel-Crafts alkylation synthesized a series of imidazolium-based HIPs with different ionic densities and porosities. Among these HIPs, [HBIM-6]Br-DCX(3) with high ionic content (2.31 mmol g−1) was prepared through Friedel-Crafts alkylation of alpha'-Dichloro-p-xylene with a monomer [BIM-6]Br, in which [BIM-6]Br produced from the reaction of 1,2,3,4,5,6-hexakis(bromomethyl)benzene with 1-benzylimidazole. What's more, in the absence of co-catalysts, solvents and additives, the metal-free catalyst [HBIM-6]Br-DCX(3) exhibited excellent catalytic activity for the conversion of CO2 with various epoxides into corresponding cyclic carbonates at atmospheric pressure in the ultrashort reaction time because its high ionic density provides abundant imidazolium cations and bromide anions as active sites, and 99% yield and 99% selectivity were achieved for cycloaddition of CO2 with epichlorohydrin and epibromohydrin within 1 h. The reaction time is shorter than most reported porous ionic polymer catalysts under the same conditions (styrene oxide, 120 ℃, 4 h, 99% yield; 100 ℃, 10 h, 97% yield). Notably, styrene oxide (SO) was converted into styrene carbonate (SC) with 90% yield under simulated flue gas (1 bar, 15% CO2 and 85 % N2) in 15 h. Furthermore, the catalyst was easily separable and maintained high reusability and stability after running five times. This work provides a new strategy to synthesize HIPs with high ionic density and the obtained HIPs can be used as efficient catalysts for rapidly converting CO2 with epoxides into cyclic carbonates at low pressure.