Polymers anchored with carboxyl-functionalized di-cation ionic liquids as efficient catalysts for the fixation of CO2 into cyclic carbonates

A series of polymers grafted with functionalized di-cation imidazolium-based ionic liquids (P-FDIILs) were fabricated and evaluated as efficient catalysts for the synthesis of cyclic carbonates from epoxides and CO2 in the absence of a co-catalyst and a solvent. The P-FDIILs, especially the carboxyl-functionalized ones, perform well in the cycloaddition reaction at a low catalyst loading of 0.3 mol%. It is suggested that a combined effect of the carboxyl group, the imidazolium cation, and the halide anion facilitates the cycloaddition reaction. Furthermore, the methylene chain length between the imidazolium cation and the functional group, and the halide anion species, affect the activity of the catalysts. It is noted that the catalyst shows no significant loss of activity in a reusability test of five cycles. From the view point of industrial application, the catalyst is attractive due to its good stability and excellent catalytic efficiency.