Imidazolium-based polymeric ionic liquids for heterogeneous catalytic conversion of CO2 into cyclic carbonates

Polyimidazolium salts are a class of important catalysts for CO2 cycloaddition with epoxides. However, initiator like azoisobutyronitrile or metal catalyst is often required to promote their synthetic process. Therefore, developing a clean route to synthesize polyimidazolium salts is still highly desirable. In this study, three crosslinked polymers PIM1, PIM2 and PIM3 containing imidazolium unit were constructed via nucleophilic substitution reaction of 1,3,5,7-tetrakis (4-(imidazole-1-yl)phenyl)adamantane and benzyl bromides. The structure and composition of the polymers were characterized by CP/MAS C-13 NMR, FT-IR and XPS. Different porosities were observed for PIMs, and PIM2 has a larger BET surface are than that of PIM1 and PIM3. Accordingly, the polymeric imidazolium salt PIM2 shows superior activity for catalyzing cyclic addition of CO2 with a variety of epoxides without any solvent or cocatalyst, giving the cyclic carbonates in excellent yields. In addition, PIM2 shows high stability and easy recyclability.