Cycloaddition of CO ₂ to epoxides catalyzed by carboxyl-functionalized imidazolium-based ionic liquid grafted onto cross-linked polymer

Carboxyl-functionalized imidazolium-based ionic liquid was grafted onto cross-linked divinylbenzene polymer (PDVB-CEIMBr) for the first time. The catalyst was characterized and used for the cycloaddition of CO ₂ to epoxides under relatively mild reaction conditions without any use of cocatalyst and organic solvent. The effects of reaction conditions (temperature, initial CO ₂ pressure, and time) and water addition on the yield of cyclic carbonate were investigated systematically. Under optimal conditions (140 °C, initial CO ₂ pressure 2.0 MPa and 4 h), propylene carbonate selectivity and yield was 99.8% and 96.1%, respectively. Moreover, the catalyst shows good stability and reusability. A plausible reaction mechanism was proposed for the catalytic reaction. It is suggested that synergetic effect among Brønsted acid COOH, Lewis base Br ^- and the support facilitates the coupling reaction. From the viewpoint of industrial application, the catalyst is attractive because of its excellent catalytic efficiency.