Robust Cationic Calix[4]arene Polymer as an Efficient Catalyst for Cycloaddition of Epoxides with CO₂

The development of green solid polymer materials bearing multiple active sites as highly efficient heterogeneous catalysts with cooperative effects toward the conversion of carbon dioxide (CO₂) to high-value-added cyclic carbonate is highly in need. Here a novel cationic polymer based on the moieties of 1-bromomethyl-4-hydroxy calix[4]­arene and tri­(4-imidazolylphenyl)­amine has been synthesized, characterized, and used as a metal-free bifunctional heterogeneous catalyst for CO₂ utilization. The presence of abundant phenolic OH groups as hydrogen bond donors and bromide anions as nucleophilic agents provides this polymer with brilliant activities in catalyzing the epoxides into cyclic carbonates under atmospheric pressure and solvent-free conditions. More importantly, this bifunctional catalyst can be conveniently recycled and keeps catalytic ability well. This work not only offers a new method to synthesize a competitive green heterogeneous catalyst but also provides the first example of an ionic polymer that contains calixarene for synthesizing cyclic carbonate through the CO₂ cycloaddition reaction.