Facile construction of bifunctional porous ionic polymers for efficient and metal-free catalytic conversion of CO2 into cyclic carbonates

Abstract

Hydrogen bond donors (e.g., OH, COOH) functionalized porous ionic polymers, featuring high specific surface areas and bi/multi-functional active sites, are promising candidates for metal- and co-catalyst free catalytic conversion of CO2. Herein, a facile method for the preparation of hydrogen bond donors (HBDs) functionalized porous ionic polymers (PIPs) was developed via the strategy of integrating free-radical polymerization and HBDs functionalization reactions into a single operation. Through this one-pot method, bifunctional PIPs with dual active sites (HBDs and Br−), high surface areas and large pore volumes were easily synthesized. Among the designed catalysts, the catalyst bearing carboxyl groups (PQPBrCOOH) presented better catalytic performance in the cycloaddition of CO2 into cyclic carbonates than that with hydroxyl groups (PQPBrOH); meanwhile, the HBDs-free catalyst (PQPBr) exhibited the lowest catalytic activity. Also, under atmospheric CO2 pressure and co-catalyst free conditions, PQPBrCOOH showed high catalytic activity, excellent reusability and broad substrate tolerance. Results of the catalytic tests and density functional theory (DFT) calculations suggested that the synergism between Br− and HBDs was critical for the activation of epoxides, and therefore enhanced the catalytic activities. Thus, this work provided not only an active, stable and heterogeneous catalyst for the conversion of CO2, but, more importantly, a facile and one-step strategy for constructing bifunctional porous ionic polymers.