Synthesis of Polycarbonates from CO2 Promoted by Immobilized Ionic Liquid Functionalized di-Mg Complex Catalyst

The capture and conversion of anthropogenic CO2 is a paramount challenge for our global ecosystem. An optimal way of to cope with the emitted CO2 is to efficiently convert it to value-added materials. Whereas nature sequesters CO2 by making sugar-based polymers, utilizing CO2 to make highly demanded synthetic polymers such as polycarbonates is of great value. The present work reports the synthesis of a new supported ionic liquid (IL) functionalized organic ligand that is able to accept metal sites. After incorporating di-nuclear magnesium, it was utilized as a single-component solid catalyst for the copolymerization of CO2 and cyclohexene oxide. The obtained solid catalyst was found to be active under mild CO2 pressures of (1-15 atm) giving a turnover number of up to 283 and turnover frequency up to 11.8 h(-1). To the authors knowledge, these rates are the highest obtained using a heterogeneous catalyst, maintaining 96-99 % polycarbonates selectivity and 97-99 % carbonate repeat units. In addition, the obtained polymers showed high molecular weights (16.7 to 11.7 kg/mol) with 1.05 to 1.6 dispersity (D). The catalyst was recycled 4 times, under regular laboratory conditions and without any intermediate reactivation steps, which provided similar to 3 g of polycarbonate for similar to 0.03 g catalyst (100 : 1) at 80 degrees C in neat cyclohexene oxide and 15 atm CO2.

Automated summary

This study presents a new supported ionic liquid (IL) functionalized organic ligand that can accept metal sites. After incorporating di-nuclear magnesium, it was used as a single-component solid catalyst for the copolymerization of CO2 and cyclohexene oxide. The obtained solid catalyst showed high activity under mild CO2 pressures, with high selectivity towards polycarbonates and high molecular weights of the obtained polymers.