A DFT-metadynamics study disclosing key properties of ring-opening polymerization catalysts to produce polyethercarbonate polyols from cyclic ethylene carbonate as part of an emerging CCU technology

Abstract

The ring opening polymerization of cyclic carbonates made from epoxide and CO₂ to CO₂-containing polymers constitutes an emerging technology of particular industrial interest. Considering the reaction of ring-opening polymerization of cyclic ethylene carbonate to produce polyethercarbonate polyols, several types of catalysts were tested experimentally and mechanistic pathways were proposed, but a detailed analysis of structure property relationship including the CO₂-liberation pathways is still lacking. This contribution is using computational methods to investigate reported benchmark catalysts with the lead structure A_xM_yO_z (A: alkali metal or alkyl, M: main group element or transition metal) that are particularly approved as effiecient catalysts for industrial purpose. Employing DFT-metadynamics simulations, free energy surfaces (FESs) for the key-steps in the catalytic polymerization of cyclic ethylene carbonate (cEC) are generated. Important structural criteria and characteristics of the catalysts that influence the catalytic performance and (side)reaction pathways are determined. It turns out that less nucleophilicity of the catalyst anion and more labile cations remain major criteria for prohibiting CO₂ liberation during polymerization. The key learnings of this contribution currently serve as a basis to develop the next generation of catalysts to bring this emerging carbon capture and use (CCU) technology into industrial application.