A green catalytic pathway to sustainable poly(propylene carbonate) production: potassium phenyl thiolate/triethylboron mediated copolymerization of CO2 and propylene oxide

Abstract

The ring-opening copolymerization (ROCOP) of propylene oxide (PO) and CO₂ offers a practical and sustainable approach for producing poly(propylene carbonate) (PPC). However, when this copolymerization is mediated by heavy-metal catalysts, the process often suffers from limited CO₂ incorporation, undesirable formation of polyether linkages, and poor selectivity toward PPC. To overcome these limitations, we introduce a potassium phenyl thiolate/triethylborane (PhSK/Et₃B) catalytic system that enables highly selective production of strictly alternating PPC while completely suppressing polyether formation. Mechanistic studies supported by density functional theory (DFT) reveal that the catalyst operates through a cooperative pathway: PhSK initially captures CO₂ to generate a phenyl carbonate nucleophile, which subsequently attacks Et₃B-activated PO. This synergistic polarization significantly lowers the kinetic barriers for both PO ring-opening and CO₂ insertion, thereby facilitating efficient alternating copolymerization. A systematic investigation further highlights the strong interplay among CO₂ pressure, temperature, and catalyst loading in governing polymer growth. Under optimized conditions, this approach yields high average molecular weight PPC (M_n = 40.33 kg mol⁻¹) with narrow dispersity (Đ = 1.04), excellent selectivity (99%), and complete suppression of polyether linkages. Overall, the PhSK/Et₃B system provides a scalable and environmentally benign platform for CO₂ utilization, advancing the development of high-performance polycarbonate materials.