Metal-free catalysts have shown promise as alternatives to transition metal based homogeneous catalysts in a range of ring-opening polymerization and copolymerization reactions, but this area remains quite underdeveloped. We have shown that arylboranes, BPh3 and B(C6F5)3, can be used as catalysts, in the presence of a suitable co-catalyst or as a pre-formed Lewis acid/base adduct, to prepare either cyclic organic carbonate or polycarbonate products from epoxides and carbon dioxide. Selectivity towards cyclic or polymer product is dependent on the substrate used. Lower activity was observed using B(C6F5)3 due to its increased Lewis acidity. Kinetic studies of this metal-free reaction revealed a process that is first order in all reagents with the surprising exception of carbon dioxide, where an inverse dependence was discovered. Following on from this work, we have investigated tandem copolymerization-polymer functionalization reactions where the catalytic borane can hydrosilylate pendent olefin groups along the polycarbonate chain. BPh3 with a suitable nucleophile is also able to copolymerize cyclic anhydrides with epoxides including bioderived limonene-oxide. Due to differences in reactivity between epoxides and anhydrides, block polyester-carbonates can be produced. Further to this, B(C6F5)3 can selectively depolymerize the polycarbonate blocks in these polymers to yield polyester and cyclic carbonate.

Borane catalyzed ring-opening polymerization, copolymerization and depolymerization reactions controlled by Lewis acid strength

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.