Efficiency and synergy of bis-urea anions for the polymerization of cyclic esters

Organocatalytic ring-opening polymerization of lactones is a highly versatile approach to obtain well-defined, biodegradable polyesters. Despite its sustainability advantages, a major challenge remains achieving both high activity and precise control over polymerization, particularly at low catalyst loadings. Here we report that bis-urea anions, in the presence of an alcohol, are excellent catalysts for the ring-opening polymerization of lactide and various lactones. These catalytic systems exhibit “living/immortal” polymerization behavior, producing high molecular weight polymers with exceptional turnover frequencies (up to 250,000 h−1) even at catalyst loadings as low as 0.06 %. Density functional theory calculations, supported by X-ray characterization, confirm the remarkable catalytic performance arises from synergistic interactions between urea moieties, which facilitate cooperative activation of the monomer. These interactions are further enhanced by metal-ion templating effects and the conformational flexibility of alkyl linkers, collectively contributing to the remarkable efficiency and control of the polymerization process.