Commercialized Cyclic (thio)urea for ring-opening polymerization of rac-lactide and ε-caprolactone

The (thio)urea/base bifunctional activation catalyst system activates monomers or propagating alcohols through hydrogen bonding, demonstrating exceptional selectivity and activity. A series of economical cyclic (thio)urea-base combinations were employed as catalytic systems for rac-lactide and ε-caprolactone ring-opening polymerization (ROP). Among these, cyclic ureas combined with potassium methoxide (MeOK) exhibited superior catalytic activity over their thiourea counterparts, with the U3/MeOK system displaying remarkable controllability in rac-lactide polymerization, producing polymers with exceptionally low dispersity (Đ < 1.10). Kinetic studies confirmed that the polymerization process was well-controlled and adhered to first-order kinetics. Comparative analyses indicated that the dual hydrogen atoms on the urea moiety enhance the regulation of rac-lactide ROP. A plausible catalytic mechanism for the urea/MeOK system in rac-lactide polymerization was postulated. Additionally, in toluene solution, the urea/ MeOK system showed moderate catalytic performance for ε-caprolactone polymerization with reduced control, yielding poly(ε-caprolactone) of higher polydispersity. This study offers a straightforward approach toward the production of biodegradable polymeric materials.