Solvent-free ring-opening polymerization of lactones with hydrogen-bonding bisurea catalyst

Development of effective organocatalysts for the living ring-opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen-bond donating bisurea catalysts is reported for the ROP of lactones under solvent-free conditions. ROP of lactones mediated by the bisurea/7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well-defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD-catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε-caprolactone- co -δ-valerolactone) [P(CL- co -VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL- co -VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57 , 90–100