Preparation of high-molecular-weight polylactide by ring-opening polymerization of l-lactide using base/bisurea binary organocatalyst

Despite the advantages of organocatalysts, the preparation of high-molecular-weight polylactide using organocatalysts remains as a challenge probably due to the transesterification or back-biting side reactions at low catalyst and initiator loadings. In this contribution, a series of organobases and ureas were combined as binary catalysts and screened for the ROP of lactide. The bisurea as the co-catalyst exhibited higher catalytic activity while remaining good controllability over the polymerization compared to the monourea. The controlled ROP of l-lactide was achieved by judiciously chosen of suitable combination of organobase and bisurea. Well-defined polylactides bearing various terminal groups were prepared using different alcohols as initiators. Remarkably, a high-molecular-weight PLA sample with a Mn up to 73.8 kDa was obtained at a low catalyst loading of 0.05 mol% relative to the monomer, which exhibited good mechanical properties that comparable to the commercial PLA.