Lactide cyclopolymerization by an alumatrane-inspired catalyst

A new catalyst for the ring-expansion polymerization of lactide to cyclic poly(lactic acid) was investigated. Catalyst 1(alumatrane-inspired catalyst, (N,N-bis(3,5-di-tert-butyl-2-benzyloxy)-2-(2-aminoethoxy)ethoxy)aluminum) was active for the polymerization of lactide in the melt and in solution and produced polymers with high molecular weights and narrow polydispersities. At constant concentration of monomer and catalyst with increasing reaction time, the conversion of monomer to polymer steadily increased, consistent with a well-defined catalyst. The result shows that the catalyst is active for polymerization of lactide in solution and in the melt and shows a linear increase in conversion with either catalyst loading or polymerization time under either polymerization condition, consistent with a well-defined active site. The expected trends are also observed for molecular weight and intrinsic viscosity. The polymer produced displays physical characteristics consistent with a cyclic architecture.