Monoamidinate titanium complexes: highly active catalysts for the polymerization and copolymerization of l-lactide and ε-caprolactone

Abstract

A series of titanium trichloroamidinate complexes have been synthesized with two distinct ligand sets bearing a phenyl or a methyl substituent at the carbon atom of the amidinate framework. The steric bulk of the substituents at the N-atoms was also varied to evaluate the impact of different hindrances on the catalytic performance in the ring-opening-polymerization (ROP) of cyclic esters. All complexes resulted in active catalysts for the ROP of ε-caprolactone (ε-CL) and L-lactide (L-LA) showing a productivity that increases with the steric encumbrance offered by the ancillary ligand. Kinetic studies showed short induction periods after which the polymerizations exhibited first-order dependences on ε-CL and L-LA concentrations. All complexes were very active and robust, able to promote the polymerization of unpurified monomer under industrially attractive melt conditions. They showed different abilities in the copolymerization of ε-CL and L-lactide producing polymers ranging from gradient to truly random microstructures depending on the initiator architecture.