Controlled stereoselective polymerization of lactide monomers by group 4 metal initiators that contain an (OSSO)-type tetradentate bis(phenolate) ligand

Group 4 metal complexes Zr-1 to Zr-4, Ti-4 and Ti-4a that contain an (OSSO)-type tetradentate bis(phenolate) ligand were found to initiate the ring-opening polymerization of meso-, rac-, and L-lactides in toluene solution. The polymerizations were controlled with initiator efficiency values around one and gave polymers with low polydispersity (Mw/Mn < 1.2). The polylactides were atactic when rac-lactide was used as the monomer and heterotactic biased when meso-lactide was used. Kinetic measurements showed that meso-lactide was polymerized generally faster than rac- and L-lactide.