Single-site cobalt and zinc catalysts for the ring-opening polymerization of lactide

Novel zinc(II) and cobalt(II) complexes containing tripodal mono(phenolate) ligands have been synthesized and characterized. The resulting mononuclear complexes act as efficient initiators in the polymerization of rac-lactide to provide the corresponding biodegradable poly(lactic acid). Most of these polymerizations proceeded in a controlled fashion, giving polymers with narrow polydispersities and experimental molecular weights in good agreement with calculated values.