Ring-opening polymerization of L-lactide catalyzed by calcium complexes

A series of calcium complexes supported by NNO-tridentate ketiminate ligands have been synthesized and characterized. X-ray structural studies indicate that these complexes bear a mononuclear feature with hexa-coordinated calcium centers bonding to two ketiminate ligands. Polymerization of L-lactide catalyzed by these complexes proceeds rapidly and well controlled in the presence of a variety of alcohols. In addition, these complexes reveal good catalytic activity even with the addition of up to 80 equiv. of benzyl alcohol as a transfer agent. Furthermore, kinetic studies show ROP of L-lactide is a first-order dependency on [LA] and a second-order dependency on [BnOH].