rac-Lactide polymerization using aluminum complexes bearing tetradentate phenoxy-amine ligands

A family of aluminum-methyl complexes supported by tetradentate phenoxy-amine ligands has been prepared and employed in the ring-opening polymerization of rac-lactide; the ligands include N'N-bis(3,5-dimethyl-2-hydroxybenyl)N',N'-dimethyl-1,2-diaminoethane (L-1), NN-bis(3,5-diisopropyl-2-hydroxybenyl)-N,N'-dimethyl-1,2-diaminoethane (L) and N,N-bis(3,5-dichloro-2-hydroxybenyl)-N',N'-dimethyl-1,2-diaminoethane (L-3). Polymerizations of rac-lactide were carried out by treatment of the aluminum-methyl complexes with PhCH2OH and rac-lactide at 70 degrees C, affording well-controlled formation of polylactide (PLA) and a moderate isotactic bias for initiators bearing L-1 and L-2; the chloro-substituted ligand L-3 afforded largely atactic PLA. (c) 2006 Elsevier Ltd. All rights reserved.