Efficient initiators for the ring‐opening polymerization of <scp>L</scp>‐lactide: Synthesis and characterization of NNO‐tridentate Schiff‐base zinc complexes

Abstract

Abstract A series of efficient catalysts, based on zinc alkoxides coordinated with NNO‐tridentate Schiff‐base ligands (L 1 H‐L 6 H), for ring opening polymerization of L ‐lactide have been prepared. The reactions of diethyl zinc (ZnEt 2 ) with L 1 H‐L 6 H yielded [(μ‐L)ZnEt] 2 ( 1a–6a ), respectively. Further reaction of compounds 1a–6a with benzyl alcohol (BnOH) produced the corresponding compounds of [LZn(μ‐OBn)] 2 ( 1b–6b), respectively. X‐ray crystal structural studies reveal that all of these compounds 1a–6a are dimeric bridging through the phenolato oxygen atoms of the Schiff‐base ligand. However, the molecular structures of 1b–6b show a dimeric character bridging through the benzylalkoxy oxygen atoms. Ring‐opening polymerization of L ‐lactide, initiated by 1b–6b , proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. Experimental results show that the substituents on the imine carbon of the NNO‐ligand affect the reactivity of zinc complexes dramatically. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6466–6476, 2008