Efficient zinc initiators supported by NNO‐tridentate ketiminate ligands for cyclic esters polymerization

Abstract

Abstract A series of zinc benzylalkoxide complexes, [L n Zn(μ‐OBn)] 2 (L = L 1 H – L 5 H ), supported by NNO‐tridentate ketiminate ligands with various electron withdrawing‐donating subsituents have been synthesized and characterized. X‐ray crystal structural studies revealed that complexes 2b and 4b are dinuclear bridging through the benzylalkoxy oxygen atoms with penta‐coordinated metal centers. All the metal complexes have acted as efficient initiators for the ring‐opening polymerization of L ‐lactide (within 12 min, 0 °C). Remarkably, a molecular weight of PLLA up to 580,000 can be achieved using [(L 5 Zn(μ‐OBn)] 2 ( 5b ) as an initiator. The kinetic studies for the polymerization of L ‐lactide with complex 3b at −10 °C corresponded to first‐order reactions in the monomer. The ring‐opening polymerization (ROP) of ε‐caprolactone, ε‐decalactone, β‐butyrolactone and their copolymer with complex 3b was investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013