A series of zinc benzylalkoxide complexes, [LnZn(mu-OBn)]2 (L = L1HL5H), 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 degrees C). Remarkably, a molecular weight of PLLA up to 580,000 can be achieved using [(L5Zn(mu-OBn)]2 (5b) as an initiator. The kinetic studies for the polymerization of L-lactide with complex 3b at -10 degrees C corresponded to first-order reactions in the monomer. The ring-opening polymerization (ROP) of e-caprolactone, e-decalactone, beta-butyrolactone and their copolymer with complex 3b was investigated. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013