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



A series of zinc benzylalkoxide complexes, [LnZn(μ-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 °C). Remarkably, a molecular weight of PLLA up to 580,000 can be achieved using [(L5Zn(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