Synthesis And Catalytic Activities Of ?-Ketiminate Multinuclear Zinc Complexes

Polylactide is a polymer with good biocompatibility and recyclability.Its excellent properties make it widely used in industry,such as drug sustained-release materials and artificial tissue materials.At present,a more effective method for synthesizing polylactide is to use metal complexes to catalyze the ring-opening polymerization of lactide to obtain polylactide.After literature research,it is found that the binuclear or polynuclear metal complexes obtained by bearing appropriate polydentate ligands are effective catalysts for catalyzing the ring-opening polymerization of lactide,and different kinds of metal complexes can be obtained by adjusting different substituents in the branched chain of the ligands.In this paper,?-polydentate ketimine was used as the ligand and diethylzinc as the reaction raw material for the coordination synthesis to obtain a series of multinuclear zinc complexes,[Nacac^CH2CH2OZn]₄?2a?,[Nacac^CH2CH2CH2OZn]₄?2b?,[Nacac^{CH2CH2CH2CH2O}Zn]4?2c?,[Nacac^CH2CH?CH3?OZn]4?2d?,[(Nacac₄^{CH2CH2CH2CH2O})Et₂?OH?₂Zn₆]?3c?.The catalytic activities of 2a-2d towards the ring-opening polymerization of racemic lactide have been investigated.The results show that Complex 2b shows better catalytic activity under solution condition.With a molar ratio of monomer to catalyst being 100:1,95%monomer conversion was achieved within 5 minutes,yielding polymers with molecular weights?Mn?of1.76×10⁴ g/mol and TOF of 1140 h^-1.Complex 2d shows better catalytic activity under bulk catalysis at 130 ^oC.With a monomer to catalyst molar ratio of 1000:1,the monomer conversion could be reached to 95%within 3 minutes,and polylactide with a relative molecular mass of 9.12×10⁴ g/mol was obtained.The catalytic activity TOF value was as high as 19000 h^-1.Complex 2d is not sensitive to the moisture with the high catalytic activity it deserves to be further investigated.Furthermore,the polymerization mechanisms of complexes 2b and 2d under solution and melt conditions were also explored in detail.