METAL COMPLEXES FOR ROP OF LACTIDE AND CYCLOADDITION oF CO2 WITH EPOXIDES

Abstract

The purposes of the present investigations is to study the electronic effect and steric effect of the substituents affecting the activity of Schiff-base metal complexes on the polymerization rate of cyclic ester such as lactide for the synthesis of biodegradable and biocompatible polymer Poly lactic acid and also on the fixation of CO2 with epoxide. newlineAlthough, extensive investigations on the Schiff-base metal type catalysts have been reported, the steric and electronic effect of the substituents on imine carbon is rare. For this purpose, a series of nickel(II), copper(II) and zinc(II) complexes supported on tetracoordinated (-ONNO-) from bidentate ON- and tetradentate -ONNO- Schiff-base ligands (HMBD-2,6-DMA and HMBDED) have been synthesized successfully. Further reaction of compounds with benzyl alcohol (BnOH) produced the corresponding alkoxide complexes. The X-ray crystal structural studies of HMBDED and HMBD-2,6-DMA ligands reveal that all of these compounds are tetra-coordinated and bis-coordinated in nature. The catalytic activities of the nickel(II), copper(II) and zinc(II) complexes are insignificant in the absence of co-catalyst (BnOH) and by use of two or four equivalent benzyl alcohol in polymerization reactions of cyclic ester, the molecular weights of polyester (polylactide) became half or one fourth respectively. All the complexes proceed rapidly with good molecular weight control, and yields polymers with a very narrow molecular weight distribution toward the ringopening polymerization of cyclic ester (L-lactide). Experimental results demonstrate that for the metal complexes, the nature of back bone of ligand, substituents on the ligand, solvent and temperature affect the reactivity of metal complexes significantly. All the PLA produced by ROP of L-lactide show moderate molecular weight with gt80% conversion rate. The rate of polymerization is greatly dependent on the initiator used. The metal complexes allow controlled ROP as shown by the linear relationship between the conversion of percentage