Preparation of biocompatible, biodegradable and sustainable polylactides catalyzed by aluminum complexes bearing unsymmetrical dinaphthalene-imine derivatives via ring-opening polymerization of lactides

Abstract

A number of half-salen aluminum complexes bearing unsymmetrical [ONN]-type ligands were prepared from tridentate dinaphthalene-imine derivatives. These complexes were characterized by H-1 and C-13 NMR spectroscopy, elemental analysis and single crystal X-ray diffraction analysis. These complexes were employed for rac-lactide and L-lactide polymerization. Upon activation with isopropanol, complex (S)-B-6 (R-1 = R-2 = R-4 = H; R-3 = F) showed the highest activity (a monomer conversion of 94.6%) amid these aluminum complexes for the ring-opening polymerization of L-lactide; and complex (S)-B-2 (R-1 = R-2 = R-3 = H; R-4 = Bu-t) showed the highest stereoselectivity for the ring-opening polymerization of rac-lactide, obtaining a polylactide (PLA) with a Pm of 0.69. The polymerization kinetics utilizing (S)-B-6 as a catalyst were researched in detail. The data on the polymerization kinetics revealed that the rate of polymerization was first-order with respect to the monomer and the catalyst. There was a linear relationship between the L-lactide conversion and the number-average molecular weight of PLA