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

A number of half-salen aluminum complexes bearing unsymmetrical [ONN]-type ligands were prepared from tridentate dinaphthalene-imine derivatives. These complexes were characterized by 1 H and 13 C 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)-B6 (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)-B2 (R 1 = R 2 = R 3 = H; R 4 = t Bu) showed the highest stereoselectivity for the ring-opening polymerization of rac -lactide, obtaining a polylactide (PLA) with a P m of 0.69. The polymerization kinetics utilizing (S)-B6 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.