Synthesis of biodegradable and biorenewable polylactides initiated by aluminum complexes bearing m-xylylenediamine derivatives via the ring-opening polymerization of lactides

A series of aluminum complexes bearing [ONNO]-type ligands were prepared using m-xylylenediamine and modified salicylaldehyde. These complexes were characterized by NMR spectroscopy and elemental analysis. These complexes were employed in L-lactide and rac-lactide polymerization. Upon activation with isopropanol, complex 3 showed the highest activity (monomer conversion 97.4%) amid these aluminum complexes for the ring-opening polymerization of L-lactide and complex 2 showed the highest stereoselectivity for the ring-opening polymerization of rac-lactide providing isotactic polylactide (PLA) with a Pm of 0.70. The polymerization kinetics utilizing 2 as an initiator was researched in detail. The kinetics of the polymerization data revealed that the rate of polymerization was first-order with respect to the monomer and the initiator. There was a linear relationship between the L-lactide conversion and the number-average molecular weight of PLA.