Bimetallic salen–aluminum complexes: synthesis, characterization and their reactivity with rac-lactide and ε-caprolactone

A series of bimetallic Schiff-base ligands were synthesized and used to prepare aluminum complexes. All the complexes were characterized by 1H, 13C NMR and elemental analysis. These complexes were used as catalysts in the rac-lactide and ε-caprolactone polymerization. Isotactic enriched polylactides were obtained by using these complexes. All polymerizations were living with the narrow molar mass distributions. The Mn(obsd) of the isolated polymers was in good agreement with Mn(calcd). Kinetic studies showed that the polymerizations were first-ordered with respect to both lactide and caprolactone monomers. The more bulky substituents with more steric hindrance of the complexes had relatively poor activity. The increasing temperature had a positive effect as the polymerization rate increased with increasing temperature.