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

Abstract

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 M_n(obsd) of the isolated polymers was in good agreement with M_n(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.