Synthesis and characterization of half-salen complexes and their application in the polymerization of lactide and ε-caprolactone

Abstract

A series of half-salen ligands and their aluminum Al(III) complexes that contained different substituents were designed and synthesized. All the ligands and their complexes were characterized by ¹H, ¹³C NMR and elemental analysis. The complexes can be used as catalysts to produce polylactide and poly-ε-caprolactone. All polymerizations were living with narrow molar mass distributions. The M_n(obsd) values of the isolated polymers were in good agreement with M_n(calcd). The polymerization rate of the electrophilic substituted complex was higher than the non-electrophilic substituted analogues. The more bulky substituents with more steric hindrance of the complexes showed relatively low polymerizing activity. The aluminum complexes showed a moderate stereo-selectivity to the ring opening polymerization of rac-lactide to give isotactic enriched polylactide.