Ring-opening polymerization of lactide using salen–aluminum complexes bearing Schiff-base ligands derived from <i>cis</i>-1,2-cyclohexanediamine

<p>Three aluminum complexes supported by salen ligands derived from <i>cis</i>-1,2-cyclohexanediamine and salicylaldehyde derivatives were synthesized. They were characterized by ¹H, ¹³C NMR spectra, and elemental analysis. X-ray diffraction analysis revealed that aluminum was in distorted square pyramidal geometry in <b>2</b>. These complexes were employed as catalysts for the ring-opening polymerization (ROP) of L-lactide and <i>rac</i>-lactide. Complex <b>2</b> showed the highest activity among these complexes with isopropanol for the ROP of L-lactide and <b>3</b> showed the highest stereoselectivity for the ROP of <i>rac</i>-lactide attaining partially isotactic polylactide with a <i>P</i>_m of 0.75. The kinetic data of the polymerization utilizing <b>3</b> as catalyst showed that the polymeric rate was first order to the monomer and catalyst.</p