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

Abstract

Three aluminum complexes supported by salen ligands derived from cis-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 2. These complexes were employed as catalysts for the ring-opening polymerization (ROP) of L-lactide and rac-lactide. Complex 2 showed the highest activity among these complexes with isopropanol for the ROP of L-lactide and 3 showed the highest stereoselectivity for the ROP of rac-lactide attaining partially isotactic polylactide with a P_m of 0.75. The kinetic data of the polymerization utilizing 3 as catalyst showed that the polymeric rate was first order to the monomer and catalyst.

Keywords:

• Aluminum
• salen
• biodegradable
• lactide
• ring-opening polymerization

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

¹ P_m is the probability of meso linkages: [mmm] = P_m² + (1 − P_m)P_m/2, [mmr] = [rmm] = (1 − P_m)P_m/2, [rmr] = (1 − P_m)²/2, and [mrm] = [(1 − P_m)² + P_m(1 − P_m)]/2.