Copolymerization and terpolymerization of glycolide with lactones by dimethyl(salicylaldiminato)aluminum compounds

The aliphatic poly(esters) are the most common biodegradable and biocompatible synthetic materials used by far for diverse biomedical applications. Co-polymers and ter-polymers of glycolide with ε-caprolactone and lactide are produced in the presence of dimethyl aluminum compounds, bearing salicylaldiminato bidentate ligands differing for the steric hindrance on the ortho position of the phenolato ring. The formation of random poly[glycolide-co-(ε-caprolactone)] samples is favored with more encumbered catalyst. Transesterification reactions of the second mode also contribute to randomize the structure. Copolymers from semi-crystalline to amorphous are produced by decreasing the glycolide/ε-caprolactone feed ratio. The terpolymerization of glycolide with ε-caprolactone and rac-lactide with the same catalysts affords amorphous and random poly[(glycolide-co-lactide-co-(ε-caprolactone)] samples. The incorporation of the monomers is in this case determined by the bulkiness of the catalysts and by the higher coordination ability of the cyclic diesters.