Living polymerization of D,L-3-methylglycolide initiated with bimetallic (Al/Zn) mu-oxo alkoxide and copolymers thereof

D,L-3-Methylglycolide (MG) was successfully polymerized with bimetallic (Al /Zn) mu -oxo alkoxide as an initiator in toluene at 90 degreesC. The effect of the initiator concentration and monomer conversion on the molecular wei ght was studied. It is shown that the polymerization of MG follows a living process. A kinetic study indicated that the polymerization approximates th e first order in the monomer, and no induction period was observed. H-1 NMR spectroscopy showed that the ring-opening polymerization proceeds through a coordination-insertion mechanism with selective cleavage of the acyl-oxyg en bond of the monomer. On the basis of H-1 NMR and C-13 NMR analyses, the selective cleavage of the acyl-oxygen bond of the monomer mainly occurs at the least hindered carbonyl groups (P-1 = 0.84, P-2 = 0.16). Therefore, the main chain of poly(D,L-lactic acid-co-glycolic acid) (50/50 molar ratio) o btained from the homopolymerization of MG was primarily composed of alterna ting lactyl and glycolyl units. The diblock copolymers poly(epsilon -caprol actone)-b-poly(D,L-lactic acid-alt-glycolic acid) and poly(L-lactide)-b-pol y(D,L-lactic acid-alt-glycolic acid) were successfully synthesized by the s equential living polymerization of related lactones (epsilon -caprolactone or L-lactide). C-13 NMR spectra of diblock copolymers clearly show their pu re diblock structures. (C) 2000 John Wiley & Sons, Inc. J Polym Sci A: Poly m Chem 39: 357-367, 2001.