ABSTRACT
Linear lactide-and glycolide-based polymers are most commonly synthesized by ring-opening melt polymerization of lactide and glycolide at 140-180°C for 2-10 h using a catalyst (24,25). When polymerization temperature is less than the melting point of polymer (175°C), crystallization of the polymerizing polymer occurs, resulting in solid-state polymerization as with poly(glycolide) (PG). Solid-state polymerization has been found useful for very high molecular weight polymers, around 1000 kD (26). The polymerization reaction was studied and several mechanisms were proposed including cationic (27-30), anionic (31-34), and coordination-insertion (35,36). The common polymerization catalysts are tin derivatives such as tin octoate or tin hexanoate. A hypothetical mechanism of the ring-opening polymerization of lactide using a tin catalyst was suggested by Kissel et al. (Scheme 1) (37).
