Synthesis of metal-free poly(1,4-dioxan-2-one) by enzyme-catalyzed ring-opening polymerization

To avoid the harmful effects of metallic residues in poly(1,4-dioxan-2-one) (PPDO) for medical applications, the enzymatic polymerization of 1,4-dioxan-2-one (PDO) was carried out at 60 °C for 15 h with 5 wt % immobilized lipase CA. The lipase CA, derived from Candida antarctica, exhibited especially high catalytic activity. The highest weight-average molecular weight (Mw = 41,000) was obtained. The PDO polymerization by the lipase CA occurred because of effective enzyme catalysis. The water component appeared to act not only as a substrate of the initiation process but also as a chain cleavage agent. A slight amount of water enhanced the polymerization, but excess water depressed the polymerization. PPDO prepared by enzyme-catalyzed polymerization is a metal-free polyester useful for medical applications.