Enzyme-Catalyzed Ring-Opening Polymerization of Four-Membered Lactones: Preparation of Poly(β-propiolactone) and Poly(β-malic acid)

Lipase-catalyzed ring-opening polymerization of β-propiolactone (PL) and benzyl β-malolactonate (BM) was studied with respect to the influence of reaction conditions on molecular weight of the polymers and the monomer conversion. PL and BM were polymerized in bulk using lipase as a catalyst to yield the corresponding polyesters having molecular weights of greater than 50,000 and 7,000, respectively. It was found that the molecular weight of poly(β-propiolactone) produced by the lipase-catalyzed polymerization of PL was inversely dependent on the concentration of lipase. Both molecular weight and polymerization speed were increased with increasing reaction temperature from 40 to 60°C. BM was readily polymerized by porcine pancreatic lipase or Novozym 435 lipase at 60°C to yield poly(benzyl β-malate), which was readily debenzylated by catalytic hydrogenolysis to form poly(β-malic acid). This polyester was readily biodegraded both by the aerobic and anaerobic microbes.