Lipase-catalyzed ring-opening polymerization of medium-size lactones to polyesters

Enzymatic ring-opening polymerization of medium-size lactones, epsilon-caprolactone (epsilon-CL) and delta-valerolactone (delta-VL), was performed by using a lipase as a catalyst. For the polymerization of epsilon-CL in bulk, a lipase derived from Pseudomonas fluorescens (lipase PF) showed the highest catalytic activity among the powdery lipases examined, i.e., the highest molecular weight was achieved by using lipase PE The polymerization behavior depends on the lipase origin as well as on the polymerization condition. From H-1 and C-13 NMR analyses the polymer was found to possess one terminal carboxylic acid group and one hydroxyl group. delta-VL was enzymatically polymerized, yielding the corresponding polyester. The polymerization rate of delta-VL catalyzed by lipase PF is larger than that of epsilon-CL, whereas the molecular weight of poly(delta-VL) is lower than that of poly(epsilon-CL) obtained under similar reaction conditions. These lactones were also enzymatically polymerized in organic solvents. The relationship between the type of the solvent and the polymerization behavior was investigated. An immobilized lipase derived from Candida antarctica causes a much faster polymerization of the lactones than the powdery lipases. The immobilized lipase can he reused as a catalyst for the polymerization of epsilon-CL.