Ring-opening bulk polymerization of epsilon-caprolactone and trimethylene carbonate catalyzed by lipase Novozym 435.

The affects of lipase concentration on ring-opening bulk polymerizations of epsilon-caprolactone and trimethylene carbonate were studied by using Novozym 435 (immobilized form of lipase B from Candida antarctica) as biocatalyst. The polymerization of epsilon-caprolactone was carried out in bulk at 70 degrees C. Three lipase concentrations of 9.77, 1.80 and 0.50 mg/mmol epsilon-CL were used in the experiment. The results showed that increasing the lipase concentration used in the polymerization system resulted in an increased rate of monomer consumption. For an enzyme concentration of 9.8 mg lipase per mmol monomer, an 80% monomer conversion was achieved in a 4-h time period, while for the lower enzyme concentration of 1.8 mg lipase per mmol monomer, 48 h were needed to reach monomer conversion. Linear relationships between Mn and monomer conversions were observed in all three enzyme concentrations, suggesting that the product molecular weight may be controlled by the stoichiometry of the reactants for these systems. At the same monomer conversion level, however, Mn decreased with increasing enzyme concentration. After correcting for the amount of monomer consumed in initiation, the plot of ln[([M]o - [M]i)/([Mt] - [M]i)] versus reaction time was found to be linear, suggesting that the monomer consumption followed a first-order rate law and no chain termination occurred. For the TMC systems, the polymerization was carried out in bulk at 55 degrees C. Similar to the epsilon-CL systems, increasing the Novozym 435 concentration from 8.3 to 23.6 mg/mmol TMC increased the rate of monomer conversion. Unlike the epsilon-CL systems, however, nonlinear relationships were obtained between Mn and monomer conversion, indicating that possible chain transfer and/or slow initiation had taken place in these systems. Consistent with the above result, nonlinear behavior was observed for the plot of ln[[M]o/[M]t] versus reaction time.