High-Molecular-Weight Poly(1,5-dioxepan-2-one)via Enzyme-Catalyzed Ring-Opening Polymerization

To avoid organometallic catalysts in the synthesis of poly(1,5-dioxepan-2- one), the enzymatic ring-opening polymerization of 1,5-dioxepan-2-one (DXO)was performed with lipase CA (derived from Candida antarctica)as a biocatalyst. A linear relationship between the number-average molecular weight and monomer conversion was observed, and this suggested that the product molecular weight could be controlled by the stoichiometry of the reactants. The monomer consumption followed a first-order rate law with respect to the monomer, and no chain termination occurred. Water acted as a chain initiator, but it could cause polymer hydrolysis when it exceeded an optimum level. An initial activation via the heating of the enzyme was sufficient to start the polymerization, as the monomer conversion occurred when samples were left at room temperature after an initial heating at 60 8C. A high lipase content led to a high monomer conversion as well as a high molecular weight. An increase in the monomer conversion and molecular weight was observed when the polymerization temperature was increased from 40 to 80 8C. A further increase in the polymerization temperature led to a decrease in the monomer conversion and molecular weight because of the denaturation of the enzyme at elevated temperatures. The polymerization behavior of DXO under lipase CA catalysis was compared with that of e-caprolactone (CL). The rate of monomer conversion of DXO was much faster than that of CL, and this may have been due to differences in their specificity toward lipase CA.