Humicola insolens cutinase-catalyzed lactone ring-opening polymerizations: Kinetic and mechanistic studies

Abstract

This paper explores reaction kinetics and mechanism for immobilized Humicola insolenscutinase (HIC), an important new biocatalyst that efficiently catalyzes non-natural polyester synthetic reactions. HIC, immobilized on Lewatit, was used as catalyst for ∈-caprolactone (CL) and ω-pentadecalactone (PDL) ring-opening polymerizations (ROPs). Plots of percent CL conversion vs time were obtained in the temperature range from 50 to 90 °C. The kinetic plot of In([M]0[M]1) vs time (r2 = 0.99) for HIC-catalyzed bulk ROP of CL was linear, indicating that chain termination did not occur and the propagation rate is first order with respect to monomer concentration. Furthermore, linearity to 90% conversion for Mn, vs fractional CL conversion is consistent with a chain-end propagation mechanism. Deviation from linearity above 90% conversion indicates that a competition between ring-opening chain-end propagation and chain growth by steplike polycondensations takes place at high monomer conversion. HIC was inactive for catalysis Of L-lactide and (R,S)-β-butyrolactone ROP. HIC-catalyzed ROP of ∈-CL and PDL in toluene were successfully performed, giving high molecular weight poly(∈-caprolactone) and ω-poly(pentadecalactone). In addition, the relative activities of immobilized Candida antarctica lipase B (CALB) and HIC for ∈-CL and PDL polymerizations are reported herein. © 2008 American Chemical Society.