Title

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

Document Type

Article

Publication Date

2008

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 epsilon-caprolactone (CL) and omega-pentadecalactone (PDL) ring-opening polymerizations (ROPs). Plots of percent CL conversion vs time were obtained in the temperature range from 50 to 90 degrees C. The kinetic plot of ln([M]0/[M]t) 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 M(n) 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)-beta-butyrolactone ROP. HIC-catalyzed ROP of epsilon-CL and PDL in toluene were successfully performed, giving high molecular weight poly(epsilon-caprolactone) and omega-poly(pentadecalactone). In addition, the relative activities of immobilized Candida antarctica lipase B (CALB) and HIC for epsilon-CL and PDL polymerizations are reported herein.

Journal

Biomacromolecules

Volume

9

First Page

518

Last Page

522