Lipase-catalyzed synthesis of poly(ε-caprolactone) and characterization of its solid-state properties

Abstract

Ring-opening polymerization of ε-caprolactone has been successfully conducted using an immobilized form of Candida antarctica lipase B as catalyst. The effects of enzyme concentration, reaction medium, reaction temperature and time on monomer conversion and product molecular weight were investigated. Through optimization of reaction conditions, poly(ε-caprolactone) (PCL) was obtained with 99% monomer conversion and a number-average molecular weight (Mn) of 18870 g/mol. The reaction system was then scaled up, and PCL was synthesized in 78% isolated yield, with Mn and polydispersity index of 41540 g/mol and 1.69, respectively. The solid-state properties of this sample were systematically evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). The product PCL showed excellent thermal stability, with degradation of the main chain in the temperature range of 280–450°C. Remarkably, this high molecular weight PCL was a typical crystalline polymer with a high degree of crystallinity observed by DSC, WAXD and POM.