Enzymatic synthesis of poly(ε-caprolactone-co-ε-thiocaprolactone)

This study presents the successful enzymatic ring opening copolymerization of epsilon-caprolactone(epsilon-CL) and epsilon-thiocaprolactone (epsilon-TCL) catalyzed by Novozyme 435, immobilized lipase B from Candida antarctica. Various monomers feed ratio (from 0 to 100% in TCL content) were tested using two polymerization strategies. The first one is a direct one-step strategy, starting with both monomers mixed in the feed, while the two-steps strategy consists in a first step of epsilon-CL homopolymerization followed by a second step with epsilon-TCL addition in the medium and its polymerization from the previously formed PCL chains. The obtained copolymers have been fully characterized by NMR, DSC, SEC and MALDI-ToF MS spectroscopy. Main results of the one-step strategy showed a decrease in the final copolymer molar mass with the increase in epsilon-TCL content as well as minimum values of crystallinity and melting temperature for the 50:50 feed composition. An in-depth analysis of the MALDI-TOF mass spectra of the copolymers showed interesting patterns that suggest a micro-structuration of polymers from the one step strategy resulting from an uncommon multistep chain growth mechanism of trimers addition. The two-steps strategy produced copolymers showing a more blocky structure, as confirmed by their two distinct melting temperatures. (C) 2016 Elsevier Ltd. All rights reserved.