Enzymatic synthesis and characterization of muconic acid-based unsaturated polymer systems

Abstract

The design of unsaturated aliphatic (co)polyester systems, based on different diester-modified muconic acid isomers, was performed via an eco-friendly pathway by utilizing enzymatic polymerization using Candida antarctica lipase B (CALB) as catalyst. The obtained fully unsaturated oligoesters and polyesters reached lower molecular weights from 2210 to 2900 g mol−1 for the cis,cis-(Z,Z)-muconate isomer, and higher molecular weights of up to 21 200 g mol−1 for the polymers with cis,trans-(Z,E) isomeric structures. The obtained (co)polyesters were thoroughly characterized and compared with their saturated polyester analogues. The applied biobased catalyst Novozym®435 (an immobilized form of CALB) showed higher selectivity towards the open cis,trans-muconate compared to the more closed-structure cis,cis-muconate. Results of 1H NMR analysis showed that alkene functionality is present, and no stereo conformational changes were detected in the resulting polymers. The thermal properties of the muconate-based polyesters showed a glass transition between −7 and 12 °C, and a one-step degradation process with a maximum rate of weight loss between 415 and 431 °C, depending both on the conformation of the applied diester derivatives and on the segment lengths of the polyoxyalkylenes. Mass spectrometric analysis of the resulting saturated and unsaturated polyesters revealed five different microstructures with different terminal end groups, such as ester/hydroxyl, acid/ester, ester/ester and acid/hydroxyl, and cyclic polyesters without functional end groups. Overall, this study demonstrates that enzymatic polymerization is a robust approach for the synthesis of unsaturated polyesters. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.