Enzymatic synthesis of 2,5-furandicarboxylic acid-based semi-aromatic polyamides: enzymatic polymerization kinetics, effect of diamine chain length and thermal properties

Abstract

2,5-Furandicarboxylic acid (FDCA)-based semi-aromatic polyamides are novel biobased alternatives to petrol-based semi-aromatic polyamides (polyphthalamides), that have a broad commercial interest as engineering thermoplastics and high performance materials. In this study, a series of FDCA-based semi-aromatic polyamides is successfully produced via Novozym®435 (N435, an immobilized form of Candida antarctica lipase b (CALB))-catalyzed polycondensation of (potentially) biobased dimethyl 2,5-furandicarboxylate and aliphatic diamines differing in chain length (C4–C12), using a one-stage method at 90 °C in toluene. The obtained polyamides reach high weight-average molecular weights ranging from 15 800 to 48 300 g mol⁻¹; and N435 shows the highest selectivity towards 1,8-octanediame (C8). MALDI-ToF MS analysis indicates that no byproducts are formed during the enzymatic polymerization. Study of the kinetics of the enzymatic polymerization suggests that phase separation of FDCA-based oligoamides/polyamides takes place in the early stage of polymerization, and the isolated products undergo an enzyme-catalyzed solid-state polymerization. However, the isolation yields of the purified products from the enzymatic polymerizations are less than ∼50% due to the production of a large amount of low molecular weight products that are washed away during the purification steps. Furthermore, the thermal properties of the enzymatic FDCA-based semi-aromatic polyamides are carefully investigated, and compared to those of the FDCA-based and petrol-based counterparts produced via conventional synthesis techniques as reported in literature.