Entropically driven enzymatic ring-opening polymerization of biobased poly(alkylene furanoate)s and ω-pentadecalactone-based copolyesters

Enzymatic synthesis of cyclic oligomers constitutes an attractive and sustainable route toward the preparation of high-molecular-weight polyesters through entropically driven ring-opening polymerization. In this work, Candida antarctica lipase B (CALB) was employed to efficiently synthesize cyclic alkylene furanoate oligomers from renewable 1,4-butanediol, 1,5-pentanediol, 1,10-decanediol and dimethyl 2,5-furandicarboxylate under high dilution solution and mild reaction conditions. The cyclization process proceeded with remarkably high yields, affording the corresponding cyclic oligomers (from dimer to hexamer) within only 48 h. Their chemical structure, molecular composition and purity were comprehensively characterized by 1H NMR spectroscopy, HPLC and MALDI-TOF mass spectrometry, while their thermal behaviour was investigated by DSC and TGA. The isolated cyclic oligomers were subsequently subjected to entropically driven enzymatic ring-opening polymerization, both in solution and in the melt, yielding high-molecular-weight semicrystalline poly(alkylene furanoate)s with excellent thermal stability. Furthermore, the cyclic furanoate oligomers were successfully copolymerized enzymatically with ω-pentadecalactone, producing random aromatic-aliphatic copolyesters over the entire composition range. All copolyesters exhibited semicrystalline behaviour together with high thermal stability, demonstrating the versatility of the enzymatically synthesized cyclic furanoate oligomers as efficient building blocks for the sustainable production of fully biobased high-performance polyesters and copolyesters.