Enzymatic synthesis of biobased aliphatic-hetero-aromatic furanic copolyesters: Influence of furan dimethyl ester isomerism

Due to environmental concerns, there is a growing demand for more sustainable materials. As a result, the renewability of the raw materials and catalysts involved in production is important for rendering sustainable and circular polymers. Due to its environmentally friendly nature and high selectivity, enzymatic polymerization is a viable approach for producing such polymers. Recent developments in the field of biobased furan building blocks have led to renewed interest in 2,4-furandicarboxylic acid (2,4-FDCA) and 3,4-FDCA. Furthermore, far too little attention has been given to 2,5-bis(hydroxymethyl)furan (2,5-BHMF), another class of hetero-aromatic diol that can be derived from carbohydrates. These furan monomers are attractive due to their potential for producing novel biobased polyesters with interesting properties. To date, however, there has been little discussion about the use of these materials for polymerization via enzymatic approaches. Hence, a comparative study of CALB-catalyzed copolymerization involving two FDCA dimethyl ester isomers, either 2,4- or 3,4-DMFDCA, with 2,5-BHMF and various aliphatic diols has been carried out. This provides further insight into the regioselectivity promoted by CALB for asymmetrical 2,4-DMFDCA over symmetrical 3,4-DMFDCA. This is evidenced by the high degree of polymerization achieved with a weight-average molecular weight of up to 14 kg mol⁻¹. In agreement with previous findings, a preference for the formation of cyclic species from symmetrical monomers catalyzed by CALB was observed. Structural characterization and thermal and crystallinity analyses were used to assess the correlation between structure and material properties.