The Impact of Diethyl Furan-2,5-dicarboxylate as an Aromatic Biobased Monomer toward Lipase-Catalyzed Synthesis of Semiaromatic Copolyesters

Furan-2,5-dicarboxylic acid has been introduced in recent years as a green aromatic monomer toward the design of aromatic (co)polyesters with enhanced properties, i.e., polyethylene furanoate (PEF) that can definitely compete with its petroleum-based counterpart, i.e., polyethylene terephthalate (PET). In an attempt to produce biobased semiaromatic copolyesters in an efficient eco-friendly approach, we report herein the polycondensation of diethyl furan-2,5-dicarboxylate (DEFDC) with different aliphatic diols and diesters of variable chain length catalyzed by an immobilized lipase from Candida antarctica using a two-step polymerization reaction carried out in diphenyl ether. The influence of diol and diester chain length, the molar concentration of DEFDC, and the effect of enzyme loading were assessed via nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and wide-angle X-ray scattering (WAXS). With high quantities of DEFDC, significant differences in terms of M̅n buildup were noticed. Only longer diols starting from octane-1,8-diol successfully reacted with up to 90% DEFDC as opposed to only 25% DEFDC reacting with short diols such as butane-1,4-diol. While varying the chain length of the diester, it was evident that shorter diols such as hexane-1,6-diol have better reactivity toward longer diesters, while dodecane-1,12-diol was reactive toward all tested diesters. The incorporation of long chain fatty dimer diols such as Pripol 2033 led to polyesters with higher M̅n and was successfully used to overcome the limitations of poor reactivity observed in the case of short diols in the presence of high furan content. The DSC results showed a pseudoeutectic behavior as a function of increasing the mol % of DEFDC, and a change in the crystalline phase was confirmed via WAXS analysis. Finally, this work showed the successful enzyme-catalyzed synthesis of several DEFDC biobased semiaromatic copolyesters with variable interesting properties that can be further optimized for possible applications in food packaging as well as other possibilities.