A furan-based synthetic biopolymer composed of a bifuran monomer and ethylene glycol was synthesized through melt polycondensation, and the resulting polyester was found to have promising thermal and mechanical properties. The bifuran monomer, dimethyl 2,2′-bifuran-5,5′-dicarboxylate, was prepared using a palladium-catalyzed, phosphine ligand-free direct coupling protocol. A titanium-catalyzed polycondensation procedure was found effective at polymerizing the bifuran monomer with ethylene glycol. The prepared bifuran polyester exhibited several intriguing properties including high tensile modulus. In addition, the bifuran monomer furnished the polyester with a relatively high glass transition temperature. Films prepared from the new polyester also had excellent oxygen and water barrier properties, which were found to be superior to those of poly(ethylene terephthalate). Moreover, the novel polyester also has good ultraviolet radiation blocking properties.

Two homopolyesters and a series of novel random copolyesters were synthesized from two bio-based diacid esters, dimethyl 2,5-furandicarboxylate, a well-known renewable monomer, and dimethyl 2,2′-bifuran-5,5′-dicarboxylate, a more uncommon diacid based on biochemical furfural. Compared to homopolyesters poly­(butylene furanoate) (PBF) and poly­(butylene bifuranoate) (PBBf), their random copolyesters differed dramatically in that their melting temperatures were either lowered significantly or they showed no crystallinity at all. However, the thermal stabilities of the homopolyesters and the copolyesters were comparable. Based on tensile tests from amorphous film specimens, it was concluded that the elastic moduli, tensile strengths, and elongation at break values for all copolyesters were similar as well, irrespective of the furan:bifuran molar ratio. Tensile moduli of approximately 2 GPa and tensile strengths up to 66 MPa were observed for amorphous film specimens prepared from the copolyesters. However, copolymerizing bifuran units into PBF allowed the glass transition temperature to be increased by increasing the amount of bifuran units. Besides enhancing the glass transition temperatures, the bifuran units also conferred the copolyesters with significant UV absorbance. This combined with the highly amorphous nature of the copolyesters allowed them to be melt-pressed into highly transparent films with very low ultraviolet light transmission. It was also found that furan–bifuran copolyesters could be as effective, or better, oxygen barrier materials as neat PBF or PBBf, which themselves were found superior to common barrier polyesters such as PET.

With the goal of achieving high barrier with bio-based materials, for example, for packaging applications, a series of novel furfural-based polyesters bearing sulfide-bridged difuran dicarboxylic acid units with high oxygen barrier properties were synthesized and characterized. For the novel poly(alkylene sulfanediyldifuranoate)s, a 11.2–1.9× higher barrier improvement factor compared to amorphous poly(ethylene terephthalate) was observed which places the novel polyesters in the top class among previously reported 2,5-furandicarboxylic acid (FDCA) and 2,2′-bifuran-based polyesters. Titanium-catalyzed polycondensation reactions between the novel synthesized monomer, dimethyl 5,5′-sulfanediyldi(furan-2-carboxylate), and four different diols, ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, afforded difuran polyesters with high intrinsic viscosities (0.76–0.90 dL/g). These polyesters had good thermal stability, decomposing at 342–363 and 328–570 °C under nitrogen and air, respectively, which allowed processing them into free-standing films via melt-pressing. In tensile testing of the film specimens, tensile moduli in the range of 0.4–2.6 GPa were recorded, with higher values observed for the polyesters with shorter diol units. Interestingly, besides the low oxygen permeability, the renewable sulfide-bridged furan monomer also endowed the polyesters with slight UV shielding effect, with cutoff wavelengths of ca. 350 nm, in contrast to FDCA-based polyesters, which lack significant UV light absorption at over 300 nm.

Bifuran-5,5′-dicarboxylic acid (BFDCA), a highly promising biobased diacid monomer, was used to modify poly(ethylene terephthalate) (PET) to obtain copolyesters with increased biocarbon content and improved properties compared with PET. Antimony-catalyzed copolymerization of the bifuran and terephthalate 2-hydroxyethyl esters was used to afford the PETBF copolymers. When compared against PET, these random copolymers with 5, 10, or 15 mol % of the bifuran comonomer in the feed (relative to the total amount of the starting esters) showed a slightly elevated glass transition range, higher tensile moduli, enhanced oxygen gas barrier properties, and superior UV blocking while maintaining good transparency otherwise. Based on our results, PETBF copolyesters seem to have promise as materials with enhanced properties that are desirable in advanced packaging applications.

Two renewable dicarboxylic acids, furan-2,5-dicarboxylic acid and 2,2′-bifuran-5,5′-dicarboxylic acid, were applied as bisphenol A substitutes to prepare partially bio-based dimethacrylate resins. The furan-based dimethacrylates were synthesized using their diglycidyl esters as intermediates, which were then reacted with methacrylic acid. This reaction was found to give isomeric mixtures, where the formed methacrylate end group had three different configurations as elucidated using one-dimensional (1D) and two-dimensional (2D) NMR. The ratio between the different end groups could be controlled to an extent by using 1,1,1,3,3,3-hexafluoroisopropanol as the sole reagent to facilitate a reaction between the furan diglycidyl esters and methacrylic acid. The control over the configuration of the methacrylate end group is demonstrated to be a possible tool to influence the properties of the resultant dimethacrylate monomer and the cured resin. The bifuran dimethacrylates were found to have viscosities of ca. 110–120 Pa·s at 25 °C, while the furan dimethacrylate had a viscosity of about 40 Pa·s at 25 °C. It is demonstrated that by diluting the furan-based dimethacrylates with 40 wt % of methacrylated eugenol, a bio-based reactive diluent, the liquid resins could be cured into thermosets with glass-transition temperatures of 177–209 °C and 5% mass loss temperatures of 359–375 °C under a nitrogen atmosphere.