Biobased Poly(ethylene-co-hexamethylene 2,5-furandicarboxylate) (PEHF) Copolyesters with Superior Tensile Properties

Poly(ethylene-co-hexamethylene 2,5-furandicarboxylate) (PEHF) copolyesters with high intrinsic viscosity were synthesized from 2,5-furandicarboxylic acid (FDCA), ethylene glycol (EG), and 1.6-hexanediol (HDO) through two-step melting polycondensation, characterized with 1H NMR, DSC, WAXD, and TGA, and assessed by tensile and impact tests. The molar fraction of HF unit in PEHF (ϕHF), namely, copolymer composition, is higher than the molar fraction of HDO in the feeding diols and can be predicted empirically via Mayer–Lewis equation with apparent reactivity ratio rHDO = 4.6 and rEG = 0.74. All the PEHFs exhibited a single glass transition temperature and excellent thermal stability. HF-rich (ϕHF ≥ 88 mol %) PEHFs are semicrystalline but the others are almost amorphous. In comparison with PEF, PEHFs with ϕHF of 28–36 mol % possess significantly improved tensile ductility (elongation at break 54–160%) and retain high tensile modulus (2.6–2.2 GPa) and yielding strength (71–65 MPa). The tensile properties are comparable to those of bottle-grade PET.