Insights into Conformation, Crystal Structure, and Material Properties of Plant-Derived Poly(alkylene 2,5-furandicarboxylate)s as Sustainable Alternatives to Petroleum-Derived Analogues

Conformational characteristics and conformation-dependent properties of poly(ethylene 2,5-furandicarboxylate) (PEF), poly(trimethylene 2,5-furandicarboxylate) (PTF), and poly(butylene 2,5-furandicarboxylate) (PBF) have been revealed via NMR experiments and molecular orbital calculations on their model compounds, along with refined rotational isomeric state calculations for the polymers. The O(CH2)yO (y = 2, 3, and 4) segments of the polyesters exhibit conformational preferences similar to those found in the corresponding poly(alkylene terephthalate)s. The most stable conformations identified for PEF, PTF, and PBF are tg ± t, tg ± g ± t, and tg ± tg∓t, respectively. Their spatial configurations and conformational flexibilities significantly depend on conformations around the (furan)C–C(═O) bonds. Additionally, periodic density functional theory calculations were employed to optimize the α′ crystal structure of PEF, resulting in the equilibrium α form with a monoclinic lattice containing two all-trans chains. Young's moduli along the a, b, and c axes of the optimized α crystal were calculated to be 26.8, 12.5, and 141 GPa, respectively. These values are comparable to those of poly(ethylene terephthalate).