Synthesis and crystallinity of poly(butylene 2,5-furandicarboxylate)

Poly(butylene 2,5-furandicarboxylate) (PBF) was obtained by esterification of 2,5-furandicarboxylic acid (FDCA) and 1,4-butylene glycol (BG). By using ¹H NMR at 750 MHz to recognize the trace end groups at different polymerization stages, the study provides a clear picture that the polymerization proceeds cleanly to give the desirable linear structure. On the basis of the end group analysis, the degree of polymerization of PBF was determined to be as high as 125, which is in agreement with the molecular weight from the viscosity study. Solid state ¹³C NMR revealed that one of the furan carbons is sensitive to local morphology. DSC and X-ray diffraction further revealed that the polymer had high tendency to form crystalline materials (T_m = 130 °C & 169 °C; T_g = 32 °C). On the basis of DSC and NMR evidences, the two crystalline states are assumed to be β-phase (less stable) and α-phase (more stable), respectively, by analogy with the crystalline structure of PBT. High tendency of forming crystalline structure allows the continuous fibers to be drawn from the PBF's melt. The results thus raise the hope that the biomass-derived PBF could be a promising furan counterpart of the petroleum-based poly(butylene terephthalate) (PBT).