Poly(trimethylene 2,6-naphthalate) (PTN) is one of the 1,3-propanediol (PDO)-based aromatic polyesters which has potential applications for special barrier films and
packaging due to its excellent oxygen and carbon dioxide gas barrier property. In this work, we investigated the chain conformation and phase transition behavior of poly-
(trimethylene 2,6-naphthalene) (PTN) α-form crystal with synchrotron wide- and small-angle X-ray scattering (WAXS and SAXS), attenuated total reflection Fourier transform
infrared (ATR-FTIR) spectroscopy, and differential scanning calorimetry (DSC) methods. ATR-FTIR results showed that the infrared bands at 1327 and 987 cm?1 were sensitive to PTN α-form crystalline phase and were assigned to trans conformers of trimethylene group, whereas the infrared bands at 1357 and 1372 cm?1 were sensitive to PTN β-form crystalline phase and were assigned to gauche conformers of the trimethylene group. The
results showed that the conformation of trimethylene glycol residue in PTN α-form crystalline phase adopted G′TTG or GTTG′ conformation. The DSC, WAXS, SAXS, and ATR-FTIR results indicate that the PTN α-form crystal undergoes structure changes
at above 170 °C. We found that the PTN α-form crystal can transform to more stable crystalline phase (named as α′-form) by annealing. The crystal changes of PTN α-form crystal are associated with interchains rearrangement rather than with conformation changes of trimethylene glycol residue. The interchains rearrangement in PTN α-form crystalline phase may be caused by the internal force field change generated by the surface recrystallization process.
