Surface chain orientation during crystallization induction period of poly(pentamethylene 2,6-naphthalate) studied with polarized FTIR-ATR

Abstract

Thermoinduced surface orientation behaviors were studied in situ by Fourier transform infrared spectroscopic (FTIR) measurements along with attenuated total reflection (ATR) and transmission methods during the cold crystallization of melt-quenched amorphous poly(pentamethylene 2,6-naphthalate) (PPN) film. The chain in the crystalline phase formed during the cold crystallization process was found to orient parallel with the film surface with a naphthalene ring perpendicular to the film plane. By observing the isothermal crystallization process via polarizing optical microscopy and wide-angle X-ray diffraction methods, it was revealed that PPN shows very slow crystallization kinetics, even when crystallized at the temperature associated with the fastest crystallization rate. Furthermore, the crystallization induction period was longer than 150 min, during which time a significant amount of crystalline phase was not to be formed. The chain orientation at the surface during the crystallization induction period was again measured via polarized FTIR-ATR spectroscopy. It was found that the preferential surface orientation occurs during the early stage of the induction period, and no further orientation was observed during the subsequent crystallization process. Rapid local ordering that occurred during the crystallization induction period, especially at the surface, appears to be followed by gradual packing of the locally ordered chain to form the crystalline phase.