Terahertz vibrational spectroscopy of poly(3-hydroxybutyrate) and nylon: Potential of terahertz spectroscopy for polymer science

Terahertz absorption spectra of poly(3-hydroxybutylate) (PHB) and nylon were measured by a terahertz time domain spectrometer and a Fourier transform far-infrared spectrometer. Clear differences were observed between the spectra of crystalline and amorphous PHB, indicating that the absorption peaks observed in the THz spectra originated in the higher-order conformation of PHB. Direction of the vibrational transition moments was obtained by the polarization spectra of stretched sample in which the crystal axis were aligned. On the basis of these results, the structural change in PHB is studied. The isothermal crystallization of PHB is monitored with the help of THz absorption spectra. The observed spectra clearly show the crystal growth, and the crystallization rate is estimated by Avrami´s model. The higher order conformations of the nylon were determined by the X-ray diffraction measurement. Different spectral features among the samples were interpreted as the characteristics of higher order conformations of nylons.