DIRECTIONAL ANISOTROPY OF DIELECTRIC BETA-RELAXATION IN ORIENTED POLY(ETHYLENE-TEREPHTHALATE)

The dielectric beta -relaxation in oriented poly(ethylene terephthalate) was investigated over wide ranges of frequency and temperature, with the electric field applied at inclinations of 0 degree , 45 degree , and 90 degree to the draw direction. Pronounced directional anisotropy is observed over the entire range of temperature and frequency. With the external field parallel to the draw direction the dielectric loss is considerably smaller than the value obtained with the field normal to the draw direction. The value obtained with the electric field at 45 degree to the draw direction is intermediate between the other two. On the other hand, the activation energy is largest for 0 degree inclination and smallest for 90 degree inclination. It is suggested that motions of the dipoles involve localized rocking of the molecular chain backbone, particularly when the external electric field is parallel to the chain direction.