Dielectric beta relaxation behavior of ethylene terephthalate p-hydroxybenzoic acid copolymer

Dielectric beta relaxation processes were measured for a series of ethylene terephthalate/p-hydroxybenzoic acid (ET/PHB) copolymers with different PHB contents. The copolymers with the PHB content lower than 30% were in an isotropic amorphous glass phase, while those with higher PHB contents were in a liquid crystalline glass phase. The latter exhibited a larger dielectric strength than the former. This observation was not fully explained In terms of only the difference in the correlation length of the torsional vibration of the main chains. The orientation distribution of the main chains relative to the electric field direction was assumed to obtain a reasonable explanation. To confirm this assumption, the dielectric measurements were carried out on two film samples with different orientations: one with parallel orientation and the other with perpendicular orientation with respect to the film surface, both prepared by using a magnetic field. The results of the dielectric measurements for these two samples were in favor of the assumption.