DIELECTRIC-RELAXATION OF ISOTACTIC POLYSTYRENE ABOVE THE GLASS-TRANSITION TEMPERATURE

The alpha-relaxation was investigated by dielectric measurements in isotactic polystyrene crystallized isothermally for various crystallization times at crystallization temperatures from 423 to 483 K. The thickness of the amorphous layer in crystallized samples, determined by small-angle X-ray scattering, increases with increasing crystallization temperature. The relaxation time obeys the Williams-Landel-Ferry equation and increases with increasing crystallinity and with decreasing crystallization temperature. The decay function was calculated directly from the dielectric loss. The decay function shows a crossover from a stretched-exponential decay (the Williams-Watts equation) to a power-law decay (t(-n)) as the relaxation proceeds. The exponent n of the power-law decay increases with decreasing crystallinity and with increasing crystallization temperature.