Glass transition in polymers

Glass transition phenomena in several polymers were studied by dielectric and dilatometric measurements. The dielectric measurements were made over the frequency range of 10−4 or 10−1 to 106 cycles/sec. and the temperature range of the glass transition. In the dilatometric study, volume relaxation curves and volume vs. temperature curve were obtained. The transition in three amorphous polymers, (polyvinyl acetate, polystyrene, and polymethyl methacrylate), depends upon frequency or rate of cooling and seems to be an apparent transition. In three crystallizable polymers, (vinylidene chloride-vinyl chloride copolymer, polyethylene terephthalate, and polyacrylonitrile), the magnitude of the dielectric absorption decreases steeply with decreasing temperature in the transition range, and the transition by the volume expansion remains when equilibrium is attained. The transition in the three crystallizable polymers seems to be a real one. Temperature dependences of the activation energies of the dielectric relaxation processes have been described.