ULTRASONIC EXAMINATION OF THE DYNAMIC GLASS-TRANSITION IN AMORPHOUS POLYMERS

Ultrasonic measurements were performed at 1 MHz for two amorphous polymers, polybutadiene (M(w) = 13000) and polyphenylmethylsiloxane (M(w) = 4100), in order to derive the temperature dependence of the longitudinal moduli components, M'(T) and M"(T). The results were analyzed in the framework of linear viscoelasticity using the Kohlrausch-Williams-Watts (KWW) relaxation function incorporating the Vogel-Fulcher-Tammann-Hesse equation which describes the temperature dependence of the main relaxation time. The only adjustable parameter was the KWW parameter beta. The possibility of a temperature-dependent beta-parameter to describe the data was also considered.