Temperature Dependence of Velocity and Attenuation of Ultrasonic Waves in High Polymers

Measurements of velocity and attenuation of ultrasonic waves are carried out for polystyrene, polymethyl methacrylate, phenol resin, polyethylene, nylon 6 and other commercial resins in the temperature from -60°C to 90°C and at frequencies of 100 kc, 1.46 Mc, 4.38 Mc and 7.30 Mc. A correlation between sound velocity in the megacycle range and density is pointed out for glassy polymers. In the case of linear polymers, the temperature coefficient of ultrasonic velocity, β, exhibits a relatively abrupt change in the glass trasition region at the temperature T m , which is independent of frequency of sound agrees with the transition point associated with thermal expansion. The ratio of β to volume expansion coefficient α is found to be constant below and above T m for each polymer. These facts indicate that the change in β at T m should be ascribed to the temperature dependence of intermolecular free volume. For some polymers a change in β and a peak of loss factor are observed at lower temperatures.