抄録
The variation of ultrasonic velocity with temperature in polymethyl methacrylate and polystyrene polymers was measured in the range of 0_??_90°C, using the total reflection method at frequencies of 1.46, 4.38 and 7.30 MC. An abrupt change in slope was found in the velocity vs. temperature curves of both polymers. This transition temperature is independent of the frequency and agrees with the second order transition temperature determined from the thermal expansion measurement. In case of polymethyl methacrylate, a slow change in slope was also found near 15°C in the velocity-temperature curve as well as in the thermal expan-sion curve.
For both polymers, the function ui/4.5/ρ (u: sound velocity, ρ: density) was found to be independent of temperature over the whole temperature range of the experiment. It is expected, therefore, that the ultrasonic velocity in high polymers is closely related to the intermolecular free volume, in the same manner as in liquids of low molecular weight. The free length between segments was determined from it and p, using Kincaid-Eyring theory with slight modification.
