Low-Temperature Excess Heat Capacity in Glassy Polymers

Measurements of the velocity of longitudinal and transverse sound waves in polymethyl methacrylate and polystyrene are presented from room temperature to about 140°K. Using these values and values deduced from low-temperature elastic modulus measurements, it is shown that the measured heat capacity of these polymers is considerably larger than is predicted by Debye theory. This is interpreted as evidence of a low-temperature heat capacity anomaly similar to that observed in several other disordered solids.