Effect of annealing on the secondary relaxations in glasses

The dielectric loss in a rigid-molecular glass (toluene–pyridine) and in poly(propylene oxide) has been measured from 50 to 2×105 Hz during the course of isothermal annealing at several temperatures. The decrease in the loss on annealing is predominantly due to a decrease in the number of molecules participating in the secondary relaxation. Measurements of the loss at different temperatures, but a fixed frequency, indicate a similar effect of annealing. Explanations for the secondary or β relaxations in amorphous polymers in terms of the motion of the side group attached to the main chain seem inconsistent with the observed temperature dependence of the amplitude of secondary relaxation. Several implications for our concepts of small scale molecular motions in glasses arising from these results are considered. It is suggested that the discrepancy between the relaxation rates determined from the loss spectrum at a constant temperature and from the loss-temperature plots at a constant frequency arises from a rapid increase in the amplitude of secondary relaxation with temperature.