Physical aging of polystyrene investigated by dynamic viscoelasticity

Physical aging of polystyrene (PS) in the glassy state was investigated by dynamic viscoelasticity measurements. Two kinds of PS sample (Tg=110°C), almost equal in weight-average molecular weight but different in molecular weight distribution, were used. Physical aging was observed for the samples aged at 60 and 80°C after having been quenched from 190°C. The physical aging was not affected by molecular weight distribution. The temperature dispersion curves of the dynamic viscoelastic functions of the samples changed with aging time from the lower temperatures below Tg during aging at 60°C. In a high-temperature range, however, the curves of the aged samples agreed with that of the sample right after quenching. On the other hand, the curves of the samples aged at 80°C changed within the whole temperature range. The experimental results were discussed in terms of the segmental motion.