Segmental and chain dynamics in polymers

All polymers exhibit a breakdown of time-temperature superpositioning in the softening zone, where both local and global chain modes contribute to the measured dynamic response. This differing behavior of the two modes is also seen in the volume and pressure dependences of the respective relaxation times. Nevertheless, the superposition of local segmental and global chain modes can be achieved by expressing the relaxation times as a function of the product of temperature, T, times specific volume, V, with the latter raised to a constant gamma. Moreover, the value of gamma is the same for the two modes. These experimental facts reveal that the relative contribution of temperature and volume is the same for the two modes, although their response to either variable differs; that is, while having the same functional form, the combined effect of T and V on the respective modes is different.