Pressure-temperature study of dielectric relaxation of a polyurethane elastomer

The effect of hydrostatic pressure up to 1,361 atms on the dielectric prope rties of a segmented polyurethane elastomer (Dow 2103-80AE) is studied at t emperatures from 0 degrees C to 80 degrees C. The experimental results show that the relaxation time for both the I-process, associated with the molec ular motions in the hard segments, and the alpha-process, associated with t he glass transition, increases with pressure, and this shift is more pronou nced for the I-process. Besides the glass transition, it is found that the I-process can be described by the Vogel-Fulcher (V-F) and Williams-Landel-F erry (WLF) relations. At atmospheric pressure, T-g and T-0 for the I-proces s are 235.9 K and 4.2 x 10(3) K, respectively. Based on the V-F and WLF rel ations and experimental results, it is found that a parameter, C-1, in the WLF relation is independent of the pressure. Thus, a method is introduced t o determine the values of both the characteristic transition temperature (T -g) and activation energy (T-0) for the processes at different pressures. A s the pressure increases from atmospheric to 1,361 atms, the increase of T- g for the I-process is about 30 degrees C. The results also show that, for both the I- and the alpha-processes, To decreases with increasing pressure. (C) 1999 John Wiley & Sons, Inc.