Dynamic properties of polyvinylmethylether near the glass transition

Dielectric spectroscopy, encompassing 13 decades of frequency, was used to investigate local segmental relaxation in polyvinylmethylether (PVME). Measurements were obtained over a 110 degree range of temperatures, at pressures up to 725 MPa. At atmospheric pressure, time-temperature superpositioning is valid; however, application of pressure changes the shape of the dielectric spectrum. Similarly, the relaxation times and dc-conductivity have the same temperature dependence at ambient pressure, while a breakdown of the Debye-Stokes-Einstein relation is observed at elevated pressures. The pressure dependence of the relaxation times is weak, corresponding to an activation volume about equal in magnitude to the molar volume of the PVME repeat unit. The pressure coefficient of the glass transition temperature (T-g=247.5 K at ambient pressure) is small, 177 K/GPa. From the ratio of the isochronic and isobaric expansivities, =2.2, thermal energy is found to have a stronger effect on the relaxation times than does the volume, although the contribution from the latter is significant. A comparison was made of the relaxation properties of PVME to those of the structurally similar polyvinylacetate. Distinct, qualitative differences are noted at both ambient and elevated pressure. (C) 2003 American Institute of Physics.