ISOTHERMAL AND ISOBARIC PVT-MEASUREMENTS OF ANIONIC POLYSTYRENES - RELAXATION ZONES WITHIN THE GLASS-TRANSITION RANGE

PVT-measurements of anionic polystyrenes on heating have shown that, d epending on the mode of operation, specific 'relaxation zones' within the glass transition range are observed. Isothermal PVT curves exhibit always 'relaxation zones' independent whether the pressure is increas ed or decreased during the scan. The shift of the relaxation zones to higher temperatures is, however, higher for isothermal scans with incr easing pressure. These 'relaxation zones' are explained by pressure-de pendent changes of the state of the polymeric sample isothermally scan ned within the glass transition range. At lower pressures the polymer is actually in the molten state, whereas at higher pressures it may be in the metastable glassy state and the actual state depends on the ra te of pressure change. In isobaric PVT curves 'relaxation zones' in he ating scans are exhibited only if the pressure applied during glass fo rmation differs from the pressure applied during the heating scan. The observed pressure-dependent shift of the glass temperatures to higher temperatures was higher for the studied polystyrenes of different mol ecular weight that had a higher glass temperature at normal pressure. But the specific molecular weight influence on the width of the 'relax ation zone' could not be ascertained. An attempt to calculate characte ristic volume relaxation times failed because of insufficient precisio n of the measurements.