Molecular mobility in a thermoset as seen by TSR and DMA near T-g

The conformational mobility of a polyester thermoset in the glass transitio n region is studied by dynamic mechanical analysis (DMA) and thermally stim ulated recovery (TSR). All experiments were carried out in a commercial DMA apparatus, in the flexural mode. With this equipment thermally stimulated creep (TSCr) and thermal sampling (TS) experiments were also performed. Eac h TS curve was analysed according to a simple Voigt-Kelvin model where the retardation time follows the Arrhenius equation. Both the activation energy and the pre-exponential factor show the usual trends with temperature and present the well-known compensation phenomenon. The activation energy incre ases with temperature in the glassy state and even for lower temperatures t he isolated processes are found to be highly cooperative. Two master curves for the storage modulus and the storage compliance were successfully const ructed from the isothermal DMA experiments. The Vogel-Fulcher-Tamman-Hesse curve plot was directly obtained from the WLF parameters that were calculat ed without any non-linear fitting. The complementary character of the TSR a nd DMA techniques can be seen in an Arrhenius plot. The equivalent frequenc y of the TSR elementary processes increases with increasing temperature, wi th values around similar to 10(-2.8) Hz. Some results obtained by simulatio n were shown, allowing to conclude that this increase of frequency is a con sequence of the increase of the activation energy with temperature in a sys tem showing a compensation behaviour.