Radiation crosslinking effect on thermally stimulated current spectra of unsaturated polyester resins

The thermally stimulated depolarization(TSD) currents of unsaturated polyester(UP) resin thermoelectrets have been measured in the low temperature range. The study of the decrease of the current intensity as a function of the absorbed dose reveals important differences between the peaks of the spectrum; the low temperature peaks can be attributed to dipolar volume polarization, and £he high temperature peaks to an ionic space charge polarization. The shift of the peaks may be indicative of plasticization of the polyester by styrene, and of restriction upon motions of the chain imposed by the crosslinks. The l-peak could be manifestation of the liquid-liquid(Tll) transition, from the Tll/Tg ratio, and here it corresponds to the thermally activated disintegration of phase separated structures, which were well documented in the inherently heterogeneous UP resins.