Dielectric and thermal analysis of radiation curing of insaturated polyester resins

Abstract

Radiation curing of unsaturated polyester resins were studied by combining dielectric and thermal analysis. Dielectric permitivities were measured by stepwise changing of frequency during the course of 60Co y-irradiation at constant temperature or by simultaneous change of frequency and temperature after irradiation. A continuous shift of the glass-transition of the resin and a change of the dielectric relaxation time distribution was observed as radiation crosslinking reaction proceeded. The shape of the dielectric spectrum bands indicated a heterogeneous nature of the transition which increased with increasing degree of curing. The long reaction time limiting values of the permittivity were found to be considerably higher than the unrelaxed limit showing the existence of a limiting conversion effect.