Modeling the dielectric response of unsaturated polyester resin during cure

Abstract The dielectric relaxation of unsaturated polyester resin during cure was modeled using a modified Williams–Watts decay function. The dielectric response was studied using dielectric measurements coupled with two dynamic mechanical measurement methods. It was found that the variation of the relaxation time during cure is a WLF process using T g (α) (α‐conversion) as the varied temperature. It was shown that this process fits the Williams‐Watts decay function Φ( t )=exp(‐( t /τ) β ) where τ‐relaxation time and β‐empirical parameter are time dependent. It was found that τ obeys a time dependent power law rule and β depends linearly on log(time). Using this modified decay function, it was shown that the experimental dielectric response measured during cure agrees well with the computed response. Relaxation times above and below the dielectric measurement system capability were computed thus, demonstrating the capability of yielding the entire relaxation times spectrum during cure, out of a single limited frequency dielectric measurement.