SYNOPSIS
Dielectric properties have been investigated for a bisphenol-A type epoxide oligomer, whose weight average molecular weight (&,) was 9454. The dielectric a-relaxation of the oligomer was found to be governed by the Havriliak-Negami equation as well as the same series of oligomers with smaller M,,,s (388 5 M w 5 3903). The dielectric relaxation times ( T S ) for the oligomers with different Mws (1396 5 Mw 5 9454) can be expressed by the Williams-Landel-Ferry ( W L F ) equation as a function of the glass transition temperature ( T,) a t fixed temperatures from 70 to 100Β°C. The finding indicates that the T, of the epoxide oligomer is calculated from the 7 through the WLF equation, providing the relation between T, and 7. The same type of WLF equation was also successfully applied to describe the T, dependence of the practical dielectric relaxation time ( T ~) , which was obtained from the peak of the dielectric loss vs. frequency curve. The T~ can be calculated more easily than the T , based on the Havriliak-Negami equation, not only in the measurement of epoxide oligomer, but also in that of the reactive epoxy resin systems during curing. The Tg of an epoxy-aromatic amine system, which was determined from the T~ nondestructively detected in the dielectric cure monitoring, was consistent with the Tg experimentally measured by differential scanning calorimetry (DSC) .
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