Specific volume, dielectric properties, and mechanical properties of cured epoxy resins in the glass‐transition region

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Abstract
A diglycidyl ether of bisphenol A was crosslinked with dodecenylsuccinic anhydride at various conditions. The dilatometric, dielectric, and dynamic mechanical measurements were carried out on the cured resins in the glass‐transition region. The effects of the ratio of anhydride to epoxy resin, of accelerator concentration, and of curing condition on the measured properties of the cured resins were studied. The reduction of accelerator concentration causes a marked decrease of the crosslinking density and in consequence has a great influence on the glass‐transition temperature and other properties of the cured resin system. The observed values of specific volume at the glass‐transition temperature increase with increasing ratio of anhydride to epoxy resin and also increase with increasing crosslinking density. These values can be predicted approximately as sums of the atomic volumes. The temperature dependence of the dielectric relaxation time for the α process can be represented by the universal WLF equation. The values of the WLF reference temperatureTsare 55–61°K. higher than the observed values of the glass‐transition temperatureTg.The temperatures of maximum loss tangent for Young's modulus are 3–10°K. higher than those of maximum dielectric loss tangent at the same frequency. The concentrations of the network chains effective in rubber elasticity are 20–40% of the theoretical concentrations predicted from the compositions.

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