Effect of Amine Hardener Molecular Structure on the Thermal Conductivity of Epoxy Resins

Epoxy resins with enhanced thermal conductivity are in great demand to improve the thermal management of electrical motors. However, the thermal conductivity of epoxy resin is typically low, comparable to 0.2 W/(m K), and a predictive understanding of the connection between molecular structure and thermal conductivity is not yet established. In this work, we present data for the thermal conductivity of seven thermosets synthesized from one commercially available diepoxide (resorcinol diglycidyl ether) and seven phenylenediamines to systematically examine the dependence of thermal conductivity on the molecular structure of the phenylenediamine hardener. Variations in the molecular structure of phenylenediamines, for example, positions of amine groups and the addition of an electron-withdrawing group, produce up to a factor of 2 change in the thermal conductivity of the cured resins. The highest thermal conductivity of 0.27 W/(m K) is obtained with 5-chloro-m-phenylenediamine; the lowest thermal conductivity of 0.14 W/(m K) is obtained with o-phenylenediamine. Thermal conductivities of these seven epoxy resins are 10-40% lower than the prediction of the minimum thermal conductivity model.