Effect of Aromatic/Aliphatic Structure and Cross-Linking Density on the Thermal Conductivity of Epoxy Resins

High thermal conductivity polymers are in great demand as thermal management materials. However, the thermal conductivity of polymers is typically low, ∼0.2 W/(m K), and a predictive understanding of the relationship between the thermal conductivity and the molecular structure of polymers is not yet established. In this work, 14 epoxy resin thermosets are synthesized from one aliphatic epoxide and one aromatic epoxide with seven amine hardeners. These thermosets are used to systematically examine the dependence of the thermal conductivity on the molecular structure of the epoxide and the hardener. In general, aromatic structures have a higher thermal conductivity than aliphatic structures. Moreover, naphthalene-based hardeners provide the highest thermal conductivity, 0.34 W/(m K), 230% higher than the lowest thermal conductivity among the 14 epoxy resin thermosets. The cross-linking density is controlled by mixing different molar ratios of diamine and triamine and does not influence the thermal conductivity, volumetric heat capacity, density, or longitudinal speed of sound. Measured thermal conductivities of 14 epoxy resins lie between 50 and 115% of the prediction of the minimum thermal conductivity model.