Effect of Hardener Functional Groups on the Higher-Order Structures and Thermal Conductivity of Cured Epoxy Resins

As silicon-based power electronics reach their limits in miniaturization and efficiency, attention has shifted toward next-generation power devices. This transition is expected to increase heat density, requiring resins with enhanced thermal conductivity for efficient thermal management. Epoxy resins, which are widely used for their excellent adhesive properties, play a vital role in this context. However, the relationship between molecular structure and thermal diffusivity is still not well understood. In this study, we investigated how the substituents of curing agents influence the higher-order structure and thermal diffusivity of cured epoxy resins. A curing agent containing both amine and phenolic hydroxyl groups (4-(4-aminophenoxy)phenol (APP)) was synthesized and reacted with a liquid-crystalline epoxy monomer, [1,1′-biphenyl]-4,4′-diyl bis(4-(4-(oxiran-2-yl)butoxy)benzoate). Curing analysis revealed a sequential mechanism: the primary amine reacted first, followed by the phenolic hydroxyl group and the secondary amine. X-ray analysis showed that both cured resins with 4,4′-oxydianiline (ODA) and APP formed a smectic-like network. The thermal diffusivities of cured resins cured at 160 °C with APP and ODA were 3.09 and 2.55 ×10^-7 m² s^-1, respectively. The coexistence of different functional groups promoted prepolymer formation and enhanced molecular alignment, leading to more efficient heat transport in the cured resin.