Odd-even effect on the thermal conductivity of liquid crystalline epoxy resins

Rapid developments in high-performance computing and high-power electronics are driving needs for highly thermal conductive polymers and their composites for encapsulants and interface materials. However, polymers typically have low thermal conductivities of ∼0.2 W/(m K). We studied the thermal conductivity of a series of epoxy resins cured by one diamine hardener and seven diepoxide monomers with different precise ethylene linker lengths (x = 2-8). We found pronounced odd-even effects of the ethylene linker length on the liquid crystalline order, mass density, and thermal conductivity. Epoxy resins with even x have liquid crystalline structure with the highest density of 1.44 g/cm³ and highest thermal conductivity of 1.0 W/(m K). Epoxy resins with odd x are amorphous with the lowest density of 1.10 g/cm³ and lowest thermal conductivity of 0.17 W/(m K). These findings indicate that controlling precise linker length in dense networks is a powerful route to molecular design of thermally conductive polymers.