Effect of Flexible\nChains on Thermal Conductivity\nof Liquid Crystalline Epoxy Resins

Liquid crystalline epoxy resins (LCEs) have attracted\nscientific\nattention due to their excellent physical properties, including thermal\nconductivity. In this study, we report biphenyl epoxy resins (BPER<sub><i>n</i></sub>)a series of LCEsand their\nintermolecular interaction depending on the network structure. Biphenyl\nderivatives of the liquid crystalline monomers were synthesized by\nintroducing various lengths of alkyl chains and epoxy functional groups\nat both ends of side monomers and exhibited a mesomorphic orientation\nin the specific temperature range. The BPER<sub><i>n</i></sub> were prepared by hot compression molding, employing hexamethylene\ndiamine as a curing agent. The curing behavior was monitored by polarizing\noptical microscopy and differential scanning calorimetry. The formation\nof an LC orientation was observed during the polymerization process.\nThe thermal properties were optimized by using thermogravimetric analysis,\ndifferential scanning calorimetry, dynamic mechanical analysis, and\nthermal conductivity measurements. The microstructure was optimized\nby X-ray scattering analysis. The thermal conductivity of the BPER<sub><i>n</i></sub> increased with the flexible chain length,\nand BPER<sub>8</sub> with the longest alkyl chain reached 0.50 W/m·K.\nThe bulk specimens of BPER<sub><i>n</i></sub> exhibited\na faster temperature change than conventional commercial samples when\nobserved by an infrared thermal imaging camera. These results suggest\nimprovement in the thermal conductivity of the LCE suitable for application\nin electronic materials.