Ortho-, Meta-, versus Para-Substituted Mesogens Inducing Higher-Order Structures for Highly Thermal-Conductive Cured Epoxy Resins

Mesogenic monomers are beneficial, but few studies have investigated the effects of the molecular structure of liquid crystalline epoxy monomers on the higher-order structure and thermal conductivity of their cured resins to obtain highly thermally conductive and insulating epoxy resins. This study focused on the symmetry of the mesogenic part. Four different epoxy monomers were copolymerized with 1,4-phenylenediamine. Cured resins form a nematic-like network. Molecules array more orderly in epoxy resin with the most symmetric epoxy monomer. The thermal conductivities of epoxy resin prepared with ortho-, meta-, and para-substituted epoxy monomer were 0.26, 0.31, and 0.44 W m–1 K–1, respectively. Epoxy resin with the most symmetric epoxy monomer showed over 1.7 times as high as epoxy resin with low symmetric epoxy monomer. It is clarified that the symmetricity of the primary structure of epoxy monomer is an essential factor for the higher-order structure and thermal conductivity of cured epoxy resin.