Effect of Molecular Chain Structure on the Thermal Conductivity of Liquid Crystal Epoxy Composites

With technological advances, electronic devices are trending towards higher power, miniaturization, and increased density, making the thermal conductivity of electronic packaging materials particularly critical. In this study, biphenyl-type and biphenyl-aromatic-ester-type liquid crystal epoxy resins (LCERs) were synthesized, and the thermal conductivities of their composites were investigated. A biphenyl-type LCER monomer (DGEBP) was synthesized using 4,4' -dihydroxybiphenyl and epichlorohydrin A biphenyl-aromatic-ester-type LCER monomer (LCER) was prepared by reacting 4,4' -dihydroxy-biphenyl with 3,5-dihydroxybenzoic acid. Composites were then fabricated by curing these liquid crystal epoxy monomers with methylhexahydrophthalic anhydride (MHHPA) as the curing agent and 2,4,6tris(dimethylaminomethyl)phenol (DMP-30) as the accelerator. The molecular structure, liquid crystalline properties, and thermal conductivity of the composites based on both LCER monomers were analyzed. The test results indicated that the thermal conductivity of the composites gradually increased with increasing liquid crystal content. When the liquid crystal content reached 20 wt%, the peak thermal conductivity of DGEBP/E-51 and LCER/E51 was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.361 \mathrm{W} /(\mathrm{m} \cdot \mathrm{K})$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.379 \mathrm{W} /(\mathrm{m} \cdot \mathrm{K})$</tex>, which was 124 % and 135% higher than the base value, respectively. The LCER monomer with a biphenyl ester main chain structure enhanced the thermal conductivity of the composites more effectively.