High-efficiency improvement of thermal conductivities for epoxy composites from synthesized liquid crystal epoxy followed by doping BN fillers

Liquid crystal epoxy resin presents high intrinsic thermal conductivity coefficient (lambda) . However, the complex molecular structure design and tedious synthesis process severely limit its rapid development and further industrial application. In this work, a kind of liquid crystal epoxy (LCE) based on biphenyl mesomorphic unit is synthesized from 4,4'-biphenol, triethylene glycol, and epichlorohydrin. Curing agent of 4,4'-diaminodiphenyl methane (DDM) and boron nitride (BN) fillers are both performed to prepare the intrinsic highly thermally conductive liquid crystal epoxy resin (LCER) and BN/LCER thermally conductive composites via casting method. LCE has been successfully synthesized with expected structure, presenting nematic liquid crystal with range of 135-165 degrees C. LCER shows liquid crystal property with intrinsic lambda up to 0.51 W/mK, about 3 times higher than that of general bisphenol lambda epoxy resin (E-51, 0.19 W/mK). Simultaneously, LCER has good thermal stability with heat resistance index (T-HR(I)) being 183.9 degrees C. In addition, the lambda values of the BN/LCER thermally conductive composites increase with the increasing loading of BN fillers. When the content of BN fillers is 30 wt%, the lambda value of BN/LCER thermally conductive composites is 1.02 W/mK, twice as much as that of pure LCER, also much higher than that of 30 wt% BN/E-51 composites (0.52 W/mK).