Influence of Schiff Base Structure on Thermal Conductivity and Electrical Properties of Epoxy Composites

Abstract To meet the growing demand for epoxy resin matrix performance in the electronics industry, this study systematically explores the effects of main-chain/side-chain molecular design and liquid crystal structure regulation on the thermal conductivity and dielectric properties of epoxy composites. Three liquid crystal epoxy (LCE) monomers were synthesized: LCE1 (main chain with biphenyl structure (−C6H4–C6H4–)), LCE2 (main chain with Schiff base structure (–C═N–)), and LCE3 (side chain with Schiff base structure). GaussView simulations calculated the total dipole moment and surface electrostatic potential to analyze the influence of different liquid crystal structures on composite properties from the molecular polarity perspective. At 30 wt % liquid crystal epoxy content, the thermal conductivities of LCE1/E-51, LCE2/E-51, and LCE3/E-51 composites were 0.397, 0.403, and 0.434 W/(m·K), respectively. The thermal conductivity of the LCE3/E-51 composite was approximately 2.3 times that of pure E-51 (0.188 W/(m·K)). At 1 MHz and room temperature, the dielectric constants decreased from 3.27 (pure E-51) to 2.84, 2.58, 2.34, and dielectric loss tangents (tanδ) from 0.056 to 0.053, 0.042, 0.031. Side-chain LCE performance depends on flexible main-chain/rigid side-chain interaction; Schiff base (with liquid crystal characteristics) reduces dipole moment, polarity, and π–electron delocalization, collectively enabling high thermal conductivity and low dielectric properties. This work provides a novel molecular design strategy for high-performance epoxy composites for electronic packaging.