Regulating the intrinsic thermal conductivity of daidzein-based liquid crystalline epoxy resins via spacer length

The continuous advancement toward high integration of electronic devices has placed stringent, synergistic requirements on the intrinsic thermal conductivity and low-dielectric performance of packaging materials. Conventional epoxy resins exhibit extremely low intrinsic thermal conductivity, failing to meet the application demands of high-power devices. In this work, using bio-based daidzein as the rigid mesogenic, four liquid crystalline epoxy monomers with dual mesogenic units and tunable flexible alkyl spacer lengths are designed and synthesized. The monomers were cured with 4,4′-diaminodiphenyl sulfone (DDS) and the fluorinated diamine 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (BP6FA), respectively, to systematically investigate the regulation mechanism of spacer length on the aggregated structure and properties of the materials. The results demonstrate that extending the flexible spacers significantly promotes the ordered self-assembly of mesogenic units. The stable smectic liquid crystalline structure locked in the crosslinked network after curing enables simultaneous enhancement of intrinsic thermal conductivity and optimization of dielectric properties. The optimal D10E/BP6FA system exhibits an intrinsic thermal conductivity of 0.42 W/(m·K), a low dielectric constant of 2.90 and an ultralow dielectric loss of only 0.0087 at 100 Hz, along with excellent thermal stability and thermomechanical properties. This work sheds light on the rational design of high intrinsic thermal conductivity liquid crystalline epoxy resins, and is expected to advance the high-performance application of such materials in electronic packaging.