Thermally Conductive Naphthalene Epoxy Resin by Tailoring Flexible Chain Length and Liquid Crystal Structure

Epoxy resins with high thermal conductivity (λ) are widely used in electronic packaging, bonding, and coating. However, those with high intrinsic λ, typically synthesized using biphenyl or aromatic rings extended by ester linkages as the mesogenic unit, often exhibit high liquid crystal transition temperatures and poor processability. In this study, a series of naphthalene-based liquid crystal epoxy monomers (LCEs) were synthesized, using naphthalene as the mesogenic unit and modifying the flexible chain length on both sides. The resulting LCEs were cured within its liquid crystal phase to form naphthalene liquid crystal epoxy resin (LCER). The results show that the network order, radius of gyration, and low-frequency vibrational density of states all initially increase and then decrease with increasing flexible chain length. For LCER₂, with a three-carbon flexible chain, these parameters reach their maximum values, facilitating phonon diffusion and enhancing λ. The liquid crystal transition temperature, λ, heat resistance index, and storage modulus of LCER₂ were 67–78 °C, 0.40 W m⁻¹ K⁻¹, 158.8 °C, and 2059 MPa, respectively, approximately 2.2 times higher than that of E-51 resin (0.18 W m⁻¹ K⁻¹). This work offers insights into designing epoxy resins with low liquid crystal transition temperature, high intrinsic λ, and excellent mechanical properties for thermal management.