Biobased Imine-Containing Liquid Crystalline Epoxy Resins with Versatile Recyclability and Enhanced Intrinsic Thermal Conductivity

In modern society, there is widespread interest in the development of sustainable and functional polymer materials. Herein, three imine-containing diphenol hardeners with different numbers of conjugated benzene rings and one trifunctional phenol-amine hardener were successfully synthesized using vanillin, a biobased feedstock derived from lignin. The curing kinetics of epoxy systems based on these hardeners was studied using Kissinger and Ozawa methods. The obtained liquid crystalline epoxy resins cured by these hardeners show high glass transition temperatures (136–144 °C), mechanical strengths (76.2–119.3 MPa), and intrinsic thermal conductivities (0.26–0.32 W m –1 K –1 ). The X-ray diffraction results indicate that the structural order of the cured epoxy resins increases with the number of benzene rings in the hardeners. In addition, the incorporation of aromatic imine bonds endows the cured epoxy resins with dynamic structures and recyclability. These epoxy resins can be reprocessed through hot pressing and are degradable in acid or amine solutions. Notably, the degradation products in the acid solution can be used to prepare the epoxy resins. Compared with their pristine counterparts, the reprocessed and chemically recycled epoxy resins demonstrate high retention of glass transition temperature, tensile strength, and thermal conductivity. Overall, the findings in this work offer a simple and effective approach to develop recyclable liquid crystalline epoxy resins with high thermal conductivity from biobased hydroxybenzaldehydes.