Unlocking intrinsic thermal conductivity in BioBased liquid crystal epoxy and enabling alkali-developable photocurable dielectric coatings from epoxidized daidzein

The development of biobased renewable resources is expected to alleviate the threat to the ecological environment and the obstacles to sustainable development caused by relying on fossil fuels. Here, based on biobased daidzein (DD) with rigid benzene rings and two hydroxyl groups was firstly prepared into epoxy compound (DDDE) by reacting with epichlorohydrin. Daidzein is a liquid crystal mesogen, by curing with 1,5-naphthalene diamine (NDA) in the liquid crystal state, the locally ordered structure can be preserved, thereby exhibiting intrinsic thermal conductivity characteristics. The curing system DDDE/NDA 105 (105 means cured at 105 °C) under liquid crystal phase obtained better thermal conductivity (λ = 0.34 W/(m·K)), storage modulus (G’ = 2548 MPa), and glass transition temperature (T g  = 230 °C) than E51/NDA. On the other hand, photocurable alkali developer resin (DDAT) was synthesized by DDDE with acrylic acid (AA) and tetrahydro phthalic anhydride (THPA), and subsequently, a series of DDAT/DDDE/filler composite inks were prepared. Finally, the C8:2 ink stands out on PCB with the comprehensive performance of tensile strength (53.67 ± 1.41 MPa), elongation of fracture (4.11 ± 0.23 %), G’ (3761 MPa), T g (227 °C), and dielectric constant (3.54 at 100 Hz). The present work broadens the application of bio-based daidzein in high-performance inherently thermally conductive epoxy resins and alkaline developing photocuring inks.