Epoxy resin with imine bonds and biphenyl liquid crystalline groups for intrinsic high thermal conductivity and recyclability

Epoxy resins face a dual challenge in advanced miniaturized and high-power devices: the need for efficient thermal management to ensure operational stability, alongside the inherent difficulty in recycling their covalently cross-linked networks at end-of-life. To address these issues, two epoxy monomers (H-LM and F-LM) containing imine bonds and biphenyl-based liquid crystalline mesogens were synthesized. X-ray diffraction analysis (XRD) showed crystallite sizes of 23.64 nm (H-LM) and 30.93 nm (F-LM), with relative crystallinities of 39 % and 41 %, respectively. Cured epoxy resins (H-LMD, F-LMD) exhibited intrinsic high thermal conductivity due to enhanced phonon transport via π-π conjugation between imine bonds and biphenyl units in the crosslinked network. H-LMD achieved in-plane ( λ ‖) and through-plane ( λ ⊥ ) thermal conductivities of 0.614 W/(m·K) and 0.299 W/(m·K), respectively, surpassing conventional epoxy resins ( λ ‖ = 0.23–0.38 W/(m·K)). Fluorination enhanced molecular rigidity and structural order in F-LMD, yielding higher λ ‖ (0 . 718 W/(m·K)) and λ ⊥ (0 . 42 W/(m·K)), along with a tensile strength of 99.67 MPa, fracture strain of 6.33 %, and hydrophobicity (water contact angle: 110.95 °). Dynamic imine bonds enabled efficient resin recycling via amine exchange, Fourier transform infrared spectroscopy (FTIR) confirmed. Interestingly, although the recycled resins (H-LMD-1 and F-LMD-1) exhibited a decrease in in-plane thermal conductivity by 36.7 % and 10.5 %, respectively, compared to their pristine counterparts, their tensile strength was significantly enhanced by 23.5 % and 8.4 %. This work provides an effective strategy to concurrently tackle the coupled challenges of low intrinsic thermal conductivity and poor recyclability in conventional thermosetting epoxy resins.