High thermal conductivity biphenyl-type polyester with photochromism, thermo-responsive, and shape memory performance

Stimuli-responsive materials are widely applied in anti-counterfeiting, actuators, and thermal management fields. Two high thermal conductivity polyesters (HPE1 and HPE2) were synthesized via melt polycondensation by reacting biphenyl dicarboxylic acid and bipyridine dicarboxylic acid as raw materials with biphenyl diol. HPE2 changes color from brown to yellow under UV light irradiation. When exposed to visible light, the polymer can return to its original color. UV-visible and fluorescence spectra confirm the charge transfer (CT) interactions between molecular chains. Density functional theory (DFT) calculations further indicate that the photochromic in HPE2 originates from electron transfer from the electron-rich biphenyl group (donor) to the electron-deficient bipyridine (acceptor). The alternating arrangement of donor and acceptor units on the main chain enhances the ordered microstructure of the polymer network through π-π stacking interactions. The in-plane (λ//) thermal conductivity of HPE2 film reaches 0.67 W/(m·K), which is 3.4 times that of polyethylene terephthalate (PET). Meanwhile, HPE2 exhibits reversible thermal response, which can switch between high thermal conductivity state (λ⊥ = 0.27 W/(m·K)) and low thermal conductivity state (λ⊥ = 0.17 W/(m·K)). Furthermore, HPE2 exhibits excellent shape memory properties, with 99% shape fixed ratio and 86% shape recovery ratio.