Recyclable Side-Chain Azobenzene-Based Semicrystalline Polymer Films with Outstanding Intrinsic Thermal Conductivity and Photoresponsive Actuation.

Conventional polymers exhibit low intrinsic thermal conductivity (λ) of 0.1∼0.5 W/(m·K) due to disordered chain arrangements, failing to meet the heat dissipation demands of high-power flexible electronic devices. This study proposes a molecular level design strategy for side-chain azobenzene-containing semicrystalline polymers that demonstrate exceptional intrinsic thermal conductivity with photoresponsive actuation and recyclability. By precisely regulating the spatial distribution and content of azobenzene groups and hydrogen-bond network along the polymer chain through controlled radical polymerization, a thermal conduction network featuring "high-efficiency conduction within crystal domains and low-resistance interfacial connections" was constructed. Azobenzene moieties self-assemble into highly oriented crystalline domains through π-π stacking, where their dense packing significantly enhances phonon coupling efficiency and increases phonon mean free paths. Concurrently, the dynamic reversibility of hydrogen bonds guides domain-boundary molecular chains to form gradual phase transitions, suppressing phonon scattering at amorphous-crystalline interfaces and improving phonon transport efficiency. The film of random copolymer with 35 azobenzene units achieves an outstanding highest intrinsic λ of 2.01 W/(m·K), representing a substantial improvement over its block copolymer counterpart (with a higher crystallinity) and traditional polymers. Additionally, the photoisomerization property of azobenzene endows the material with light-controlled dynamic deformation capabilities. Meanwhile, the noncrosslinked polymer films feature easy recyclability/reprocessability.