Recyclable Side‐Chain Azobenzene‐Based Semicrystalline Polymer Films with Outstanding Intrinsic Thermal Conductivity and Photoresponsive Actuation
Qingqing Kong, Junliang Zhang, Kuan Zhang, Shuangshuang Wang, Mukun He, Yongqiang Guo, Junwei Gu
Abstract
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.