A Dipole‐Confined Charge Transport Paradigm for Ultrahigh‐Temperature Dielectric Polymers

ABSTRACT A pervasive challenge in materials science, the incompatible trade‐off among breakdown strength ( E b ), thermal stability ( T g ), and dielectric constant ( ε r ), has limited the development of polymer dielectrics for extreme‐environment film capacitors. Here, this trilemma is overcome via a dipole‐regulation strategy, confining polar methyl‐sulfonyl groups within a rigid semi‐aromatic polyimide framework using flexible methylene linkers. This dipole confinement domain structure of sulfonyl‐methylene‐benzene decouples dipolar response from charge transport: the flexible linkers enable polarization, while the rigid semi‐aromatic framework localizes charges and suppresses conduction. It results in a stable dipole network, yielding a material (STPCB‐PI) with a wide bandgap (4.38 eV) and a record T g (>400°C). It achieves a high ε r of 5.8, a modulus of 6.7 GPa, and exceptional energy storage, delivering 12.00 J cm −3 with 97% efficiency at 25°C, 9.98 J cm −3 with 94% efficiency at 150°C, and retaining 8.62 J cm −3 with 90% efficiency at 200°C, 293% improvement over the state‐of‐the‐art commercial polyetherimide. Even at 250°C, it maintains 4.24 J cm −3 with 93% efficiency. It also exhibits excellent self‐healing and cyclic endurance. This work sets a new performance benchmark and establishes a generalizable design paradigm that reconciles the intrinsic conflict between polarization and insulation in high‐temperature dielectric polymers.