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

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.