Design of Intrinsic Polyimides via a Restricted Dihedral-Rotation Structural Strategy for Superior High-Temperature...

With the advancement of high-temperature electrical insulation technology, the limited energy-storage capacity of the intrinsic polyimide (PI) matrix severely restricts application in harsh environments. This limitation primarily stems from their intrinsic structures, which hinder the coordinated optimization of suppressed charge-transfer complexes (CTC), high glass-transition temperature (T_g), and dielectric constant (ε_r). In this work, intrinsic PI dielectrics with restricted dihedral-rotation structure were successfully constructed by employing ─Cl, ─CH₃, and ─CF₃. Such a structure effectively regulates molecular chain rigidity, thereby maintaining a high T_g while preventing film failure induced by excessive internal stress. Additionally, highly electronegative substituents, together with restricted dihedral-rotation structure, synergistically suppress CTC, thereby further enhancing breakdown strength (E_b). Notably, ─Cl substituent compensates for the reduction in ε_r resulting from CTC suppression, thereby enhancing the ε_r and ultimately yielding outstanding discharged energy density (U_d) of 11.47 J/cm³ @150°C and 9.46 J/cm³ @200°C. Furthermore, HBPDA/6FClTP exhibits outstanding power density and long-term stability, with the fabricated high-temperature-resistant stacked-film capacitor device showing excellent capacitance stability. This chemical modification strategy effectively achieves synergistic optimization of CTC suppression, T_g, and ε_r, thereby providing valuable guidance for the development of scalable, high-performance polymer capacitors.