Polyimide‐Derived Carbon‐Filled Polyimide Composites With Ultrahigh‐Dielectric Constant and Ultralow Loss

In this study, flower‐like polyimide (PI) microspheres were first synthesized via a solvothermal technique, and subsequently carbonized at high temperature to produce corresponding flower‐like polyimide‐derived carbon (PIC) microspheres. PI/PIC composite films were then fabricated through the in situ polycondensation of 4,4′‐diaminodiphenyl ether (ODA) and 4,4′‐oxybisphthalic anhydride (ODPA) in the presence of PIC microspheres. Compared to the neat PI matrix, the dielectric constant of the composites was significantly increased with filler incorporation. The optimal PI/PIC composite films achieved a dielectric constant of 175 with a concurrent low dielectric loss of 0.098 at 1 MHz. Moreover, these composites exhibited a high breakdown strength (> 0.48 V/μm), outstanding thermal stability ( T 10% > 550°C), and a tensile strength exceeding 125.4 MPa. Such excellent comprehensive performance is critical for manufacturing heat‐resisting polymer film capacitors.