Largely Enhanced High-Frequency Insulation Performances of Polyimide by Incorporating Siloxane-Based Fillers

The growing demand for renewable energy promotes the rapid development of power electronic technology. A safe insulation system is extremely important for the reliable operation of power electronic devices. Different from the conventional insulation system, the insulation system of power electronic devices is subjected to high-frequency voltage for a long period. The insulation failure of polymer dielectrics under high-frequency voltage is increasingly prominent. However, seldom is attention paid to investigate the high-frequency insulation of polymer dielectrics. In this work, we incorporated a 5% equivalent molar content of silica dioxide (SiO2), 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane (GAPD), and PSS-octavinyl-substituted (POSS) into the polyimide (PI) matrix and investigated the effects of these fillers on the high-frequency insulation performance of PI films. We found that the high-frequency breakdown strength of PI composites was significantly improved compared with that of pristine PI film and the POSS/PI composites film displayed the highest high-frequency breakdown strength. We analyzed the changes of the dielectric, resistivity, and trap level properties and found that the enhancement of high-frequency strength could be attributed to the suppressed polarization loss and introduced deep traps. High frequency voltage would cause the accumulation of heat inside the film, and the suppressed dielectric loss could alleviate the heat accumulation PI films and accordingly weaken the ablation degree of film surface. Besides, the introduction of deep traps could mitigate the distortion of local electric field. The synergetic effects of above two factors contribute to the enhancement of high-frequency insulation performance of PI composites. The findings of this work are promising to provide a path for the design of high-frequency insulation polymer dielectrics.