Effect of fluorine-containing groups on the corona resistance and dielectricproperties of polyimide

The increasing use of electrical equipment at high frequencies poses greater demands on the corona aging resistance and dielectric properties of insulating materials. Therefore, it is crucial to enhance the insulation properties of insulating materials for the development of high-frequency power systems. In this study, we utilized 2, 2'-bis(trifluoromethyl)-4, 4'-diaminodiphenyl ether (6FODA), 4, 4'-diaminodiphenyl ether (ODA), and 1, 2, 4, 5-benzenetetracarboxylic anhydride (PMDA) as reactive monomers to design and synthesize block copolymerized fluoro-polyimide (FPI) three-layer films. The focus was primarily on assessing the corona-resistant and dielectric properties of these materials. Results reveal that the corona-resistant life of the block copolymerized FPI three-layer films, with varying amounts of fluorine, is higher when compared to the pure polyimide (PI) three-layer films. Furthermore, the corona-resistant life of the films increase with an increase in fluorine content. When the molar ratio of ODA to 6FODA is 1∶9, the corona resistance life of the three-layer film can reach up to 4.0 h at room temperature (20℃) and 80 kV/mm, which is 2.86 times higher than that of the pure PI three-layer film (1.4 h). Moreover, with the increase of fluorine content, the dielectric constant of FPI three-layer film shows a trend of decreasing and then increasing, and the dielectric constant of the three-layer film when the molar ratio of ODA and 6FODA is 1∶1 can be reduced to as low as 2.26 at 1 MHz, and the dielectric loss and conductivity show a trend of increasing and then decreasing. The dielectric strength decreases with the increase of fluorine content, but they are all higher than that of the pure PI three-layer film, and the dielectric strength of the three-layer film is as high as 434 kV/mm when the molar ratio of ODA to 6FODA is 9∶1.