Sulfonyl‐Containing Polyimide Dielectrics with Advanced Heat Resistance and Dielectric Properties for High‐Temperature Capacitor Applications

Abstract Polymer dielectrics, with advanced dielectric properties and heat resistance, are critical for high‐temperature capacitors in various applications. However, the high performance of heat resistance and dielectric properties are quite difficult to achieve all together due to their mutual implication. Here, by intensively investigating the correlation between molecular structure and properties, polyimide dielectrics with i) enhanced dielectric constant by introducing sulfonyl group, ii) low dissipation factor by introducing flexible linkage, and iii) high T g (glass transition temperature) by retaining an aromatic structure, are obtained. The sulfonyl‐containing polyimides with different flexible linkages exhibit simultaneously a high dielectric constant (4.50–5.98), low dissipation factor (0.00298–0.00426), and outstanding breakdown strength (most above 500 MV m −1 ), as well as superior heat resistance ( T g : 244–304 °C). Specifically, the polyimide (SPI‐1) with sulfonyl group in diamine moiety and para‐para linkage shows stable dielectric properties up to 150 °C, and the discharged energy density and charge–discharge efficiency can be as high as 7.04 J cm −3 and 91.3% at 500 MV m −1 , respectively.