Significant enhancement of dielectric properties in polyimides with sulfonyl groups in the side chains

Polymer dielectrics with excellent thermal resistance and superior energy storage behaviour are extensively demanded with the increasing development of film capacitors applied in hostile environments. In this study, novel diamine with sulfonyl-containing side chain was designed and synthesised. The corresponding polyimide (PI) dielectrics derived from the sulfonyl-containing diamine were prepared, so were the polyimides possessing the same backbone but without side chains. Consequently, superior thermal resistance of glass transition temperature ranged from 162–208°C was obtained. Moreover, the polyimides presented permittivity of 3.34–5.89 at 1 kHz, Weibull breakdown strength of 377–538 MV/m and discharged energy density of 3.82–5.85 J/cm³. In particular, sulfonyl-containing polyimide of SPI-2 with flexible backbone and sulfonyl side chain indicates the highest discharged energy density and charge-discharge efficiency simultaneously. The introduction of the strong polar sulfonyl group in the side chain enhances dielectric and energy storage properties effectively. In addition, it is found that the dipolar moment density (μ/V_vdw) calculated from molecular simulation is closely correlated to permittivity measured from experiments. The combined method of molecular simulation and experiments would offer an effective approach to assist in molecular design of high-performance polymer dielectrics.