Improving the Rotational Freedom of Polyetherimide: Enhancement of the Dielectric Properties of a Commodity High-Temperature Polymer Using a Structural Defect

Dielectric polymers that can withstand harsh conditions of simultaneous high electric field and elevated temperature are widely used in electrical and electronic systems. However, traditionally, the thermal stability of polymers is engineered based on highly conjugated aromatic molecular structures, giving rise to soring charge transport and thus poor charge–discharge efficiency under concurrent high electric field and elevated temperature. Here, we locally improved the rotational flexibility of the phenylenediamine linkage structure in polyetherimide (PEI) to decouple the conjugation of the organic molecule. p-Phenylenediamine (5 mol %) as a low-energy rotation repeat unit within PEI significantly optimized its dielectric properties, exhibiting substantially suppressed electrical conduction (more than 1 order of magnitude lower) and polarization loss (<1%). The new PEI has a largely improved charge–discharge efficiency of 91% at 400 MV/m 200 °C, outperforming the best-reported polymer-based dielectrics without any modification of the cost of goods. The high-throughput facile processing of the new PEI provides a potential candidate for energy storage applications under elevated temperatures. This work unveils a scalable approach to exploring polymer dielectrics by introducing a small amount of local structural modifications.