High-temperature resistant polyetherimides containing a twisted spirane structure for capacitive energy storage

Intrinsic polymer dielectrics with high discharged energy density and discharge efficiency at elevated temperatures have unique advantages for the film capacitors in power electronics in severe environment (e.g., electric vehicles). In this work, a novel polyetherimide with hydroxy groups and a twisted spirane structure was synthesized based on 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-5,5′-diamino-6,6′-diol (SPDD). Owing to the polar hydroxyls and twisted spirane structure, desirable physical properties are obtained: high glass transition temperatures (281–302 °C), relatively high dielectric constant (4.2–5.1), and very low dielectric loss (dissipation factor < 0.002). As a result, this kind of PEIs possessed excellent high temperature dielectric properties. Among them, the PEI with 50% of spirane units exhibited a high discharged energy density of 2.24 J cm−3 at 200 °C and 350 MV m−1 and with a high discharged efficiency of 90%. This is attributed to the twisted spirane structures that break the π-π stacking of the aromatic rings of PEI polymers, thus decreasing both AC and DC electronic conductions at high fields and high temperatures. Based on these performance, spirane-based PEIs are suitable for high temperature capacitive energy storage.