Nanoconfined relaxation enables commercial dielectric polymer to insulate at 300 °C

Abstract As dielectric polymers are confined to nanoscale dimensions, anomalous enhancements in electrical resistivity have been widely inferred and exploited in nanocomposites and multilayered structures—yet direct experimental validation of the mechanisms remains elusive. Herein, we unveil the physical origins of this abnormal resistivity at the nanoscale through a model polymer approach. Direct experimental observations on ultrathin polymer films (down to 5 nm) reveal that the size‐dependent enhancement in electrical resistivity primarily originates from confined local β‐relaxation processes, complementing conventional explanations based on changed molecular packing and density. With this insight, we (i) rationalize the temperature‐dependent effects of nanofilling in polymer‐nanocomposite dielectrics and (ii) engineer a commercial polymer film with a bulk glass transition temperature of 237 °C that retains stable insulating performance up to 300 °C. These findings provide a unified framework for molecular‐dynamics‐driven charge transport and offer a strategy to design thermally robust dielectrics for next‐generation electronics, power modules, and harsh‐environment applications. image