Stereoisomerism of Vicinal Polydichloronorbornene for Ultra‐High‐Temperature Capacitive Energy Storage

Abstract The emergence of high‐density electronics in aerospace and renewable energies demands high temperature dielectrics. Molecular engineering represents a vital strategy for designing dielectric polymers, yet the influence of stereochemistry remains untapped. Herein, by designing halogen substituents of an aromatic pendant attached to a bicyclic mainchain, vicinal polydichloronorbornene (PDCNB) with a high glass‐transition temperature ( T g ) of 263 °C is obtained. Further study unveils the profound effect of stereochemistry on the properties of exo‐ and endo‐PDCNB. Both isomers show identical high T g and bandgap (4.3 eV), imparting PDCNBs with remarkable capacitive energy storage, outperforming existing polymers and nanocomposites with two orders of magnitude lower conduction at an ultra‐high temperature of 250 °C. Moreover, the effect of stereoisomerism is manifested in the differences in backbone spacing, π‐stacking, barrier height, and trap states, and the resulting distinct high field performance. Exo‐PDCNB displays an extremely low conduction of 6.8 × 10 −14 S m⁻ 1 at 200 m V m⁻ 1 and maintains a record charge‐discharge efficiency of 82% at 450 m V m⁻ 1 , while endo‐PDCNB exhibits a high breakdown strength of 600 m V m⁻ 1 with a remarkable discharged density of 4.47 J cm⁻ 3 , all at 250 °C. This study unleashes a stereochemistry‐based strategy with vicinal dichloro substitution to further boost the T g of polynorbornene for ultra‐high‐temperature applications.