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

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 mV m⁻¹ and maintains a record charge-discharge efficiency of 82% at 450 mV m⁻¹, while endo-PDCNB exhibits a high breakdown strength of 600 mV 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.