Manipulating Polymer Side-Chain Configuration via Substituent Steric Hindrance for Enhanced High-Temperature Capacitive Energy Storage Performance

A major challenge in developing high-temperature polymer dielectrics is the difficulty in simultaneously achieving a high dielectric constant, a wide bandgap ( E g ), and a high glass transition temperature ( T g ). To address this challenge, this study designed and synthesized a series of polynorbornene imides with methyl groups at the para position and substituents of varying steric hindrance and electronegativity (F, Cl, Br, CF 3 ) at the meta position from the perspective of molecular side-chain configuration. Molecular dynamics simulations and density functional theory calculations reveal that the steric hindrance of meta -substituents can regulate the side-chain configuration ratio in polymers. Specifically, as the substituent steric hindrance increases, the proportion of the isotactic configuration decreases while the syndiotactic configuration increases. The isotactic configuration enhances the polarization performance by strengthening the local dipole moment and the syndiotactic configuration improves insulation by increasing free volume and suppressing charge migration. The meta -chloro-substituted PNIM-Cl achieves a balance between isotactic and syndiotactic configurations through its moderate steric hindrance and electronegativity and results a high dielectric constant (4.04), a wide E g (4.27 eV), and an elevated T g (231.8°C). Consequently, the PNIM dielectric achieves remarkable discharged energy densities of 11.4 J cm − 3 at 150°C and 6.4 J cm − 3 at 200°C.