Synergistic Molecular Engineering of Crosslinked Polymer Dielectrics for High-Temperature Capacitive Energy Storage

Polymer dielectric capacitors are critical for high-temperature energy storage, yet current materials face a trade-off between thermal stability and capacitive performance due to conduction loss or insufficient polarization. Here, a modular molecular engineering to simultaneously optimize molecular polarity, topological crosslinking, and free volume in alicyclic polymers is designed. By incorporating thermally crosslinkable benzocyclobutene (BCB) and sulfone-methyl (─SO₂CH₃) groups into norbornene-based monomers via ring-opening metathesis polymerization (ROMP), crosslinked networks with decoupled non-conjugated backbones and polar moieties are constructed. The polymers exhibit a wide optical bandgap (E_g > 3.7 eV), high thermal stability (T_g > 350 °C), and suppressed dissipation (D_f ≈ 0.0006). Optimized P50-B250 delivers an exceptional discharged energy density (U_d) of 8.00 J cm^-3 at 150 °C (≥90% efficiency), while fully crosslinked P0-B300 retained U_d of 7.34 J cm^-3 at 200 °C and 4.65 J cm^-3 at 250 °C, outperforming conventional dielectrics. Molecular dynamics (MD) simulations revealed that crosslinking increases free volume fraction by ≈40%, inhibiting interchain charge transfer complexes (CTCs). Density functional theory (DFT) calculations confirm that sulfonyl-enhanced polarization and crosslinking collectively restrict charge migration. This work establishes a general framework for designing polymer dielectrics by integrating structural modularity and topological control, offering pathways for next-generation energy storage applications under extreme conditions.