Curing‐Induced Nanophase Engineering in Boronic‐Ester Epoxy Vitrimers for Low‐Loss, High‐Breakdown, and Stress‐Relaxed Insulation

ABSTRACT Epoxy dielectrics for high‐frequency power‐electronic insulation face a persistent trade‐off between electrical reliability and network adaptability: rigid cross‐linked networks provide high dielectric strength but lock in cure‐induced stress, while epoxy vitrimers often struggle to maintain low dielectric loss and stable breakdown performance under electrical stress. Here, we report a boronic‐ester epoxy vitrimer in which catalyst‐free bond exchange is coupled with curing‐induced nanophase‐separated morphology. The resulting vitrimer network releases > 87.7% of curing stress while maintaining low dielectric loss across a broad frequency range, with tan δ as low as 4.2 × 10 −4 at 100 Hz. More importantly, it retains low dielectric loss at 30 kHz, leading to reduced electrothermal heating, an 84% decrease in partial‐discharge activity, and a 78%–101% increase in alternating‐current (AC) breakdown strength relative to conventional epoxy. Multiscale experiments, together with density‐functional‐theory (DFT) and phase‐field simulations, show that polarized B─O motifs and interfacial permittivity/conductivity contrast jointly regulate charge trapping, redistribute local electric fields, and suppress damage localization and Joule‐heating hot spots, while dynamic exchange relaxes cure‐induced residual stress. Mechanical scratch healing restores up to 93% of breakdown strength, and reprocessed samples preserve low‐loss, high‐breakdown performance, establishing a recyclable epoxy‐insulation platform for reliable high‐frequency dielectrics.