Dielectric Performance and Reprocessability of Boronic-Ester Vitrimeric Epoxy with Nanoscale Phase Separation
Аннотация
Epoxy resins are widely employed as insulating materials in ultra-high-voltage (UHV) power equipment thanks to their excellent electrical properties, yet their permanently cross-linked networks are insoluble, infusible and difficult to recycle, and the electrical behavior of their dynamic-bonded counterparts remains poorly understood. Here, Bisphenol A diglycidyl ether (BADGE) was co-cured with a boronic-ester diamine and a flexible monoamine to generate a vitrimer network (EP-NBN) featuring 10 nm hard/soft periodic domains. The electrical behavior of EP-NBN was systematically evaluated at 20 ℃ to 60 ℃: Dielectric analysis and Havriliak–Negami fitting show that increasing temperature weakens interfacial polarization while activating local boronic-ester–related relaxation. The fitted apparent dc conductivity (σ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dc</sub>) decreases with temperature, accompanied by reduced low-frequency dielectric loss, due to diminished electrical contrast between hard and soft phases. Space-charge peaks at both electrodes decrease in magnitude and broaden with temperature. The current density-electric field (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J-E</i>) curves evolve from a two-regime ln<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J-E</i> behavior consistent with field-assisted interfacial hopping to an approximately single-slope behavior at 60 ℃. EP-NBN shows high AC breakdown strength (38.32 kV/mm) and retains 69.2 % of this value after reprocessing, outperforming the non-dynamic EP-ref. EP-NBN can also self-heal surface scratches and breakdown channels at elevated temperature. DFT calculations indicate a bipolar localization tendency in boronic-ester units, where electrons preferentially localize near boron sites and holes near O/N sites, providing a microscopic basis for interfacial trapping behavior associated with boronic-ester units, while the wide band gap (7.3 eV) supports the high intrinsic insulation level of the network. Overall, the microphase separation + boronic-ester dynamic bonds strategy enables high insulation performance together with reprocessability and self-healing.