High Breakdown and Energy Storage Properties of PMMA via Conformational Transition Induced by a Heat Treatment Strategy

Given the strict energy density requirements for renewable energy grid-connected film capacitors, developing polymer dielectrics with high breakdown field strength and high efficiency is essential. This study aims to improve the energy storage performance of poly(methyl methacrylate) (PMMA) by employing molecular chain conformational engineering. Following heat treatment, the primary chain conformation in PMMA can transition from trans-trans (tt) to trans-gauche (tg). This tg configuration facilitates a denser packing of the polymer chains, leading to a decrease in free volume fraction. Consequently, it mitigates dielectric relaxation losses while preserving PMMA's inherent low-loss characteristics. Moreover, it impedes charge carrier injection and migration under high electric fields, thereby augmenting the breakdown field strength. Density functional theory computations indicate that the tg conformation exhibits a energy gap of 5.23 eV, suggesting a formidable energy barrier for charge injection into the polymer matrix. Finally, the stepped heat treatment at 80-150 °C enhanced the breakdown electric field of PMMA films to 768 MV/m, achieving an energy density of 14.91 J/cm³ and an efficiency of 83%. This study highlights the potential to manipulate polymer dielectric properties through chain conformation engineering, providing a theoretical basis for high-performance dielectric material design.