Side-chain engineering of polyethylene dielectrics toward tremendously enhanced electrical breakdown performances

Polymer dielectrics are utilized in high-voltage power systems and miniaturized electronics, yet face a critical bottleneck due to inadequate dielectric breakdown strength. Side-chain engineering is an emerging strategy for improving dielectric performance superior to nano-doping; however, the correlation mechanism between the molecular structure of side chain and dielectric/electrical properties has not been established, resulting in limited performance improvement based on extensive functional group selection and trial testing. Here, conjugated benzene ring and non-conjugated dicyclopentadiene group are, respectively, incorporated onto polyethylene via gradient copolymerization, enabling precise modulation of charge trapping behaviors. Experimental and density functional theory results reveal that π-electron delocalization of the conjugated ring expands intramolecular charge separation, thereby enhancing electrostatic potential and forming deep charge traps with the higher energy level in PESt compared to PEDCP and cross-linked polyethylene (XLPE). Such deep traps suppress charge transport, thus making its breakdown strength higher than that of PEDCP containing non-conjugated rings and achieving an 86% increase compared to XLPE. By clarifying the trap-forming mechanisms of conjugated and non-conjugated rings and elucidating the side-chain structure dominated electrical performance, this work provides experimental foundations, rather than the commonly achieved simulation results, for designing branched conjugated structures of high-performance polyolefin dielectric polymers and accurately customizing their electrical properties.