Branched Chain Structure Dependent Breakdown Characteristics of Polyethylene

Polymer dielectrics are the key insulation components in high-voltage power equipment. Further enhancing their breakdown strength is the foundation for promoting the miniaturization and high reliability of the equipment. Polyethylene (PE) is widely employed in power cables due to its high breakdown strength, low dielectric loss and large-scale production advantages. However, the complexity of the branched structure leads to high dispersion of its breakdown strength. More importantly, the correlation between branch length and electrical performance has not been established, which hinders further improvement in the breakdown characteristics of PE. Here, we construct a series of molecularly designed ethylene- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\alpha$</tex>-olefin copolymers to systematically reveal the influence of branched chain length on charge traps and breakdown characteristics. The results show that short-branched PE exhibits ordered molecular chain structures with elevated crystallinity. Such enhanced crystallinity increases the interfacial areas between crystalline and amorphous regions, thereby deepening the trap energy levels and substantially improving DC breakdown strength. Medium-branched PE significantly reduces crystallinity by disrupting the regularity of the backbone. Furthermore, since a large number of branched moieties are excluded from the crystal lattices, the proportion of amorphous regions increases and the shallow trap energy levels decrease with increasing density, ultimately decreasing breakdown strength by effectively capturing charge carriers. The mechanism of longbranched chains is more complicated, potentially involving localized ordered structures and a dynamic equilibrium between crystallization and defects, which paradoxically restores crystallinity and enhances breakdown strength. This work systematically reveals the connection between the branching structure and breakdown characteristics in PE, providing novel insights for designing high performance PE and related polyolefin electrical materials.