Side group topological structure modified orbital and condensed state characteristics enhance the electrical anti-breakdown performance of polyolefin†

Abstract

As an effective method to enhance the dielectric performance of polyolefin materials, polar side group modification has been extensively applied in the insulation and energy storage materials of electrical and electronic systems. In this work, two side groups with different topological structures were adopted, namely, vinyl acetate (VAc, aliphatic chain) and N-vinyl-pyrrolidone (NVP, saturated ring), to modify polypropylene (PP) via chemical grafting, and the effects of structural topology of the polar side group on the microscopic and macroscopic characteristics of PP, particularly on its electrical anti-breakdown ability, were investigated. Experimental results showed that the side group structural topology directly affected the crystallization and thermal properties of PP. The in-depth computational analysis indicated that the grafted NVP possessed a lower deep trap depth than VAc, which is related to the topological structure and corresponding orbital interaction within the side group. Furthermore, molecular dynamic (MD) simulations revealed the presence of a saturated ring in the NVP side group that led to more free volume within the material's condensed state than VAc. Therefore, by contrast, VAc-grafted PP with deeper trap orbitals and less free volume exhibited higher breakdown strength enhancement up to 21% and 14% at 30 and 90 °C, respectively. Thus, this work provides a novel understanding of the topological structure effect of the side group on the macroscopic dielectric performance from the viewpoint of microscopic physical chemistry. Furthermore, this work would serve as a reference for the refined design and property modulation of dielectric materials in modern electrical power facilities.