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

Abstract

As a rather 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 in electrical and electronic systems. This work adopts two side groups with different topological structure, namely vinyl acetate (VAc, aliphatic chain) and N-vinyl-pyrrolidone (NVP, saturated ring) to chemically grafting-modify polypropylene (PP), and studies how the structural topology of polar side group affects the microscopic and macroscopic characteristics of PP, particularly the electrical anti-breakdown ability. Experimental results show that the side group structural topology can directly affect the crystallization and thermal properties of PP. Whilst the in-depth computational analysis indicates the grafted NVP possesses lower deep trap depth than VAc, which is connected with the topological structure and corresponding orbital interaction within the side group. Furthermore, molecular dynamics (MD) simulation reveals the saturated ring in NVP side group leads to more free volume within the material condensed state than VAc. Therefore by contrast, VAc-grafted PP with deeper trap orbitals and less free volume exhibits higher breakdown strength enhancement up to 21% and 14% under 30 and 90 °C, respectively. This work provides a novel understanding upon the topological structure effect of side group on the macroscopic dielectric performance from the view of microscopic physical chemistry, and would be referable for the refined design and properties modulation of dielectric materials in modern electrical power facilities.