Effects of cross-linked networks on dielectric properties of epoxy resins based on molecular dynamics

In this paper, three epoxy resin systems commonly used in power equipment are prepared to obtain cross-linked networks with structural differences. The relationship between microscopic structures and dielectric properties of epoxy resins is investigated and discussed. Experimental results show that the polarization and conductance losses are inhibited in the anhydride-cured systems with methyl groups. The molecular dynamics (MD) simulation shows that rigid anhydride structures (such as methyl groups) play a major role in reducing the local segment mobility and increasing the free volume at cross-linking points. The decrease in local segment mobility has been confirmed by the decrease of mean square displacement (MSD) at the cross-linking points, which is consistent with the change of measured polarization and conductance loss. In the glassy state, the dielectric properties of different anhydride-cured systems can be reflected by local MSD at the cross-linking points. At high temperatures near the glass transition temperature, both the free volume and network mobility increase significantly, which reflects the increased dielectric relaxation strength and conductance loss. The understanding of the structure–property relationships could provide a theoretical foundation for epoxy modification in a controlled manner for power equipment applications.