Stoichiometric and molecular chain structure effects of functional network modifiers on epoxy resin performance: A combined molecular dynamics and DFT study

As reactive network modifiers in epoxy resin systems participate directly in the curing and crosslinking process, they inevitably affect the stoichiometric balance, crosslinked network structure, and insulation performance of the material. By constructing BDGE and HDGE bisphenol A epoxy/anhydride systems with different modifier contents and epoxy to anhydride equivalent ratios, the effects of network structure regulation on the thermal and electrical properties of the systems are systematically investigated through glass transition temperature, dielectric spectra, volume resistivity, and dielectric breakdown strength measurements, together with molecular dynamics and density functional theory calculations. The results show that increasing modifier content and chain length promotes network loosening and leads to decreases in glass transition temperature, volume resistivity, and dielectric breakdown strength. Molecular dynamics and density functional theory results further indicate that the observed deterioration in insulation-related properties is more closely associated with increased free volume and weakened electron confinement, whereas the HOMO–LUMO bandgap differences among the representative segments are relatively small. These results provide a basis for understanding the structure property relationship and for optimizing the formulation design of epoxy insulating materials.