Comparison and Optimization of Dual-Dynamic Covalent Bonds in Electrically Insulating Epoxy Vitrimer

Epoxy polymers with irreversible cross-link networks are widely used in various fields due to their excellent mechanical, thermal, and electrical insulating performances yet also make them difficult to recycle. Although ester bonds in commonly dielectric insulating epoxy polymers can be activated under certain conditions to endow recyclability, the activation energy of ester bonds is high, and the reprocessability and stability are difficult to balance. The design of epoxy vitrimers with multiple dynamic bonds may achieve excellent recyclability while also possessing high mechanical strength and electrical insulating properties. Herein, epoxy vitrimers with different proportions of disulfide and ester bonds were developed, whose mechanical strength and dynamic thermomechanical and electrical properties were systematically investigated. Results showed that the DDA20 system exhibited excellent comprehensive properties, with a tensile strength of 76.35 MPa, a bending strength of 167 MPa, a glass transition temperature (Tg) of 139.6 °C, an activation energy Ea of 59.9 kJ/mol, a power–frequency (50 Hz) dielectric constant of 4.33 at 30 °C and 5.10 at 105 °C, and a breakdown strength of 31.64 kV/mm, respectively. The recovery rate in mechanical strengths of the DDA20 system reached above 80% at a pressure of 8 MPa, 180 °C for 2 h. This work promotes the application of epoxy vitrimers instead of traditional epoxy resin in electrical equipment.