Effect of Disulfide Bonds on Dielectric Properties of Recyclable Epoxy Vitrimer

Introducing dynamic covalent bonds in the crosslinked network of the epoxy resin is considered an effective method to prepare recyclable epoxy vitrimers. In this study, epoxy vitrimers with dynamic disulfide bonds were prepared and recycled by hot-pressing. The dielectric properties of the conventional thermoset epoxy resin (Sample I), epoxy vitrimer (Sample II) and the recycled sample (Sample III) were investigated. The results showed that with increasing frequency, the real part of the relative permittivity (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon^{\prime}$</tex>) of Samples II and III displayed a more pronounced decrease than that of Sample I, while the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\varepsilon^{\prime}$</tex> of Sample III was lower than that of Sample II. The dielectric loss tangent (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\tan \delta$</tex>) of Samples II and III was higher than that of Sample I, and the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\tan \delta$</tex> of Sample III was further increased at higher frequencies (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&gt;10^{4} \text{Hz}$</tex>). For both deep and shallow traps, Sample II exhibited lower energy levels and higher densities compared to Sample I. After hot-pressing, Sample III showed even shallower traps and the trap densities were noticeably increased. It is considered that the dielectric properties of epoxy vitrimers with disulfide bonds decrease compared with those of thermoset epoxy resin. After being remolded by hot-pressing, the dielectric properties are further compromised.