Copoly(2-nonyl-2-oxazoline)-stat-poly(2-dec-9′enyl-2-oxazoline)s can be crosslinked by the thiol-ene reaction with glycol dimercaptoacetate. The copoly(2-oxazoline)-stat-copolyester is tested as dielectric for high-voltage applications, either as unfilled resin or as composite with nanoscaled fillers of silica, alumina, and hexagonal boron nitride. During AC voltage tests, all materials have an average breakdown strength of 45–50 kV mm−1. For DC voltage tests, samples with SiO2 (hBN) have an average breakdown strength of ≈100 (80) kV mm−1, while the unfilled copoly(2-oxazoline) has an average breakdown strength of ≈60 kV mm−1. Permittivity measurements at 20 °C and 50 Hz reveal that all nanocomposites are dielectrics (D = 0.06–0.08), while the unfilled copoly(2-oxazoline)s has a high loss factor of D = 8.43. This phenomenon can be retraced to the phase separation in the crosslinked copolymer, the M-OH functionality of silica and alumina particles, and models of polymer–particle interactions such as the Tanaka model, revealing that the nanofillers reduce the interfacial and dipolar polarizability.

Many researchers have reported an improvement of the properties of polymer dielectrics by introducing nanofillers. However, the influence of ambient conditions and sample storage under different conditions are often not taken into account. The epoxy matrix itself is a polar polymer susceptible to water absorption, and the presence of hydrophilic nanofillers such as silica will enhance the uptake of moisture from the environment. The dielectric response both of neat epoxy resin and an epoxy-based nanocomposite under an electrical stress greatly depends on the amount of absorbed water. This study investigates the effect of water absorbance on the dielectric spectrum of epoxy-silica nanocomposites containing different concentrations of nanoparticles.