Space Charge Contributions to the Dielectric Response and Breakdown Strength of High-Temperature Poly(ether imide)/Polyimide Blends

Dielectric properties of poly(ether imide)/polyimide blends, prepared by the solution casting method, were measured over broad frequency and temperature ranges and compared to the response of pristine polymers. While the intrinsic dielectric permittivity only slightly decreases, the electrical conductivity of blends is approximately 40% lower than the conductivity of poly(ether imide) and polyimide. A detailed low-frequency investigation revealed a significant reduction of accumulated space charges in blend systems and thus confirmed that the enhancement of their breakdown strength occurs due to strong electrostatic interactions between the differently charged phenyl groups in poly(ether imide) and polyimide chains. Because a notable influence of absorbed water on the overall dielectric response was found, particularly in the presence of γ relaxation, the impact of high-temperature annealing on the dielectric breakdown strength was also examined.