Crystallinity and Dielectric Properties of PEEK, a Thermoplastic Poly(ether ether ketone)

The overall objective of this study was to investigate the interdependence of specific dielectric properties of polymers on their fundamental molecular parameters in order to optimize the application of these polymeric materials in critical SMC systems. SMC systems utilize polymeric materials in applications involving high voltage HV insulation in systems aboard DSCS, Nilstar, and several classified spacecraft. Studies of polymer dielectrics have shown that changes in polymer morphology can influence fundamental electrical properties leading to premature breakdown. This investigation focused on the effect of polymer morphology on the electrical characteristics of PEEK, a high temperature insulating thermoplastic, as part of an effort in understanding the causes of dielectric breakdown. This amorphous material was thermally annealed to produce a range of crystallinities. The results of this effort showed that as the crystallineamorphous ratio of the polymer increases, the dielectric breakdown strength is reduced. Electrical conductivity of the material was also shown to decrease. When translated to resins, blends, and advanced composites where environmental aging or thermal cycling can influence the morphology of the material, any reliance on the maintenance of stable electrical properties may have to be carefully considered. The introduction of advanced materials with tailored properties that involve different families of polymers will require a sophisticated understanding of the morphology of materials and the processes by which it varies. This will not only be important for enhancing mechanical properties of materials but also for recognizing the subtle influences that affect electrical properties of materials.