**Abstract**

Nearly five decades of effort has focused on identifying and developing new polymer capacitor films for higher-than-ambient temperature applications, but simultaneous demands of processability, dielectric permittivity, thermal conductivity, dielectric breakdown strength, and self-clearing capability limit the number of available materials. Demands on these criteria are even more stringent in growing numbers of applications demanding high power performance. Aromatic polyimides, though not a panacea, are a class of heat-resistant polymers of great interest to researchers as capacitor dielectrics because of good thermal and mechanical stability. In this chapter, the key aspects and advantages of metallized polymer film capacitors are compared to analogous alternative technologies (polymerfilm-metal-foil, ceramic, and electrolytic capacitors), followed by a comprehensive review of commercial resin development leading up to recent research on polyimides targeted for operating temperature above 150°C. Finally, this chapter provides a brief discussion on the recent effort on combining computation and synthesis to design polymers with desirable dielectric properties.

**Keywords:** Kapton, Ultem, polyimides, high temperature, capacitor dielectrics, thermal conductivity, self-clearing, metallized film capacitors, power electronics, DC link capacitors
