Polyimides are one class of high temperature materials that have been extensively used in the microelectronics industry in passivation and protection. The extremely good thermal stabilities, along with desirable mechanical and electrical properties, have led to their use in integrated circuits and thin film multi-layer packaging. Due to rapid advances in the microelectronics industry, stringent demands have been placed on the improvement of electric performance of the packaging systems. This has resulted in a search for materials with extremely low dielectric constants while maintaining the desirable thermal and mechanical properties. In the past, the incorporation of fluorine into polyimides has been shown to decrease the dielectric constant. In this research, the concept of a foamed morphology has been utilized to obtain a decrease in the dielectric constant, by taking advantage of the low value for air. To achieve compatibility with the microscopic features of the electronic circuitry, polyimide foams with pore sizes in the nanometer regime have been developed. Block and graft copolymers consisting of thermally stable polyimide and labile poly(propylene oxide) were synthesized to first develop the desired microphase separated morphology. Both semicrystalline and fluorinated polyimides were evaluated as low dielectric matrices with improved mechanical properties and solvent resistance. The labile component was degraded with thermal treatment in air, leaving behind pores where the size and shape were largely determined by the original multiphase copolymer morphology. / Ph. D.