Capacitors are two terminal devices for energy storage. Polymers like polyethylene (PE), biaxially oriented polypropylene (BOPP), polystyrene (PS), polyethylene terephthalate (PET) are widely used in capacitor applications because of their good film forming properties including low cost, high dielectric strength and low loss. State of art of polymeric dielectric films are BOPP with breakdown strength of 600-700 V/µm (for 10 µm thickness) and with dielectric constant of ~2.2 (1,2). Various strategies have been used to increase the dielectric constant and the dielectric strength of polymeric dielectrics. One of them is to orient crystalline domains of polymers to create a torturous path, by applying mechanical deformation in semi-molten state. Details of these structural reorganization processes under uni and biaxial deformation are still not well understood. This could be partly alleviated by birefringence during deformation together with true stress and true strain. Off line structural characterization techniques including AFM, WAXS and SAXS , TEM can enhance the understanding of fundamental mechanisms that take place during deformation. In this research, the blends of Polyether imide (PEI) which is an amorphous thermoplastic polymer with Tg ~220C and polybutylene terephthalate (PBT) a semi crystalline thermoplastic polymer is investigated. By blending these two polymers together with different ratios high Tg material for high temperature applications can be produced and film processibility of PBT can be increased by suppressing its thermal crystallizability. It is found that blends with high PBT amount can be stretched substantially and undergo stress induced crystallization. Details of the structural evolution and their implications on stress and strain optical behavior in uni and biaxial stretching mode and their electrical properties will be discussed during presentation. (1) Barshaw, E. J. et al., IEEE Trans., Magn. 2007, 43, 223−225. (2) Offenbach, I et al., Macromolecules, 2015 48, 6294-6305