Mechano Optical Behavior of Novel Polymers for Capacitor Application During Their Processing Cycles

This work is a part of collaborative project between Multidisciplinary University Research Initiative (MURI) through which an advanced polymeric capacitor films for military applications were designed. Two of those novel polymers were PPOH (hydroxyl functionalized isotactic polypropylene with comonomer of 10-hydroxy-1-undecen) and PI(BTDA-DAH) (Polyimide 3,',4,4'-benzophenone tetracarboxylic dianhydride and 1,6-diaminohexan). This dissertation focused on the effect of processing conditions on the mechano-optical behavior of PPOH and PI(BTDA-DAH).Firstly, the real-time mechano-optical behavior of PPOH containing 0.4 mol % comonomer and its comparison with unmodified polypropylene (PP) were studied in the partially molten state during processing cycle of heating, stretching, annealing, and cooling. It was revealed that the crystalline network dominated the material response during the processing cycle for both polymers. However, the presence of hydrogen bonding between the hydroxyl groups in PPOH was found to affect the structural evolution of the PPOH copolymer significantly more than compared to the PP homopolymer. Secondly, the real-time mechano-optical behavior of PI(BTDA-DAH) was studied in the glassy and the rubbery states as a function of processing temperature and stretching rate during uniaxial deformation. Thee regimes of stress optical behavior were revealed. First, at the early stage of deformation the stress optical rule is observed; birefringence linearly increased with a stress optical constant of 17.8 GPa-1 - regime I. Second, a deviation from linearity took place. At higher temperature and/or lower stretching rate the deviation is positive and the birefringence rapidly increases while the stress slowly increases- regime II. At lower temperature and/or higher stretching rate this deviation of linearity is negative- regime IIIa. Third, in cases where regime II is revealed, it was followed by a negative deviation of birefringence and reached a plateau while stress rapidly increased -regime IIIc. According to off-line characterization techniques: differential scanning calorimetry and wide-angle X-ray diffraction showed that the material remains amorphous during regime I and the early stage of regime II. By the end of regime II, a rapid increase in the crystallinity was observed. This implies stress induced crystallization associated with regime II. There was no significant change in the crystallinity with further stretching into regime III where the polymer chains reach to their finite extensibilities.Thirdly, the real-time infrared-mechano-optical behavior of PI(BTDA-DAH) during uniaxial deformation followed by relaxation was studied. The relaxation showed high dependency on the polymer structure pre-relaxation. Three regimes of stress optical behavior and stress reho (orientation function) behavior were revealed. At the early stage of deformation (regime I), birefringence and orientation function linearly decreased with a stress. At early stage of deformation in regime II, the birefringence and orientation function slowly decrease. These behaviors changed with the deformation level in regime II. At intermediate stage of the deformation in regime II, the birefringence and orientation function did not change while the stress rapidly decreases, and then birefringence and orientation function started slowly to increase, while the stress slowly decreased. At the high stage of the deformation in regime II, the birefringence and orientation function were slowly increased while the stress rapidly decreases, and then birefringence and orientation function rapidly increased while the stress slowly decreases. At the high stage of the deformation, regime III, the birefringence and orientation function were slowly increased while the stress rapidly decreased, and then birefringence slowly increased while the stress slowly decreased. It also was found that the birefringence and orientation function increased with enough relaxation time at all level of deformation in regime II.Fourthly, the real-time mechano-optical behavior of PI(BTDA-DAH) during biaxial deformation and their effect on dielectric properties was studied. It was found that during the biaxial stretching, the phenyl groups in the PI(BTDA-DAH) chains became parallel to the surface plane which reduced the polarizability of the polymer chain in the film thickness direction. As a result, the dielectric constant decreased with increasing in the stretching ratios.