Miscibility and phase transformations in rigid rod molecular composites

Miscibility and phase transformations in several systems consisting of rigid rod and flexible coil molecules were studied to develop a thermally stable molecular composite.; The entrapped single-phase blend of poly-p-phenylene terephthalamide (PPTA)/amorphous nylon (AN) was identified. This miscibility has been attributed to the cross-hydrogen bonding between PPTA and AN. However, these mixtures were thermodynamically unstable and underwent phase segregation upon thermal treatment. Phase behavior and kinetics of phase separation in PPTA/AN mixtures were investigated by time-resolved light scattering. Tensile properties of PPTA/AN composites were determined as a function of composition.; The miscibility between commercial flexible polyimide (PI) and polyamideimide (PAI) was examined. The origin of the miscibility between PI/PAI was investigated by Fourier transform infrared (FT-IR) spectroscopy. Upon heating, phase separation occurs implying that the molecular interaction between PI and PAI is inadequate to prevent it.; Three kinds of newly synthesized rigid aromatic polyimides (PI) were mixed with a commercial grade polyetherimide (PEI). The mixtures show a single glass transition temperature (Tg) in all compositions and the Tg is repeatable in subsequent heating runs, suggesting the true miscibility of the blends. The composition-dependence of tensile properties of PI/PEI molecular composites was investigated.; The understanding of the solution properties of biphenyldianhydride perfluoromethylbenzidine (BPDA-PFMB)/m-cresol is crucial for solution processing. The thermodynamics, kinetics, and morphology of this solution were investigated. Partial phase diagram consisting of phase separation and phase transition was established. Upon quenching the solution from isotropic to anisotropic region, nematic textures evolve within the domains. The average domain size was found to depend on the depth of supercooling. The kinetic of phase transition has been analyzed according to the classical nucleation and growth theories.; The cast films of BPDA-PFMB/PEI were drawn at an elevated temperature. The composition-dependence of the tensile modulus of the films have been evaluated. The chain orientation of specimen was related to draw ratio by birefringence measurement and wide-angle X-ray diffraction. The radius of gyration parallel and perpendicular to the drawing direction was calculated from the Guinier plots of small-angle X-ray scattering scans. The results of micro-deformation were compared with the prediction of affine deformation.