In this research project, at initially, a new series thermally stable polyamide (bis(3-aminophenyl)(phenyl)phosphine oxide and 5-hydroxyisophthalic acid) and poly(benzimidazole) (bis(3,4-diaminophenyl)methanone and pyridine-2,6-dicarboxylic acid) were prepared. The polymerization reactions of poly amide were carried out in tetrabutylammonium bromide as a molten ionic liquid salt and in the presence of triphenyl phosphite as the condensing agent. The effect of reaction variables on the physical properties of the prepared polyamide was investigated. Structure of the obtained polymers was studied by Fourier Transform Infrared spectroscopy (FT-IR), 1 H-NMR and elemental analysis. Thermal stability of the polymers was studied using thermogravimetric analysis (TGA) technique. The results showed that the polymers have good thermal stability. Crystallinity of the polymers was investigated by X-ray diffraction (XRD) technique. The diffraction patterns showed that the synthesized polymers were amorphous. The surface morphology of polymers was also studied by field emission scanning electron microscopy (FE-SEM) analysis. The resulting images showed that the polymer particles were almost spherical but after sulfonation was exchanged to the soft and layer particles. In the second section of project, in order to increase interaction and dispersion of carbon nanotubes in the polymer, sulfonated carbon nanotubes were prepared, studied and evaluated by different analytical methods like FT-IR, XRD, TGA, FE-SEM and elemental analysis. The final section, polymer-based nanocomposites containing sulfonated multi-walled carbon nanotubes were prepared, by ultrasonic-assisted solution blending method, carbon nanotubes were dispersed in the polymers matrix with different weight percentages (5, 10, and 15% by weight of the polymer) and the related naocomposites were prepared. The fabricated nanocomposites were investigated and studied by different analytical methods such as FT-IR, XRD, TGA, FE-SEM and transmission electron microscopy (TEM). TGA data from two types of nanocomposites showed that the thermal stability of nanocomposites based on sulfonated polyamide with increasing the content of carbon nanotubes, slightly improved while the thermal stability of nanocomposites based on poly(benzimidazol), due to interactions between amin groups of polymer and sulfone group of carbon nanotubes was reduced. The obtained micrographs from FE-SEM and TEM depicted uniform dispersion of functionalized carbon nanotubes in the polymer matrix and nanocomposite based on s-MWCNT/s-PA has seen better dispersion.