Chiral poly(amide-imide)/organoclay nanocomposites derived from pyromellitoyl-bis-l-isoleucine and benzimidazole containing diamine: synthesis, nanostructure, and properties

In this study, a series of polymer–clay nanocomposite materials, consisting of organosoluble poly(amide-imide) (PAI) matrix and dispersed nanolayers of inorganic montmorillonite clay, were successfully prepared by solution dispersion technique. At first, the reactive organoclay was prepared by using protonated l-isoleucine amino acid as a swelling agent for silicate layers of Cloisite Na⁺. Then, organosoluble PAI containing isoleucine amino acid was synthesized through step-growth polymerization reaction of N,N′-(pyromellitoyl)-bis-isoleucine diacid and 2-(3,5-diaminophenyl)-benzimidazole under green condition using molten tetrabutylammonium bromide. This polymer was end-capped with amine end groups near the completion of the reaction to interact chemically with acidic group of organoclay. Finally, PAI/organoclay nanocomposite films containing 2%, 5%, 10%, and 15% of organoclay were prepared via solution intercalation method through blending of organoclay with the PAI solution. Dispersion of the modified clay in the PAI matrix resulted in a nanostructured material containing intercalated polymer between the silicate layers. Structures of exfoliation were confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis data indicated that the addition of organoclay into the PAI matrix increased the thermal decomposition temperatures of the obtained nanocomposites compared to the pure PAI.