Synthesis and Characterization of Novel Heat Stable and Processable Optically Active Poly(Amide–Imide) Nanostructures Bearing Hydroxyl Pendant Group in an Ionic Green Medium

Ionic liquids (IL)s have been recognized as ‘green’ alternatives to the organic solvents in a range of synthesis, catalysis and electrochemistry due to their unique chemical and physical properties. In this investigation, a series of organosoluble, thermally stable and optically active hydroxyl-containing poly(amide–imide)s (PAI)s were prepared via polycondensation reaction of an aromatic diamine, 3,5-diamino-N-(4-hydroxyphenyl)benzamide (4), and different chiral amino acid-based diacids (3a–3e) in the presence of molten tetrabutylammonium bromide as a molten IL and triphenyl phosphite under classical heating method. This process is safe and green since toxic and volatile organic solvents such as N-methylpyrrolidone (NMP) and N,N′-dimethylacetamide (DMAc) were eliminated. The resulting new polymers were obtained in good yields with inherent viscosities ranging between 0.23 and 0.54 dL g⁻¹ and were characterized by Fourier transform infrared spectroscopy, specific rotation, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis, elemental analysis, and in some cases by ¹H-NMR techniques. The FE-SEM micrographs and XRD showed that the synthesized PAIs were nanostructured and amorphous polymers. The effect of ultrasonic irradiation on the size of polymer particles was also investigated and the results showed that the size of polymer nanoparticles after ultrasonication became smaller than the size of them, before ultrasonic radiation. All of the polymers were readily soluble in many organic solvents such as N,N′-dimethyl sulfoxide, DMAc and NMP.