Straightforward and green method for the synthesis of nanostructure poly(amide-imide)s-containing benzimidazole and amino acid moieties by microwave irradiation
Owing to unique advantages such as shorter reaction times, higher yields, limited generation of by-products, and relatively easy scale-up without detrimental effects, microwave (MW)-assisted polymer synthesis has become an interesting synthetic tool. Also, the usage of ionic liquids (ILs) as perfect “MW solvents” has opened up a new research area among MW-assisted polymerizations. In this investigation, an attempt is made to synthesize several chiral nanostructure poly(amide-imide)s (PAIs) via fast, green, and simple polymerization reaction of several amino acid-based chiral diacids with an aromatic diamine, 2-(3,5-diaminophenyl)-benzimidazole, in tetrabutylammonium bromide as a molten IL under MW irradiation. Organo-soluble and high-performance PAIs were synthesized with high yields and inherent viscosities in the range of 0.40–0.52 dL g−1. These obtained PAIs were characterized using Fourier-transform infrared spectroscopy, specific rotation measurements, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis, and 1H-NMR spectra techniques. The FE-SEM micrographs and XRD showed that the synthesized PAIs were nanostructure and amorphous polymers. To see the efficiency of MW irradiation conjugated with IL, this method was compared with polycondensation under conventional heating method. The combined merits of MW irradiation and IL make the polycondensation reactions with safe operation, low pollution, rapid access to products, and simple workup.