Nanostructured amino acid containing poly(amide-imide)s from different diisocyanates: synthesis and morphology properties in molten TBAB as a green media

In this investigation, a series of nanostructured optically active poly(amide-imide)s (PAI)s were prepared via solution polycondensation of N-trimellitylimido-l-isoleucine as a chiral diacid monomer containing naturally occurring α-amino acids with different aliphatic and aromatic diisocyanates in the presence of molten tetrabutylammonium bromide (TBAB) as an environmental friendly medium and a volatile organic solvent and the results of them were comparable. In these step-growth polycondensations amino acid was used as a chiral inducing agent. The obtained polymers were characterized with respect to chemical structure and purity using specific rotation experiments, FT-IR techniques and elemental analysis. The surface morphology of these polymers was investigated by field emission scanning electron microscopy. The results indicated that the aforementioned polymers have nanostructured morphology. The obtained polymers have inherent viscosities in a range of 0.12–0.45 dL/g. Thermal stability of the resulting PAIs was studied by thermogravimetric analysis. A comparison with conventional solvents was exhibited smoothly higher inherent viscosities and better yields and thermal stability. The results showed that the molten TBAB was superior polymerization media. This process was safe and green, since toxic and volatile organic solvent such as N-methyl-2-pyrrolidone was eliminated. The observation of optical rotation confirms the optical activity of these polymers.