Polycondensation of new optically active diacid with diisocyanates in the presence of tetrabutylammonium bromide as a green media under microwave heating

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, (2S)-5-(3-phenyl-2-phthalimidylpropanoylamino)isophthalic acid was prepared in three steps. The step-growth polymerization reaction of this novel diacid with various aromatic and aliphatic diisocyanates such as 4,4′-methylene bis(4-phenylisocyanate) (8a), toluylene-2,4-diisocyanate (8b), hexamethylene diisocyanate (8c) and isophorone diisocyanate (8d) were carried out in the presence of tetrabutylammonium bromide (TBAB) as a molten ionic liquid under microwave irradiation conditions and was compared with polymerization in traditional solvent like N-methyl-2-pyrrolidone (NMP). This process is safe and green since toxic and volatile organic solvent such as NMP was eliminated. The resulting new polymers were obtained in good yields with inherent viscosities ranging between 0.25 and 0.46 dL g⁻¹ and were characterized with FT-IR, ¹H-NMR, elemental and thermogravimetric analysis techniques.