Efficient and Rapid Synthesis of Novel Optically Active Polyamides in the Presence of Tetrabutylammonium Bromide as Ionic Liquid under Microwave Irradiation

There is increasing interest in using ionic liquids (ILs) as solvents for polymerization processes. The use of an inexpensive and readily available IL such as tetrabutylammonium bromide (TBAB) as a solvent for clean synthesis and catalytic processes is becoming widely recognized and accepted. This article reports an extension of a microwave method, describing the synthesis of optically active polyamides (PAs) in TBAB. Polycondensation reactions of diacid 5-(3-methyl-2-phthalimidylpentanoylamino) isophthalic acid with different diisocyanates such as 4, 4′-methylenebis(phenyl isocyanate), toluylene-2,4-diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate were carried out in the presence of TBAB as a molten salt under microwave irradiation and with a conventional heating method, and they were compared with polymerizations in a traditional solvent such as 1-methyl-2-pyrrolidone. A series of optically active PAs with high yields and inherent viscosities ranging from 0.20 to 0.60 dL/g were obtained. These PAs were characterized with Fourier transform infrared spectroscopy, specific rotation measurements, ¹H-NMR, elemental analysis, thermogravimetric analysis, and differential scanning calorimetry. All data agreed with the proposed structures. Some physical properties and structural characterizations of these PAs are reported.