A study of the ionic liquid mediated microwave heating for the synthesis of new thermally stable and optically active aromatic polyamides under green procedure

Abstract

Ionic liquids (ILs) of the 1,3-dialkylimidazolium-type have great potential for the innovative application of microwaves in synthesis and separation. The use of ILs as reagents in conjunction with microwave heating makes it possible to prepare new organsoluble optically active aromatic polyamides (PAs) by a direct polycondensation reaction of our synthesized dicarboxylic acid: (2S)-4-[(4-methyl-2-phthalimidylpentanoylamino)benzoylamino]- isophthalic acid (9), with several aromatic diamines. The polymerization reactions provided chiral PAs in high yield and inherent viscosities in the range of 0.43–0.85 dLg−1. The chemical structures of some of these samples as representatives were characterized by 1H NMR and elemental analysis. All polymers were characterized by FTIR and specific rotation tools. Their thermal properties were determined by differential scanning calorimetry and thermogravimetric analysis. The efficiency of microwave irradiation conjugated with ILs was compared with that of the polycondensation of this monomer in ILs using conventional heating. The results showed that much shorter reaction times, higher yields and inherent viscosities were obtained under microwave assisted conditions. Furthermore, the use of ILs as a media and catalyst for the above polymerization reactions will eliminate the need of volatile and toxic solvents and reagents as condensing agents and provide a environmentally benign process.