Preparation and characterization of thermostable chiral extended polyamides bearing N-phthaloyl-L-leucine pendent architectures in green media

Ionic liquids (ILs) are often well-known benign solvents capable of replacing conventional organic solvents, and they have become attractive solvents for many chemical reactions. Aromatic polyamides (PAs) have received particular interest in past years because of their high thermal and chemical resistance and their potential as high-performance materials for different applications. In this investigation, the preparation of extended PAs derived from 5-aminoisophthalic acid containing chiral pendent linkage (N-phthaloyl-l-leucine) with various aromatic diamines was studied. The bulky monomer 5-(4-methyl-2-phthalimidylpentanoylamino)isophthalic acid was prepared in three steps. Direct polyamidation of this monomer with several commercially available diamines in the presence of IL (1,3-dipropylimidazolium bromide) and triphenyl phosphite gave novel PAs in good yields and inherent viscosities in the range of 0.38–0.55 dL g⁻¹. Because of the existence of amino acid in this architect, the resulting polymers are optically active. All of these PAs showed good solubility and readily dissolved in many organic solvents. Characterization of all the products was performed by FTIR, specific rotation, and representative ones by ¹H NMR, elemental analysis, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). TGA exhibited that two elite polymers were stable, with 10% weight loss recorded above 410 and 430°C in the nitrogen atmosphere.