A facile, microwave-assisted synthesis of novel optically active polyamides derived from 3-methyl-2-(phthalimidylpentanoyl-amino)isophthalic acid and different diisocyanates
5-(3-Methyl-2-phthalimidylpentanoylamino)isophthalic acid as a novel aromatic diacid monomer was prepared in three steps. In the first step, phthalic anhydride was reacted with -isoleucine in acetic acid solution, and the resulting imide acid was obtained in high yield. In the second step, treatment of this imide acid with excess thionyl chloride gave aliphatic acid chloride in good yield. In the last step, this acid chloride was reacted with 5-aminoisophthalic acid to provide novel bulky chiral aromatic diacid monomer. The direct polycondensation reactions of this diacid with several aromatic and aliphatic diisocyanates such as 4,4′-methylenebis(phenyl isocyanate), toluylene-2,4-diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate were carried out under microwave irradiation. In order to compare this method with classical heating, the polymerization reactions were also performed under solution polycondensation conditions. The polymerization reactions occurred rapidly under microwave conditions and produced a series of novel optically active polyamides (PA)s containing pendent phthalimide group, with good yields and moderate inherent viscosities of 0.17–0.60 dL/g. Some of the new PAs showed good solubility and are readily soluble in organic solvents. The resulting macromolecules were characterized by FT-IR, specific rotation, and representative ones by 1H NMR, elemental and thermogravimetric analyses (TGA).