Wholly aromatic chiral polyamides bearing pendant phthalimido and L-isoleucine moities

 A potential biodegradable and optically active bulky chiral aromatic amide-imidic diacid monomer, (2S,3S)-5-(3-methyl-2-phthalimidylpentanoylamino)isophthalic acid (7), containing a rigid phthalimide and flexible L-isoleucine pendant group was synthesized in three steps. New aromatic polyamides including pendant phthalimido groups and flexible side spacers have been synthesized by direct polycondensation reaction of equimolar amounts of different aromatic diamines with an optically active diacid 7, using N-methyl-2-pyrrolidone (NMP) as a solvent and triphenyl phosphite/CaCl₂/pyridine as a condensing agent. These polyamides were characterized by FTIR, 1H-NMR spectroscopy, specific rotation, thermogravimetric and elemental analysis. The resulting polymers have inherent viscosities in the range of 0.21-0.45 dL/g. Amino acid existence in this backbone results in optically active polymers. Due to introduction of bulky and flexible groups in these polyamides, they show improved solubility in polar aprotic solvents such as NMP and dimethylacetamide and also good thermal stability (10% weight loss temperatures in excess of 330°C, and char yields at 600°C in nitrogen higher than 62%).