Synthesis and properties of novel soluble aromatic polyamides derived from 5-(2-phthalimidyl-3-methyl butanoylamino)isophthalic acid and aromatic diamines

Wholly aromatic polyamides are high-performance and attractive materials, but, due to their low solubility, their applications have been restricted. In this work a new class of wholly aromatic and optically active polyamides (PAs) having phthalimide and S-valine pendent groups were prepared by the reaction of 5-(2-phthalimidyl-3-methyl butanoylamino)isophthalic acid (1) as a diacid monomer with various readily available aromatic diamines. Triphenyl phosphite/pyridine in the presence of calcium chloride and N-methyl-2-pyrrolidone (NMP) were successfully applied for direct polycondensation. The resulting novel polymers were obtained in good yields, inherent viscosities ranging between 0.21 and 0.74 dL g⁻¹ and were characterized with elemental analysis, FT-IR, ¹H NMR, specific rotation and thermogravimetric analysis techniques. Bulky pendent groups of the polymer chains disturb interchain and intrachain interactions and make thesePAs readily soluble in polar, aprotic solvents such as N,N-dimethylacetamide, N,N-dimetheylformamide, dimethyl sulfoxide, NMP and solvents such as sulfuric acid. Thermogravimetric analysis showed that the 10% weight loss temperature in a nitrogen atmosphere were more than 320 °C, which indicates that the resulting PAs have good thermal satiability as well as excellent solubility. In addition because of existence of chiral center and optical activity of these polymers, they have potential to be used as chiral stationary phase in chromatography technique for the separation of racemic mixtures.