Synthesis and characterization of novel, optically active polyamides derived from S-valine natural amino acid and bulky anthracenic side chain

This is the first description of the application of molten tetrabutylammonium bromide (TBAB) in the presence of triphenyl phosphite (TPP) for the synthesis of novel polyamides (PAs). Monomer diacid, 5-[(9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximido)-3-methylbutanoylamino]isophthalic acid (4), having anthracenic and amino acid S-valine pendant group, was synthesized in four steps. Several novel, optically active PAs were prepared by the condensation of synthesized diacid monomer 4 with various aromatic diamines using two different techniques: a mixture of N-methyl-2-pyrrolidone (NMP)/TPP/pyridine/calcium chloride (method I) and combination of TPP with TBAB (method II). The main goal of the present paper was to prepare novel PAs in a green media by removal of toxic reagents. Therefore, TBAB/TPP was used as a novel, easy, safe and eco-friendly method for the preparation of aromatic PAs. This method is compared with the polymerization reaction under conventional solvent and in the case of TBAB as a new method, higher yields, inherent viscosities and thermally stable of PAs are gained. The resulting polymers showed good solubility in polar aprotic solvents such as dimethyl sulfoxide, NMP, N,N-dimethylacetamide and N,N-dimethylformamide. These polymers are characterized with respect to chemical structure and purity by means of specific rotation experiments, FT-IR, H-1 NMR spectroscopy techniques and elemental analysis. The obtained PAs exhibit good thermal stability up to 335A degrees C for 10% weight loss in nitrogen atmosphere and glass transition temperatures fell in the rang of 177-185A degrees C.