Synthesis and properties of aromatic polyamides based on 4,4′-(1,5-naphthalenedioxy)dibenzoic acid

4,4′-(1,5-Naphthalenedioxy)dibenzoic acid ( 3 ), a novel aromatic dicarboxylic acid monomer, was prepared by nucleophilic substitution reaction of 1,5-dihydroxynaphthalene and p-fluorobenzonitrile in N,N-dimethylformamide (DMF) in the presence of potassium carbonate and subsequent alkaline hydrolysis of the intermediate dinitrile, 4,4′-(1,5-naphthalenendioxy)dibenzonitrile. Using triphenyl phosphite (TPP) and pyridine as condensing agents, a series of novel aromatic polyamides were synthesized by direct poly-condensation of diacid 3 and twelve aromatic diamines in N-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride. The resulting polyamides had inherent viscosities above 1,14 and up to 4,45 dL/g. Most of these polyamides are readily soluble in polar solvents, such as NMP, DMF, and N,N-dimethylacetamide (DMAc). Transparent, flexible, and tough films could be cast from their DMAc or NMP solutions. Most of these polymers were amorphous in nature, as indicated by their wide-angle X-ray diffractograms. Thermogravimetric analysis (TG) showed that all the polyamides were stable up to 450°C in both air and nitrogen atmosphere. Most of them revealed a distinct glass transition on the differential scanning calorimetry (DSC) traces in the range of 183–259°C.