Synthesis and properties of aromatic polyamides based on 4,4'-[1,4(1,3 or 1,2)-phenylenedioxy]dibenzoic acid

Three isomeric bis(ether carboxylic acid)s, 4,4'-[1,2 (1,3 or 1,4)-phenylenedioxy] dibenzoic acid (o-, m-, or p-3) were prepared by nucleophilic substitution reaction of the potassium phenolate of catechol, resorcinol, and hydroquinone, respectively, with p-fluorobenzonitrile, giving the corresponding bis(ether nitrile)s, followed by alkaline hydrolysis. Three series of isomeric polyamides were synthesized by direct polycondensation of the bis(ether carboxylic acid)s with various aromatic diamines in N-methyl-2-pyrrolidone (NMP) solution containing dissolved metal salts such as CaCl2 or LiCl using triphenylphosphite and pyridine as condensing agents. The resultant polyamides had inherent viscosities of 0,52-1,63 dL/g. Most of the polymers were soluble in polar aprotic solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), NMP, and dimethyl sulfoxide. The catechol-based polyamides revealed markedly higher solubility than those based on hydroquinone or resorcinol. Transparent, flexible and tough films could be cast from the DMAc or NMP solutions of most of the polyamides. All the casting films were characterized by tensile rests. The glass transition temperatures (T-g's) of most polyamides could be determined with the help of differential scanning calorimetry (DSC) traces, which were recorded in the range of 183 - 232 degrees C. In general, the polyamides based on catechol had T-g's comparable with the ones of the hydroquinone based polyamides and higher T-g's than the corresponding resorcinol-based ones. Thermogravimetric analysis data of these polymers indicated that all the polyamides were stable up to 400 degrees C in both air and nitrogen atmospheres.