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

Abstract

AbstractThree 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. There 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 triphenyl phosphite 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 tests. The glass transition temperatures (Tg'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°C. In general, the polyamides based on catechol had Tg's comparable with the ones of the hydroquinone‐based polyamides and higher Tg's than the corresponding resorcinol‐based ones. Thermogravimetric analysis data of these polymers indicated that all the polyamides were stable up to 400°C in both air and nitrogen atmospheres.