Synthesis and properties of ortho-linked aromatic polyamides based on 4,4'-(2,3-naphthalenedioxy)dibenzoic acid

A novel aromatic dicarboxylic acid monomer, 4,4'-(2,3-naphthalenedioxy)dibenzoic acid(3), was prepared by the fluorodisplacement reaction of p-fluorobenzonitrile with 2,3-dihydroxynaphthalene in N,N-dimethylformamide (DMF) in the presence of potassium carbonate followed by alkaline hydrolysis of the intermediate dinitrile. A series of novel aromatic polyamides containing ortho-linked aromatic units in the main chain were synthesized by the direct polycondensation of diacid 3 and a variety of aromatic diamines using triphenyl phosphite and pyridine as condensing agents in the N-methyl-2-pyrrolidone (NMP) solution containing dissolved calcium chloride. The resulting polyamides had inherent viscosities higher than 0.74 and up to 2.10 dL/g. All of these polyamides were soluble in polar solvents, such as NMP, DMF, N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide. Transparent, flexible, and tough films could be cast from their DMAc or NMP solutions. The solvent-cast films had high tensile strengths and moduli. Extensions to break were relatively low, except for the polymers derived from 2,2-bis[4-(4-aminophenoxy) phenyl] hexafluoropropane and 3,4'-oxydianiline, which had elongations of 82 and 62%, respectively. Except for the polyamide based on p-phenylenediamine, all the other polyamides were amorphous in nature. All the polymers are thermally stable to temperatures in excess of 450 degrees C in either air or nitrogen atmosphere. The polymers exhibited glass transition temperatures ranging from 183 to 260 degrees C and decomposition temperatures (10% weight loss) ranging from 462-523 degrees C in air and 468-530 degrees C in nitrogen. (C) 1997 John Wiley & Sons, Inc.