Preparation and characterization of aromatic polyamides from 4,4′-(2,6-naphthylenedioxy)dibenzoic acid and aromatic diamines

A new aromatic dicarboxylic acid, 4,4'-(2,6-naphthylenedioxy)dibenzoic acid (3), was synthesized by the fluoro-displacement reaction of p-fluorobenzonitrile with 2,6-naphthalenediol in the presence of potassium carbonate, followed by alkaline hydrolysis. A series of aromatic polyamides having inherent viscosities of 1.30-2.19 dL/g were prepared by the triphenyl phosphite activated polycondensation from the diacid 3 with sixteen aromatic diamines. Most of the resulting polymers were noncrystalline and readily soluble in a variety of polar solvents such as N,N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP). Except for those polymers derived from p-phenylenediamine, benzidine, and 4,4'-bis(p-aminophenoxy)biphenyl, transparent, tough, and flexible films were cast from the DMAc or NMP solutions. The films had tensile strengths ranging from 70 to 91 MPa, elongations at break from 6 to 50%, and initial moduli from 1.35 to 2.32 GPa. The polyamides exhibit glass transition temperatures in the range of 178 - 300 degrees C. Almost all polymers are stable up to 400 degrees C, with 10% weight loss being recorded above 500 degrees C, in air and nitrogen atmosphere.