Synthesis and characterization of soluble and heat-resistant aromatic polyamides derived from diamine; N-(3,5-diaminophenyl)-4-(naphthalen-7-yloxy)benzamide and various aromatic diacids

Abstract

The new aromatic m-catenated diamine, N-(3,5-diaminophenyl)-4-(naphthalen-7-yloxy)benzamide was synthesized from 2-naphthol and 4-fluoro benzonitrile as starting materials. A series of novel aromatic polyamides were synthesized from the diamine and several aromatic diacids such as 4,4′-Oxydibenzoic acid, Naphthalene-2, 6-dicarboxylic acid, 4,4′-Sulfonyldibenzoic acid, Biphenyl-4,4′-dicarboxylic acid and 4,4′-(perfluoropropane-2, 2-diyl) dibenzoic acid via direct Yamazaki’s phosphorylative polycondensation method with triphenyl phosphite (TPP) as a condensing agent in pyridine (Py)/LiCl/1-methyl-2-pyrrolidone (NMP) solvent system. These new m-catenated/kink structured polyamides containing pendant naphthalene-oxy-benzamide units, were characterized by inherent viscosities, solubility in organic solvents, FTIR, DSC, TGA and XRD techniques. The polyamides were obtained in good yields and had inherent viscosities in range 0.35 and 0.55 dL/g. These polyamides were soluble in amide type aprotic solvents namely N, N′ dimethyl formamide (DMF), N-methyl-2-pyrrolidone (NMP), N, N′ dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO) and partly soluble in m-cresol, tetrahydrofuran (THF) and chloroform or dichloromethane. Polyamides showed glass-transition temperatures in the range 224 °C–262 °C indicating their processability at these temperatures. Thermogravimetric analysis in nitrogen atmosphere showed the 10% weight loss temperatures were more than 555 °C, indicating a good thermal stability. X-ray diffraction patterns of these polyamides indicated the amorphous nature, which is reflected in solubility characteristics.