A dicarboxylic acid monomer, 5-phthalimidoisophthalic acid, containing a phthalimide pendent group was prepared by the condensation of 6-aminoisophthalic acid and phthalic anhydride in glacial acetic anhydride. The monomer was reacted with various aromatic diamines to produce polyamides using triphenyl phosphite and pyridine as condensing agents. These polyamides were produced with inherent viscosities of 0.64-1.14 dL g(-1). All the polymers, characterized by wide-angle X-ray diffraction, revealed an amorphous nature resulting from the presence of the bulky pendent group. These polyamides exhibited excellent solubility in a variety of solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, dimethyl sulfoxide, pyridine, and cyclohexanone. These polyamides showed glass-transition temperatures (T-g's) between 247 and 273 degreesC (by DSC) and 248 and 337 degreesC (by a dynamic mechanical analyzer). The thermogravimetric analytic measurement revealed the decomposition temperature at 10% weight-loss temperatures (Td(10)) ranging from 442 to 530 degreesC in nitrogen. The polyamides containing phthalimide groups exhibited higher T-g and Td(10) values than those having no phthalimide groups. Transparent, tough, and flexible films of these polyamides could be cast from the DMAc solutions. These casting films had tensile strengths ranging from 81 to 126 MPa, elongations at break ranging from 7 to 13%, and tensile moduli ranging from 2.0 to 2.9 GPa.