Study of the molecular conformation of an aromatic polyamide–hydrazide by intrinsic viscosity

The persistence length of poly(terephthaloyl p‐amino benzhydrazide) (X‐500) in dimethyl sulfoxide (DMSO) has been determined from intrinsic viscosities measured for several whole‐polymer samples. An approximate correction is applied for excluded volume effects, and these corrected values are fitted using the viscosity treatments of Yamakawa and Fujii and of Eizner and Ptitsyn. Both give for the persistence length of X‐500 values in the range 30–35 Å. Revised treatment of our previous light scattering data for the same polymer yields 49 Å for the persistence length. Thus the chain extension of X‐500 falls between those of para‐linked polyamides and those of typical freely coiling macromolecules. Phase diagram studies indicate the solubility of X‐500 in DMSO decreases with rising temperature, and can be increased by the addition of LiCl. No anisotropic phase is found in DMSO at the highest volume fraction of polymer, v2 = 0.19, which can be obtained with 4 g/dl LiCl. The critical concentration of X‐500 needed for the appearance of the anisotropic phase depends upon solvent since Morgan reported an anisotropic phase for this polymer in 100% H2SO4 when v2 ≈ 0.13.