Hydrodynamic and conformational characteristics of aromatic water-soluble para-sulfopolyamide

A sulfonated para-aromatic water-soluble polyamide (poly-4,4′-(sodium 2,2′-disulfonate)-diphenylene terephthalamide) was studied by viscometry, sedimentation velocity, and translational diffusion in dilute solutions in salt-free and 0.1 M NaCl solutions. The canonical and cross-scaling relations in 0.1 M NaCl were obtained. A Kuhn–Mark–Houwink–Sakurada plot normalized to the mass per unit chain length demonstrated that the conformation of the macromolecule of sulfonated para-aromatic water-soluble polyamide is no different from that of other rigid-chain para-aromatic polyamides. The equilibrium rigidity of sulfonated para-aromatic polyamide molecules was determined by the theories for the wormlike cylinder in different ways: using translational and rotational friction data and using only translational friction data. The average Kuhn segment length in 0.1 M NaCl was estimated as A = 17 ± 2 nm. In a salt-free solution, the electrostatic interactions are present, but they do not significantly change conformation of the macromolecule because the original rigid chain structure does not allow it to unfold more.