Chain stiffness and excluded-volume effects in sodium poly(styrenesulfonate) solutions at high ionic strength

Sixteen narrow-distribution samples of sodium poly(styrenesulfonate) (NaPSS ) ranging in weight-average molecular weight M-w from 2.6 x 10(3) to 6.5 x 10(5) were prepared by the radical polymerization of sodium-p-styrenesulfon ate, followed by repeated fractional precipitation, and were studied by sta tic light scattering, sedimentation equilibrium, and viscometry in 0.5 M aq ueous NaCl at 25 degrees C and in 4.17 M aqueous NaCl at 16.4 degrees C, th e Theta point, where the light scattering second virial coefficient vanishe d for high M-w. The characteristic ratio (i.e., the mean-square radius of g yration at the Theta point divided by the degree of polymerization) for hig h-molecular-weight NaPSS was found to be considerably smaller than that for polystyrene in cyclohexane. Data for the intrinsic viscosity [eta] in 4.17 M aqueous NaCl at Theta were analyzed by the theory of Yoshizaki et al. (M acromolecules 1988, 21, 165) for the wormlike chain, a special limit of the helical wormlike chain, to obtain 0.23 (+/- 0.03), 0.69 (+/- 0.07), and 1. 2 (+/- 0.1) nm for the monomeric contour length, the persistence length q, and the chain diameter, respectively. This q value is much smaller than the intrinsic persistence length of 1.2 nm widely used in the literature for e xperimental tests of available theories for the electrostatic persistence l ength. At the lower NaCl concentration of 0.5 M where intramolecular exclud ed-volume effects were significant, the molecular weight dependence of [eta ] was explained quantitatively by a combination of Yoshizaki et al.'s theor y and the quasi-two-parameter theory with a larger q of 1.6 nm and an exclu ded-volume strength parameter of 1.6 nm.