Chain Stiffness and Excluded-Volume Effects in Sodium Poly(styrenesulfonate) Solutions at High Ionic Strength

Abstract

Sixteen narrow-distribution samples of sodium poly(styrenesulfonate) (NaPSS) ranging in weight-average molecular weight M w from 2.6 × 103 to 6.5 × 105 were prepared by the radical polymerization of sodium-p-styrenesulfonate, followed by repeated fractional precipitation, and were studied by static light scattering, sedimentation equilibrium, and viscometry in 0.5 M aqueous NaCl at 25 °C and in 4.17 M aqueous NaCl at 16.4 °C, the ϑ point, where the light scattering second virial coefficient vanished for high M w. The characteristic ratio (i.e., the mean-square radius of gyration at the ϑ point divided by the degree of polymerization) for high-molecular-weight NaPSS was found to be considerably smaller than that for polystyrene in cyclohexane. Data for the intrinsic viscosity [η] in 4.17 M aqueous NaCl at ϑ were analyzed by the theory of Yoshizaki et al. (Macromolecules 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 experimental tests of available theories for the electrostatic persistence length. At the lower NaCl concentration of 0.5 M where intramolecular excluded-volume effects were significant, the molecular weight dependence of [η] was explained quantitatively by a combination of Yoshizaki et al.'s theory and the quasi-two-parameter theory with a larger q of 1.5 nm and an excluded-volume strength parameter of 1.6 nm.

Chain Stiffness and Excluded-Volume Effects in Polyelectrolyte Solutions: Characterization of Sodium Poly(2-acrylamido-2-methylpropanesulfonate) in Aqueous Sodium Chloride

“…The q values for Na PAMPS in Table II are comparable to those reported previously 8,11 for Na PSS in aqueous NaCl with the corresponding salt concentrations (1.5 nm at C s ¼ 0:5 M and 2.7 nm at C s ¼ 0:05 M, both from []), indicating that the two polyelectrolytes have similar stiffness in the aqueous salts. On the other hand, the B values for Na PAMPS are considerably larger than those for Na PSS (1.6 nm at C s ¼ 0:5 M and 4.0 nm at C s ¼ 0:05 M).…”

“…The (total) persistence lengths of 1:5 (AE 0:1) nm at the higher C s and 3.0 nm at the lower C s are comparable to those for Na PSS 8,11 in the corresponding solvents, indicating that the two polyelectrolytes have similar chain stiffness. The electrostatic contributions to q may also be similar, but discussions on q el are deferred to the forthcoming paper, in which both q el and the electrostatic excluded-volume strength for Na PAMPS in aqueous NaCl will be examined as functions of ionic strength.…”

“…[5][6][7][8] The major problem in the estimation of q el is that excluded-volume and stiffness effects can hardly be separated for those polymers without resort to a relevant excluded-volume theory. In previous studies, [5][6][7][8][9][10][11] we utilized the quasi-two-parameter (QTP) theory (the Yamakawa-Stockmayer-Shimada theory) [12][13][14] for the wormlike chain 15 or, more generally, the helical wormlike chain 14 to estimate these effects in aqueous NaCl solutions of sodium hyaluronate and sodium poly(styrenesulfonate) (Na PSS). Except for some details, the QTP scheme satisfactorily explained the molecular weight dependence of intrinsic viscosity [] and mean-square radius of gyration hS 2 i for the two polyelectrolytes at fixed salt concentrations C s higher than 10 À2 M. On the other hand, the available polyelectrolyte theories [1][2][3][4]16 failed to describe the C s dependence of the estimated q el and excluded-volume strength, though the degree of disagreement appeared to depend on the intrinsic chain stiffness.…”

Electrostatic Contributions to Chain Stiffness and Excluded-Volume Effects in Sodium Poly(styrenesulfonate) Solutions

“…These polymers differ largely in intrinsic flexibility and charge density. In fact, NaPSS has a small q of0.69 nm in 4.17 M aqueous NaCl at 16.4°C, 8 the theta point, when modeled by the wormlike chain (a special limit of the helical wormlike chain 9 ), and its linear charge density is roughly four times as high as that of Na hyaluronate. In the work reported below, we analyze the measured [1J] at different salt concentrations between 0.05 and 2 M by a combination of Yoshizaki et al's theory 17 for unperturbed wormlike chains and the QTP theory, assuming that possible helical nature ofNaPSS is weak.…”

On the Importance of Purification of Sodium Polystyrene Sulfonate

“…Indeed, several researchers [5,21,22] have employed ion exchange method for purification of NaPSS. However, as reported by Reddy and Marinsky [14], polystyrene sulfonic acid-an intermediate formed during ion exchange-is unstable at room temperatures, and thus any associated "degradation" process may inadvertently introduce impurities in the original sample, if proper care is not taken.…”