Sodium ion activity coefficients in aqueous solutions of fully neutralized poly(acrylic acid/ acrylamide) copolymers, whose charge spacing varied from 2.5 to 415 Á, were determined at 25 °C in both the absence and the presence of added simple electrolyte, NaBr. The results are compared with those predicted from additivity and from the theories of Manning and of Iwasa et al. A new empirical linear relationship between the square root of the polyelectrolyte charge density and measured counterion activity coefficients is demonstrated.

Intrinsic viscosities of the Na+, K+, and NH<+ salts of a series of acrylamide/acrylic acid copolymers of identical degree of polymerization but varying charge density have been determined at 25 6C in aqueous solutions containing NaBr, KBr, or NH4Br. It is demonstrated that when counterion binding is taken into account, a linear relationship between intrinsic viscosity and polyelectrolyte charge density is obtained when the molecular weight and concentration of simple electrolyte are kept constant.

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