AbstractBy sulfonation of poly[(maleic anhydride)‐alt‐styrene] in mild conditions (SO3/triethylphosphate, 298 K) a series of poly[(maleic acid)‐alt‐(p‐sulfostyrene, styrene)] have been prepared having the same average chain length but various content ofp‐sulfostyrene units (from 18 to 83 mol %). A behavior of diluted aqueous solutions of two polyelectrolyte series (polyacids and Na‐salts) has been compared, using viscosimetric, conductometric, and potentiometric measurements, and taking into consideration the degree of sulfonation and the kind of counterions (H+, Na+). Although the values of intrinsic viscosities [η] and equivalent conductivities λ of two copolymer series belong to two different ranges, in polyacid series they increase with increasing the degree of sulfonation, while in Na‐salt series they decrease. According to the potentiometric titration and reduced viscosity data, the intensity of conformational chain transitions of sulfonated polycids also decreases with increasing the degree of sulfonation. The noticed effects are related to structural characteristics of functional copolymers, gradual increase of a charge density along the chains, lower mobility of the Na‐salts, and to a diminished hydrophobicity of styrene units due to sulfonation. © 1995