In this study, the viscoelastic behavior of hydrophobically modified polyelectrolytes obtained from the hydrolysis of cationic acid salts (CAS's) as a function of their zwitterion fraction (x) and anion fraction (z) was studied. The dynamic viscosity (eta') dependence on frequency of polymer solutions of polybetaine /anionic polyelectrolyte (APE) with various compositions of x and z in 0.1N NaCl showed typical shear thinning behavior. eta' of a solution of CAS 4 (M-2-4 (4 mol %. hydrophobe)) attained a maximum value in the presence of 1.67 equiv of NaOH (corresponding to an x : z ratio of 33 : 67) and decreased with any further addition of NaOH. We suggest this maximum to be a result of a combined effect of coil expansion and hydrophobic association. The influence of the temperature and concentration on eta' of CAS 4 (M2-4) treated with 1.67 equiv of NaOH was also investigated. The rheology of CAS 4 (M-2-4) samples treated with 1.67, 1.81, and 2.0 equiv of NaOH suggested a reversible network. However, for APE 7 (M-2-5 (5 mol % hydrophobe)), elastic behavior was dominant, and the formation of highly interconnected three-dimensional networks was suggested. At lower x : z ratios, the effect of coil expansion due to a higher APE fraction was more than counterbalanced by the lower degree of intermolecular hydrophobic associations, whereas at higher x: z ratios, coil contraction became the predominant effect. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 125-131, 2009