Rheological behavior of pH‐responsive associating ionic polymers of diallyammonium salts and sulfur dioxide

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 (η′) dependence on frequency of polymer solutions of polybetaine/anionic polyelectrolyte (APE) with various compositions of x and z in 0.1 N NaCl showed typical shear thinning behavior. η′ 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 η′ of CAS 4 (M 2 ‐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. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009