pH-responsive ampholytic terpolymers of acrylamide, sodium 3-acrylamido-3-methylbutanoate, and (3-acrylamidopropyl)trimethylammonium chloride. II. Solution properties

The solution properties of low-charge-density ampholytic terpolymers of acrylamide, sodium 3-acrylamido-3-methylbutanoate, and (3-acrylamidopropyl)trimethylammonium chloride were studied as functions of the solution pH, ionic strength, and polymer concentration. Terpolymers with low charge densities, large charge asymmetries, or both exhibited excellent solubility in deionized (DI) water, and higher charge density terpolymers were readily dispersible in DI water; however, the higher charge density terpolymer solutions separated into polymer-rich and polymer-poor phases upon standing over time. Charge-balanced terpolymers exhibited antipolyelectrolyte behavior at pH values greater than or equal to the ambient pH (6.5 +/- 0.2); the same terpolymers behaved increasingly as cationic polyelectrolytes with decreasing solution pH because of the protonation of the 3-acrylamido-3-methylbutanoate (AMB) repeat units. Unbalanced terpolymers generally exhibited polyelectrolyte behavior, although the effects of intramolecular electrostatic attractions (i.e., polyampholyte effects) on the hydrodynamic volume of the unbalanced terpolymer coils were evident at certain values of the solution pH and salt concentration. The dilute-solution behavior of the terpolymers correlated well with the behavior predicted by several polyampholyte solution theories. In the semidilute regime, solution viscosities increased with increasing terpolymer charge density, and this indicated a significant enhancement of the solution viscosity by intermolecular electrostatic associations. Upon the addition of NaCl, semidilute-solution viscosities tended to decrease because of the disruption of the intermolecular electrostatic associations. (C) 2004 Wiley Periodicals, Inc.