Amphoteric copolymers of the carboxybetaine monomer 4-[(2-acrylamido-2-methylpropyl)dimethylammonio]butanoate (AMPDAB), 1, with the sulfobetaine monomer 3-[(2-acrylamido-2-methylpropyl)dimethylammonio]propanesulfonate (AMPDAPS), 2, have been synthesized by free radical polymerization in 0.5 M NaBr. The feed ratios of 1:2 were varied from 100:0 to 0:100 mol %. Molecular weights were determined by low angle laser light scattering and range from 1.65 × 10 6 to 3.95 × 10 6 . The homopolymer of 2 was insoluble in deionized water but soluble in aqueous solutions containing a critical concentration of added electrolytes. In contrast, the homopolymer of 1 was soluble in deionized water. The solubility behavior of copolymers of 1 and 2 is complex and varies with copolymer composition, pH, as well as the concentration and nature of the added electrolytes. Coulombic interactions and hydration effects are suggested to be the main factors affecting the solubility behavior of these amphiphilic copolymers. Low shear viscosity studies were conducted at varying electrolyte concentrations and pH values. The copolymers with a higher incorporation of AMPDAPS, 2, mer units showed greater enhancement in viscosity with increased electrolyte concentration. Copolymers containing AMPDAB, 1, mer units exhibit polyelectrolyte behavior at low pH in deionized water as the carboxylate groups are protonated, resulting in an overall cationic charge along the polymer chain. The solution behavior of these responsive systems is rationalized on the basis of competitive hydration of the zwitterionic moieties under testing conditions.

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A novel carboxybetaine monomer, 6‐(2‐Acrylamido‐2‐methylpropyldimethylammonio) hexanoate (AMPDAH), has been synthesized and copolymerized with acrylamide in an aqueous NaBr solution. The feed ratio of AM (M1): AMPDAB(M2), was varied from 98.5 : 2.5 to 0 : 100 mol %. The polymerizations were carried out to 20–30% conversion. Copolymer compositions were determined with 13C NMR by integration of the amido carbonyl resonances. Reactivity ratios determined from the nonlinear least‐squares method gave values of r1 = 0.98 and r2 = 0.85, indicating random incorporation of the comonomers into the final copolymer. Molecular weights ranged from 7.3 to 4.7 × 106 g/mol. The solubility behavior of the copolymers is dependent on the mol % AMPDAH incorporated into the copolymers. When 25 mol % or more is incorporated, the copolymers are only swellable in aqueous media and attempts to solubilize these systems were unsuccessful. AMPDAH incorporation of 10 mol % or less resulted in copolymers soluble in aqueous media under a variety of conditions. The viscometric properties of copolymers with 10 mol % or less is reported as a function of pH and added electrolytes. At high pH in deionized water, the polyzwitterions show both inter‐ and intramolecular associations, which are disrupted by the addition of sodium chloride. In deionized water, as the pH of the aqueous medium is lowered, the copolymers exhibit dramatic increases in viscosity as the carboxylate groups are protonated and charge–charge repulsions of the quaternary ammonium groups induce polyelectrolyte behavior. © 1997 John Wiley & Sons, Inc.