Solubility and solution rheology of acrylamide-sulfobetaine copolymers

The copolymer of acrylamide and 3-N-(2-methacryloxylethyl)-N,N-dimethylammonio]-propane sulfonate (PAM-MDMPS) was prepared via free radical copolymerization. Solubility of the copolymers was studied by turbidimetric titration method under different conditions. It was found for the first time that the critical salt concentration to dissolve the copolymer showed a plateau over one order of magnitude up to the critical overlap concentration. Rheological behavior and chain conformation of the copolymers in 1 M NaCl solution were also studied. The concentration regions according to scaling theory were found the same as neutral polymers in good solvent. The specific viscosities could be normalized by the overlap parameter. According to the Huggins relation, the copolymers adopted a more compact conformation in 1 M NaCl with increasing MDMPS content due to the hydrophobic association of the betaine unit in the macromolecular backbone, which was stabilized by the strongly hydrated dipolar pendant chains.