Phase separation behavior of the water soluble binary anionic acrylamide copolymer series (P3A) composed of non ionic monomer acrylamide (AM), weak acidic monomer acrylic acid (AA) and strong acidic monomer 2 acrylamido 2 methylpropanesulfonate (AMPS) was studied in the Ca 2+ ion aqueous solution. The P3A was found to exhibit an unusual phase separation behavior, which relates with structure and composition of the polymer, as well as the concentration and temperature in the dilute P3A solution. A non linear relationship appeared between the critical temperature T c of phase separation and the metal salt concentration with a minimum at the mid position, whereas the T c remains constant as varying polymer concentration. From comparison of the effects of AA and AMPS units on the phase separation behavior of P3A polymers the results obtained indicate that except for the difference in acidity of two anionic units, the phase separation is mostly affected by the structure of anion unites in the polymer chain. The AMPS units exhibit a good stability under the action of Ca 2+ ions due to their great steric influence of side chains compared to AA units. Therefore, containing more AMPS, the polymer (P3A) becomes the more resistant to phase separation in the divalent metal salt solution.
