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 acidicmonomer 2-acrylamido-2-methylpropanesulfonate (AMPS) was studied in the Ca2+ 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 Tc of phase separation and the metal salt concentration with a minimum at the mid-position

whereas the Tc remains constant as varying polymer oncentration．From comparison of the effects of AA and AMPS units on the phase separation behavior of P3A polymers the results obtained indicate that excent 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 Ca2+ 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．