40. Cai, Wensheng; Gupta, Ram B. Thermosensitive and Ampholytic Hydrogel for Salt Solution. J. Appl. Polym. Sci. (2003), 88(8), 2032-2037.
A series of 2% methylenebisacrylamide-crosslinked N-isopropylacrylamide/[3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide (NIPAAm/MPSA) copolymer hydrogels was prepd. with various compns. Water sorption of the hydrogels in water, aq. NaCl, KCl, CaCl2, and MgCl2 solns. was studied. The copolymer hydrogels have a higher degree of swelling in water and salt solns. than that of poly(N-isopropylacrylamide) (PNIPAAm). Also, the copolymer hydrogels are more salt resistant when deswelling in salt solns. For <7 mol % MPSA, the formed hydrogels retain both temp. reversibility and high swelling. A higher content of MPSA (>11 mol %) leads to better salt resistance but a decrease in thermosensitivity. The swelling of the copolymer hydrogels in 0.05M NaCl is non-Fickian. In NaCl and KCl aq. solns., the zwitterionic hydrogels do not show obvious antipolyelectrolyte swelling behavior, whereas in divalent salt (CaCl2 and MgCl2) solns., the swelling ability of the copolymer hydrogels is enhanced at low salt concn., then decreases with further increase in salt concn. The lower crit. soln. temps. of the copolymer hydrogels are also affected by concd. salt soln.