SUPERABSORBENT POLYMERIC MATERIALS .2. SWELLING BEHAVIOR OF CROSS-LINKED POLY[SODIUM ACRYLATE-CO-3-DIMETHYL(METHACRYLOYLOXYETHYL) AMMONIUM PROPANE SULFONATE] IN AQUEOUS SALT SOLUTION

A series of xerogels based on sodium acrylate (SA), 3-dimethyl (methac ryloyloxyethyl) ammonium propane sulfonate (DMAPS), and N,N'-methylene -bis-acrylamide (NMBA) are prepared by inverse suspension polymerizati on. The water absorbencies or swelling behaviors for these xerogels in water or various saline solutions are investigated. Results obtained from this study show that the water absorbency respectively exhibit a value of 1435 g H2O/g sample and 96 g H2O/g sample in deionized water and 0.9 wt % NaCl solution at a gel containing 1.88 x 10(-3) molar rat io of DMAPS while the extent of 1.53 x 10(-3) molar ratio (0.25 wt % b ased on total monomer) of NMBA was used in the polymerization. The abs orbency in the chloride salt solutions decreases with an increase in t he ionic strength of salt. For the same ionic strength of various salt solutions, the swelling amount has the following tendency: Na+ > Fe3 > Al3+ > Ca2+ for the higher ionic strength of 5 x 10(-3)-2 x 10(-2)M and Na+ > Fe3+ > Ca2+ > Al3+ for the lower ionic strength of < 2 x 10 (-4)M. The bound water found by DSC investigation is approximately equ al to 2 g H2O/g sample. The pH effect and thermal effect on the water absorbency for these xerogels are also investigated. (C) 1997 John Wil ey & Sons, Inc.