SUPERABSORBENT POLYMERIC MATERIALS .4. SWELLING BEHAVIOR OF CROSS-LINKED POLY[SODIUM ACRYLATE-CO-N,N-DIMETHYL(ACRYLAMIDOPROPYL) AMMONIUM PROPANE SULFONATE] IN AQUEOUS SALT SOLUTION

A series of xerogels based on sodium acrylate ( SA), N,N-dimethyl(acry lamidopropyl) ammonium propane sulfonate (DMAAPS), and N,N'-methylene bisacrylamide (NMBA) were prepared by inverse suspension polymerizatio n. The water absorbency or swelling behavior for these xerogels in wat er or various saline solutions was investigated. Results obtained from this study revealed a water absorbency of 721 g H2O/g sample in deion ized water and 83 g H2O/g sample in 0.9 wt % NaCl solution for a gel c ontaining a 1.50 x 10(-2) molar fraction of DMAAPS. The absorbency in the chloride salt solutions decreased with an increase in the ionic st rength of the salt. For the same ionic strength of various salt soluti ons, the swelling amount had the following tendency: Co2+ > Ni2+ > Cu2 + for the higher ionic strength of 2.44 x 10(-5)-1.8 x 10(-2) M. The C o2+, Ni2+, and Cu2+ solutions induce approximately the same degree of swelling at the lower ionic strength of <2.44 x 10(-5) M. The pH effec t on the water absorbency for these xerogels was also investigated. (C ) 1997 John Wiley & Sons, Inc.