Effect of the synthesis solvent in swelling ability of polyacrylamide hydrogels

A series of polyacrylamide hydrogels (PAAm HGs) and polymers were synthesized by free radical polymerization in the same reaction conditions but using two different media as solvent: water/ethanol at 100/0, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70, and 20/80 (V/V) and water/DMSO at 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, 40/60, 30/70 and 20/80 (V/V). In most cases hydrogels were obtained in high yields and their swelling degree showed a significant dependence with the solvent used in the synthesis. When HGs were synthesized in water/ethanol mixture, the maximum equilibrium swelling (Seq) was reached when the water/ethanol ratio was 60/40(V/V), while for water/DMSO it was obtained for a water/DMSO ratio 80/20. In both cases, these swelling values were higher than when the HGs were synthesized in pure water. The swelling degree achieved by the HGs in water/ethanol was directly related to the yields and the pore size, but this behavior was not observed for the HGs obtained in water/DMSO. In all cases the HGs obtained in water/DMSO swell more than those obtained in water/ethanol. On the other hand, the molar mass of the PAAm polymers prepared in the same reaction conditions, decrease as the proportion of ethanol or DMSO increase. However, the molar mass reached by the polymers obtained in water/DMSO were higher than those obtained in water/ethanol.