The Synthesis of a Superabsorbent Polymer

The preparation and mode of action of a superabsorbent polymer is described. The material consists of lightly crosslinked, mostly neutralized polyacrylic acid which can be prepared using either a redox or a thermal radical initiator. The resulting polymer absorbs 500-3000 times its weight in distilled water, depending on the degree of crosslinking employed. However, the absorbency is shown to be very sensitive to the presence of salt (70-250X in 0.2% NaCl) or acid (5X in dilute HCl). The impressive absorbency is explained in terms of an osmotic force to dilute the highly ionic interior of the polymer. These factors combine to make this an especially educational and enjoyable organic laboratory experiment.