Preparation of stimuli-responsive water absorbent

Temperature-responsive water absorbents, poly(sodium acrylate-co-stearyl acrylate) hydrogels, were synthesized by means of ordinary radical copolymerization of acrylic acid (AAc), stearyl acrylate (SA), and N,N-methylenebisacrylamide (MBA), and following alkali treatment. The SA hydrogels absorbed sufficient amount of water (70 ml/g resin) and exhibited thermosensitive volume-phase transition despite the presence of polyelectrolyte units such as PNaAAc. It is well known that polyelectrolytes prevent the typical thermosensitive hydrogels, poly(N-isopropylacrylamide)s (PNIPAm), from exhibiting their thermosensitive volume-phase transition. The SA hydrogels softened up and absorbed amounts of water above their phase transition temperature (T.; about 45 degreesC). That is, the SA hydrogels absorbed more water at 50 degreesC than that at 25 degreesC. It is interesting that the thermosensitivity of the SA hydrogel in the water-absorption was the opposite tendency to that of the NIPAm hydrogel. Furthermore, we could regulate the water-absorption capacity of the hydrogel by controlling the incubation temperature, and could squeeze the absorbed water from the water-saturated hydrogel by cooling the incubation temperature to 25 degreesC from 50 degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.