Crosslinked poly(N-isopropylacrylamide) gel and crosslinked copolymers of 97% N,N-diethylacrylamide and 3% sodium methacrylate which are swollen with water collapse abruptly at 33°C and near 55°C, respectively. These collapses apparently occur because each gel is near its lower critical solution temperature. The gels can be used to extract water and low molecular weight solutes from macromolecular solutions. After they have extracted the water, the gels can be regenerated by warming to release the absorbed water. The resulting separation process is effective for proteins and other polymers, and may be operated with waste heat which is usually discarded.
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Acknowledgemennts-This work was supported by the National Science Foundation grant CPE840899, by the Environmental Protection Agency grant 68031957 and by the Minnesota Sea Grant. Other support came from the Celanese Company. R.F.S.F. is supported by the “Conselho National de Desenvolvimento Cientifico e Tecnologico”, Brazil (CNPq).