Temperature-sensitive membranes prepared by UV photopolymerization of N-isopropylacrylamide on a surface of porous hydrophilic polypropylene membranes

Novel multifunctional membranes were prepared by ultraviolet photopolymeriz ation of N-isopropylacrylamide (NIPAAm) on the surface of porous hydrophili c polypropylene microfiltration membranes. The polyN-isopropylacrylamide PN IPAAm gels were generated on the surface of the membrane through a covalent bond in the presence of a crosslinking agent, N,N'-methylenebisacrylamide. The crosslinked PNIPAAm gels are temperature-responsive hydrogels that can swell and deswell reversibly in aqueous solution around the vicinity of th e lower critical solution temperature (LCST) of PNIPAAm. With a change of t emperature, the effective pore size of the membrane surface can be enlarged or shrunk as the PNIPAAm gels swell or deswell. Above the LCST of PNIPAAm, the fluxes of water and solution containing 500 ppm of dextran (molecular weight: 1.67 x 10(5) g/mol) through the temperature-sensitive membranes are about 6 and 85 times higher than those below the LCST of PNIPAAm, respecti vely. The changeable flux makes it possible to employ the temperature-sensi tive membranes as a sensor or valve that regulates filtration properties by responding to temperature. Solutions of dextran with a molecular weight fr om 6300 to 2,000,000 were used to evaluate the separation performance of th e temperature-sensitive membranes as the ultrafiltration membrane. The rang es of rejection of dextran and the flux of solution are from 0 to 90 and 8 to 32 l/m(2) h, respectively, depending on the temperature, pressure, and m olecular weight of dextran. It is clear that the temperature-sensitive memb rane exhibits multifunctional characteristics; that is, the microfiltration membrane is above the LCST of PNIPAAm, and the ultrafiltration membrane is below the LCST of PNIPAAm. (C) 1999 Elsevier Science B.V. All rights reser ved.