The grafting of oppositely charged water-soluble monomers onto:a polyacrylonitrile (PAN) ultrafiltration (UF) membrane and the consequent stratification processes were investigated by means of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The grafting of monomers with sulfo-acidic groups was increased when it was,conducted on a membrane previously grafted with the presence of oppositely charged amine groups increased the grafting of exposed,to buffer solutions having different pH values, their ATR-FTIR spectra revealed that chemical changes had occurred both within the layers and on the surface. The pH-dependent behavior of the bilayered membranes showed that,the first-layer grafts had interpenetrated, to a certain extent, into the second layer of the polyelectrolyte and vice versa. (C) 2002 Elsevier Science B.V. All rights reserved.