Preparation and characterization of layered membranes constructed by sequential redox-initiated grafting onto polyacrylonitrile ultrafiltration membranes

Layered membranes were prepared by sequential grafting - by means of redox initiators - of water-soluble monomers, with oppositely charged ionic groups, onto ultrafiltration (UF) polyacrylonitrile (PAN) membranes at room temperature. Grafting of a single layer of 2-hydroxy-ethylmethacrylate (HEMA) onto a PAN membrane gave a highly grafted membrane with a relatively high water flux. Bilayered membranes with various properties containing poly-2-(dimethylamino) ethyl methacrylate (p-2DMAEMA) as the bottom layer and polymethacrylic acid or polystyre-nesulfonic acid (p-SSA) as the upper layer were prepared and compared - by means of infrared spectroscopy and electron microscopy - with single-layered membranes of grafted polyhydroxyethylmethacrylate. Layered membranes exhibited a significant decline in water flux in comparison with the initial UF membranes. The flux could, however, be manipulated by controlling the concentration of monomers, the time of grafting, and the number of layers. When four layers of p-2DMAEMA and p-SSA were sequentially grafted onto a PAN membrane, pure water fluxes were stable over a wide range of pH values and did not change over long storage times.