CHARGED POLYACRYLONITRILE MEMBRANES HAVING AMPHIPHILIC QUATERNIZED AMMONIUM GROUPS FOR ULTRAFILTRATION

Four types of positively charged polyacrylonitriles having quaternized N,N-dimethylaminoethyl methacrylate(DAMA) were synthesized and were u sed to prepare ultrafiltration membranes by a phase-inversion method. The effect of aliphatic ethyl, octyl, and stearyl groups and the benzy l group, which covalently bind to the quaternary ammonium group, on fi ltration properties was studied by ultrafiltration under an applied pr essure of 760 mmH(2)O. Water permeability through the resultant membra nes increased as the aliphatic chain length on the quaternary ammonium group increased. For a copolymer membrane having a benzyl group on th e quaternary ammonium group, water permeability was lower than that fo r the ethyl type of copolymer membrane. The membrane permeability and pore size for the molecular size-exclusion effect were studied at vari ous NaCl concentrations in the 0-0.15M region. The membranes having oc tyl and stearyl groups showed stable filtration behavior by increase o f the NaCl concentration, while the membranes having an ethyl group an d a benzyl group on the quaternary ammonium group showed a change of t he water permeability due to a pore-size increase for the membrane by NaCl addition. Measurements of membrane potential indicated the shield ing of positively charged sites of the membranes by salt addition. Fur ther, the copolymer membranes showed a separation ability for water/2- butanol of low water content. The separation ability was attributed to the chemical structure of the membranes having different interaction characteristics with the mixture components. (C) 1998 John Wiley & San s, Inc. J Appl Polym Sci 69: 1821-1828, 1998.