AbstractThe influence of quaternization on the transport properties of water and sodium chloride under reverse osmosis conditions has been examined for alternating copolymers of styrene and 4‐vinyl pyridine. These results demonstrate quite clearly a linear relationship between log P as a function of salt rejection or reciprocal hydration. Such a relationship seems to be quite general for ionic polymers. Also, results with irradiation demonstrate that tensile properties of these copolymers can be improved by about 60% at an optimum dose of about 9 megarads. In addition, the directional permeability of graded membranes has been demonstrated for an alternating copolymer where a gradient of quaternization was imposed on the membrane. Both the water and salt flux were higher along the quaternization gradient than in the reverse orientation of the membrane.