A method for preparing an ionically-charged membrane comprising the steps (1) applying a film of curable composition to a support; (2) curing the film of curable composition to give anionically-charged membrane; and (3) removing the ionically-charged membrane from the support; wherein the curable composition comprises a) 5 to 50 wt % of curable compound comprising one ethylenically unsaturated group and anionic group; b) 10 to 70 wt % of crosslinking agent comprising at least two ethylenically unsaturated groups and having a molecular weight of at least 500 dalton per ethylenically unsaturated group; and c) 5 to 60 wt % of inert solvent.