Reverse osmosis using a composite isocyanurate membrane

A method for selective separation of at least one water-soluble useful material from an aqueous solution by reverse osmosis comprising contacting the aqueous solution under pressure maintained above the osmotic pressure of said aqueous solution with a semipermeable composite membrane, wherein said semipermeable composite membrane comprises a porous substrate, and a barrier layer about 0.01 to about 0.1 micron in thickness and composed of a cross-linked polymeric material having isocyanurate structures of Formula (I) formed on said porous substrate:

• ##STR6## wherein each of R.sub.1, R.sub.2 and R.sub.3 is selected from the group consisting of hydrogen, a glycidyl group, an alkyl radical containing from 2 to 5 carbon atoms, an alkyl radical carrying a functional hydroxyl group and an alkyl radical carrying a functional glycidyl group, with the proviso that at least two of R.sub.1, R.sub.2 and R.sub.3 are selected from the group consisting of glycidyl groups, alkyl groups carrying a functional hydroxyl group and alkyl groups carrying functional glycidyl groups;
• said cross-linked polymeric material having linkages selected from the group consisting of ether (--O--) linkages, ester ##STR7## linkages or a combination thereof connecting said isocyanurate structures to each other.