PURPOSE: To produce isocyanate substd. isophthaloyl chloride useful in the production of a multilayered reverse osmosis membrane having surprisingly increased solute rejection and permeation properties.

CONSTITUTION: A mixture of amino substd. isophthalic acid, a catalyst (e.g.; imidazole), phosgene and a halogenated solvent (e.g.; chlorobenzene) is formed to be heated in a pressure solvent under autogenetic pressure and, after the solvent is removed, the mixture is distilled to obtain isocyanate substd. isophthaloyl chloride, for example, 5-isocyanatoisophthaloyl chloride. An org. polymer, pref., polysulfone is cast on a support to form a porous substrate. Subsequently, the formed porous substrate is treated with an aq. soln. of polyfunctional diamine (pref., mphenylenediamine) and the treated substrate is immersed in a soln. of isocyanate substd. isophthaloyl chloride in a water immisible solvent to be subjected to interfacial polynm. and a polyamide urea layer is formed to produce a multilayered reverse osmosis membrane.