Abstract: Semipermeable membrane consisting of a polymer, embodying [--SO.sub.3 --] groups; said [--SO.sub.3 --] groups may be present in the continuous polymer chains or may be present in links between continuous polymer chains. The membrane may have been formed either by in situ coagulation of a polymer solution in the pores of a porous substrate or by interfacial crosslinking of a water-soluble phenolic polymer with a sulphonyl halide compound to form an [--SO.sub.3 --] groups embodying polymer in the pores of a substrate.

Abstract: A semipermeable composite membrane on a microporous substrate, such as a polysulphone membrane having on its surface a semipermeable membrane being the reaction product of a polyamine, a water soluble polymer of formula 1 ##STR1## wherein R is hydrogen or an hydrocarbongroup, x is 0-99.9%, and y is 100-x mol. % and n indicates the molecular weight and of a crosslinking agent containing a polyfunctional group having reacted with the amino groups of the polyamine and of the polymer. In the formula 1 preferably R is an alkylgroup of 1-5 carbon atoms, particularly methyl, and n is equivalent to a mol. weight of more than 10.000. The water soluble polymer is advantageously a mixture of a polymer of formula 1 wherein x and y are both 50 mol. % and a polymer of formula 2, ##STR2## this last mentioned polymer being preferably obtained by hydrolysis of a compound of formula 1. The degree of hydrolysis is preferably 70 to 99.9%.