SEMIPERMEABEL SAMMENSAT MEMBRAN

A microporous substrate, such as a polysulphone membrane having on its surface a semi-permeable membrane being the reaction product of a polyamine, a water soluble polymer of formula 1 wherein R is hydrogen or an hydrocarbongroup, x is 50 - 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, 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%. The crosslinking agent is preferably a mixture of iso-phtaloylchloride and trimesoylchloride; the polyamine is preferably an azo alkane compound having terminal amino groups with a straight chain comprising 8 to 24 carbon atoms, particularly 1.10-diamino-4.7-diazadecane; 1.14-diamino-4.8.11-triazatetradecane and 1.18-diamino-4.8.11.15-tetraazooctadecane. The flux of the membrane is at least 40 1/m .h and the salt retention at least 90%.