Semi-permeable composite membrane and process for manufacturing same

A semi-permeable composite membrane with a porous carrier substrate whereon a polymer network obtained by interfacial polymerisation is applied, said network comprises an additional polymer characterized in that said additional polymer is dissolved in the water phase or in the organic phase, from which said interfacial polymerisation occurs, which additional polymer is molecularly entangled in said network and may regulate in particular the selectivity and the permeability of the composite membrane, and, said polymer is a non-reactive polymer selected from the group consisting of a polyalkyl siloxane either branched or not with the formula ##STR3## wherein R and R.sub.1 independent of each other represent C.sub.1 -C.sub.20 alkyl or alkyl group either substituted or not and n is an integral of 20-50,000 or a copolymer thereof, a polyacrylate or methacrylate with the formula ##STR4## wherein R.sub.2 =H or CH.sub.3 and R.sub.3 is an alkyl group either branched or not with 1-20 carbon atoms, while n is an integer of .gtoreq.10, cellulose acetate, and a polyethylene oxide of the formula (CH.sub.2 --CH.sub.2 --O).sub.n wherein n is an integer of .gtoreq.20.