Composite membranes are the work horse of reverse osmosis and nanofiltration processes. Recently, we presented a chemistry in a spinneret methodology. The membrane forming polymer reacts with a monomer/cross-linker added to the bore fluid resulting into a composite membrane made by a single process step. Here, the reaction of a cross-linking agent and an amine reactant superimposes the conventional phase inversion of an inert polymer during dry-jet wet spinning. While the inert polymer precipitates as porous support structure, the cross-linking reaction forms the desired dense separation layer on the lumen-side. Such membranes have nanofiltration properties and can be backwashed extensively. Two different interfacial condensation reactions showcase the versatility of this method and the used polyethyleneimine determines the salt retention hierarchy given by its positive charge. This work suggests that the many established membrane postmodifications known in the field could be considered for this "chemistry in a spinneret" inline modification.