a process for producing an ion exchange precursor resin membrane involves co - extruding an ion exchange precursor resin with an incompatible polymer to form a multilayer film having a layer of the ion exchange precursor resin supported on a layer of the incompatible polymer . the layer of incompatible polymer is then removed from the layer of ion exchange precursor resin to provide the ion exchange precursor resin membrane . the ion exchange precursor resin membrane may be converted to an ion exchange resin membrane by hydrolysis , and subsequent acidification if desired . ion exchange resin membranes and ion exchange precursor resin membranes having a uniform thickness of 25 microns or less may be formed by the process .