High performance, quality controlled bipolar membrane

Claim 1

In a process for manufacturing a high performance, durable single film bipolar membrane having an ion selectivity above 80% in an electrolyte medium of at least 0.1 molar from a single film wherein an olefinic polymeric film matrix in uniformly impregnated with a mixture of a vinylaromatic monomer and a di- or poly-functional cross-linking agent and said mixture is subsequently polymerized to obtain on the film at least 15 percent by weight of the vinylaromatic mixture based on the total weight of the membrane and said mixture is cross-lined to a degree equivalent to that obtained by a 2 to 20 weight percent of divinylbenzene in styrene, the improvement comprising pre-cleaning the thus prepared cross-linked matrix and thereby removing surface vinylaromatic polymer accumulation, which has not penetrated the matrix surface, from the surface of the cross-linked matrix to render the aromatic nuclei of the impregnated vinylaromatic polymer more readily accessible to functionalization, and thereafter chemically bonding from about 5 to about 98% of the membrane thickness with highly dissociable cationic exchange groups to the aromatic nuclei from one side only, and chemically bonding from about 2 to 50% of highly dissociable anionic exchange groups to the remaining aromatic nuclei.