The publication deals with the sulfonation of aromatic polysulfones that results in ionomers intended to be used as membranes for Proton Exchange Membrane Fuel Cells. The mechanical properties and the lifespan of the membranes depend, in particular, on the mode of synthesis of the ionomers and on chemical degradations which can occur and cut the polymeric chains. This article gives a progress report on the various methods giving access to polysulfone ionomers based on sulfonic acid functions. Among these methods, particular attention has been paid to electrophilic substitution from commercially available polysulfone. Although electrophilic sulfonation of aromatic molecules has been known for about one century, its application to the sulfonation of polymers still raises problems, e.g. homogeneity and degradations. A mechanism of chemical degradation is proposed to explain the chain breakings occurring in the course of reaction. The difficulty in passing from the laboratory scale to an industrial production is illustrated from reactions carried out at the pilot scale.

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