| http://www.w3.org/ns/prov#value | - That is, these membranes are prepared by chemical treatment of a copolymer of a fluorinated olefin with a sulfur containing fluorinated vinylether as represented by the following formula formed in the shape of a membrane or a hydrolyzed product thereof having sulfonic acid groups: ##STR2## wherein n' is an integer of 0 to 2.
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