| http://www.w3.org/ns/prov#value | - Incidentally, the copolymers synthesized are all inferred to have the structures represented by the general formula (7): ##STR1## wherein each of R11 to R14 is a group selected from the group consisting of hydrogen and sulfonic acid group; R' is a group selected from the group consisting of hydrogen and alkyl groups having 1 to 4 carbon atoms; the number of the sulfonic acid group is 40 to 80% of
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