om, an alkali metal atom or an ammonium group and R4 is a hydrogen atom or a methyl group and a vinyl monomer of the formula: ##STR7## wherein R5 is a hydrogen atom or a methyl group, optionally with a vinyl monomer of the formula: ##STR8## wherein R6 is a hydrogen atom or a methyl group and R7 is a phenyl group, --CN or --COOR8 in which R8 is methyl, ethyl, phenyl or --(CH2)n OH wherein n is 2 or