omers, sulfonate monomers, and carboxylic acid monomers represented by the general formula [I] ##STR5## wherein R1 is a hydrogen atom, alkyl group having 1 to 20 carnon atoms, phenyl group, derivative of phenyl group, or halogen atom, X is CONH, ##STR6## COO(CH2)r or (CH2)n (where R2 and R3 are each a hydrogen atom or alkyl group having 1 to 15 carbon atoms, R4 is an alkylene group having 1 to 15