onomers represented by the general formula [I] ##STR1## wherein R1 is a hydrogen atom, alkyl group having 1 to 20 carbon atoms, phenyl group, derivative of phenyl group, or halogen atom, X is CONH, ##STR2## COO(CH2)m or (CH2)n (wherein 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 carbon atoms, m is an integer of 1 to 20, and