re R.sup.4 and R.sup.5 individually represent a hydrogen atom or a monovalent hydrocarbongroup with 1 to 20 carbon atoms, X is a halogen atom or an RCOO-- group and l represents an integer of 1 to 6; and a compound represented by the general formula (IV):wherein B.sup.1 represents a hydrocarbon group with 4 to 40 carbon atoms, Z represents a halogen atom or an RCOO-- group (R has the same meaning