where X is a halogen atom, R2 is an alkylenoxyalkylene group or an alkylene group comprising 1 to 6 carbon atoms, R3 is an alkyl group comprising 1 to 6 carbon atoms or an alkoxyalkyl group comprising 2 to 4 carbon atoms, R4 is a monovalent hydrocarbon group, and n is an integer of 1 to 3;