where Y is a halogen atom such as Cl or I; R3 is a divalent organic group represented by --R4 --, ##STR5## (where R4 is a divalent hydrocarbon group having 1-20 carbon atoms, for example, alkylene, cycloalkylene, arylene or aralkylene group), with R3 being preferably selected from among --CH2 --, and ##STR6## (R is a hydrocarbon group having 1-10 carbon atoms).