. "ls such as 3-chloropropyl, 4-bromobutyl, 3,3,3trifluoropropyl, chlorocyclohexyl, bromophenyl, chlorophenyl and the like, and sulfur containing radicals such as mercaptoethyl, mercaptopropyl, mercaptohexyl, mercaptophenyl and the like; preferably R is an alkyl radical containing from 1 to about 6 carbon atoms; and most preferably R is methyl." . . .