Disclosed are compounds of the formula 1 wherein Y is a hydrogen atom or a bromine atom, n is an integer of 0, 1, 2, 3, or 4, R1 is an alkylene group or an arylalkylene group, and X is (a) a hydrogen atom, (b) a group of the formula 2 wherein R2 is an alkyl group, an aryl group, an arylalkyl group, or an alkylaryl group, (c) an alkyleneoxy, aryleneoxy, arylalkyleneoxy, or alkylaryleneoxy group, or (d) a group of the formula 3 wherein R4 is an alkyl group, an aryl group, an arylalkyl group, or an alkylaryl group.