prov:value
| - wherein Y and Y??? each, independently of the other, is a hydrogen atom or a bromine atom, n and n??? each, independently of the other, is an integer of 0, 1, 2, 3, or 4, R1 and R1??? each, independently of the other, is an alkylene group or an arylalkylene group as defined in further detail for the alkylene and arylalkylene R1 groups hereinabove, and X is (a) a group of the formula
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