Compounds of formula (I), wherein each of R and R′ are independently selected from hydrogen, a hydroxyl group, a carboxyl group, an alkyl, aryl or alkaryl group or a hydroxy or carboxy substituted alkyl, aryl or alkaryl group, provided that R and R′, together have a total of less than 23 carbon atoms, R″ may either be hydrogen or a CHR═CR1 group or be selected from the same categories as R′″; R′″ is a group, or polymeric chain comprising from 1 to 100,000 groups, said group or groups being derived form at least one ethylenically unsaturated compound wherein the double bond is activated by an adjacent electron withdrawing group, and n is greater than 1 are novel, are useful corrosion inhibitors and are valuable intermediates in preparing telomers for use in water treatment.