X2 O3 P CHY CZ2 where Y and each Z are each H, PO3 X2, SO3 X or CO2 X (e.g. vinyl phosphonic acid or vinylidene diphosphonic acid) with hypophosphorous acid in the presence of free radicals provides novel compounds X2 O3 PCHYCZ2 PO2 XH which react with monomers such as vinyl sulphonate, vinyl phosphonate, vinylidene diphosphonate and acrylic acid to form telomers useful for scale inhibition, espec