The present invention provides compositions comprising particles or agglomerates of one or more phosphorus oxide telomer or cotelomer ((co)telomer) of one or more unsaturated carboxylic acids or anhydrides having a mean average particle size of from 2 μm to 1 mm, preferably from 5 to 500 μm, preferably, comprising at least one carboxylic acid anhydride group. In addition, the present invention provides methods comprising aqueous solution addition polymerizing a monomer mixture of one or more unsaturated carboxylic acid in the presence of a phosphorus oxide acid or salt compound, drying the resulting copolymer at a temperature of from 120 to 230° C. and reducing its particle size to make a phosphorus oxide (co)telomer particle or agglomerate; the methods may further comprise reacting the (co)telomer particle or agglomerate with one or more polyether polyol, alkyl polyether polyol, polyether amine or alkyl polyether amine, with heating, to form a comb polymer useful, e.g. as a superplasticizer or dispersant.