Phosphonylation of polysiloxane and cyclosiloxane oligomers is described. Hydrosilylation of vinylbenzyl chloride (VBC) with a poly(methylhydrosiloxane), or its cyclic monomer, followed by phosphonylation with triethyl phosphite leads to the production of stable phosphonosiloxanes that are characterized by -Si-C and -C-P bonds. The polymer, which is a liquid with a glass transition temperature of -38.3 degrees C, is soluble in alcohols and an alcohol and water mixture. The phosphonylated siloxanes dissolve and chelate uranyl nitrate and transition metal salts. The hydrosilylation of VBC yields alpha and beta isomers: -Si-CH2-CH2 and -Si-CH(CH3); the ratio between these two depends upon the type of solvent and the reaction conversion. A kinetic study of the hydrosilylation reaction of VBC suggests a second order in respect to the reactants. The reaction rate is dependent upon the catalyst concentration and temperature. Hydrosilylation of vinylbenzyl phosphonate could not be accomplished with the platinum (complex) catalyst; this is attributed to the presence of phosphoryl groups that are strong electron donors.