This invention provides chlorohydrocarbyloxy phosphonate oligomers, organophosphonate oligomers, and processes for the preparation of such oligomers. The chlorohydrocarbyloxy phosphonate oligomers can be represented by the formula (IV) where R1 is a linear or branched hydrocarbylene group or oxygen-containing hydrocarbylene group, which hydrocarbylene group has about two to about twenty carbon atoms, or a hydrocarbylene group having at least one cycloaliphatic or aromatic ring; R2 is an alkyl group or an aromatic group; and n is a number from about 2 to about 20.