A cyclophosphazene substituted organic monomer, 2-(4’-vinyl-4-biphenylyloxy) pentachlorocyclotriphosphazene (CPHVB), has been copolymerized with methyl acrylate (MA), ethyl acrylate (EPI) and methyl methacrylate (MMA) using free radical methods. Flame retardant thermally stable copolymers with up to a maximum of 90% phosphazene content were obtained. Reactivity ratios and Alfrey-Price parameters suggest that the biphenylyloxy unit successfully insulates the vinyl moiety from the sigma-electron withdrawing effect of the cyclophosphazene ring.