The synthesis and homopolymerization of a fluorocyclotriphosphosphazene with a directly bonded styrene moiety is presented. A multistep sequence was employed wherein commercially available p-bromostyrene is first converted to 1-(4-bromophenyl)-1-methoxyethene, 4-BrC6H4C(OCH3)CH2 which in turn is lithiated and added to N3P3F6 to give (4-(1-methoxyethenyl)phenyl)pentafluorocyclotri phosphazene, N3P3F5(4-C6H4C(OCH3)˭CH2)(2). Addition of tri(n-butyl)tin hydride to 2 followed by elimination of tri(n-butyl)tin methoxide over silica produced the target monomer, (4-ethenylphenyl)- pentafluorocyclotriphosphazene, and N3P3F5(4-C6H4CH˭CH2)(3). The new phosphazene derivatives were characterized by mass spectrometry, NMR (1H,13C,19F,31P) and IR spectroscopy. Radical addition polymerization of 3 resulted in the formation of poly(p-pentafluorocyclotriphosphazenylstyrene)(4). Molecular weights of the new polymer were determined by GPC and membrane osmometry. The GPC data suggested the occurrence of chain transfer in the polymerization. TGA studies showed that 4 exhibits high thermal stability compared to other organophosphazene polymers. The Tg value is significantly greater than that of polystyrene.