Influence of reaction parameters on the living cationic polymerization of phosphoranimines to polyphosphazenes

A new approach to the synthesis of poly(dichlorophosphazene) and poly(organophosphazenes) has been developed via the cationic condensation polymerization of phosphoranimines. The effects of solvent, temperature, concentration, and initiator on the cationic condensation polymerization of Cl₃P = NSiMe₃ and PhCl₂P = NSiMe₃ are described. The ambient temperature polymerization of PhCl₂P = NSiMe₃ is faster in toluene, benzene, and dioxane than in methylene chloride or chloroform. The polymerizations of Cl₃P = NSiMe₃ and PhCl₂P = NSiMe₃ were monitored by both NMR (³¹P and ¹H) and GPC methods. The initial polymerization rates are slow, presumably because of the precipitation of phosphazene short chain salts, RCl₂P = N-[PR(Cl) = N]_n-PCl₃⁺PCl₆^- (where R = Cl or Ph; n = 0, 1, 2, ...). After the chains redissolve (approximately 15-60 min), polymerization proceeds, with the propagation rates following pseudo-first-order kinetics for both monomers. The reactions in toluene, benzene, or dioxane yielded polymers with controlled molecular weights in the range of 10⁵, with narrow polydispersities (<1.3). The usefulness of this approach for the synthesis of a biomedically important polyphosphazene has also been demonstrated.