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 Cl 3 P NSiMe 3 and PhCl 2 P NSiMe 3 are described. The ambient temperature polymerization of PhCl 2 P NSiMe 3 is faster in toluene, benzene, and dioxane than in methylene chloride or chloroform. The polymerizations of Cl 3 P NSiMe 3 and PhCl 2 P NSiMe 3 were monitored by both NMR ( 31 P and 1 H) and GPC methods. The initial polymerization rates are slow, presumably because of the precipitation of phosphazene short chain salts, RCl 2 P N−[PR(Cl) N] n −PCl 3 + PCl 6 - (where R = Cl or Ph; n = 0, 1, 2, ...). After the chains redissolve (∼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 10 5, with narrow polydispersities (<1.3). The usefulness of this approach for the synthesis of a biomedically important polyphosphazene has also been demonstrated.