Synthesis of Polyphosphazenes by a Fast Perfluoroaryl Azide-Mediated Staudinger Reaction

We report the synthesis of polyphosphazenes by a fast Staudinger reaction between a bis-PFAA (perfluoroaryl azide) and a bis-phospine. Polymerization was completed within 30 min after mixing the two monomers (20 mM) in CH₃CN under ambient conditions to give polyphosphazene with molecular weight of up to over 59 000 and a narrow dispersity (D) of 1.1-1.2. This is a significant improvement over the polyphosphazenes obtained from the classic Staudinger reaction which had lower molecular weight (M_n = 10 000-25 000) and higher D (1.7). This reaction applies to bis-PFAAs and bis-phosphines with either an aromatic or an aliphatic linker. Polarity of the solvent influenced the degree of polymerization, and more polar solvents such as acetonitrile gave higher molecular weight polymer in comparison to less polar solvents such as dichloromethane. The synthesized polyphosphazenes showed high thermal stability, with the aromatic polyphosphazenes giving decomposition temperature and char yield of up to of 441 °C and 53%, respectively.