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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 CH<sub>3</sub>CN under ambient conditions to give polyphosphazene
with molecular weight of up to over 59 000 and a narrow dispersity
(<i>Đ</i>) of 1.1–1.2. This is a significant
improvement over the polyphosphazenes obtained from the classic Staudinger
reaction which had lower molecular weight (<i>M̅</i><sub>n</sub> = 10 000–25 000) and higher <i>Đ</i> (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