Phosphazene monomers from the regiospecific reaction of tert-butylhydroquinone with hexachlorocyclotriphosphazene: a new composite material precursor

A new synthesis of a phosphazene-based polymer precursor is described. tert-Butylhydroquinone was found to react with hexachlorocyclotriphosphazene in the presence of a base, 4-picoline, in cyclohexane to yield a regiospecifically substituted hexa-tert-butylcyclotriphosphazene. This reaction proceeds more rapidly to completion and in a higher yield than data previously reported for analogous cyclotriphosphazenes. Nuclear magnetic resonance spectroscopy and thermal methods (differential scanning calorimetry and thermogravimetric analysis) were employed to characterize this material, and it is observed that the bifunctional tert-butylhydroquinone substitutes only at the least hindered phenolic hydroxyl under the reported reaction conditions. This conclusion clarifies published data that suggests that without the tert-butyl substituent on the hydroquinone ring, crosslinking between phosphazene rings occurs to some extent.