Bomb Calorimetric Correlation Study between Chemical Structure and Enthalpy of Formation for a Linear Energetic Polyphosphazene

Energetic polyphosphazenes constitute a novel class of insensitive binders which potentially outperform conventional carbon-based systems in terms of their energy-densities and glass transition temperatures. To facilitate the calculation of energetic performance for these materials, we report here on the use of bomb calorimetry to determine the standard enthalpies of combustion (ΔcH°) and formation (ΔfH°) of 2,2,2-trifuoroethan-1-oxy-/2,3-dinitratopropan-1-oxy-polyphosphazene (I) as the proportion of (energetic) 2,3-dinitratopropan-1-oxy substituents (% Energetic Substitution, % ES) is varied between 31% and 78%. Similar data is presented for the parent polymer bis(2,2,2-trifuoroethan-1-oxy)-polyphosphazene (II) (% ES = 0). ΔcH° was found to vary between -2275 kJ·mol-11for the parent polymer II (% ES = 0) and -3415 kJ·mol-1 for I with % ES = 78. The corresponding values for ΔfH° were -3184 kJ·mol-1 and -1566 kJ·mol-1. These data indicate that, as expected, the polymer heats of formation become more favourable – with respect to the energetic performance of the polymer – as the percentage of energetic side chain functionalities (% ES) increases.