Thermal stability/structure relations of some polynitroaliphatic explosives

Abstract

Thermal stability/chemical structure relations were investigated for different classes of energetic compounds containing trinitromethyl, fluorodinitromethyl, and gem-dinitroethyl groups. In the vacuum thermal stability test used to determine the thermal characteristics of the materials, samples are heated to elevated temperatures under vacuum and the amounts of gaseous decomposition products are measured. The following results were obtained: (a) The thermal stabilities of energetic compounds containing trinitromethyl groups are lower than those of materials containing fluorodinitromethyl or gem-dinitroethyl groups if these groups are in a sterically unhindered environment. The trinitromethyl compounds generally have acceptable stability up to 150°C when solid and 100°C when molten. The fluorodinitromethyl compounds have acceptable stability at 180°C or higher when solid, and up to 165°C when liquid. Fluorodinitromethyl and dinitroethyl compounds have thermal decomposition rates that are 1 80 -to 1 200 of those of trinitromethyl compounds. (b) Energetic materials containing C(NO 2) 3-, FC(NO 2) 2-, or CH 3C(NO 2) 2- groups in an environment which is sterically hindered by neighboring bulky substituents all have substantially decreased thermal stability compared to unhindered materials. The rationale suggested is that intramolecular rotational modes serve as an enthalpy sink, and that “freezing out” these modes causes more energy to be distributed into the vibrational modes which lead eventually to bond homolysis.