Computational studies of impact sensitivity in energetic plasticizers – using DFT on BuNENA, MeNENA and DINA

Energetic materials are key constituents in rocket propellants. Modern solid rocket propellants contain energetic plasticizers, whose purpose is to adjust propellant properties such as thermal stability, energy content, mechanical properties, oxygen balance and burning behavior. We studied the impact sensitivity of three such energetic plasticizers. In this project, we studied the energetic plasticizers 2-[butyl(nitro)amino]ethyl nitrate (BuNENA), 2-[methyl(nitro)amino]ethyl nitrate (MeNENA) and (nitroazanediyl)bis(ethane-2,1-diyl) dinitrate (DINA). We tried to predict their impact sensitivity based on molecular bonding energies using density functional theory with the exchange-correlation functional M06-2X and the TZVP basis set. We studied two different elimination reactions: homolytical dissociation of nitro groups and elimination of nitrous acid. Based on these calculations, the O–NO2 bond is the one that breaks the easiest, which is consistent with the literature. We also showed that these bonds are stronger in BuNENA than in MeNENA and DINA, and that the latter two have similar bond strengths. This finding is not consistent with experimentally measured sensitivity. Therefore, the difference in impact sensitivity indicated in the literature cannot be explained solely by the dissociation energy of the nitro group. The elimination of nitrous acid should be studied more thoroughly to gain an improved understanding. We also performed a comparison of some different exchange-correlation functionals with coupledcluster singles and doubles with perturbed triples. Our results showed that the bond dissociation energy calculated with a CAM-B3LYP functional was closest to the coupled-cluster result. Finally, we carried out a fallhammer experiment on BuNENA. Our experiment showed significantly lower impact sensitivity than reported in the literature. This may be due to variations in the experimental method. Further investigations should therefore be conducted.