A positional isomer of LLM-116: N—NO2 moiety enhancing the laser ignition combustion performance of nitrogen-rich energetic materials

It has long been a driving force in the development of energetic materials to hunt for novel energetic materials (EMs) with high energy and low sensitivities. Recently, the combination of nitrogen-heterocycles and NNO2 moiety could generate novel energetic derivatives with high energy content and low sensitivity benefiting from the high heat of formation and abundant hydrogen bonding interactions. The critical role of isomerism strategy in tuning the laser ignition combustion performances of EMs is rarely mentioned in the chemical enterprise, although some researches reveal that isomerism strategy has significant effects on their thermal behaviors, mechanical sensitivity and detonation performance. In this work, the positional isomerism of nitramine-pyrazole was investigated, and 3-nitramine-4-nitropyrazole and a series of energetic derivatives were synthesized and well characterized. Their physical properties, energy performance, as well as laser-ignited combustion performance, were further explored. The experimental results showed that all compounds possess excellent detonation pressure, and detonation velocity (P: 26.5∼30.4 GPa, D: 7876∼8377 m·s−1), which were much better than those of trinitrotoluene (TNT) (P: 19.5 GPa and D: 6881 m·s−1). Moreover, all of the resulting energetic derivatives exhibited low mechanical sensitivities (IS>40 J). Interestingly, they also had excellent laser ignited combustion properties owing to the NNO2 moiety attached to nitropyrazole backbone.