Energetic alkylnitramine-functionalized pentanitro hexaazaisowurtzitanes: towards advanced less sensitive CL-20 analogues

Abstract

High energy and moderate sensitivity are the two most important demands for modern energetic materials. The powerful CL-20 and its previously obtained derivatives do not meet safety requirements. To reach the desired goal of high-performance polycyclic cage multi-nitramine structures with reduced sensitivity, a novel family of energetic compounds was designed and synthesized by the incorporation of an alkylnitramine moiety into the pentanitro hexaazaisowurtzitane backbone. All obtained compounds were fully characterized by high-resolution mass spectrometry, IR and multinuclear NMR (¹H, ¹³C{¹H}, ¹⁴N, and ¹⁵N{¹H}) spectroscopy, and some of them with single-crystal X-ray diffraction. For the target substances, the enthalpies of formation were determined experimentally by combustion calorimetry. Thermal stability measurements and safety testing were carried out. Their energetic potential as components of rocket propellants was studied using high-temperature chemical equilibrium thermodynamic calculations. The most attractive of the new materials, N-methyl-N-[(2,6,8,10,12-pentanitro-2,4,6,8,10,12-hexaazaisowurtzitan-4-yl)methyl]nitramide and N,N′-bis[(2,6,8,10,12-pentanitro-2,4,6,8,10,12-hexaazaisowurtzitan-4-yl)methyl]nitramide, exhibit high density (1.86–1.92 g cm⁻³), heat resistance (decomposition onset at about 223 °C) and enthalpy of formation (up to about 10³ kJ kg⁻¹). Moreover, they are the most insensitive among energetic hexaazaisowurtzitane derivatives known and are up to 2/4 times safer against impact/friction than CL-20. The combination of admirable properties makes these materials promising for use in high-energy condensed systems. The target compounds are highly effective energetic components for metal-free rocket propellants, providing, at moderate contents, specific impulse values 6.5–8 s higher than similar formulations based on CL-20.