Synthesis and characterization of novel nitrofurazanyl ethers as potential energetic plasticizers

Energetic plasticizers are used to improve the mechanical properties of advanced energetic formulations while increasing the overall energy content. Although nitro-1,2,5-oxadiazoles (nitrofurazans) possess excellent energetic properties such as a favorable oxygen balance and high heat of formation, their use as plasticizers has received little attention in the scientific literature. Four nitrofurazanyl ethers were synthesized by substitution of dinitrofurazan with linear alkoxides. The synthesized compounds were extensively analyzed by Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), electrospray ionization (ESI) mass spectroscopy, mechanical sensitivity test, 1H nuclear magnetic resonance (NMR) spectroscopy and 13C NMR spectroscopy. They have lower mechanical sensitivity (>40 J) compared to modern energetic plasticizers in use, including 2,2-dinitropropyl formal/acetal (BDNPA/F), n-butylnitratoethylnitramine (BuNENA), and dinitrodiazaalkane (DNDA-57). In addition, the most promising compound 3-(2-(2-(2-azidoethoxy)ethoxy)ethoxy)-4-nitro-1,2,5-oxadiazole (NFPEG3N3) exhibits competitive thermal properties, with a lower glass transition temperature of -72 °C compared to BNDPA/F (-67 °C) and a higher thermal decomposition temperature of 179 °C compared to BuNENA (173 °C). The enthalpy of formation and heat of explosion of NFPEG3N3 were calculated to be -41.7 kJ mol-1 and 3421 J g-1, respectively. The impact of NFPEG3N3 on the glass transition temperature, viscosity and decomposition of the energetic binder glycidyl azide polymer (GAP)-diol was investigated and showed a remarkable decrease in viscosity (45.4%) and glass transition temperature (-3.3 °C) when compared to benchmark plasticizers in 10 wt% mixtures. These results demonstrate the potential of NFPEG3N3 as an insensitive and highly energetic plasticizer.