1,2,4-Oxadiazole-Bridged Polynitropyrazole Energetic Materials with Enhanced Thermal Stability and Low Sensitivity

A family of mono or di(1,2,4-oxadiazole)-bridged polynitropyrazole derivatives with C-nitro/N-nitro functionalities is reported. All compounds were fully characterized by IR, NMR (¹ H, ¹³ C), elemental analysis and differential scanning calorimetry (DSC). The solid-state structure features were further investigated with X-ray diffraction. Of these, compounds 3,5-bis(3,4-dinitro-1H-pyrazol-5-yl)-1,2,4-oxadiazole (3 a) and 5,5'-bis(3,4-dinitro-1H-pyrazol-5-yl)-3,3'-bi(1,2,4-oxadiazole) (3 b) possess high thermal stability (3 a: T_dec =274 °C; 3 b: T_dec =272 °C), sensitivity (IS >30 J, FS >360 N) and comparable detonation properties (3 a: D_v =8741 m s^-1 , P=34.0 GPa; 3 b: D_v =8685 m s^-1 , P=33.4 Gpa) to RDX. In addition, 3,5-bis(4-nitro-1H-pyrazol-3-yl)-1,2,4-oxadiazole (4 a) and 5,5'-bis(4-nitro-1H-pyrazol-3-yl)-3,3'-bi(1,2,4-oxadiazole) (4 b) have high decomposition temperature (4 a: T_dec =314 °C; 4 b: T_dec =317 °C), low sensitivity (IS >40 J; FS>360 N) and superior detonation performances (4 a: D_v =8027 m s^-1 , P=26.4 GPa; 4 b: D_v =7991 m s^-1 , P=25.2 Gpa) than conventional heat-resistant explosive hexanitrostilbene (HNS: T_dec =318 °C; IS=5 J; FS=240 N; D_v =7612 m s^-1 , P=24.3 GPa), thus suggesting their potential application as heat-resistant explosives.