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.