Abstract:Migration and leaching of plasticizers will severely affect the physical and mechanical properties of polymers. In this study， two new monomers， 3-（4-nitrofurazan-3-oxy-methyl）-3-bromomethyl oxetane （BrNFMO） and 3，3-bis（4-nitrofurazan-3-oxy-methyl） oxetane （BNFMO）， were synthesized by the combination of 3-nitro-4-hydroxy-furazan and dibromomethyl oxetane （BBMO）. Using hydroxy-terminated polyether （HTPE） as macromolecular initiator， three block copolymers containing azide groups were synthesizd by polymerization of BrNFMO， BNFMO and BBMO under the catalysis of boron trifluoride ether followed by azidation process. Then the detonation performance of the designed monomer structure was evaluated by quantum chemistry. Besides， the copolymerization process was optimized by the control variate method， and better copolymerization conditions were obtained. The results show that this series of novel energetic copolymers can further improve the energy level of the binders， and the intramolecular plasticizing strategy can result in energetic polymers with lower glass transition temperature （T_g） and viscosity by introducing azide groups into the polymer through the structure of azidofurazan ether， compared with directly introducing azide groups into the polymer. T_g can be reduced by 5.27 ℃， viscosity can be reduced by 4.90 Pa·s， and its thermal stability is also improved （thermal decomposition temperature （T_d） can be increased by 7.3 ℃）.

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Abstract:A novel nonmetallic salt， 3，5，7-triamino［1，2，4］triazolo［4，3-a］［1，3，5］triazine pentazolate （4）， was synthesized through a metathesis reaction by employing AgN₅ as precusor with 3，5，7-triamino［1，2，4］triazolo［4，3-a］［1，3，5］triazine hydrochloride. The structural characterization were carried out by X-ray single crystal diffraction， infrared spectroscopy （IR）， elemental analysis （EA）， nuclear magnetic resonance （NMR）， and thermal decomposition behavior were determined by thermogravimetric analysis （TG） and differential scanning calorimetry （DSC）. The enthalpy of formation of compound 4 was calculated using atomization method， the detonation performance was predicted using EXPLO5， and sensitivity was tested using BAM testing method. The results show that compound 4 exhibits a monoclinic crystal structure with a crystal density of 1.644 g·cm^-3 and belongs to the P2₁/n space group. This compound has a nitrogen content of 77%， a thermal decomposition temperature of 113.8 ℃， and an enthalpy of formation of 491.5 kJ·mol^-1. Furthermore， its detonation velocity was calculated at 7913 m·s^-1， detonation pressure at 19.6 GPa； The impact sensitivities measured were >40 J， and friction sensitivity >360 N.

Abstract:Polycyclic energetic compounds with high nitrogen content have attracted much attention owing to their distinctive advantages in constructing novel energetic molecules with low mechanical sensitivity， good thermal stability and high density. The construction of polycyclic skeletons involves the incorporation of tetrazole into fused heterocycle， serving as high-energy organic fuel and hydrogen bond donors. Three self-assembled non-hydrated energetic compounds， namely 7-amino-6-（2H-tetrazol-5-yl）-pyrazolo［1，5-a］pyrimidine （1）， 7-diamino-6-（2H-tetrazol-5-yl）-［1，2，4］triazolo［1，5-a］pyrimidine perchlorate （2）， and 2，7-diamino-6-（2H-tetrazol-5-yl）-［1，2，4］triazolo［1，5-a］pyrimidine perchlorate （3）， were synthesized through noncovalent self-assembly of polycyclic skeleton with the oxidizing structural unit HClO₄ rich in hydrogen bond acceptors. The structural characterization employed nuclear magnetic resonance （NMR） spectroscopy and single crystal X-ray diffraction， while thermal behaviors and mechanical sensitivities were determined by differential scanning calorimetry-thermogravimetry and BAM methods. Detonation performances were predicted utilizing the Gaussian 09 program and EXPLO5 V6.05.02. The results show that three compounds exhibit high crystal densities （ρ： 1.75-1.86 g·cm^-3）， good thermal stabilities （decomposition temperature （onset）： 184-260 ℃）， and good detonation performances （detonation velocity： 7343-7570 m·s^-1； detonation pressure： 21.1-22.8 GPa）， surpassing those of traditional explosives trinitrotoluene （TNT）. Both compound 1 （impact sensitivity （IS） > 40 J， friction sensitivity （FS）=216 N） and compound 3 （IS=25 J， FS=240 N） exhibit low mechanical sensitivity.

Abstract:

Abstract:Azido-bridged nitrogen-rich heterocyclic energetic compounds have high heat of formation and low mechanical sensitivity， making them widely applicable in the field of energetic materials. However， traditional preparation methods often involve oxidative coupling， which poses high safety risks and severe environmental pollution. In contrast， the electrochemical synthesis method is favored by researchers for its efficiency， controllability， and environmental friendliness. By adjusting the electrochemical reaction conditions， selective synthesis of azido-bridged nitrogen-rich heterocyclic energetic compounds with different structures can be achieved， opening up new possibilities for their synthesis. This study reviews the electrochemical synthesis methods， effects of electrolytes and electrodes， and possible reaction mechanisms of azido-bridged nitrogen-rich heterocyclic energetic compounds such as furazan， pyrazole， 1，2，4-triazole and tetrazole. Additionally， future research directions are proposed， including the electrochemical preparation of energetic molecules that cannot be synthesised by traditional methods， the construction of nitrogen-nitrogen bonds， carbon-nitrogen bond through electrochemical method， and the synthesis of various fused/bis-heterocylcic energetic compounds. Furthermore， the scaled-up synthesis of these compounds via the electrochemical method is also discussed. The study provides a reference for the research and development of electrochemically synthesized azido-bridged rich nitrogen-containing energetic molecules.

Abstract:The development of energetic materials faces many challenges， and the traditional trial-and-error research model often results in long development cycles and low efficiency. With the advancement of data science and artificial intelligence （AI） technologies， a data-driven research model has emerged as a new path for the development of energetic materials. Polycyclic energetic compounds are currently a hot topic in the field of energetic materials， among which nitrogen-containing polycyclic frameworks， due to the presence of π electrons for delocalized resonance and multiple modifiable sites， exhibit enhanced molecular structural stability. At the same time， the presence of energy groups ensures the energy level of the molecules， achieving a good balance between energy and stability， overcoming the inherent contradiction between them. This study briefly introduces the workflow of data-driven development of novel energetic materials， outlines the latest research progress of data-driven methods for the development of nitrogen-containing polycyclic energetic compounds， and finally proposes prospects for the application of data-driven methods in the development of novel energetic materials. Future directions should consider supplementing data volume through means such as data augmentation and governance to improve the accuracy and generalization ability of model predictions. Machine learning models can be used to predict the molecular synthetic feasibility by establishing chemical reaction conditions and synthetic pathways， thereby accelerating the development of novel nitrogen-containing polycyclic energetic compounds.

Abstract:A trifluoromethyl-containing fused triazole-triazine energetic molecule， 3-（1H-tetrazol-5-yl）-7-（trifluoromethyl）-1，2，4-triazolo［5，1-c］-1，2，4-triazin-4-amine （2）， was synthesized in two steps from 5-（trifluoromethyl）-1，2，4-triazol-3-amine. The crystal structure of this compound was characterized by X-ray single crystal diffraction. Its structure and properties were characterized by ¹H and ¹³C Nuclear Magnetic Resonance Spectroscopy （NMR）， Fourier Transform infrared spectroscopy （FT-IR） and differential scanning calorimetry （DSC）. The detonation performance of compound 2 was predicted by EXPLO5 and and sensitivity testing was performed according to the BAM standard method. Results show that compound 2 belongs to the triclinic space group Pī， a=4.9035（10） Å， b=10.219（2） Å， c=15.194（3） Å， V=720.4（3） ų， α=107.163（6）°，β=92.486（7）°，γ=96.4438（7）°， Z=2. The theoretical detonation velocity and pressure of compound 2 are 6933 m·s^-1 and 17.1 GPa， respectively. Its measured impact sensitivity is more than 40 J and the friction sensitivity is larger than 360 N.

Abstract:The compound 5，7-bis（trifluoromethyl）-2-（dinitromethyl）-［1，2，4］triazolo［1，5-a］pyrimidine （1） was designed， synthesized， and thoroughly characterized. Thermal properties were determined using Differential Scanning Calorimetry （DSC）， while Gaussian 03 and EXPLO5 v6.05 programs were employed to calculate the heat of formation and detonation properties of compound 1， respectively. In addition， a comparative analysis of Hirschfeld surface， 2D fingerprint and electrostatic potentials （ESP） was conducted between compound 1 and other known dinitromethyl-containing compounds in this study. The result demonstrate that compound 1 exhibits exceptional insensitivity （IS > 40 J， FS > 360 N） toward external stimuli compared to other dinitromethyl-containing compounds. Furthermore， the presence of halogen bonding （C—F⋅⋅⋅X） effectively disrupts the formation of O…O interactions in energetic materials and leads to a favourable distribution of electrostatic potentials. This finding provides valuable insights for the development of novel insensitive energetic materials.

Abstract:Based on two urotropine cage-like cationic structures， two new pentazolate salts， urotropine pentazolate salt （C₆H₁₃N₉， 1） and methylated urotropine pentazolate salt （C₇H₁₅N₉， 2）， were synthesized. The synthesized pentazolate salts were structurally characterized by X-ray single crystal diffraction， infrared spectroscopy （IR）， mass spectrometry （MS） and nuclear magnetic resonance （NMR）， and were analyzed by thermogravimetric analysis （TG） and differential scanning calorimetry （DSC） to evaluate their thermal decomposition behaviors. The formation enthalpy of compound 1 and 2 was calculated using the atomization method， the detonation performance was predicted using EXPLO5， and the impact sensitivity and friction sensitivity were tested using the BAM method. The results show that compound 1 belongs to the monoclinic crystal system （P2₁/c）， and the crystal cell parameters are a=13.6795（2） Å， b=11.6892（1） Å， c=12.5941（2） Å， V=1937.53（5） ų， α=γ=90°， β=105.822（1）°， Z=8， D_c=1.448 g·cm^-3； compound 2 belongs to the monoclinic crystal system （P2₁/m）， and the crystal cell parameters are a=6.9025（5） Å， b=7.6042（5） Å， c=10.6808（9） Å， V=538.50（7） ų， α=γ=90°， β=106.148（8）°， Z=2， D_c=1.389 g·cm^-3. The thermal decomposition temperature of compound 1 is 90.0 ℃， and 82.8 ℃ for compound 2. The detonation velocity and pressure of compound 1 and 2 are 8291 m·s^-1 and 20.33 GPa， 7862 m·s^-1 and 17.41 GPa， respectively. While the measured impact sensitivity and friction sensitivity of compound 1 and 2 are 5 J and 288 N， 3 J and 86 N， respectively.

Abstract:A coupling reaction using hydrochloric acid and potassium permanganate as oxidizing agents was carried out to synthesize compound 1 from the polyamino fused heterocyclic compound 5-（6，7-diamino-3-imino-3H-［1，2，4］triazolo［4，3-b］［1，2，4］triazolo-2（7H）-yl）tetrazole. Subsequent displacement reaction in perchloric acid gave the perchlorate 2. The structure and thermal performance of compound 2 were characterized by X-ray single crystal diffraction， Fourier Infrared spectroscopy， Nuclear Magnetic Resonance， elemental analysis， differential scanning calorimetry （DSC） and thermogravimetry analysis （TG）. Additionally， the heat of formation was computed using Gaussian software， and the detonation properties of compound 2 were calculated using EXPLO5 software. The results showed that compound 2 crystallizes in the monoclinic crystal system， possessing a crystal density of 1.750 g·cm^-3 with four molecules per unit cell. The onset thermal decomposition temperature of compound 2 is 232.6 ℃， its theoretical detonation velocity and pressure are 8373 m∙s^-1 and 29.05 GPa， respectively. Remarkably， compound 2 exhibited insensitivity to external mechanical stimuli， evidenced by an impact sensitivity of 40 J and a friction sensitivity of 360 N， indicative of its robust performance overall.

Abstract:Two nitrogen-rich energetic salts， 5，5''-（hydrazine-1，2-diyl）bis（5，7-dihydro-［1，2，5］oxadiazolo［3，4-e］［1，2，4］triazolo［4，3-a］pyrimidine-8（4H）-one） perchlorate （2） and 5，5''-（diazene-1，2-diyl）bis（［1，2，5］oxadiazolo［3，4-e］［1，2，4］triazolo［4，3-a］pyrimidine-8（7H）-one） nitrate （3） were accomplished from the raw material of 5，6-diamino-［1，2，5］oxadiazolo［3，4-b］pyrazine （1）. Structure characterization of energetic ionic salts 2 and 3 were achieved through various techniques， including Nuclear Magnetic Resonance Spectroscopy （NMR）， Fourier Transform infrared spectroscopy （FTIR）， elemental analysis （EA） and X-ray single crystal diffraction （XRD）. Their thermal decomposition behaviors were investigated using differential scanning calorimetry （DSC） method， while their friction and impact sensitivities were identified according to BAM standard test methods. Moreover， their detonation performances were predicted based on the combination of Isodesmic Reactions and EXPLO5 software. The results prove that compounds 2 and 3 crystallize in the monoclinic system， belonging to space groups Pn and P2₁/n， respectively. The cationic parts of their crystal structures show good planarity and intensive hydrogen bonds in the crystal packing are observed. The thermal decomposition temperatures of compounds 2 and 3 are 154 ℃ and 130 ℃， respectively. Their theoretical detonation velocities are 7722 m·s^-1 and 8008 m·s^-1， while their theoretical detonation pressures are 26.3 GPa and 28.4 GPa， respectively. Their friction sensitivities are both 360 N， and impact sensitivities are greater than 40 J. Compounds 2 and 3 outperform traditional explosives TNT in terms of detonation performance， friction sensitivity， and impact sensitivity.

Abstract:5-amino-2H-pyrazol-3，4-dione-3-oxime-4-hydrazone （3） and its perchlorate （4）， nitrate （5） and 5，5′-dinitramino-3，3′-azo-1，2，4-oxadiazolate salts （6） were prepared from 4-chloro-3，5-dinitro-1H-pyrazole via amination and substitution/reduction reactions. The single crystals of 3 and 4 were obtained by solvent evaporation method and the crystals were characterized by single crystal X-ray diffraction. The structures of energetic compounds 3-6 were characterized by nuclear magnetic resonance spectroscopy and infrared spectroscopy. Moreover， the capacities of those compounds were confirmed by gas pycnometer， differential scanning calorimetry， impact and friction sensitivity testers. Their enthalpies of formation and detonation parameters were estimated using theoretical calculation methods. The results show that 3 has a planar molecular configuration. The ketone oxime and ketone hydrazone have unique double bond characteristics， reducing the conjugation of the pyrazole ring and making it easier to form salts. After salt formation， different anions have various effects on the performance of the neutral compound. Among those examined anions， the perchlorate anion not only improves the oxygen balance， but also increases the density， resulting in the detonation velocity and pressure of 4 （8499 m·s^-1 and 30.2 GPa） higher than 3 （8072 m·s^-1 and 22.5 GPa）. In addition， 5，5′-dinitramino-3，3′-azo-1，2，4-oxadiazole significantly increases the decomposition temperature of 3， rising from 135 ℃ to 285 ℃. These results indicate that a rational combination of anions and cations can effectively regulate the performances of target energetic compound.

Abstract:Compared with the research and development model guided by experience and calculations， machine learning-assisted high-throughput virtual screening technology for energetic molecules has shown obvious advantages in terms of molecular design efficiency and quantitative analysis of structure-activity relationships. In view of the fact that nitrogen-rich fused ring energetic compounds usually show better energy-stable balance properties， this study uses machine learning-assisted high-throughput virtual technology to conduct chemical space exploration of ［5，6］ nitrogen-rich fused ring energetic molecules. Based on the ［5，6］ all-carbon skeleton， this study obtained 142，689 ［5，6］ fused ring compounds through combined enumeration and aromatic screening. At the same time， a machine learning algorithm was used to establish and optimize an energetic molecular property prediction model （including density， decomposition temperature， detonation velocity， detonation pressure， impact sensitivity and enthalpy of formation）. The effects of nitrogen and oxygen atoms on the fused ring and functional groups on the molecule on the performance of energetic compounds were analyzed. The research results show that the structure-activity relationship of the generated fused ring compounds is consistent with the general correlation between energy and stability of energetic compounds， verifying the rationality of the prediction model. Taking detonation velocity and decomposition temperature as the criteria for energy and thermal stability， five molecules with outstanding comprehensive properties were screened， and the quantum chemical calculation results were in good agreement with the machine learning prediction results， which further verified the accuracy of the prediction model.