Study On Preparation,Characterization And Properties Of CL-20/Nitroimidazole Cocrystal

Traditional high energetic explosives have been gradually unable to meet energetic materials development for the ammunition in the future due to the requirements of ammunition damage efficiency and battlefield survivability.High energetic explosive with low sensitivity has become the target of the research in energetic material field.CL-20 as the highest crystal density and strongest detonation performance of explosive can be synthesized in a large scale at present.It is considered as a potential substitute for HMX which is used as the main charge explosive.However,the application of CL-20 has been restricted by the high sensitivity and crystal transition.Now,cocrystal technology has become a hot spot approach which decreases the sensitivity effectively and avoids the sharp deduction of detonation power.Although multiple CL-20 cocrystals have been reported,effective theoretical screening methods for coformer,series of CL-20-based cocrystals and the structure-activity relationship research has not been involved.In this study,the regularity of molecular surface electrostatic potential extremum was utilized to rapidly screen potential coformer of CL-20-based cocrystal.Single crystal diffraction verified the true existence of cocrystal between the chosen coformer and CL-20.Meantime,the structure-activity relationship of CL-20-based cocrystal has been studied.The main content of this paper are as follow:(1)The distribution law of the extreme electrostatic potential on the molecular surface of coformer was proposed.Through Gaussian software and Multiwfn software,the electrostatic potential extremums of coformers were analyzed,which were the components in 28 CL-20 cocrystals with the single crystal structure data.The molecular surface electrostatic potential minimum value,electrostatic potential maximum value,sum of absolute value of electrostatic potential extreme value and sum of electrostatic potential extreme value all presents a certain regularity which exhibited anti-U type.The proportions of coformers in middle area occupied 71.4%,53.6%,92.9% and 67.9% respectively.Thus,it could be seen that screening the coformer by the regularity of anti-U type has high accuracy.(2)Eleven energetic materials,including 2,4-DNI,3,4-DNP,1,4-DNI,4,5-DNI,2,4-MDNI,4,5-MDNI,LLM-105,NTO,ANTZ,ANTA and LLM-116 have been screened via the molecular surface electrostatic potential extremum.The result showed that the molecular surface electrostatic potential extremum of 1,4-DNI,2,4-MDNI,4,5-MDNI and LLM-105 locked at the concentrated area of electrostatic potential extremum.So those four energetic materials were planed to be as the candidate coformer of CL-20 corystal.And it is worth noting that 1,4-DNI,2,4-MDNI and 4,5-MDNI belong to the range of imidazole energetic compound.(3)Based on choosing appropriate reagent and the reasonable preparation method,four cocrystals including CL-20/1,4-DNI(1:1)cocrystal,CL-20/2,4-MDNI(1:1)cocrystal,and CL-20/4,5-MDNI(1:1)and CL-20/4,5-MDNI(1:3)cocrystals were prepared via solvent evaporation method.The single crystal diffraction,powder diffraction,DSC,impact sensitivity and detonation properties of the four cocrystals are studied.Single crystal data analysis reveals the different building mechanism of four cocrytals.The DSC test illustrates the distinction of thermal properties between the cocrystal and raw materials.The results of impact sensitivity and detonation performance show that the four cocrystals has excellent performances,such as impact sensitivity and detonation performance of CL-20/1,4–DNI(1:1)is better than those of HMX,and the impact sensitivity and detonation performance of CL-20/4,5-MDNI(1:3)is equal to LLM-105.(4)The analysis between structures of coformers and properties of CL-20 cocrystals showed that the different quantities of nitro and methyl groups in the same series of coformers has significant effects on the construction and properties of cocrystal.The density and detonation performance of CL-20 cocrystal will be decreased if the coformer contains more methyl groups,while the density and detonation performance of CL-20 cocrystal will be improved if the coformer has more nitro groups.In addition,the CL-20 cocrystal with excellent comprehensive properties is more easily obtained via assembling CL-20 and coformer with high density,low sensitivity and good detonation.The density of CL-20 cocrystal is affected by the stacking coefficient of crystal at a macroscopic level,but the density is essentially affected by the weak interactions between molecules at a microscopic level.The density and oxygen balance of CL-20 cocrystal has a certain relationship with the sensitivity and detonation performance.The detonation performance increases with the density of cocrystal,and the impact sensitivity of cocrystal increases with the oxygen balance.