二氟氨基二硝甲基芳香杂环含能材料的理论研究

Theoretical Study on Energetic Materials Containing(Difluoramino)dinitromethyl Substituted Heteroaromatic Rings

近几十年以来,传统含能材料的发展遇到了瓶颈.如何继续提高能量水平,打破瓶颈,是这一领域亟待攻克的难题.氟是比氧更强的氧化剂,预期分子内引入氟可以进一步提高能量水平,因此设计了13种二氟氨基二硝甲基取代的芳香杂环含能材料分子.为了保证这些分子合成的可能性,所有结构设计都是从已有的中间体出发,并且原则上均可经由成熟的合成方法转化为目标分子.对它们的分子结构、初始热分解机理以及能量特性进行的理论研究表明,多数分子具有足够的动力学稳定性.本工作通过深入分析,揭示了分子结构与动力学稳定性之间的关系.使用硝酸酯增塑聚醚(NEPE)固体推进剂配方对这些分子的能量特性进行了理论评价,最终优选出4种分子,其中最好的一个不仅动力学稳定性较好,而且配方比冲高达280.1 s,比传统的环四亚甲基四硝胺(HMX)配方提高了8.4 s.

In recent decades,the development of traditional energetic materials has encountered a bottleneck.How to continue to improve the energy level and break the bottleneck has become an urgent problem in the field of energetic materials.Fluorine is a stronger oxidizing agent than oxygen,and theoretically the introduction of fluorine can further increase energy density.Thirteen kinds of energetic molecules containing(difluoramino)dinitromethyl substituted heteroaromatic rings were designed.To ensure the possibility of synthesis,all the structural designs are based on existing intermediates and could be transformed into target molecules through mature synthesis methodologies.The molecular structure,initial thermal decomposition mechanism and energy characteristics were studied theoretically with density functional theory(DFT)methods(B3LYP/6-311+G(d,p)and M06-2X/6-311+G(d,p))using Gaussian16 program.By calculating the mechanism of the initial decomposition reaction,the trigger bond was determined to be one of the C—NO_(2) bonds in the(difluoramino)dinitromethyl group.Dynamic stability is evaluated by the energy barrier of the trigger bond breaking.The results show that most of these molecules have sufficient dynamic stability,the initial decomposition reaction barriers are around 30 kcal/mol.The relationship between the molecule structure and the dynamic stability is revealed.The carbon radical center in the transition state is connected with the strong electron-withdrawing groups(-NO_(2) and-NF2)and the heterocyclic ring with a certain electron-donating ability.This is a typical“push-pull”electronic structure,which makes the free radical particularly stable.Therefore,the homo-cleavage energy barrier of the trigger bond is determined by the stabilizing effect of heterocyclic rings on the methyl free radicals.The energy properties of these molecules were theoretically evaluated with nitrate ester plasticized polyether(NEPE)solid propellant formulations using EXPLO5 program.The results show that the specific impulse of one dynamic stable molecule is up to 280.1 s,which is about 8.4 s higher than that of the traditional HMX(Octogen)formulations.