Design And Synthesis Of Azetidinium-based Hypergolic Ionic Liquids

Propellants are the core power and play an important role in the development of aerospace industry.Hydrazine propellants are of volatile and highly toxic.It is urgent to find green alternatives of them.Hypergolic ionic liquids?HILs?have the advantages such as low vapor pressure,low toxicity and high thermal stability,and become a potential neotype propellant fuel.However,the energy of the HILs needs further improvement so as to increase engine power.This dissertation aims to design and synthesize the new HILs,and improve the power of them by increasing ring strains of compounds.The studies are as follows:?1?Azetidium-based HILs with high strain energy were designed and prepared.The properties of six HILs were characterized as liquid range?-80-200??,densities(0.99-1.05 g cm^-3),heats of formation(0.70-2.17 kJ g^-1),specific impulses?164.0-184.5 s?,and ignition delay times?23-130 ms?.With the highest energetic properties(heat of formation,2.17 kJ g^-1;specific impulse,184.5 s).N-Butyl-N-propargylazetidinium dicyanamide has the most potential to be employed as green propellants.In order to better understand the relationship between ring stains and energy of compounds,two isomers of N-butyl-N-propylazetidinium dicyanamide's?9?,N-butyl-N-ethylpyrrolidinium dicyanamide?9a?and N-butyl-N-ethylpiperidinium dicyanamide?9b?,were also synthesized for comparison.It was interesting to find that,compared with the two isomers(9a:heat of formation 0.41 kJ g^-1,specific impulse 156.5 s;9b:heat of formation:0.36kJ g^-1,specific impulse:155.3 s),9 exhibited a much higher heat of formation(0.78 kJ g^-1)and specific impulse?164.8 s?,which indicates that ring stains play an important role in the performance of energetic compounds?maximum increase of specific impulse by6%?.?2?In order to further enhance the energy of HILs,the shorter alky chain-N-propyl-azetidinium-based HILs were designed and prepared.The properties of five HILs were characterized with respect to liquid range?-80-142??,densities(1.03-1.06 g cm^-3),heats of formation(0.98-2.43 kJ g^-1),specific impulses?168.3-188.7 s?,and ignition delay times?15-43 ms?.With the best energetic properties(2.43 kJ g^-1,188.7 s),N-propyl-N-propargylazetidinium dicyanamide has the most potential to be employed as green propellants.Two isomers of N-propyl-N-propylazetidinium dicyanamide's?8?,N-ethyl-N-propylpyrrolidinium dicyanamide?8a?and N-methyl-N-propylpyrrolidinium dicyanamide?8b?,were also synthesized for comparison.Interestingly,compared with the two isomers(8a:heat of formation,0.64 kJ g^-1;specific impulse,160.9 s;8b:heat of formation,0.50 kJ g^-1;specific impulse,157.6 s),8 exhibited a much higher heat of formation(0.98 kJ g^-1)and specific impulse?168.3 s??maximum increase of specific impulse by 7%?.In addition,the heats of formation and specific impulses of N-propyl-azetidinium-based hypergolic ILs are higher than that of N-butyl-azetidinium-based HILs,respectively?maximum increase of specific impulse by 2%?.In short,under the guidance of the correlative theory of molecular ring strains and energy,azetidinium-based HILs with high strain energy were designed and synthesized.The structures,phase transition temperatures,thermal stabilities,hypergolic ignition times,heats of formation and specific impulses of the resulted HILs were characterized and fully discussed.The results showed that two series of HILs had high energy with the highest specific impulse up to 188.7 s,which provides a new method for the study of high energy HILs.