Design And Computational Study Of Energetic Organic Azido Plasticizers

Organic azido compounds are a kind of energetic materials.They have attracted great attentions since they possess a unique role in the propellant as plasticizers,binders,oxidants,and other additives,etc.In this work,various aliphatic and aromatic organic azido compounds have been studied using the methods of quantum chemistry,molecular mechanics,and molecular dynimics.For the potential azido plasticizers,a series of binder/plasticizer composites were constructed and investigated to find the suitable plasticizers for propellants.This thesis provides a systematic theoretical method and guidance to screen the plasticizers for the solid propellants.The main contents include:1.Structures and properties of typical azido plasticizers(Chapter 2)The thermodynamic properties,IR spectra,detonation properties,pyrolysis mechanism,and thermal stability of four typical azido plasticizers,i.e.,1,5-diazido-3-nitrazapentane(DIANP),1,3-diazido-2-methyl-2-nitropropane(DAMNP),3,3-di(azidoacetoxyl)-2,2-di(azidomethyl)-propane(PEAA),and pentaerythritol diazido dinitrate(PDADN),were studied using the density functional theory(DFT)method.Results confirm the potential values of these four plasticizers in the propellant applications from the view of theoretical research and verify the reliability of the adopted methods.2.Relationships between the structures and properties of the azido compounds(Chapters 3,4,and 5)2.1 The effect of substituent groups(Chapter 3)Different number of substituent groups(-NNO2,-ONO2 or-NO2)was incorporated into the molecules of 1,5-diazidopentane(Ⅰ),1,7-diazidoheptane(Ⅱ),and 1,9-diazidononane(Ⅲ).27 derivatives were obtained and studied using the DFT method.Results show that the contribution of substituent groups has the order of-ONO2>-NO2>-NNO2 on the thermodynamic properties and-NNO2>-ONO2>-NO2 on the energetic properties.With the introduction of substituent groups,the thermal stability decreases slightly.The studies on 2-azido-1,3-imidazole(Ⅳ),3-azido-1H-1,2,4-triazole(Ⅴ),5-azido-1H-tetrazole(Ⅵ),and azido-pentazole(Ⅶ)show that the order of thermal stability is Ⅴ>Ⅳ>Ⅵ>Ⅶ and that of energetic properties is Ⅳ<Ⅴ<Ⅵ<Ⅶ.2.2 The effect of isomerization(Chapter 4)1H/2H and azide/tetrazole(AZ/TZ)isomerizations in 3-nitro-5-azido-1,2,4-triazole(NAzTA),3-amino-5-azido-1,2,4-triazole(AAzTA),and 5-azido-1,2,4-triazole(AzTA)were studied using the DFT method.The 1H/2H tautomerization proceeds easiest for AAzTA while hardest for NAzTA.The AZ/TZ isomerization takes place easiest for AzTA,and then AAzTA and NAzTA in sequence.The AZ/TZ isomerization is much easier to take place than the 1H/2H tautomerization.The 1H/2H tautomerization decreases while the AZ/TZ isomerization increases the stability.2.3.The effect of hydrogen bonding interaction(Chapter 5)The intermolecular hydrogen bonding interactions in 3,5-diazido-1,2,4-triazole(DATZ)and the intramolecular hydrogen bonding interaction in 3,5-diazido-1,2,4-triazolium 5-nitrotetrazolate(DATZNTZ)were studied using the DFT and dispersion corrected DFT(DFT-D)methods in combination with the natural bond orbital(NBO)and the quantum theory of atoms in molecules(QTAIM)analyses.The hydrogen bonding interactions are critically important in increasing the stability of DATZ and the trimer is the most stable existent form.The formation of the hydrogen bond leads to 1)a red-shifted N-H vibration,2)an increasing chemical shift of the H atom,and 3)proton transfer and production of tautomers.DATZNTZ exists as ionic structures in aqueous solution while acid-base molecular complexes in gas phase.3.Molecular design of new high-energy azido compounds(Chapter 6)According to the relationships between structures and properties,an aliphatic azido compound AFCTEE(1-azido-formic acid 1,1,1-trinitro-ethyl ester)and two aromatic azido compounds TNDFAPATA(N-(2,4,6-trinitro-3,5-bis(bifluoroamine)phenyl)-3-azido-1H-1,2,4-triazole)and TNTFMPATA(N-(2,4,6-trinitro-3,5-bis(trifluoromethyl)phenyl)-3-azido-1H-1,2,4-triazole)were designed and studied using the DFT method.Results show that AFCTEE and TNDFAPATA have energetic properties higher than typical azido compounds studied in Chapter 2 and RDX(hexahydro-1,3,5-trinitro-1,3,5-trizine),and comparable to HMX(1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane).Their stabilities satisfy the requirement of the stability of energetic compounds.These suggest that AFCTEE and TNDFAPATA are two promising high-energy compounds.4.Plasticizing effect of azido plasticizers on the binders(Chapter 7)The plasticizer effect of DIANP on NC(nitrocellulose),GAP(glycidyl azido polymer),and BAMO-AMMO(3,3’-bisazidomethyloxetane-co-3-azidomethyl-3’-methyl oxetane)were explored using the molecular dynamic(MD)method.Results show that DIANP has good compatibility with NC,GAP,and BAMO-AMMO and can improve their mechanical properties.For the NCs with lower esterification degrees,NG has better plasticizing effect than DIANP,while for the NCs with higher esterification degrees,the plasticizing effect of DIANP is better.For GAP,the composite with the mass ratio of 57.7/42.3(GAP/DIANP)has the best mechanical properties.For BAMO-AMMO,the composite with the mass ratio of 49.2/50.8(BAMO-AMMO/DIANP)possesses the best mechanical properties.This provides a theoretical formula guidance for DIANP as the plasticizer of NC,GAP,and BAMO-AMMO.5.Theoretical method for screening azido plasticizers and its application(Chapter 8)Based on above researches,we put forward the theoretical method to screen the suitable azido plasticizer for the propellants from "molecular design" to "formulation design".Appling this method,8 designed nitro azido compounds(M1-M8)were studied and M2 was selected to be the suitable azido plasticizer of GAP.The suggested method is:(1)designing amount of azido compounds,optimizing their structures,and evaluating their energetic properties and stability with the DFT method to screen the ones with good performance;(2)constructing various composites with the screened compounds and binders and estimating their compatibility and mechanical properties with the MD method to screen the suitable plasticizer.This method can also be applied to screen other plasticizers.