Study On Synthesis And Properties Of Difluoroamino Energetic Binders

Difluoroamino binder was being the trend of energetic binder development for its high energy content,which could be used in solid propellants and polymer-bonded explosives.Specially,because of the outstanding stability,difluoroamino binder with neopentyl structure had a promising prospect.But some research areas could be further studied,such as the incomplete synthetic route of monomer,the high glass transition temperatures,quite limited types and properties studies of binders.Here,we mainly studied on the design and optimization of the synthetic route of DFAMO,the synthesis and properties research of PDFAMO,and copolymerization modification for more types and lower Tg of difluoroamino energetic binders.An economically feasible synthetic route of DFAMO was studied and selected based on its neopentyl structure.As a result,DFAMO was synthesized from 1,1,1-tris(hydroxymethyl)ethane by esterification,cyclization,amination,amide protection and fluorination with a total yield of 43%.Specifically,the synthetic technology and reaction efficiency were improved by using ammonium salt of 3-bromomethyl-3-methyloxetane as reaction intermediate without reducing the total yields.PDFAMO was synthesized via cationic solution polymerization using TFBE as catalyst,BDO as initiator and DCE as solvent.The effects of catalyst's concentration and reaction temperature were studied.The results showed that the polymerization can be controlled by decreasing catalyst's concentration and reaction temperature.Thermal decomposition behaviors,kinetics and mechanism of PDFAMO were investigated using TG/DSC and FTIR spectra of the degradation residues.The thermal decomposition processes of PDFAMO behaved a two-stage mass-loss character.The first stage was mainly due to elimination of HF and had an activation energy of 110?120 kJ·mol-1.The second stage was due to degradation of the remaining monofluoroimino groups and polymer chain.The compatibility between PDFAMO and some energetic components and inert materials used in polymer-bonded explosives and solid propellants was studied by DSC method.The results fully supported the thermal decomposition mechanism of PDFAMO we suggested.In a word,the elimination of HF is the first step during the thermal decomposition process.Materials with functional groups which could activate the a-H or provide active hydrogen to easier the HF loss step will make PDFAMO thermal unstable and vice versa.Azido and nitrato groups could be introduced into the polymer structures via cationic solution copolymerization technique to increase the types and improve the properties of difluoroamino energetic binders.Specially,BAMO,AMMO and NIMMO were chosen to be copolymerized with DFAMO for the synthesis of PDB,PDA and PDN using TFBE/polyol as catalytic system and DCE as solvent.The glass transition temperatures of PDB,PDA and PDN all shifted to high temperatures,which were deeply affected by BAMO,AMMO and NIMMO segments.The value of Tg increased in the order PDA<PDB<PDN.The introduction of BAMO segment could decrease the decomposition temperature of DFAMO segment,which made PDB thermal instable.DFAMO segment could be compatible with AMMO and NIMMO segments at the same time.The relative thermal stability decreased in the order PDA>PDN>PDB.The glass transition temperatures of difluoroamino energetic binders could be decreased by using THF as soft segments via cationic bulk copolymerization technique.PBT,PDT and PBDT were synthesized using TFBE/polyols as catalyst system.The values of Tg of PBT,PDT and PBDT significantly decreased to-40.0?,-50.8? and-38.8?,respectively.The decrease ranges of PBT and PDT were 170.78? and 10? comparing with PBDFAO and PDFAMO.The thermal decomposition behaviors,kinetics and mechanism were studied via TG/DSC and FTIR techniques.The thermal decomposition processes of these polymers all behaved a two-stage mass-loss character with different activation energy.The first stage was mainly caused by the incomplete two-step HF loss with the activation energy varying from 95?110 kJ·mol-1.The decomposition of the remaining monofluoroimino groups and polymer backbones dominated the second stage.The observation could be confirmed by the thermal decomposition of PDFAMO.