Study On Synthesis And Curing Behavior Of Polyfluoroalkoxy Glycidyl Ether

In the construction process of explosives and solid propellants,an important ingredient,the binder,is usually added to maintain the basic skeleton of the energetic material,to achieve the purpose of molding and provide corresponding mechanical properties support.In order to improve the energetic features of the formula,the researchers obtained a series of energetic binders by introducing energetic groups into the binder,which not only improved the overall mechanical properties,but also further improved the energetic properties.The composite propellant is formulated with energetic material as the matrix and a large amount of aluminum powder as fuel.The calorific value loss during the combustion process will affects the energy release of the propellant.The results showed that the addition of fluorine-containing binder can promote the combustion of aluminum powder in the formulation of energetic materials,improve the calorific value,and thus obtain greater energy.In this thesis,two novel trifunctional polyfluoroalkoxy glycidyl ether polymers were prepared by cationic ring-opening polymerization,and four corresponding energetic copolymers containing nitrate group and azide group were obtained by copolymerization and azide substitution.The structure and properties of these six novel trifunctional polymers were characterized.Based on the hydroxyl values of these six polymers,the curing experiments of six polymers were carried out with two different functional isocyanates as curing agents.A series of curing samples were prepared by adjusting the curing temperature,catalyst and its dosage,and the content of curing agent.The curing behavior was studied to screen out the best curing conditions and the best performance formula.The research contents are as follows:（1）Synthesis and characterization of polyfluoroalkoxy glycidyl ether polymer.A trifunctional chain-extending initiator was obtained by trimethylolpropane（TMP）reacted with boron trifluoride etherate（BF₃·Et₂O）.Then,two novel trifunctional fluoropolymers were obtained by the cationic ring-opening polymerization of trifluoroethoxy glycidyl ether（TFGE）and pentafluoropropoxy glycidyl ether（PFGE）,as fluorine-containing monomers respectively.On the basis of the synthesis of two trifunctional fluoropolymers,four diblock copolymers containing nitrate and azide groups were obtained by cationic ring-opening and azide substitution with glycidyl ether nitrate and epichlorohydrin as comonomers.The structures of six fluorinated polyether compounds were determined by FT-IR and NMR tests,indicating that the characteristic functional groups had been successfully introduced into the structure of prepolymer.The physical and chemical properties of the polymers were tested by GPC,DSC,density cup and rotary viscometer.The results showed that the relative molecular mass distribution of the six polymers was in the range of 2000–3000,and the polydispersity index（PDI）was less than or close to 1.5,indicating that the method of preparation was stable and efficient,and the molecular weight was relatively concentrated and controllable.The glass transition temperatures（T_g）of the six polymers were lower than or close to-60°C.The viscosity of each prepolymer was lower than 1000 c P,and the density was distributed in the range of 1.3–1.5.Compared with traditional binders,polymers prepared in this thesis had higher density,lower viscosity and lower glass transition temperature,which was conducive to its low-temperature performance and related applications,and has potential of application prospects.（2）Research on mechanical properties of curing elastomer.Firstly,the mechanical properties of the curing samples obtained at five temperature points within the range of 40–80°C were studied by 23 wt.%PAPI+poly（PFGE）as a model reaction,and the influence of temperature on the curing performance was obtained.Combined with the conditions of glass transition temperature and mechanical properties,60°C was selected as the temperature of the subsequent curing experiment.Polymethylene polyphenyl polyisocyanate（PAPI）was used as a multi-functional curing agent,and isophorone diisocyanate（IPDI）was used as a linear（difunctional）curing agent,curing with the obtained six polymers respectively.A series of standard curing splines were obtained by adjusting the content of isocyanate.The uniaxial tensile test results of the curing samples showed that the tensile strength of the elastomer gradually increased with the increase of the amount of isocyanate,while the elongation at break decreased due to the decrease of the mobility of the soft segment.The tensile properties of three systems reached more than 6 MPa.The PAPI+poly（GN-b-PFGE）system with the best tensile properties had yield deformation during the tensile process,and the maximum yield stress was 6.45 MPa.The PAPI+poly（PFGE）system has the best elastic deformation,and the maximum elongation at break can reach 276.64%.The tensile properties were generally higher than those of IPDI curing series by using PAPI as curing agent,indicating that the multifunctional curing agent can improve the crosslinking network formed by curing reaction,thus improving the mechanical properties.（3）Research on thermal properties of curing elastomer.The DSC test was carried out on the curing samples obtained under the above different conditions,and the glass transition temperatures（T_g）of the samples were obtained by extrapolation of the DSC heat flow curves.It was found that the T_g values of the curing samples under different process conditions were not the same,which was related to the mechanical properties to a certain extent.The T_g values after curing were generally lower than-40°C,further indicated that the fluorine-containing binder had the better low temperature performance.The thermal stability of the curing formulations was studied by TGA.The weight loss behavior of the curing samples was studied by the TGA test.It was found that the initial decomposition temperatures of the ten binder formulations were higher than 200°C,and all reached the maximum decomposition rate after340°C,indicating that the synthesized several fluorine-containing binder formulations have good thermal stability.