| Energetic composite materials（ECMs）are the basis of polymer binder explosives（PBXs）and composite solid propellants（CSPs）,and are mainly composed of polymer adhesives and high-energy solid particles.However,the polymer adhesives without energetic groups have negative contributions to the overall energy level of the ECMs.The implantation of azide groups with higher enthalpy of formation on the polymer adhesives is undoubtedly more in line with the high energy requirements of the ECMs in the future.In addition,under the stimulation of the external environment（temperature,humidity,shock,etc.）,micro/fine cracks and defects tend to form inside the ECMs.The formation of cracks and defects will lead to a decrease in mechanical properties;at the same time,the existence of cracks will lead to greater thermal resistance and friction at the crack interface,affecting the performance and safety of the weapon system.In response to this problem,the design strategies for self-healing energetic supramolecular adhesives were proposed,and the energetic supramolecular polymers based on reversible non-covalent bonds were designed and constructed to obtain excellent mechanical properties,energy properties and self-healing properties,and their application performance in ECMs was preliminarily explored.（1）An energetic self-healing adhesive,polyazide glycidyl ether-isophorone diisocyanate-4,4’-methylene diphenylamine（GAP-IDI-MDA）,with multistrength and multphase dynamic hydrogen-bonding cross-linking network was designed.The basic characteristics of GAP-IDI-MDA included:（i）rapid rearrangement of the hydrogen bonds,（ii）plenty of hydrogen bond sites,and（iii）abundant azide groups.Abundant dynamic hydrogen bonds endowed the adhesives with efficient room-temperature self-healing ability;Plentiful hydrogen bond sites endowed the ECMs with good mechanical properties,and a large number of azide groups endow the adhesives with a good energy level.For the synthesized energetic adhesives,the enthalpy of formation is+1.95 k J g-1,which is higher than some small molecules and oligomers;the mechanical properties could be recovered within 2 h after fracture at room temperature;the ECMs prepared from the designed adhesives and explosive crystalline 1,3,5-triamino-2,4,6-trinitrobenzene（TATB）exhibited good mechanical properties(maximum tensile strength:1.39MPa,toughness:8.05 MJ m-3)and excellent crack repair ability（12 h at room temperature,repair efficiency:97.91%）.In addition,compared with non-energetic adhesive-based ECMs,energetic adhesive-based ECMs exhibited excellent combustion properties.Therefore,the GAP-IDI-MDA adhesive demonstrated a certain application potential and this strategy is expected to provide new ideas for the improvement of weapon system security.（2）The GAP-IDI-MDA adhesive designed in Chapter 2 has a low tensile strength（0.03MPa）,and the applicability is limited to high-energy particles with a large number of hydrogen bonding sites on the surface.Therefore,on this basis,a design strategy for micro-scale regulation is proposed in Chapter 3 to prepare energetic adhesives with both robust mechanical properties and efficient self-healing properties.First,acyl semicarbazides（ASCZ）,a multiple hydrogen bond motif,was utilized to endow energetic adhesives with strong and tough mechanical properties.Subsequently,the asymmetric structure was introduced to regulate the hydrogen bonding array density and micro-scale trim the size of the hard domain,thereby improving the hydrogen bonding dynamics and the polymer-chains mobility.Finally,the synthesized energetic polymer adhesive（EPA）has a maximum tensile strength of 3.61 MPa,an elongation at break of 1158%,and a toughness of 32.81 MJ m-3.For the broken adhesive strips,the maximum tensile strength was recovered by 100.2%,and the strain at break was recovered by 80.5%at 60℃for 24 h.When the temperature was increased to 80℃,the fracture strain could be recovered to more than 90%after 24 h.Hereafter,the adhesives were further to be used with Al powder for the preparation of the ECMs（EPA/Al）with a maximum tensile strength of 8.85 MPa and a toughness of 12.49 MJ m-3,which could be mechanically comparable to commercial non-energetic adhesive-based ECMs.In addition,the mechanical properties of the scratched EPA/Al splines could be basically recovered after being placed at 80℃for 56 h.（3）Compared with high-temperature-driven（80℃）self-healing energetic adhesives,energetic adhesives that could achieve high self-healing efficiency at room temperature undoubtedly would reduce the complexity and cost during the healing process.However,room temperature self-healing polymers require more flexible molecular chains and weaker interaction,which is not conducive to mechanical properties.Aiming at this problem,an energetic self-healing adhesive containing asymmetric alicyclic structures and multiple urea groups was designed in chapter 4.The asymmetric alicyclic structures could be used to construct loosely packed hard domains;the irregular arrangement of multiple urea groups could be used to strengthen physical cross-linking and improve the strength of hard domains.Thus,significantly increases tensile strength and toughness while meeting the dynamic adaptability and responsiveness required for self-healing at room temperature.Finally,the maximum tensile strength,elongation at break,and toughness of the designed adhesive（GPU-3.0）could reach1.77 MPa,1237%,and 10.49 MJ m-3,respectively.When the severed GPU-3.0 was placed at room temperature for 48 h,the tensile strength could be completely recovered,and the healing efficiency of ductility could reach 96.8%.Furthermore,compared with the recently reported room-temperature self-healing adhesives,the GPU-3.0 adhesive exhibited excellent comprehensive performance in terms of toughness,adhesion strength,and healing efficiency.The ECMs（GPU/Al）prepared by GPU-3.0 adhesive and Al has a maximum tensile strength of2.52 MPa and a toughness of 2.45 MJ m-3.After 72 h at room temperature,the scratches on the GPU/Al surface disappeared and the mechanical properties were completely recovered.Therefore,compared with the energetic self-healing adhesives designed in chapters 2 and 3,GPU-3.0,which has both high-efficiency room temperature self-healing ability and good mechanical properties,is more in line with the current demand for energetic adhesives in ECM self-healing systems. |
