Structure Design And Property Control Of Huisgen Reaction Curing Crosslinking Material System Containing Urethane Segments

The main components of composite solid propellant are oxidant,combustion agent,plasticizer,bonding agent,binder and curing agent.The chemical bond between binder and curing agent provides structural integrity and excellent mechanical properties for propellant components.Propellant can release high density energy and produce high specific impulse through regular combustion.Binder technology is one of the key technologies to promote the development of explosives.Especially in solid propellants,binder is considered to be the heart of solid propellants and the symbol of the upgrading of solid rocket propellants.The traditional binder is isocyanate curing system,because of its special polyurethane microphase separation structure,it can realize the continuous optimization of mechanical properties,and is widely used in the actual solid propellant.However,its curing temperature is high,humidity sensitive,side reaction with other additives,and high requirements for actual storage.It can be seen that the development of binder system with high mechanical properties and the corresponding curing system insensitive to ambient humidity and filler moisture content has become a very practical technical demand for solid propellants.The curing reaction system of Huisgen triazole based on azide polyether has rapidly become a hot spot of adhesive technology research due to its humidity insensitive,room temperature curing,no small molecular products,and specific and stable reaction.However,due to the strong polar-CH₂N₃ group on its side chain,the molecular chain has poor flexibility and mechanical properties,which can not meet the requirements of practical application.Therefore,it is still a huge challenge to avoid the practical application problems caused by water sensitivity in the curing process and realize the continuous optimization of mechanical properties to meet the requirements of practical application.In order to improve the mechanical properties of Huisgen reaction curing system,triazole curing system is applied to rocket solid propellant.In this paper,ethylene oxide tetrahydrofuran copolyether（difunctional p-PET and trifunctional t-PET）with high flexibility is selected as the research object,and the advantages of Huisgen reaction curing system are followed.According to the characteristics of its low mechanical properties,the terminal alkyne group containing urethane segments is designed from the design of molecular structure Polyether and azido compounds were used for alkynyl azide click reaction to construct a Huisgen reaction curing cross-linking material system containing urethane structure.The conclusions are as follows:（1）Using p-PET as the reaction substrate,based on the different activity of two isocyanate groups on 2,4-toluene diisocyanate（TDI）,propynyloxycarbonylamine-terminated ethylene oxide tetrahydrofuran copolyether（p-Pr PET）was synthesized by reacting with TDI,and then with propargyl alcohol.Trifunctional azide-terminated ethylene oxide tetrahydrofuran copolyether（t-ATPET）was synthesized by chlorination of t-PET with dichlorosulfoxide and then with sodium azide.Tetrafunctional pentaerythritol tetraazide（Az PTO）was synthesized by reaction of pentaerythritol with chloroacetic acid and then with sodium azide.Fourier transform infrared spectroscopy（FTIR）and nuclear magnetic resonance（NMR）analysis showed that hydroxyl groups were completely substituted by alkynyl and azide groups.Gel permeation chromatography（GPC）showed that the molecular weight and molecular weight distribution of the two molecules were almost unchanged before and after the reaction.The results showed that the target products p-Pr PET,t-ATPET and Az PTO were obtained.（2）Using Az PTO（F=4）as curing agent,p-Pr PET/Az PTO and p-PPET/Az PTO elastomers with different molar ratios of alkynyl to azide（R=0.8,0.9,1.0,1.1,1.2）were prepared by using p-Pr PET and alkynyl terminated ethylene oxide tetrahydrofuran copolyether（p-PPET）as adhesive respectively.The effects of reaction equivalent and urethane structure on the properties of Huisgen reaction cured crosslinked materials were studied.The tensile test results show that with the increase of R value,the tensile strength and Young’s modulus of the elastomer first increase and then decrease,while the elongation at break first decrease and then increase.The mechanical properties of elastomer with urethane structure are better than those without urethane structure.When R=1.0,the mechanical properties of p-Pr PET/Az PTO elastomer are the best,the elongation at break,tensile strength and Young’s modulus are 198.23%,3.34 MPa and33.62 MPa,respectively.Swelling test and FTIR test show that the network structure of elastomer is the most complete when R=1.0.Atomic force microscopy（AFM）and scanning electron microscopy（SEM）showed that the urethane structure formed a microphase separation structure which was beneficial to enhance the elastic mechanical properties.（3）Using t-ATPET（F=3）as curing agent,p-Pr PET/t-ATPET and p-PPET/t-ATPET elastomers with different molar ratios（R=0.8,0.9,1.0,1.1,1.2）of alkynyl to azide groups were prepared by using p-Pr PET and p-PPET as adhesive respectively.The effects of reaction equivalent and the structure of urethane on the properties of the materials were studied.The tensile test results show that with the increase of R value,the tensile strength,Young’s modulus and elongation at break of the two elastomers show a synchronous trend,which first increases and then decreases.The mechanical properties of elastomer with urethane structure are better than those without urethane structure.When R=1.0,the mechanical properties of p-Pr PET/t-ATPET elastomer are the best,the elongation at break,tensile strength and Young’s modulus were 1070.28%,2.66 MPa and 2.51 MPa,respectively.Swelling test and FTIR test show that the network structure is the most complete when R is 1.0.AFM and SEM tests showed that the urethane structure promoted the formation of microphase separation structure,which improved the mechanical properties of the elastomer.The strategy of introducing the urethane structure into the Huisgen reaction curing crosslinking material system can achieve the purpose of improving the mechanical properties of the triazole curing system,and it is suitable for both small molecule curing agent and polymer curing agent system.