Study On The Programming,Preparation And Application Of Epoxy Based Vitrimer Polymers

Due to their excellent dimensional stability,corrosion resistance,electrical insulation and other properties,epoxy resins and their composites have been widely used in ship transportation,machinery manufacturing,aerospace and other fields.However,as a typical type of thermosets,epoxy resinswere formed by irreversible covalent bonds.Therefore,they are insoluble and infusible while difficult to be recovered,degraded and self-repaired after molding,which affects the further development of such materials.The appearance of vitrimer provided the possibility for recycling of epoxy resins and their composites.Frustratingly,most of the recycling process for epoxy resins researched by the predecessors were time-consuming and conduct in highly temperature.Therefore,it is urgent to find a method to adjust the dynamic properties of epoxy vitrimer to optimize the recycle conditions.Which is of vital importance for the controllable design and applications of epoxy vitrimer.Vitrimer's dynamic property is caused by exchange reactions between dynamic covalent bonds.By adjusting the density of the exchangeable bonds in the network may affect the dynamic propertyof vitrimer.Based on this conjecture,in this paper we firstly designed and synthesized soft/hard epoxy vitrimer with different density of exchangeable ester bonds by changing the length of the epoxy monomer or the curing agent.And then we explored the effect of density of the ester bonds on the dynamic property of epoxy vitrimer.It was found that the higher the density of the ester bonds,the better the dynamic properties of the material.Then,a catalyst-free dual disulfide epoxy vitrimer was designed and synthesized,in which curing agent and epoxy monomer were introduced into exchangeable aromatic disulfide simultaneously.Compared to single disulfide epoxy vitrimer,which only introduce aromatic disulfide bonds in the curing agent,the dual disulfide epoxy vitrimer network has more exchangeable bonds,in other words,the more density of the exchangeable bonds in the network.Dual disulfide epoxy vitrimer maintains excellent mechanical properties(storage modulus of 1.7 GPa and tensile strength of 68.6 MPa)and has excellent dynamic property(stress relaxation at 200? in only 11.1 s,degraded in 90? DTT/DMF solution in 30 min,cracks healed at 200? in 2 min etc.).Finally,a carbon fiber reinforced dual disulfide epoxy vitrimer was prepared.This composites has extremely high mechanical properties(storage modulus up to 10.5 GPa and tensile strength of 394.6 MPa).And the carbon fiber cloth can be completely recovered from the epoxy matrix under milder conditions(90?,<1 h).A new composites was prepared from the recycled carbon fiber.The composites maintains excellent mechanical strength(storage modulus of 8.2 GPa and tensile strength of 358.2 MPa),indicating that carbon fiber in the composites can be well recycled.