Design,Preparation And Self-healing Performance Of Thermoreversible Epoxy-Anhydtide Polymers Based On Diels-Alder Reaction

Epoxy resin is a structural material with a good performance and has been widely used in coatings,adhesives,and composites.However,since the traditional epoxy resin is a three-dimensional network cross-linked structure and cannot be processed twice,it is difficult to recover and repair,and its application is limited.At present,the intelligent thermally reversible self-repairing epoxy resin has received extensive attention.The main method is to introduce a covalent bond having a thermal reversible characteristic into an epoxy resin system.In this system,using diene and diene groups,using its Diels-Alder cross-linking reaction,the new epoxy resin material prepared not only retains good mechanical properties,but also has a thermally reversible self-repairing property.Currently,bismaleimide is commonly used as a dienophile,and the epoxy curing reaction and the Diels-Alder cross-linking reaction are performed step by step.The preparation process usually requires a solvent,and the operation is complicated and the processing performance is poor,and it is difficult to obtain applications.In this paper,firstly,a low-viscosity glycidyl ether(FGE)resin with bifunctional functional groups containing epoxy groups and furan rings was synthesized by one-step method.The structures of these compounds were characterized by FTIR,1HNMR and 13CNMR.The epoxy value of FGE was determined by hydrochloric acid-acetone method.The epoxy value was 0.62,which was close to the theoretical value.Next,maleic anhydride(MA)containing double bonds was selected as the curing agent,N,N-dimethylbenzylamine(BDMA)as the accelerator,and the FGE/MA system was constructed to pass the epoxy groups and anhydride groups.The ring reaction and the Diels-Alder cross-linking reaction of the furan ring with the double bond proceed simultaneously to form an epoxy-cured and Diels-Alder crosslinked hybrid 3D crosslinked network,Diels-Alder formed with the traditional bismaleimide Compared with epoxy system,the preparation process has the characteristics of one-time mixing and solvent-free.Using FITR to follow the curing process,the results show that the system has completely completed the curing reaction.DSC was used to study two problems:1,Diels-Alder reaction and its reversible process.The results show that the reversible bond can be generated by the DA reaction after the heat reversible treatment.The reversible efficiency of the DA bond is calculated to be 89.3%,indicating that the DA bond in the system has good reversibility;2.The proportion of the reactants.Taking into account the influence of the ratio of reactants on the degree of DA reaction,study it and determine the optimal proportion of reactants by the value of the endothermic peak of the retro-DA reaction on the DSC curve.Finally,determine the molar ratio of the reactants according to the functional group,1:1 is the best.The thermal decomposition properties and dynamic mechanical properties of the FGE/MA cured product were characterized by TGA and DMA.The results show that the retro-DA reaction in this system does not affect the heat resistance of the material.The glass transition temperature of the cured product is 77.3?.The dissolution experiment also shows the reversibility of the DA bond in the system.Finally,on the premise of retaining the thermal reversible property,the system was modified,and the commonly used epoxy resin DGEBA was added to the FGE/MA system to change the proportion of DGEBA to construct the FGE/DGEBA/MA thermally reversible crosslinked network.DSC was used to study the reversibility of the DA bond in FGE/DGEBA/MA cross-linked networks.The results showed that as the proportion of DGEBA increased,the enthalpy of the endothermic peak gradually decreased,indicating that the content of DA bonds in the system was continuously reduced when the ratio reached 40%.At the time,the DA response is low.Moreover,the thermal reversibility of the DA bond gradually decreases.DMA results show that the addition of DGEBA increases the crosslink density of the system,leading to higher glass transition temperatures and higher storage modulus.The mechanical properties and self-healing properties of the system were studied by tensile testing.The results showed that the tensile strength of the FGE/MA system was 57.7 MPa and the self-repairing efficiency was 89.5%.The addition of DGEBA significantly improved the mechanical properties of the system.10%of 58.5 MPa increased to 63.7 MPa with a ratio of 30%.However,due to the increase in cross-link density,the self-repair efficiency decreased from 88.7%in the proportion of 10%to 79.4%in the proportion of 30%.Therefore,by adjusting the amount of DGEBA added to adjust the control of changes in performance,to adapt to different conditions of practical application.