Study Of Self-repaired Polymer Systems Based On Dynamic Covalent Bonds

Because of their stable existence of cross-linking network,traditional thermosetting materials have excellent mechanical properties,corrosion resistance and stability.It has a wide range of applications in various industries,such as aerospace,transportation,medical treatment and coating fields.But materials in the process of use,it will inevitably be affected by external damage.In the macro or micro level,cause irreversible damage to the material,shorten the service life.Due to the stability of its internal crosslinking network,it cannot dissolve and cannot melt,making it difficult to self-repair.In the treatment brings a certain degree of resource waste and environmental pollution.Because the damage can be diagnosed and repaired by themselves and prolong the service life,self-repair polymer materials are gradually widely used.There are two types of self-repair:foreign aid and intrinsic self-repair materials.It is one of the effective strategies to solve the above problems to introduce the polymer material of the dynamic dynamic bond.When the material is damaged externally,the internal fracture reorganization is made through the external stimulation to realize the self-healing of the material.By introducing dynamic covalent bonds such as disulfide bonds,diselenium bonds and vinylogous urethane bonds,the prepared materials have as excellent thermal and mechanical properties as conventional thermosetting materials.At the same time,after the external damage,the reversible reaction occurs,the internal network of the material reorganization to repair the cracks,has the ability of self-repair.The specific study is as follows:(1)Modified castor oil was prepared by transesterification reaction thiol-ene click reaction.Curing with diamine crosslinkers to prepare bio-based coating materials containing vinylogous urethane.With the increasing crosslinking density in the material,both the mechanical and thermal properties gradually increase.Tests show that the P2 films have the highest comprehensive tensile properties,with a tensile elongation and strength of up to 52%and 5.53MPa,respectively.The subsequent stress relaxation test of P2 injection and self-repair performance characterization calculated a low activation energy of 69 k J/mol;after 6h of repair at120 ~oC,the self-healing effect was excellent,with a repair efficiency of 80%.(2)Select four amine crosslinkers containing disulfide bonds and diselenium bonds,and then react with the common epoxy species to prepare four self-healing epoxy networks.The resulting four obtained materials were tested for thermal and mechanical properties such as DSC,TGA and DMA.The results showed that the glass transition temperature(T_g),mechanical properties,crosslinking density(v_e)and thermal stability of disulfide bonds were higher than the diselenium compounds.In order to verify the stress relaxation behavior of the material,the stress relaxation experiment was conducted on the material.The activation energies of BED4DS,BED4DSe,BED2DS,and BED2DSe were calculated as 71,57,84,and 62 k J/mol,respectively.It can be seen that the epoxy network connected by diselenium compounds has lower activation energy and that to the phenyl amino network.The lower the activation energy means that the dynamic bonds are easier in exchange.Later,the healing ability of the material was tested,and the diselenium cross-linking network showed significantly higher healing efficiency than that of disulfide.