Synthesis And Properties Of Self-healing Gels Of Cyclic Polymer Containing Main-Chain Azobenzene

With the ability of self-healing,materials can maintain their own integrity and prolong their lifespan.As a kind of soft material,the mobile phase in the healing process is easier to form because of the polymer's good extension and stretch ability.Therefore,polymer is one of the best choices to make self-healing materials.The self-healing gel crosslinked by dynamic covalent bond has the advantages of both chemical gel and physical gel,which have not only high physical stability but also faster sol-gel conversion response to environmental changes and self-healing ability.The borate ester bond reaction didn't need harsh conditions and it can be happened under neutral and slightly acidic environment which make it a priority for self-healing gels.The photoisomerization behavior of azobenzene group has been widely concerned.It has good performance in protein molecular probe,drug release in nano-level and other effects in macro-level such as photomotivate materials,precise manipulation of liquid motion and so on.With the development of theoretical and industrial research on azobenzene,we will see more new azobenzene materials in the future.Cyclic polymer has some unique properties or improved performance due to the lack of chain ends.The research of cyclic polymer has attracted lots of attention in recent years.With the progress of synthesis,the new generation of cyclic polymer material has already showed great potential in information storage and drug releases.Taking good advantages of cyclic topology to prepare new materials is important in science theory innovation as well as industrial application.In this thesis,we synthesized cyclic polymer with main-chain azobenzene by click reactions,then the gels were got after crosslinked by dynamic covalent bond.After compared the differences between two gels on rheological test,stretching test,light response and other experiments,we have tried to explain the mechanism of how topology impact on the performance of materials.The detailed researches are as follows:1.Firstly,linear polymer containing azobenzene in main chain with good solubility was synthesized by the click reaction of thermally catalyzed?-alkynyl and?-azide1,3-dipolar cycloaddition.Then,the corresponding cyclic polymer was prepared by CuAAC reaction of the alkynyl group and azide group at the ends of linear polymer in high dilute solution.Finally,the cyclic and linear polymers with the side chain containing functional groups of diols were got after deacetalization by acidic ion exchange resin.The above synthetic products were characterized by GPC,~1H NMR and FT-IR.2.Secondly,the linear and cyclic polymer gels were obtained by crosslinking reaction of polymer side chain diol and p-phenylene diboric acid.We prepared the linear and cyclic polymer gels under different solvent contents and analyzed their properties by the rheological test,tensile test and the self-healing experiment.After analyzed the differences between linear and cyclic gels properties,we have been trying to make some reasonable explanations of how the cyclic topology has impact on the gels.3.Photoisomerization tests of linear and cyclic samples were did in three states,solution,polymer film and gel film.The effect of azobenzene photoisomerization in the gel on the macroscopic properties was investigated after compared the differences of photoisomerization rate between solution state and aggregation state,and reasonable explanations were made to explain these differences and experimental phenomena.