Investigation Of Selenium-Containing Dynamic Covalent Bond In Synthesis Of Polymers And Their Performance

Dynamic covalent bond is a special kind of covalent bond,which can be broken,re-formed and exchanged under certain stimulation conditions.It has attracted much attention because of its dynamic and adaptive characteristics.Many classical dynamic covalent bonds,such as disulfide bond,imide bond,hydrazide bond,ester bond,silicon-oxygen bond,imide bond,have been well studied and applied in a series of research fields.In fact,the discovery of each new dynamic covalent bond will create a hot spot in the field of supramolecular chemistry and intelligent responsive materials.Therefore,it is important to develop new dynamic covalent bonds with mild and unique reaction characteristics.In recent years,the dynamic covalent bond of alkyl diselenide can be exchanged under visible light,which is much faster than that of disulfide bond under the same conditions,and attracts many scientists' interest.Many self-healing materials and shape memory materials have been developed based on these dynamic covalent bond.However,it is still difficult to improve the property of self-healing performance under mild conditions due to the limited exchange rate of diselenide bond under such condition.At the same time,diselenide bonds are mainly used in elastomers with low Tg.How to expand their application scope,especially in materials with high Tg,high modulus and healable properties,still faces great challenges.Because of the unique properties of selenium atoms,the exchange rate of selenium containing dynamic covalent bonds could be enhanced under very mild conditions by substitution one of selenium in diselenide,such as selenium-nitrogen,selenium-sulfur,selenium-selenium and selenium-tellurium dynamic bonds.Therefore,these dynamic covalent bonds are considered the most promising dynamic covalent bonds for the preparation of dynamic polymers.In addition to the dynamic covalent bonds of selenium found above,it is also significant to explore new dynamic covalent bond based on selenium and establish a new dynamic chemistry under the new conditions.Based on the current research status,this thesis is aimed for developing polymeric materials containg selenium based dynamic covalent bond.The research is carried out through following aspects:Firstly,the exchange reaction of aromatic diselenides based dynamic covalent bond was explored.The equilibrium constants,rate constants and mechanism of the exchange of aromatic diselenides were investigated in the model reaction using substituted diaryldiselenide as reactant.The exchange rate of these aromatic diselenides were compared to their disulfide anologs.Based on the aromatic diselenide bonds and aromatic disulfide,the polyurethane elastomer was prepared.The self-healing properties and the reshaping ability of the two materials were investigated.To verify the effect of the characteristics of these dynamic covalent bond exchange reactions on the self-healing ability of materials,and lay the foundation for developing new dynamic covalent bonds for high performance self-healing polymer materials.Secondly,Synthesis and performance of diselenide-containing vitrimer.The dynamic coyalent bond characteristics of diselenide was introduced into epoxy resin materials.The epoxy resin materials with high Tg and high modulus by adjusting the crosslinking density were synthesized.The vitrimer properties of epoxy cross-linked materials containing dynamic covalent bonds of diselenides were investigated.Furthermore,the properties of epoxy resin containing selenium bond,such as self-healing,recyclability and reprocessing were investigated.The epoxy resin was applied to carbon fiber composites to realize the recyclability and reprocessing ability of carbon fiber composites.Thirdly,a new condensation polymerization reaction was developed to prepare selenium-containing polymers based on the electrophilic addition reaction of selenium chloride reagent with olefins.The reaction efficiency was validated by model compounds to explore and optimize condition in polymer synthesis.Then,the effects of polymerization conditions,such as monomer feed ratio,solvent and temperature,on the polymerization were investigated,which can adjust the molecular weight and terminal functional groups of polymers.The synthesis of block polymers was realized by sequential feeding.In addition,the application scope of this method was extended by expanding the types of monomers Finally,the properties of the obtained polymers,such as oxidation responsiveness,light responsiveness,acid-base responsiveness were investigatedFourthly,study on the properties of dynamic bonds of seleniranium ions.The dynamic bond of seleniranium ions was confirmed by model reaction.The exchange rates of olefins with different structures and selenium chloride reagents were investigated,and the equilibrium constants of these exchange reactions were calculated.The model reaction was extended to the polymer system,the dynamic exchange behavior between seleniranium ions containing polymer and small molecules was investigated.The different degrees of the degradation behavior of the polymer was realized by different equilibrium constants of the exchange system.The "dynamic covalent bond" characteristics of this seleniranium ion exchange reaction were applied to the synthesis of novel self-healing polymers.