Synthesis,stimulus Responsive And Application Of Triazolium-based Poly(ionic Liquid)s

Stimulus responsive polymers are a class of macromolecule with“smart”behavior.When stimulated by external environmental signals,such as p H,light,temperature,gas,etc.,it will change its structure or state,thereby affecting its physical and chemical properties.It has a wide range of applications in seawater desalination,sensors,drug release,etc.Poly（ionic liquid）s（PILs）are a new type of polyelectrolyte with ionic liquids（ILs）as repeating units.It integrates the unique properties of ionic liquids（such as good chemical stability,low flammability,high ionic conductivity,etc.）into the polymer chain,combining the advantages of both,and has potential applications in energy,environment,and catalysis.If PIL has stimulus responsiveness,especially multi-stimulus responsiveness,it can meet different needs and is expected to be applied in many fields.In this dissertation,a series of triazolium-based PILs with different stimulus responsiveness were synthesized.The structure or state of PILs could be easily adjusted by changes in temperature,gas,or light.The mechanism of thermo-and gas responsiveness of PILs were also explored,respectively.Finally,a new material based on stimulus responsive PILs was developed.The main results are summarized as follows:1.A series of 1,2,4-triazolium-based PILs with different alkyl chain lengths（i.e.methyl,n-butyl or n-octyl）and counter anions（i.e.I^-,Br^-,BF₄^-,PF₆^-or TFSI^-）were successfully synthesized.The influence of the structure of PILs on their solubility was also explored.This research found that 1,2,4-triazolium-based PILs showed different thermo-sensitive behaviors in different solvents,such as the upper critical solution temperature-type（UCST）phase transition of Ptriaz-C1-I methanol solution and Ptriaz-C4-Br isopropanol solution,while the lowest critical solution temperature-type（LCST）phase transition of Ptriaz-C1-PF₆ acetone solution.Such thermo-responsive has good reversibility and concentration dependence.For example,the cloud point of Ptriaz-C1-I methanol solution gradually increased from 27℃to 53℃with the concentration of PILs increased from 5 to 20 mg/m L.The microstructure changes of the UCST behavior of Ptriaz-C1-I in methanol solution were subsequently investigated.It was found that the UCST behavior was mainly caused by the solubility change of the polymer backbone in methanol.Finally,Ptriaz-C1-I PILs were mixed with multi-walled carbon nanotubes to prepare PILs-based conductive gels.The volume and conductivity of the obtained gels could be controlled by temperature.2.The gas responsiveness of Ptriaz-C1-I to NH₃ and N₂ was studied.The results of UV-visible spectroscopy and dynamic light scattering（DLS）showed that alternating bubbling NH₃ and N₂could regulate the dissolution and aggregation of Ptriaz-C1-I in methanol,which had good recyclability.¹H NMR,¹⁵N NMR and Zeta potential were employed to study the gas responsive mechanism.It was found that the proton at the C5 position on the triazolium ring was unstable and was easily taken away by the basic gas NH₃ to form a nitrogen heterocyclic carbene.The latter continued to combine with excess NH₃ and formed carbene-NH₂ adducts.In this process,the polymer gradually changed from positive to neutral.In addition,the fluorescence performance of Ptriaz-C1-I/TFSI in different solvents could also be adjusted by gas.The bubbling of NH₃ caused the red shift and weakening of fluorescence,followed by the bubbling of N₂ recovered the fluorescence somewhat,which is also attributed to structural changes.This gas-responsive PILs is expected to be used as a catalyst to regulate catalytic activity by alternately bubbling NH₃ and N₂in the system.3.The photo-reversible cross-linked PIL-based microgels were prepared by combining the UCST phase transition of Ptriaz-C1-I and the reversible photochemical bonding of styrylpyrene.Firstly,the light-responsive P（triaz-C1-I-co-SPHEMA）was synthesized by free radical polymerization.The molar ratio of the ILs to the photo-responsive groups was calculated as 15:1by ¹H NMR.Then Ptriaz-C1-I methanol solution was cooled to form micelles due to its UCST behavior.Subsequently,blue light（λ=430 nm）was used to irradiate the micelles to cause dimerization reaction between the styrylpyrene groups,thereby cross-linking and fixing the micelles,so that the photo-cross-linked PILs-based microgels were obtained.TEM showed that the microgels were spherical particles,and the hydrodynamic diameter of the microgels was 272±3 nm in its good solvent DMF measured by DLS.Finally,UV light（λ=340 nm）was used to de-dimerize the cross-linking points to realize the disintegration of the PILs-based microgels.