Study On The Synthesis And Mechanism Of Stimulus-responsive Aqueous Biphasic System Based On Poly(ionic Liquid)s

Ionic liquid is a kind of molten salt composed of organic cations and organic or inorganic anions,which appear liquid at or near room temperature.One of the applications of ionic liquids is to construct aqueous biphasic systems mixed with different kinds of salting-out agents in water for extraction.Compared with traditional aqueous biphasic systems,aqueous biphasic systems based on ionic liquids have many advantages,such as high speed of phase separation,low viscosity,not easy to emulsify and have higher extraction efficiency and distribution coefficient in the extraction of some specific natural bioactive small molecular organic compounds.Therefore,it has attracted the attention of researchers and has been deeply studied.Most of the ionic liquid aqueous biphasic systems are static systems constructed by ionic liquid,and few studies on the dynamic stimulus-response of aqueous biphasic systems and aqueous biphasic systems based on poly（ionic liquid）s.In this paper,photo-responsive poly（ionic liquid）s were prepared by quaternization modification of poly（vinyl imidazole）with azobenzene compounds and bromoethane according to a certain proportion and aqueous biphasic systems are constructed by mixing different types of salting-out agents with prepared poly（ionic liquid）s in water.A poly（ionic liquid）s aqueous biphasic system with light/temperature dual stimulus-response was successfully constructed,and its response mechanism was studied.The main contents of this thesis are as follows:1.Poly（ionic liquid）s and ionic liquid monomers with specific structures were prepared.Based on the polyvinyl imidazole prepared by free radical polymerization,the functional groups（azophenyl,benzyl）were grafted in a certain proportion,and the imidazole units without grafted functional groups were quaternized with bromoethane to prepare poly（ionic liquid）s containing azophenyl groups（PVIm Et-Azo）and poly（ionic liquid）s containing benzyl groups（PVIm Et-Bn）.The structure and physicochemical properties of the synthesized poly（ionic liquid）s were characterized by nuclear magnetic resonance hydrogen spectrum and carbon spectrum(¹H NMR and¹³C NMR),Fourier transform infrared spectroscopy（FT-IR）,ultraviolet-visible spectroscopy（UV-vis）,gel permeation chromatography（GPC）,thermogravimetric analysis（TGA）.Ionic liquid 1-methyl-3-（1-（6-azophenoxy）hexyl）imidazolium bromide（[MAzo HIm]Br）,1-methyl-3-benzyl imidazolium bromide（[MBn Im]Br）,1-methyl-3-ethyl imidazolium bromide（[MEIm]Br）,1-vinyl-3-（1-（4-azophenoxy）butyl）imidazolium bromide（[VAzo BIm]Br）,1-vinyl-3-benzyl imidazolium bromide（[VBn Im]Br）.The structure of ionic liquid monomer was characterized by ¹H NMR and ¹³C NMR.2.The aqueous biphasic system was constructed on the basis of poly（ionic liquid）s PVIm Et-Azo and different kinds of compounds as salting-out agents.the salting-out agents included conventional inorganic salts（K₃PO₄）and polymer（PEG-200,PEG-600）.In addition,the aqueous biphasic system was constructed by using ionic liquid monomer（[MEIm]Br,[MBn Im]Br）and poly（ionic liquid）s（PVIm Et-Bn,PVIm Et）as salting-out agent.An aqueous biphasic system based on poly（ionic liquid）s PVIm Et-Azo and another poly（ionic liquid）s PVIm Et-Bn as salting-out agent was successfully constructed.The effects of salting-out agents,poly（ionic liquid）PVIm Et-Azo structure and temperature on the aqueous biphasic system were studied.3.A novel aqueous two-phase system of poly（ionic liquid）s with temperature/light dual stimulus-response was constructed,the stimulus-response of the system was verified and the response mechanism was studied.The experimental results show that the aqueous biphasic system constructed by PVIm Et-Azo and PVIm Et-Bn with higher grafting ratio can realize the reversible inversion of the two-phase position in response to the change of temperature,and can return the separated two phases to one phase in response to UV irradiation.Mechanism of stimulus response of aqueous biphasic system of poly（ionic liquid）s lies in the non-covalent interaction in the system（the hydrogen bond between the imidazole ring on the main chain of the poly（ionic liquid）and the solvent water,theπ-πstacking between the azophenyl group and the benzyl group on the side chain of the poly（ionic liquid））can respond to the change of external conditions.