Construction And Mechanism Study Of Optical And Thermal Dual Stimuli-Responsive Systems Based On Poly(Ionic Liquid)s

Poly（ionic liquid）s（PILs）are a versatile type of functional material that find widespread use in various fields.PILs offer the combined benefits of excellent physicochemical properties from ionic liquids and mechanical characteristics from polymers,while also providing greater structural design flexibility than traditional polymers.By incorporating responsive groups such as pressure,temperature,light,electric field,magnetic field and guest molecules into PILs,they can exhibit intelligent responses to changing conditions.These materials have enormous potential for applications in nanotechnology,catalysis,biomedicine,and other fields due to their ability to adapt their properties according to environmental cues.Aqueous Two-Phase System（ATPS）is created when two incompatible substances are mixed in water above their critical concentration,resulting in a phase separation.ATPS is an environmentally friendly and reusable system that effectively separates and purifies various compounds.Although stimuli-responsive behavior can be easily achieved with PILs-based ATPS,there are limited reports on intelligent tunable-phase behavior of ATPS using PILs.ATPS constructed with designable stimuli-responsive polyelectrolyte liquid offers more possibilities.Hydrogel is a three-dimensional network gel that is hydrophilic,biocompatible,and functionally diverse.By adding stimulus responsiveness to hydrogels,their functionality can be enhanced,and their application range expanded.This study introduced stimulus-responsive groups into PILs and added large cyclic molecules to create non-covalent interactions.As a result,we successfully constructed tunable-phase separation and phase inversion ATPS,as well as stimulus-responsive supramolecular hydrogels.These materials have great potential for future applications such as intelligent separation.The specific research topics covered in this study are:1.PILs PVIm Bn_xEt（x=5,15,25,35,45）and PVIm Azo₅Et were prepared using a synthetic modification strategy.The structures of the PILs and intermediate products were characterized using 1H nuclear magnetic resonance spectroscopy（¹H NMR）,Carbon nuclear magnetic resonance spectroscopy(¹³C NMR)and fourier transform infrared spectroscopy（FT-IR）.The grafting degrees of benzyl group（Bn）and azobenzene group（Azo）were determined through analysis with ¹H NMR and ultraviolet-visible spectroscopy（UV-vis）,respectively.Thermogravimetric analysis（TGA）was used to study the thermal stability of PILs.To characterize an IL,a model compound[Azo C₆MIm]Br was synthesized and analyzed using ¹H NMR and ¹³C NMR.The photoresponsiveness of the compound to UV light and visible light was characterized by UV-vis spectroscopy.Using specific concentrations,two types of PILs were dissolved in water to create ATPS for studying their phase separation behavior under temperature and UV irradiation stimuli.The study found that PVIm Bn_xEt and PVIm Azo₅Et can form stable ATPS in water,with the rich phase of PVIm Bn_xEt on top and that of PVIm Azo₅Et at the bottom.As the grafting degree of Bn(GD_Bn)increased to 45%,ATPS underwent inversion and showed an increasing ability for phase separation as GD_Bn increased.When using ATPS constructed from PVIm Bn₅Et and PVIm Azo₅Et,both temperature elevation or UV irradiation could induce a transition from two phases into one phase,which is reversible.This indicates that this double aqueous phase system exhibited tunable phase behavior under thermal and photoinduced stimuli.2.ATPS,responsive to both light and heat,was created using host-guest interactions in PILs.The main component molecule,CB[8],was synthesized and characterized through ¹H NMR and high-resolution mass spectrometry.To study the phase separation behavior of this system,a stable ATPS was prepared by combining PVIm Bn_xEt+PVIm Azo₅Et+CB[8]as components.The novel ATPS was observed to undergo reversible upper/lower phase inversion in response to temperature and light stimulation.Adding 0.4 eq CB[8]resulted in high reversibility during temperature or UV-induced phase inversion.,meaning the original state could be restored by lowering the temperature or using visible light irradiation after phase inversion occurred under elevated temperature or UV conditions.However,an excess of CB[8]can cause cross-linking in the rich PVIm Bn_xEt phase without stimulus responsiveness.This also occurs when GD_Bnincreases.In ATPS with a higher GD_Bn value,the dense stacking of large molecular chains in the rich PVIm Bn_xEt phase causes it to enter the lower phase.To restore ATPS to its initial state,N,N,N-trimethyl-1-adamantylammonium iodide（[TMAda]I）can be added as a competitive guest molecule with a higher binding constant to CB[8].This displaces benzyl groups from the CB[8]cavity and restores ATPS.3.Benzyl,azobenzene and ethyl grafted PILs were designed and synthesized.With the presence of host molecule CB[8],a novel stimuli-responsive supramolecular hydrogel was successfully prepared.The structure of PILs was characterized by ¹H NMR and FTIR,while their thermal stability was analyzed using TGA.To investigate the impact of temperature,light and other factors on response behavior,we formulated several supramolecular hydrogels.Results showed that higher concentrations of PILs,more CB[8],and higher GD_Bn values led to stronger mechanical strength in the hydrogels.However,due to dynamic reversible properties of host-guest interaction and photoresponsive characteristics of azobenzene groups,heating or UV irradiation caused significant decreases in mechanical strength for this stimuli-responsive hydrogel.This smart material has a wide range of potential applications in the field of intelligent materials.