Aggregation Behavior And Application Of N-alkyl Imidazolium-based Poly(Ionic Liquid)s In Solvent

Poly?ionic liquid?s?PILs?are a class of polymers that combine the unique properties and structural designability of ionic liquids?ILs?with the mechanical stability and improved processability of polymers,which have potential to form assemblies with ordered structures.Compared with ILs,the assemble process of PILs is more complex.Generally,the ordered PILs assemblies are fabricated by the self-assemble of IL monomers,and then the in-situ “locking” using a polymerization of ordered IL monomers.However,the ordered structures formed by IL monomers could be destroyed during polymerization,which limits its further application.In recent years,PILs-based functional materials have been attracted much attention,but investigation on the detailed self-aggregation process of PILs in organic solvent,especially the determination of thermodynamic parameters for their aggregates formation has seldom involved.Therefore,in this paper,the PILs were prepared by free radical polymerization and dissolved in the solvent,and the self-aggregation behavior of PILs in solution,particularly the effect of the length of alkyl chains,counter-anions and solvent quality is investigated in detail.In addition,the potential properties of the resultant PILs as p H-response materials and antibacterial material needs to be further evaluated.Based on the anion structure and the designability of PILs,a series of alkyl imadazolium-based PILs were synthesized.The focuses are fixed at the aggregation behavior of PILs in solvents and their application in stimuli-responsive materials and antibacterial materials.The results are shown as follows:?1?Alkyl imadazolium-based poly[C_nVIm⁺][Br^-] with different alkyl chains length were synthesized through free radical polymerization.Poly [C_nVIm⁺][Br^-]?n=8,12,16?can self-aggregate into ordered structure in n-propanol.When the length of alkyl chain is 16,the PILs aggregation in n-propanol displays an ordered "onionlike" multilamellar morphology,which is independent of their counteranions.Furthermore,the obtained ordered structures display a desirable stability.?2?The aggregation process of a series of N-alkyl imidazolium-based PILs with different chemical composition in their n-propanol solution was investigated by conductivity measurements.The thermodynamic parameters suggest that aggregation of PILs in n-PrOH is spontaneous process,which is driven by an entropy change associated with a hydrophobic effect.The critical aggregation concentration?CAC?decreases,while the contribution of per alkyl chain to Gibbs free energy??G_m^?alkyl?enhances with the increase in the length of alkyl chains.The nonsolvent contribution to change of Gibbs free energy as well as critical aggregation concentration?CAC?decrease linearly with the volume fraction of water in mixed solvents,implying that PIL aggregation becomes more favorable with the addition of nonsolvent.?3?The functional PILs were synthesized through anion-exchange with methyl orange.The obtained PILs shows interesting pH response phenomenon,with color changes directly visible from red to yellow with the increasing of solution pH,and the size of well-defined PILs aggregates increase dramatically with the increasing pH.PILs with high anion exchange rate show more sensitive to the change of pH.When the length of alkyl chains increase,the pH sensitivity becomes “retarded”.?4?Poly[C_nVIm⁺][Br^-]?n=8,12,16?micelles were prepared througha dialysis process to explore the antibacterial properties against Staphylococcus aureus?S.aureus?and Escherichia coli?E.coli?.The results showed that the critical inhibitory concentration?MIC?values increase in the following order: poly[C₁₂VIm⁺][Br^-]<poly[C₈VIm⁺][Br^-]<poly[C₁₆VIm⁺][Br^-],and the bacterial viability rate was almost 0 after contacting with poly[C₁₂VIm⁺][Br^-] for 1h.The contribution of alkyl chain to antibacterial properties was studied by charge shielding experiment.For poly [C₁₂VIm⁺][Br^-],the contribution of alkyl chain to antibacterial properties against S.aureus reached 60%,while,the contribution of alkyl chain to antibacterial properties against E.coli reached 67%.This paper explored systematically the aggregation behaviors and thermodynamics of poly [C_nVIm⁺][Br^-]?n=8,12,16?in the presence of good solvents and bad solvents and their application in stimuli-responsive materials and antibacterial materials.The results provide a facile idea for the structural design and performance optimization of PILs-based functional materials.