Preparation Of Imidazolium-based Poly(Ionic Liquid)s And Their Application In Azeotrope Separation

Poly（ionic liquid）s（PILs）is a kind of polyelectrolyte with repeating unit of ionicliquids monomer（ILM）.It not only inherits the non-volatile,high chemical stability,high thermal stability,excellent solubility and strong molecular recognition ability from ionic liquids,but also has mechanical stability,safety and self-assembly as a polymer.It has great potential in the field of azeotrope separation.Due to the difficulty in controlling the molecular weight of polymers polymerized by traditional free radical polymerization and the potential biological toxicity of ionic liquids in azeotrope separation,it is of great significance to explore the effect of narrow molecular weight distribution PILs which synthesized by the reversible addition-fragmentation chain transfer polymerization（RAFT）on vapor-liquid equilibrium of azeotrope.Three kinds of imidazolium-based ILs,[VBIm]Br,[VMIm][DMP]and[VEIm][DEP]are synthesized as monomers to prepare PILs by RAFT method.The positions of the peaks in the ¹H NMR spectra all correspond to the characteristic peaks of the target product hydrogen,which indicates that the target products have been synthesized successfully.GPC results showed that the increase of the ratio of ILM to CTA increased the number-average molecular weight of PILs,and the polydispersity of PILs are between 1.15-1.39,the conversion of ILM are between 65%-78%.TGA results show that the initial decomposition temperature of PILs is higher than that of ILM,and the initial decomposition temperature of PILs increases with the increase of molecular weight.The thermal decomposition rate of P[VBIm]Br is higher than that of P[VMIm][DMP]and P[VEIm][DEP].Taking ethanol-water system and trioxane-water system as examples,the influence of20 wt%ILs/PILs on vapor-liquid equilibrium of binary azeotrope are studied at 101.325k Pa.The results show that when the polymerization degree and concentration are the same,the order of effect of ILs/PILs on the VLE of ethanol-water is:P₆₉[VMIm][DMP]>P₁₄[VMIm][DMP]>[VMIm][DMP],P₆₆[VEIm][DEP]>P₁₄[VEIm][DEP]>[VEIm][DEP],[VMIm][DMP]>[VEIm][DEP].The order of effect of ILs/PILs on the VLE of trioxane-water is:P₆₉[VMIm][DMP]>[VMIm][DMP].In addition,with the increase of polymerization degree,the ability of breaking VLE of binary azeotrope is stronger.Based on molecular dynamics simulation,the equilibria of ILs/PILs with ethanol-water systems and trioxane-water systems are simulated at 298.15 K and 101.325 k Pa for 50 ns.The calculated results of the total non-bonded interaction energy show that when the concentration ratio of ILs/PIL:ethanol/trioxane:water is 1:1:1,the total non-bond interaction energy of P[VMIm][DMP]for water in ethanol-water system and trioxane-water system is-506.001 k J·mol^-1 and-489.440 k J·mol^-1,respectively.It is higher than that of P[VMIm][DMP]for water in ethanol-water system and trioxane-water system,-438.78 k J·mol^-1,-270 k J·mol^-1.The results indicate that the polymerization of ILs is beneficial to improve the effect ability of binary azeotrope VLE.The order of peak height in the radial distribution function diagram is P[VMIm][DMP]>[VMIm][DMP]>[VEIm][DEP],which indicates that the probability of water molecules around the PILs is the highest,and consistent with the results of phase equilibrium experiment.The spatial distribution function analysis results from the three-dimensional perspective also confirm this conclusion.