Synthesis Of Poly（Ionic Liquid）s And Their Application In CO₂ Cycloaddition

The massive emission of CO₂leads to aggravation of the greenhouse effect,which seriously endangers the living environment of human beings.In fact,CO₂is a non-toxic,cheap,and renewable C1 resource.The cycloaddition between CO₂and epoxides to generate cyclic carbonates with high economic value is an efficient and green way for the fixation of CO₂.Due to the stable structure and inactive of CO₂,efficient catalysts are required to catalyze its conversion.Most of the reported catalysts have low catalytic activity and the separation of products are difficult to achieve.Poly（ionic liquid）s are characterized by the designability,high stability,and rich charge density,which were used to catalyze the conversion of CO₂and epoxides into cyclic carbonates frequently.In this paper,four ionic liquids named[PVIM-6]Br,[DHP-VIM]Cl,[TVIM-3]Br,[VBA]Cl were synthesized,and six poly（ionic liquid）s were synthesized by free radical polymerization,then the as-prepared poly（ionic liquid）s were applied to catalysis CO₂cycloaddition reaction respectively.The synthesized heterogeneous catalyst has the characteristics of excellent selectivity,high conversion and good recyclability.This paper will elaborate according to the following aspects:（1）In this chapter,the monomer[PVIM-6]Br was synthesized by using hexachlorotripolyphosphazene as raw material.The free-radical homopolymerization of monomer[PVIM-6]Br and the copolymerization with dihydroxy ionic liquid[DHP-VIM]Cl were carried out by adjusting the ratio of[PVIM-6]Br and[DHP-VIM]Cl,and finally two kinds of tripolyphosphazene-based polyimidazole ionic liquids named P[PVIM-6]Br and P[PVIM-6-OH]Br were synthesized.The specific surface areas(S_BET)of P[PVIM-6]Br and P[PVIM-6-OH]Br were 14 m²g^-1and 8 m²g^-1,respectively,and the CO₂uptake capacities under 273 K and 1 bar were measured to 0.37 and 0.13 mmol g^-1,respectively.P[PVIM-6]Br and P[PVIM-6-OH]Br were subsequently used to catalyze the cycloaddition of CO₂with epoxides.Theexperimentalresultsshowthatwhen n（[PVIM-6]Br）:n（[DHP-VIM]Cl）=1:1（molar ratio）,the highest catalytic effect of P[PVIM-6-OH]Br can be achieved.After reaction for 48 h,the conversion and selectivity of epichlorohydrin were both as high as 99%at 70 ^oC and 1 bar.（2）According to the previous chapter,we designed and synthesized a series of triazine-based polyimidazole ionic liquids.Based on the monomer[TVIM-3]Br,activated functional groups（hydroxyl groups）and quaternary ammonium salts were introduced to improve the catalytic activity of poly（ionic liquid）s.Four triazine-based polyimidazole ionic liquids named P[TVIM-3]Br,P[TVIM-VBA]Br,P[TVIM-OH]Br,P[TVIM-VBA-OH]Br were obtained through the free-radical homopolymerization of[TVIM-3]Br and the copolymerization among the[VBA]Cl and2-hydroxyethylmethyl acrylate（HEMA）.The morphologies of the four catalysts are all formed by the accumulation of massive fragments.The results of XRD analysis showed that the four catalysts were all amorphous structures.Thermogravimetric analysis（TGA）tests showed that all four catalysts had good thermal stability.Then four catalysts were used to catalyze the cycloaddition reaction of CO₂with epoxides.The experimental results show that P[TVIM-VBA-OH]Br with the ratio of n（[TVIM-3]Br）:n（[VBA]Cl）:n（HEMA）=1:2:1（molar ratio）had the highest catalytic activity compared with the other poly（ionic liquid）s.Under the conditions of 70 ^oC,1bar and 5 wt%catalyst（based on the mass of epoxy compound）,the conversion and selectivity of epichlorohydrin were both as high as 99%after reaction for 24 h.Fourier transform infrared spectroscopy（FTIR）showed that the active functional groups on the catalyst were well-preserved after six cycles of catalytic cycloaddition of CO₂to epoxides.