Porous Poly(Ionic Liquid)s Synthesized by Anion Exchange and their application

Author:Qin Li

Supervisor:gao guo hua


Degree Year:2019





Poly(ionic liquid)s(PILs)refer to a subclass of polyelectrolyte material containing ionic liquid(IL)units on the repeating polymer backbones unit.PILs have both ionic conductivity of the ionic liquid and processability of polymer.The porous PILs combine the high specific surface area and porous structure of the porous materials with the conductivity and ion exchange characteristics of PILs.Porous PILs have wide application prospects in the fields of catalysis,electrochemistry,adsorption and separation,and functionalized materials.Therefore,it is of great significance to develop a porous PILs synthesis method and to control the pore size distribution of porous PILs.Based on the anion exchange method,a novel synthesis method of porous PILs was developed.Anions occupy the interstitial voids in the process of polymerization of IL monomers.Thus,theoretically,the exchange of bulky anions in PILs by smaller ones can release the occupied space and form a porous structure,thereby porous PILs with high specific surface area were synthesized.The synthesized porous PILs with high specific surface area were applied as catalysts,catalyst supports and dye adsorbents.The main results were as follows:1.Hierarchical Porous PILs by Anion Exchange for the Conversion of Carbonate ReactionsA novel method for the synthesis of porous PILs,namely anion exchange method,was developed.Salicylate could form dimers/clusters through hydrogen bonding between hydroxyl and carboxyl to generate different sizes of anions.Thus,The parent PILs were synthesized by the copolymerization of 3,3’-(alkyl-1,n-diyl)bis(1-vinyl)-3-imidazolium disalicylate ionic liquids(alkyl=methyl.ethyl,propyl,butyl,pentyl and hexyl,n=1,2,3,4,5 and 6)with different alkyl chains of N3 position in imidazolium as monomers and divinylbenzene(DVB)as a cross-linker using azobisisobutyronitrile(AIBN)as an initiator.The salicylate in the parent PILs were exchanged by using smaller chloride,bromide and acetate,respectively,and PILs having high specific surface areas and hierarchical porous structure.The structure of the porous PILs was characterized by solid nuclear magnetic resonance(MAS NMR),Fourier transform infrared spectrometer(FT-IR),thermogravimetry(TGA),elemental analysis(EA),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and argon adsorption desorption(BET).The specific surface area of salicylate PIL was15.10 m~2/g.After exchange with chlorides,bromides and acetates,the specific surface area increased to 129.2,180.6 and 227.5 m~2/g.The porous PILs was used to catalyze the cycloaddition reaction of epoxides with carbon dioxide and the N-heterocyclic carboxymethoxylation reaction of nitrogen-containing compounds.The porous PILs exhibited higher catalytic activities than the non-porous PILs.The high catalytic activities were attributed that the high specific surface area and hierarchical porous structure promoted sufficient exposure of the active to increase the degree of contact with the reaction substrate.By investigating the catalytic activity of different specific surface area of PILs,there was a positive correlation between the specific surface area and the catalytic activity of porous PILs.2.Precise Control of Pore Size of Porous PILs by Anion Exchange and Size Matching in Dye AdsorptionThe initial parent PILs were synthesized by the copolymerization of 3,3’-(butyl-1,4-diyl)bis(1-vinyl-3-imidazolium)ionic liquids with different aryl borates(phenyl trifluoroborate,tetraphenylborate and tetranaphthylborate)as counter anions as a monomer and DVB as an cross-linker under AIBN as an initiator.After exchange of the large aryl borates to chloride or acetate,the space occupied by large aryl borates was released,thereby the obtained PILs may exhibit regular porous structures.Their successful formations,porosities and morphologies were fully characterized by MAS NMR,FT-IR,TGA,SEM,TEM,BET and EA.Impressively,depending on the sizes of the initial template anions and new anions,the pore sizes of these PILs were accurately regulated from 0.78,0.81,6,8,18 to 22 nm,The pore size of the porous PILs increased with the increase of the size of the parent anion template,and decreases with the increase of the anion size after exchange.These porous PILs were then used for the adsorption of anionic dyes,such as congo red,methyl blue,sirius red and sodium lignosulphonate,and exhibited a high maximum adsorption capacity with a maximum adsorption capacity of up to 3644.1 mg/g.The porous polyionic liquid exhibits a"size matching"effect in dye adsorption.This phenomanon allowed us to selectively isolate the“size-matching”one from other anionic dye mixture.3.Porous PILs Supported Ruthenium Nanoparticles for Hydrogenation of Methyl BenzoatePorous PILs supported ruthenium nanoparticles were synthesized by one step reduction of the ruthenium precursors(ruthenium trichloride,dichloro(p-methylisopropylphenyl)ruthenium(II)dimer,ruthenium acetylacetonate)which were supported by the porous PILs synthesized by anion exchange method,using sodium borohydride as reducing agent.The pore structure and morphology of the porous PILs supported ruthenium nanoparticles were characterized by TEM,EDS and BET.The supported ruthenium nanoparticles having a particle diameter of 2-5 nm were highly dispersed and not easily clustered,which was attributed to the stabilizing effect of the pore structure of the porous PILs and the anion and cation units.Porous PILs supported ruthenium nanoparticles exhibited 100%conversion and selectivity in the reaction of hydrogenating methyl benzoate to methyl cyclohexanecarboxylate.