Patent Application: US-65948405-A

Abstract:
polymerizable ionic liquid monomers and their corresponding polymers s ) are created and found to exhibit high co2 sorption . the polys have enhanced and reproducible co2 sorption capacities and sorption / desorption rates relative to room - temperature ionic liquids . furthermore , these materials exhibit selectivity relative to other gases such as nitrogen , methane , and oxygen . they are useful as efficient separation agents , such sorbents and membranes . novel radical and condensation polymerization approaches are used in the preparation of the poly .

Description:
in this description , each material is introduced by its full chemical name followed by a shortened name in parenthesis , for example , 1 -[ 2 -( methacryloyloxy ) ethyl ]- 3 - butyl - imidazolium tetrafluoroborate ([ mabi ][ bf 4 ]). following the initial introduction , only the shortened name is used . ionic liquids are organic salts with melting points usually below 200 ° c ., often below room temperature . they can be substitutes for the traditional organic solvents in chemical reactions . the most common examples are imidazolium and pyridinium derivatives , but phosphonium or tetralkylammonium compounds have also been explored . ionic liquid monomers of the present application are ionic liquids that are suitable for polymerization of the ionic liquid monomers to form poly ( ionic liquid ) s . specific examples of ionic liquid monomers of the present application have a double bond that forms a radical when broken . the ionic liquid monomers may include an inorganic moiety . specific examples of ionic liquid monomers used for polymer synthesis and other applications include but are not limited to : ( 1 ) ionic liquid monomers based on imidazolium , such as 1 -[ 2 -( methacryloyloxy ) ethyl ]- 3 - butyl - imidazolium tetrafluoroborate ([ mabi ][ bf 4 ]), 1 - p - vinylbenzyl )- 3 - butyl - imidazolium tetrafluoroborate ([ vbbi ][ bf 4 ]), 1 -( p - vinylbenzyl )- 3 - methyl - imidazolium tetrafluoroborate ([ vbmi ][ bf 4 ]), 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium hexafluorophosphate ([ vbbi ][ pf 6 ]), 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium o - benzoic sulphimide ([ vbbi ][ sac ]), 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium trifluoromethane sulfonamide ([ vbbi ][ bf 4 ]), ( 1 - butylimidazolium - 3 ) methyl - ethylene oxide ([ bieo ][ bf 4 ]); ( 2 ) ionic liquid monomers based on ammonium , such as ( p - vinylbenzyltrimethyl ) ammonium tetrafluoroborate ([ vbtma ][ bf 4 ]), ( p - vinylbenzyl ) triethyl ammonium tetrafluoroborate ([ vbtea ][ bf 4 ]), p - vinylbenzyl ) tributyl ammonium tetrafluoroborate ([ vbtba ][ bf 4 ]), [ 2 -( methacryloyloxy ) ethyl ] trimethyl ammonium tetrafluoroborate ([ matma ][ bf 4 ]), ( p - vinylbenzyl ) trimethyl ammonium hexafluorophosphate ([ vbtma ][ pf 6 ]), p - vinylbenzyl ) trimethyl ammonium o - benzoic sulphimide ([ vbtma ][ sac ]), ( p - vinylbenzyltrimethyl ) ammonium trifluoromethane sulfonamide ([ vbtma ][ tf 2 n ]); ( 3 ) ionic liquid monomers based on phosphonium , such as ( p - vinylbenzyl ) triethyl phosphonium tetrafluoroborate ([ vbtep ][ bf 4 ]), ( p - vinylbenzyl ) triphenyl phosphonium tetrafluoroborate ([ vbtpp ][ bf 4 ]); ( 4 ) ionic liquid monomers based on pyridinium , such as 1 -( p - vinylbenzyl ) pyridinium tetrafluoroborate ([ vbp ][ bf 4 ]); ( 5 ) ionic liquid monomers for condensation polymerization , such as bis ( 2 - hydroxyethyl ) dimethyl ammonium tetrafluoroborate ([ bhedma ][ bf 4 ]), 2 , 2 - bis ( methylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ([ bmimp ][ bf 4 ]), and 2 , 2 - bis ( butylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ([ bbimp ][ bf 4 ]). poly ( ionic liquid ) s as used in this specification means polymers formed using ionic liquids as monomers via radical polymerization or other kind of polymerization . certain of the poly ( ionic liquid ) s have a gas sorption capacity and / or rate that is greater than that of the corresponding ionic liquid monomer for the corresponding gas . radical polymerization is a common and useful reaction for making polymers from vinyl monomers , that is , from small molecules containing carbon - carbon double bonds . polymers made by radical polymerization include polystyrene , poly ( methyl methacrylate ), poly ( vinyl acetate ) and branched polyethylene . radical polymerization begins with a molecule called an initiator ; common initiators are benzoyl peroxide or 2 , 2 ′- azo - bis - isobutyrylnitrile ( aibn ). 4 - vinylbenzyl chloride , methacryloyl chloride , 1 - butylimidazole , 2 - bromoethanol , lithium trifluoromethane sulfonimide , potassium hexafluorophosphate , sodium tetrafluoroborate , 2 , 6 - di - tert - butyl - 4 - methyl phenol ( dbmp ), 2 , 2 ′- azobisisobutyronitrile ( aibn ), aluminum isopropoxide , epichlorohydrin , n , n - dimethylformamide ( dmf ), acetonitrile , and acetone were purchased from aldrich . 1 - methylimidazole , and o - benzoic sulphimide sodium salt hydrate were purchased from lancaster synthesis inc . these chemicals were used without further purification . 1 -[ 2 -( methylacryloyloxy ) ethyl ]- 3 - butyl - imidazolium tetrafluoroborate ([ mabi ][ bf 4 ]) and 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium tetrafluoroborate ([ vbbi ][ bf 4 ]) were synthesized according to our published reports , 27 , 28 as shown in schemes 1 and 2 . 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium hexafluorophosphate ([ vbbi ][ pf 6 ]), 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium o - benzoic sulphimide ([ vbbi ][ sac ]), 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium trifluoromethane sulfonamide ([ vbbi ][ tf 2 n ]) were synthesized by a similar procedure except using napf 6 , o - benzoic sulphimide sodium salt hydrate ( nasac ) or lithium trifluoromethane sulfonamide ( litf 2 n ) for anion exchange reactions . the yields were 93 . 0 %, 49 . 6 %, 39 . 9 %, respectively . 1 - p - vinylbenzyl )- 3 - methyl - imidazolium tetrafluoroborate ([ vbmi ][ bf 4 ]) was synthesized as follows : to a 50 ml flask , p - vinylbenzyl chloride ( 10 ml , 0 . 064 mole ), a small amount of dbmp , and 1 - methylimdazole ( 5 . 14 ml , 0 . 064 mole ) were added and heated at 45 ° c . overnight . the solution became gradually viscous . nabf 4 ( 5 . 2 g , 0 . 47 mole ) and dry acetone ( 30 ml ) were added . the mixture was stirred at room temperature . the viscous liquid dissolved gradually while a white solid precipitated . after 12 h reaction , the precipitate was removed by filtration . the solvent was removed under vacuum . the solid was washed with water and ether , and dried by vacuuming at room temperature , producing 14 g of white crystals ( yield 76 . 5 %). [ vbbi ][ bf 4 ]: 1 h nmr ( 400 mhz , dmso - d 6 , ppm ): δ 9 . 24 ( 1h , s ), 7 . 80 ( 2h , s ), 7 . 51 ( 2h , d ) 7 . 35 ( 2h , d ), 6 . 73 ( 1h , m ), 5 . 89 ( 1h , d ) 5 . 27 ( 1h , d ), 5 . 40 ( 2h , s ), 4 . 14 ( 2h , t ), 1 . 78 ( 2h , m ), 1 . 24 ( 2h , m ), 0 . 88 ( 3h , t ). mp : 67 - 68 ° c . [ vbbi ][ pf 6 ] 1 h nmr ( 400 mhz , dmso - d 6 , ppm ): δ 9 . 22 ( 1h , s ), 7 . 80 ( 2h , s ), 7 . 48 ( 2h , d ) 7 . 35 ( 2h , d ), 6 . 73 ( 1h , m ), 5 . 89 ( 1h , d ), 5 . 30 ( 1h , d ), 5 . 46 ( 2h , s ), 4 . 14 ( 2h , t ), 1 . 79 ( 2h , m ), 1 . 22 ( 2h , m ), 0 . 87 ( 3h , t ). mp : 87 - 88 . 5 ° c . [ vbbi ][ sac ] 1 h nmr ( 400 mhz , dmso - d 6 , ppm ) δ 9 . 38 ( 1h , s ), 7 . 80 ( 2h , s ) 7 . 66 ( 1h , d ), 7 . 61 ( 1h , d ), 7 . 59 ( 2h , d ), 7 . 49 ( 2h , d ), 7 . 40 ( 2h , d ), 6 . 72 ( 1h , m ) 5 . 84 ( 1h , d ), 5 . 42 ( 2h , s ), 5 . 26 ( 2h , d ) 4 . 16 ( 2h , m ) 1 . 73 ( 2h , m ), 1 . 21 ( 2h , m ), 0 . 84 ( 3h , m ). mp : − 36 -− 38 ° c . [ vbbi ][ tf 2 n ] 1 h nmr ( 400 mhz , dmso - d 6 , ppm ): δ 8 . 83 ( 1h , s ), 7 . 44 ( 2h , s ), 7 . 34 ( 2h , d ) 7 . 27 ( 2h , d ), 6 . 70 ( 1h , m ), 5 . 79 ( 1h , d ) 5 . 33 ( 1h , d ), 5 . 31 ( 2h , s ), 4 . 17 ( 2h , t ), 1 . 84 ( 2h , m ), 1 . 35 ( 2h , m ), 0 . 94 ( 3h , t ). mp : − 61 -− 62 ° c . [ vbmi ][ bf 4 ]: 1 h nmr ( 400 mhz , dmso - d 6 , ppm ): 9 . 13 ( 1h , s ), 7 . 71 ( 1h , s ), 7 . 63 ( 1h , s ), 7 . 52 ( 1h , d ), 7 . 42 ( 2h , d ), 6 . 75 ( 1h , m ), 5 . 88 ( 1 , d ), 5 . 41 ( 2h , s ), 5 . 26 ( 1h , d ), 3 . 86 ( 3h , s ). mp : 42 - 44 ° c . poly ( ionic liquid ) s were prepared from above ionic liquid monomers by free radical polymerization . a typical example is as the following : [ vbbi ][ bf 4 ] ( 3 g ), aibn ( 30 mg ) and dmf ( 3 ml ) were charged into a reaction tube . the tube was tightly sealed , and degassed . it was immersed in an oil bath at 60 ° c . for 6 h . the solution was poured into methanol to precipitate out the polymer . the polymer was dried under vacuum at 100 ° c . the yield was 2 . 3 g ( 75 %). poly [ 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium tetrafluoroborate ] ( p [ vbbi ][ bf 4 ]): 1 h nmr ( dmso - d 6 , 400 mhz , ppm ): δ 9 . 12 ( s , 1h ), 7 . 8 ( br , 1h ), 7 . 4 ( br , 1h ), 7 . 1 ( br , 2h ), 6 . 4 ( br , 2h ), 5 . 6 - 4 . 9 ( br , 2h ), 4 . 1 ( br , 2h ), 2 . 1 - 1 . 0 ( m , 7h ), 0 . 8 ( s , 3h ). anal . calcd for ( c 16 h 21 bf 4 n 2 ) n : c , 58 . 56 %; h , 6 . 45 %; n , 8 . 54 %. found : c , 58 . 35 %; h , 6 . 43 %; n , 8 . 50 %. poly [ 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium hexafluorophosphate ] ( p [ vbbi ][ pf 6 ]): 1 h nmr ( dmso - d 6 , 400 mhz , ppm ): δ 9 . 16 ( s , 1h ), 7 . 72 ( br , 1h ), 7 . 47 ( br , 1h ), 7 . 04 ( br , 2h ), 6 . 42 ( br , 2h ), 5 . 23 ( br , 2h ), 4 . 15 ( br , 2h ), 2 . 1 - 0 . 8 ( m , 10h ) anal . calcd for ( c 16 h 21 f 6 n 2 p ) n : c , 49 . 75 %; h , 5 . 48 %; n , 7 . 25 %; found : c , 49 . 70 %; h , 5 . 37 %; n , 7 . 12 %. poly [ 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium o - benzoic sulphimide ] ( p [ vbbi ] [ sac ]): 1 h nmr ( dmso - d 6 , 400 mhz , ppm ): δ 9 . 44 ( s , 1h ), 7 . 5 - 7 . 9 ( br , 6h ), 7 . 19 ( br , 2h ), 6 . 35 ( br , 2h ), 5 . 35 ( br , 2h ), 4 . 15 ( br , 2h ), 1 . 9 - 0 . 5 ( m , 10h ) anal . calcd for ( c 23 h 25 n 3 o 3 s ) n : c , 65 . 25 ; h , 5 . 91 ; n , 9 . 93 . found : c , 64 . 11 ; h , 6 . 05 ; n , 9 . 68 . poly [ 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium trifluoromethane sulfonamide ] ( p [ vbbi ][ tf 2 n ]): 1 h nmr ( dmso - d 6 , 400 mhz , ppm ): δ 9 . 20 ( s , 1h ), 7 . 73 ( br , 1h ), 7 . 44 ( br , 1h ), 6 . 94 ( br , 2h ), 6 . 33 ( br , 2h ), 5 . 19 ( br , 2h ), 4 . 13 ( br ; 2h ), 2 . 0 - 1 . 0 ( m , 7h ), 0 . 81 ( s , 3 h ). anal . calcd for ( c 18 h 21 n 3 f 6 o 4 s 2 ) n : c , 41 . 46 ; h , 4 . 03 ; n , 8 . 06 . found : c , 41 . 46 ; h , 4 . 13 ; n , 7 . 94 . poly { 1 -[ 2 -( methylacryloyloxy ) ethyl ]- 3 - butyl - imidazolium tetrafluoroborate } ( p [ mabi ][ bf 4 ]): 1 h nmr ( dmso - d 6 , 400 mhz , ppm ): δ 9 . 1 ( br , 1h ), 7 . 9 - 7 . 6 ( d , 2h ), 4 . 8 - 3 . 8 ( m 6h ), 2 . 0 - 0 . 2 ( m , 12h ). anal . calcd for ( c 9 h 18 bf 4 no 2 ) n : c , 48 . 17 h , 6 . 49 ; n , 8 . 65 . found : c , 47 . 68 ; h , 6 . 48 ; n , 6 . 48 . poly [ 1 -( p - vinylbenzyl )- 3 - methyl - imidazolium tetrafluoroborate ] ( p [ vbmi ][ bf 4 ]): 1 h nmr ( dmso - d 6 , 400 mhz , ppm ): δ 9 . 10 ( 1h , br ), 7 . 60 - 7 . 30 ( 2h , br ), 7 . 10 ( 2h , br ), 6 . 40 ( 2h , br ), 5 . 30 ( 2h , br ), 3 . 70 ( 2h , br ) 2 . 1 - 0 . 5 ( 3h , br ). anal . calcd for ( c 13 h 15 bf 4 n 2 ) n : c , 54 . 58 ; h , 5 . 25 ; n , 9 . 80 . found : c , 52 . 74 ; h , 5 . 33 ; n , 9 . 38 . the poly ( ionic liquid ) with poly ( ethylene oxide ) backbone was synthesized from poly ( epichlorohydrin ) ( scheme 3 ). aluminum isopropoxide ( 0 . 18 g , 0 . 88 mmol ) was added into a 100 ml flask . the flask was degassed by repeated vacuum / nitrogen purging ( 5 cycles ). degassed thf ( 25 ml ) and epichlorohydrin ( 5 . 0 ml , 66 mmol ) was added by degassed syringes . after the reaction flask was immersed into a 40 ° c . oil bath for 12 hours , the poly ( epichlorohydrin ) was precipitated out by adding a large amount of hexane . 3 . 3 g of poly ( epichlorohydrin ) was dissolved in 50 ml of dmf . n - butylimidazole ( 5 . 0 g , 40 mmol ) was added to the dmf solution . this solution was stirred at 80 ° c . for 5 days , and then nabf 4 ( 4 . 4 g , 40 mmol ) was added . after the mixture was stirred at room temperature for 2 days , sodium chloride precipitate was removed by filtration . anhydrous ethyl ether was added to the filtrate to precipitate the poly ( ionic liquid ). the obtained p [ bieo ][ bf 4 ] was washed with ethyl ether and dried in vacuum oven at 50 ° c . for one day . 1 h - nmr ( acetone - d 6 ): δ 8 . 86 ( 1h , s ), 7 . 69 ( 2h , br ), 4 . 44 - 4 . 31 ( 4h , br ), 3 . 97 ( 1h , br ), 3 . 67 ( 2h , br ), 1 . 88 ( 2h , br ), 1 . 34 ( 2h , br ), 0 . 93 ( 3h , br ). anal . calcd for ( c 10 h 17 bf 4 n 2 o ) n : c , 44 . 80 ; h , 6 . 34 ; n , 10 . 46 . found : c , 44 . 66 ; h , 6 . 26 ; n , 10 . 11 . the syntheses of ionic liquid monomers are shown in schemes 1 - 3 . two steps were generally involved in the preparations : the quaternization reaction of 1 - butylimidazole or 1 - methylimidazole with 4 - vinylbenzyl chloride or 2 - bromoethyl methacrylate , and the anion exchange reaction of the halide ions with tetrafluoroborate , hexafluorophosphate , sac or tf 2 n anions . the quaternization with 4 - vinylbenzyl chloride was fast with a high yield . the anion exchange of the resulting chloride [ vbbi ][ cl ] and [ vbmi ][ cl ] with bf 4 − produced the monomers , [ vbbi ][ bf 4 ] and [ vbmi ][ bf 4 ], as crystalline solids , which are soluble in acetone , acetonitrile , dichloromethane , dmf , and dmso , but insoluble in diethyl ether . [ vbbi ][ pf 6 ] is also a solid with similar solubility . [ vbbi ] [ sac ] and [ vbbi ][ tf 2 n ] are liquid at room temperature and soluble in acetone , acetonitrile , dmf , and dmso . [ vbbi ][ tf 2 n ] is also soluble in ethyl ether . the quaternization of n - butylimidazole with 2 - bromoethyl methacrylate was slow and difficult to get high yield of [ mabi ][ br ]. after the anion exchange , [ mabi ][ bf 4 ] is also a liquid at room temperature and soluble in above polar solvents but insoluble in ethyl ether and other nonpolar solvents . all above ionic liquid monomers , unlike their corresponding chloride salts , are insoluble in water . so unreacted chloride salts could be easily removed by washing with water . silver nitrate test indicated that no chloride was present in all the ionic liquid monomers . the poly ( ionic liquid ) s , except for p [ bieo ][ bf 4 ] which was synthesized by the polymer reaction shown in scheme 3 , were prepared by free radical polymerization of the ionic liquid monomers using aibn as initiators . dmf was used as solvent because all poly ( ionic liquid ) s are soluble in it . all these ionic liquid monomers are easily polymerized with high conversions . poly ( ionic liquid ) s were precipitated in methanol to remove unreacted monomers . dmf residue in polymers was removed by drying at 100 ° c . under vacuum . all poly ( ionic liquid ) s can dissolve in dmf , dmso , acetonitrile , but are insoluble in water , dichloromethane and toluene . h 1 nmr and element analysis indicated the poly ( ionic liquid ) s were pure . the co 2 sorption of the poly ( ionic liquid ) s was measured using a cahn 1000 electrobalance . the sample pan and the counterweight of the balance were configured symmetrically to minimize buoyancy effects . the microbalance has 100 g capacity and 1 . 0 μg sensitivity and is suitable for study of sorption and diffusion of gases on / in solid or liquid materials . co 2 gas ( 99 . 995 %) was dried by passing two drying columns ( length × diameter : 15 in × 2 in ) packed with p 2 o 5 . the fine powder of the ionic liquid polymer was dried and degassed at 70 ° c . under vacuum for 12 h to remove moisture or other volatile contaminants . it was further dried in the balance by evacuating the chamber at high vacuum until its weight reached constant for at least 30 min . co 2 was introduced into the chamber and the sample weight increase was recorded until the weight did not change significantly in 30 min . the buoyancy effects in these measurements were corrected according to the literature . 29 the system was validated by measuring the co 2 sorption of an ionic liquid , 1 - n - butyl - 3 - methyl imidazolium tetrafluoroborate ([ bmim ][ bf 4 ]). the measured co 2 sorption capacity of [ bmim ][ bf 4 ] was identical to the reported . 19 co 2 has remarkable solubility in imidazolium - based ionic liquids because of its interactions with the anions and cations of ionic liquids . 19 the co 2 sorption of ( p [ vbbi ][ bf 4 ]( a ), p [ vbbi ][ tf 2 n ]( b ), p [ mabi ][ bf 4 ]( c ), p [ vbbi ][ sac ]( d )), with their corresponding monomers ([ vbbi ][ tf 2 n ]( e ), [ mabi ][ bf 4 ]( g ), [ vbbi ][ bf 4 ]( h ), [ vbbi ][ sac ]( i )), and an ionic liquid [ bmim ][ bf 4 ] ( f ) as a function of time ( 592 . 3 mmhg co 2 , 22 ° c .) is shown in fig1 . the co 2 solubility of [ bmim ][ bf 4 ] was tested first and found consistent with that reported in the literature , 19 which validated the setup of the apparatus . at the equilibrium , p [ vbbi ][ bf 4 ], p [ vbbi ][ tf 2 n ], p [ mabi ][ bf 4 ] and p [ vbbi ][ sac ], respectively , took up 2 . 27 mol %, 2 . 23 mol %, 1 . 78 mol % and 1 . 55 mol % of co 2 in terms of their monomer units . in comparison , room temperature ionic liquid [ bmim ][ bf 4 ] absorbed 1 . 34 mol % of co 2 under the same conditions . [ vbbi ][ bf 4 ] monomer had no measurable sorption of co 2 because of its crystalline structure . [ mabi ][ bf 4 ], [ vbbi ] [ sac ] and [ vbbi ][ tf 2 n ] monomers are liquid at room temperature . [ mabi ][ bf 4 ] had the same co 2 sorption capacity as [ bmim ][ bf 4 ]. [ vbbi ][ tf 2 n ] had a co 2 sorption capacity of 1 . 96 mol %, higher than that of [ bmim ][ bf 4 ], which is consistent with the report that the ionic liquid with tf 2 n anions had higher capacity than ionic liquids with bf 4 anions . 14 [ vbbi ][ sac ] did not take up any co 2 when it was exposed to co 2 ( fig1 ). this comparison shows that polymerizing ionic liquids can increase the co 2 sorption capacity . meanwhile , the co 2 sorption of the ploy ( ionic liquid ) s was much faster than that of ionic liquids . it takes only several minutes for the poly ( ionic liquid ) s to reach their 90 % capacity and less than 30 minutes to reach their equilibrium capacity . in contrast , room temperature ionic liquids [ mabi ][ bf 4 ] and [ bmim ][ bf 4 ] needed more than 400 min to reach their equilibrium capacity ( fig1 ). the co 2 sorption of poly ( ionic liquid ) s with different backbones , cations , and anions was compared to understand the factors affecting the co 2 sorption . the co 2 sorption kinetics of poly ( ionic liquid ) s with different backbones are shown in fig2 . at the equilibrium , the polymers sorbed 2 . 27 mol % ( p [ vbbi ][ bf 4 ]), 1 . 78 mol % ( p [ mabi ][ bf 4 ]) and 1 . 06 mol % ( p [ bieo ][ bf 4 ]), respectively , in terms of their monomer units at 592 . 3 mmhg of co 2 and 22 ° c . with the same butylimidazolium cation and bf 4 − anion , the polymer with polystyrene backbone had a higher co 2 sorption capacity than those with polymethylmethacrylate and polyethylene glycol backbones . the polymer with polyethylene glycol backbone had the lowest capacity . the effect of substituent of the imidazolium cation on the co 2 sorption is shown in fig3 . p [ vbmi ][ bf 4 ], which has a methyl substituent on its imidazolium cation , had a higher capacity ( 3 . 05 mol . %) than p [ vbbi ][ bf 4 ] ( 2 . 27 mol . %) with butyl group . this indicates that a large substituent on the imidazolium cation may block the co 2 sorption . the effect of the anions on the co 2 sorption capacity of the poly ( ionic liquid ) s is shown in fig4 . the co 2 sorption capacity the p [ vbbi ]- based polymers depends on the type of the anions : it was 2 . 80 mol . % for p [ vbbi ][ pf 4 ], 2 . 27 mol % for p [ vbbi ][ bf 4 ], 2 . 23 mol . % for p [ vbbi ][ tf 2 n ] and 1 . 55 mol . % for p [ vbbi ][ sac ], respectively , in terms of their monomer units at 592 . 3 mmhg of co 2 and 22 ° c . this trend is different from that of ionic liquids . the co 2 solubility in ionic liquids with tf 2 n − anions is much higher than those with pf 6 − or bf 4 − anions . 19 by contrast , the poly ( ionic liquid ) with pf 6 — anions ([ pvbbi ][ pf 6 ]) had the highest sorption capacity , and those with bf 4 − and tf 2 n − anions had a similar capacity . the poly ( ionic liquid ) with sac − anions could take up 1 . 55 mol % of co 2 even though the anion contains no fluorine atoms . these results indicate that for poly ( ionic liquid ) s , fluorine - atoms are not a decisive factor for co 2 sorption but fluorine - atoms in the anions indeed enhance the co 2 sorption . the co 2 sorption of the polymers is very selective , as shown in fig5 . there was no weight increase when the polymers were exposed to n 2 or o 2 under the same conditions , which means that poly ( ionic liquid ) s can selectively absorb co 2 . the selective co 2 sorption of the poly ( ionic liquid ) s was also confirmed by a gas - replacement experiment . the co 2 sorption of p [ vbbi ][ bf 4 ] ( 1 gram ) and desorption by replacing co 2 with n 2 are shown in fig6 . after introducing co 2 into the balance , the sample weight increased rapidly until it became constant after 12 min . the weight increase was 2 . 1 mg , and the actual weight increase was 3 . 10 mg after a buoyancy correction . when n 2 was introduced into the chambers while maintaining the total pressure in the chambers at ambient pressure ( 592 . 3 mmhg ), the sample weight decreased gradually , and finally reached − 0 . 56 mg , which was equal to the buoyancy of the sample under n 2 . this experiment indicates that the poly ( ionic liquid ) does not take up n 2 . similar experiments conformed that there was no o 2 sorption . the sorption isotherms of p [ vbbi ][ bf 4 ] and p [ mabi ][ bf 4 ] at different co 2 partial pressures and 22 ° c . are shown in fig7 . the different co 2 partial pressures were obtained by adjusting the n 2 / co 2 ratio of the mixed gas charged to the balance chambers because p [ vbbi ][ bf 4 ] and p [ mabi ][ bf 4 ] had no n 2 sorption . as shown in fig7 , the co 2 mole fraction in the polymers increased with the increase of co 2 partial pressure . where h is henry &# 39 ; s constant , x is the mole fraction of gas sorbed in the polymer in term of monomeric unit , and p is the co 2 partial pressure since the x vs . p plots were not linear in the entire pressure range , henry &# 39 ; s constants were calculated by fitting the data and extrapolating the slope to the zero co 2 partial pressure . 16 henry &# 39 ; s constant was 26 . 0 bar for p [ vbbi ][ bf 4 ] and 37 . 7 bar for p [ mabi ][ bf 4 ], which is lower than that of room temperature ionic liquid [ bmim ][ pf 6 ] ( 38 . 7 bar at 10 ° c . and 53 . 4 bar at 25 ° c .). 16 stable sorption capacity after repeated sorption / desorption is important for materials used for co 2 separation . four cycles of co 2 sorption and desorption of p [ vbbi ][ bf 4 ] and p [ mabi ][ bf 4 ] were tested by filling the chambers with co 2 and then vacuuming ( fig8 a ). the sorption and desorption of p [ vbbi ][ bf 4 ] and p [ mabi ][ bf 4 ] were all very fast . it took only about 30 min to take up co 2 and to have a complete desorption of co 2 . the desorption was complete , suggesting that the sorption / desorption was reversible . no change in sorption / desorption kinetics and sorption capacity was observed after the four cycles . by contrast , the desorption of co 2 from room temperature ionic liquids [ bmim ][ bf 4 ] was very slow ( fig8 b ) the enhanced sorption capacity and fast sorption / desorption rates of the poly ( ionic liquid ) s were unexpected because all polymers are solid at room temperature . an immediate question is whether the sorption occurred on the surface ( adsorption ) or in the bulk ( absorption ) or both . the bet surface area of p [ vbbi ][ bf 4 ] was measured by nitrogen sorption and its morphology was examined by sem . the measured bet surface area of p [ vbbi ][ bf 4 ] sample was 0 . 295 m 2 / g , the calculated co 2 - adsorption assuming a monolayer of co 2 on this surface was only 0 . 0128 wt %, much less than the measured co 2 sorption capacities . the sem ( fig9 a , b ) indicated that the particles had a nonporous structure , and the average diameter of the particles was about 100 μm . the co 2 sorption of p [ vbbi ][ bf 4 ] samples with different particle sizes was tested ( fig1 ). the particle size did not significantly affect the capacity of co 2 sorption and the sample with a big size even had a slightly higher sorption capacity . however , the particle size affected the rate of co 2 sorption . the co 2 sorption of the sample with big particle sizes (& gt ; 250 μm in diameter ) was slow , and needed about 120 minutes to reach its full sorption capacity , while those with the particle diameters less than 125 μm in diameter only needed less than 30 mins . without being bound to any particular theory , it appears that the co 2 sorption of the polymer particles involves more absorption ( the bulk ) but less adsorption ( the surface ). their co 2 sorption capacity mainly depends on the chemical structure of poly ( ionic liquid ) s , while the rate of co 2 sorption depends on the particle size due to the co 2 diffusion in the polymers . 4 - vinylbenzyl chloride ( 90 %), 1 - methylimidazole ( 98 %), lithium trifluoromethane sulfonimide 99 . 95 %, potassium hexafluorophosphate 98 %, sodium tetrafluoroborate ( 98 %), 2 , 6 - di - tert - butyl - 4 - methyl phenol ( 98 %) ( dbmp ), n , n - dimethylformamide ( 99 . 8 %) ( dmf ), acetonitrile ( 99 . 5 +%), acetone ( 99 . 5 +%), aqueous [ 2 -( methacryloyloxy ) ethyl ] trimethyl ammonium chloride solution ( 75 wt . %), ( p - vinylbenzyl ) trimethylammonium chloride ( 98 %), triethylamine ( 99 . 5 %), tributylamine ( 99 . 5 %) triphenylphosphine 99 %, α , α ′- azobis ( isobutyrobitrile )( aibn ) ( 98 %) were purchased from aldrich . 1 - methyl imidazole 99 %, o - benzoic sulphimide sodium salt hydrate ( 97 %) were purchased from lancaster synthesis inc . pyridine was purchased from fisher scientific . all chemicals were used as received . ( p - vinylbenzyl ) trimethyl ammonium tetrafluoroborate ([ vbtma ][ bf 4 ]) and 2 -( methacryloyloxy ) ethyltrimethylamnonium tetrafluoroborate ([ matma ][ bf 4 ]) were synthesized as described previously 30 using ( p - vinylbenzyl ) triethyl phosphonium tetrafluoroborate ([ vbtep ][ bf 4 ]), ( p - vinylbenzyl ) triphenyl phosphonium tetrafluoroborate ([ vbtpp ][ bf 4 ]). the synthesis of p - vinylbenzyl ) triphenyl phosphonium tetrafluoroborate ([ vbtpp ][ bf 4 ]), 1 -( p - vinylbenzyl ) pyridinium tetrafluoroborate ([ vbp ] [ bf 4 ]) and 1 -( p - vinylbenzyl )- 3 - methyl - imidazolium tetrafluoroborate ([ vbmi ][ bf 4 ]) is similar to 1 -( p - vinylbenzyl )- 3 - butyl - imidazolium tetrafluoroborate ([ vbbi ][ bf 4 ]) [ vbbi ][ bf 4 ] ( vbit ), as reported previously , 28 using triphenylphosphine , pyridine and 1 - methyl imidazole instead of 1 - butylimidazole , respectively . the synthesis of ( p - vinylbenzyl ) triethylammonium tetrafluoroborate [ vbtea ][ bf 4 ] and ( p - vinyl benzyl ) tributylammonium tetrafluoroborate [ vbtba ][ bf 4 ] was follows : in a 50 ml flask , 4 - vinylbenzyl chloride ( 6 . 1 g , 0 . 04 mol ) and triethylamine ( 4 . 2 g , 0 . 042 mol ) mol were mixed and heated at 50 ° c . under n 2 atmosphere for 2 days . the formed solid was washed with diethyl ether . the resultant white solid ( 8 . 5 g , 0 . 033 mol ) was mixed with nabf 4 ( 3 . 8 g , 0 . 035 ) in 50 acetonitrile and stirred at room temperature for 2 days . the salt precipitate was removed by filtration . the filtrate was concentrated and poured into 200 ml diethyl ether to precipitate out product . white crystal precipitate was formed , collected by filtration , and dried under vacuum . the total yield was 9 . 2 g ( 75 %). [ vbtba ][ bf 4 ] was synthesized according to a similar procedure with yield of 64 %. in the synthesis of bis [ p - vinylbenzyl ) dimethylammonium ] ethane , [ bvdea ][ bf 4 ], which is an ionic liquid crosslinker , tetramethylethylenediamine ( 5 . 8 g , 0 . 05 mol ), 4 - vinylbenzyl chloride ( 16 . 0 g , 0 . 105 mol ) and 0 . 1 g dbmp were mixed in 50 ml dmf . the resulting solution was heated at 50 ° c . for 2 days . the solution was poured into 400 ml diethyl ether to precipitate out the product . after filtration and drying under vacuum , 15 . 8 g white crystal product was obtained . the product was reacted with nabf 4 ( 4 . 3 g , 0 . 04 mol ) in 50 ml dried acetonitrile for 2 days . after the reaction , the insoluble chloride salt was removed by filtration . the product was collected by filtration and dried under vacuum . the overall yield was 16 . 7 g ( 63 . 7 %). poly ( ionic liquid ) s were synthesized by free radical polymerization using aibn as initiator in dmf as described previously . 30 the crosslinked p [ vbtma ][ bf 4 ] was synthesized in the same way except for adding 5 wt % of the crosslinker . the polymers were characterized by 1 h nmr on a bruker advance drx - 400 spectrometer using d 6 - dimethylsulfoxide ( dmso - d 6 ) as solvent . the elemental analyses of polymers were tested by midwest microlab llc ( us ). the co 2 sorption of the poly ( ionic liquid ) s was measured using a cahn 1000 electrobalance . the structures of poly ( ionic liquid ) s are shown in schemes 4 and 5 . two steps were generally involved in the preparation of ionic liquid monomers : the quaternization reaction and the anion exchange reaction of the halide ions with tetrafluoroborate , hexafluorophosphate , sac or tf 2 n anions . the resulting monomers are soluble in polar solvents , such as dmf , acetone , or acetonitrile . all monomers based on ammonium except for p [ vbtma ][ tf 2 n ] are soluble in h 2 o . the ionic liquid monomers based on phosphonium , pyridium , imidazolium are insoluble in h 2 o . the poly ( ionic liquid ) s are soluble in dmf . the 1 h nmr and elemental analyses indicated that the ionic liquid monomers and poly ( ionic liquid ) s obtained were pure . fig1 shows the effect of cation types on co 2 sorption of poly ( ionic liquid ) s . the co 2 sorption capacity of poly ( ionic liquid ) s with different cations is as follows : p [ vbtma ][ bf 4 ] ( 10 . 2 mol . %)& lt ; p [ vbtpp ][ bf 4 ] ( 7 . 8 mol . %)& lt ; p [ vbp ][ bf 4 ] ( 3 . 6 %)& lt ; p [ vbmi ][ bf 4 ] ( 3 . 0 %). the solubility increases with increasing cation polarity . the polymer based on ammonium has the highest solubility because of its highest cation polarity . the polymer based on imidazolium , with the lowest cation polarity , has the lowest solubility . fig1 shows the effect of anion types on the co 2 solubility of poly ( ionic liquid ) s . the four polymers have the same cation structure , but different anions . p [ vbtma ][ bf 6 ] and p [ vbtma ][ bf 4 ] have a similar co 2 solubility of 10 . 7 mol . % and 10 . 2 mol . %, respectively . p [ vbtma ][[ sac ] and p [ vbtma ][ tf 2 n ] have a solubility of 2 . 8 mol . % and 2 . 7 %, respectively . the two poly ( ionic liquid ) s with inorganic anion have much higher solubility than the two with an organic anion , which can be explained in terms of the anion polarity effect on the interaction between the poly ( ionic liquid ) s with co 2 ; the higher the anion polarity , the higher the affinity to co 2 . as a result the poly ( ionic liquid ) with high anion polarity exhibit a higher co 2 solubility . the co 2 sorption kinetics of poly ( ionic liquid ) s with different backbones are shown in fig1 . at the equilibrium , the polymers took up 10 . 22 mol % ( p [ vbtma ][ bf 4 ]), 7 . 99 mol % ( p [ matma ][ bf 4 ]), respectively , in terms of their monomer units at 592 . 3 mmhg of co 2 and 22 ° c . with the same ammonium cation and bf 4 − anion , the polymer with polystyrene backbone had a higher co 2 sorption capacity than that with polymethylmethacrylate backbone . the effect of substituent of the ammonium cation on the co 2 sorption is shown in fig1 . their co 2 sorption capacities are as follows : p [ vbtma ][ bf 4 ] ( 10 . 2 mol . %)& gt ; p [ vbtea ][ bf 4 ] ( 4 . 85 mol . %)& gt ; p [ vbtba ][ bf 4 ] ( 3 . 1 mol . %). obviously , the co 2 sorption capacity decreases with increasing length of the substituent , which indicates that a large substituent on the ammonium cation blocks co 2 sorption . fig1 shows the effect of crosslinking on co 2 sorption of poly ( ionic liquid ). compared with p [ vbtma ][ bf 4 ] without crosslinking , the co 2 sorption capacity of 5 %- crosslinked p [ vbtma ][ bf 4 ] decreased by 17 . 3 %. bis ( 2 - hydroxyethyl ) dimethyl ammonium chloride ( acros , 99 %), 2 , 2 - bis ( bromomethyl )- 1 , 3 - propanediol ( aldrich , 98 %), 1 - methylimidazole ( lancaster , 99 %), 1 - butylimidazole ( aldrich , 98 %), 1 , 1 - carbonyldiimidazole ( aldrich , reagent grade ), terephthaloyl chloride ( aldrich , 99 +%), sodium tetrafluoroborate ( aldrich , 98 %, nabf 4 ), dimethyl sulfoxide ( aldrich , 99 . 9 +%, dmso ) and methanol ( a . c . s . reagent ) were used as received . acetonitrile ( aldrich , 99 . 5 +%), n , n - dimethylformiamide ( aldrich , 99 . 8 %, dmf ) and triethylamine ( emd , 99 . 5 %, et 3 n ) were used after removing water by molecular sieves . the synthesis of the monomers , bis ( 2 - hydroxyethyl ) dimethyl ammonium tetrafluoroborate ([ bhedma ][ bf 4 ]) 1 , 2 , 2 - bis ( methylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ([ bmimp ][ bf 4 ]) 2 and 2 , 2 - bis ( butylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ([ bbimp ][ bf 4 ]) 3 is shown in scheme 6 . the reagents and conditions were : a ) nabf 4 , acetonitrile , room temperature , 48h , 96 %; b ) 1 - methylimidazole , n 2 , 60 ° c ., 24h , 98 %; c ) nabf 4 , acetonitrile , room temperature , 48h , 96 %; d ) 1 - butylimidazole , n 2 , 80 ° c ., 24h , 97 %; d ) nabf 4 , acetonitrile , room temperature , 48h , 96 %. monomer 1 is an ammonium - based ionic liquid , while 2 and 3 are imidazolium - based ionic liquids . the synthesis of polycarbonate ( pc ) and polyethylene terephthalate ( pet ) types of ionic liquid polymers by condensation polymerization is as follows . the pc type of ionic liquid polymers can be synthesized using the monomers 1 ( 2 or 3 ) reacted with 1 , 1 - carbonyldiimidazole . the pet type of ionic liquid polymers can be synthesized using the monomers 1 ( 2 or 3 ) reacted with terephthaloyl chloride , respectively . both kinds of condensation polymerizations required a strict 1 : 1 ratio of the reagents with different difunctional groups . all the reactions were carried out in dmf at 60 ° c . for 24 h . all the polymers were precipitated by methanol after polymerization and dried under vacuum at 50 ° c . the ionic liquid monomer 1 is colorless , while 2 and 3 have a light yellow color . synthesis of 2 and 3 in a n 2 atmosphere is necessary because the imidazole group is liable to be oxidized by the o 2 in the air , which will make the product have a brown color . for the 1 methylimidazole is more active than 1 - butylimidazole , it will react with 2 , 2 - bis ( bromomethyl )- 1 , 3 - propanediol at a lower temperature ( 60 ° c .) than that of the 1 - butylimidazole ( 80 ° c .). all the monomers ( 1 , 2 and 3 ) are viscous liquids , and they all absorb moisture quickly when contacting air , so all of them need to be dried in a rotating evaporator before the polymerization . the polycondensation synthesis of the pc type polymers , poly ( bis ( 2 - hydroxyethyl ) dimethyl ammonium tetrafluoroborate ) carbonate ( p [ bhedma ][ bf 4 ] c ) 4 , poly ( 2 , 2 - bis ( methylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ) carbonate ( p [ bmim ][ bf 4 ] c ) 5 , and poly ( 2 , 2 - bis ( butylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ) carbonate ( p [ bbimp ][ bf 4 ] c ) 6 is shown in scheme 7 . polymer 4 is white , while 5 and 6 have a light yellow color . at room temperature , all polymers are easily crashed into fine powders . polymer 4 is soluble in acetonitrile , and polymer 5 and 6 are soluble in chloroform . they all can be cast into membranes for co 2 separation using a solvent evaporation method . the synthesis of the pet type polymers , poly ( bis ( 2 - hydroxyethyl ) dimethyl ammonium tetrafluoroborate ) terephthalate ( p [ bhedma ][ bf 4 ] t ) 7 , poly ( 2 , 2 - bis ( methylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ) terephthalate ( p [ bmimp ][ bf 4 ] t ) 8 and poly ( 2 , 2 - bis ( butylimidazolium methyl )- 1 , 3 - propanediol tetrafluoroborate ) terephthalate ( p [ bbimp ][ bf 4 ] t ) 9 , is shown in scheme 8 . triethylamine was added to the reaction system slowly to remove the hydrogen chloride . the obtained three polymers ( 7 , 8 and 9 ) are all white powders . but the solubilities of them are not as good as those for the corresponding pc types because their phenyl groups increase the rigidity of the polymer chains greatly . because they are only soluble in solvents with strong polarity and high boiling points , such as dmso and dmf , it is difficult to fabricate them into membranes using the solvent evaporation method . poly ( ionic liquid ) membranes for co 2 / ch 4 and co 2 / n 2 separations 31 copolymers of ionic liquid and polyethylene glycol ( peg ), for example p [ vbtma ][ bf 4 ]- co - peg and p [ matma ][ bf 4 ]- co - peg were synthesized as follows : ionic liquid monomer ([ vbtma ][ bf 4 ] or [ matma ][ bf 4 ]) ( 2 gram ), poly ( ethylene glycol ) methyl ether methacrylate ( mn = 2000 ) ( 2 g ), aibn ( 40 mg ) and dmf ( 8 ml ) are charged into a reaction tube . the tube is tightly sealed , degassed , and immersed in an oil bath at 60 ° c . for 12 h to get complete polymerization . these copolymer solutions were used to cast membranes for co 2 / ch 4 and co 2 / n 2 separations at 35 ° c ., 50 ° c . and 70 ° c ., all at 40 psig . these membranes were tested for permeability and selectivity . fig1 shows the co 2 ch 4 selectivity . fig1 shows that our copolymers have better properties than the previously studied representative polymers for co 2 / ch 4 separation . fig1 shows the selectivity of co 2 / n 2 for both p [ vbtma ][ bf 4 ]- co - peg and p [ matma ][ bf 4 ]- co - peg at 35 ° c ., 50 ° c . and 70 ° c . fig1 illustrates that both p [ vbtma ][ bf 4 ]- co - peg and p [ matma ][ bf 4 ]- co - peg membranes exhibit better ideal separation performance than the representative polymers because the data lie well above the upper limit bound curve , particularly for p [ matma ][ bf 4 ]- co - peg . the foregoing description and drawings comprise illustrative embodiments of the present inventions . the foregoing embodiments and the methods described herein may vary based on the ability , experience , and preference of those skilled in the art . merely listing the steps of the method in a certain order does not constitute any limitation on the order of the steps of the method . the foregoing description and drawings merely explain and illustrate the invention , and the invention is not limited thereto , except insofar as the claims are so limited . those skilled in the art who have the disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention . 2 . ruether , j . a . fetc programs for reducing greenhouse gas emissions . report no . doe / eftc - 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