Patent Application: US-201314409034-A

Abstract:
a method for the production of substrate coated with a poly , which method comprises the steps of : • providing a monomer which comprises both a polymerisable functional group and a nitrogen centre ; • providing a substrate ; • contacting the substrate with the monomer in an exciting medium , in order to cause polymerisation of the monomer and deposition of the resultant precursor polymer on the substrate ; and • subsequently contacting the precursor polymer with a cation - generating agent , in order to convert it into a poly containing an imidazolium cation .

Description:
fig1 shows how , in accordance with the invention , a substrate 1 can be coated with a poly ( ionic liquid ) in the form of a poly ( n - butyl imidazolium ) compound . the monomer ( i ) is in this case 1 - allylimidazole 2 . using a pulsed plasma to excite this monomer , as indicated by the arrow 3 , results in deposition of a poly ( 1 - allylimidazole ) film 4 on the substrate 1 ; this corresponds to the precursor polymer ( ii ) in the invented method . the polymer 4 carries pendant imidazole groups , each of which comprises a tertiary amine moiety 5 . the polymer film 4 is then quaternised , as indicated by the arrow 6 , using 1 - bromobutane 7 in the vapour phase , for example at 70 ° c . this results in a poly ( ionic liquid ) film 8 , which now carries pendant imidazolium moieties 9 . the pendant imidazolium cations , and their associated bromide anions , provide a high degree of ionic conductivity in the film 8 . it can be seen that the invented method can provide a simple , two - step process for preparing a poly ( ionic liquid ), which can yield a highly conductive product without the need for further doping agents . the use of plasma deposition to prepare the precursor polymer 4 can allow the generation of a high quality polymer coating with good structural retention , and with good surface uniformity . it can also allow the coating of a wide range of substrate materials and geometries , with good surface conformity . in the example below , a polymer - coated substrate was prepared according to the fig1 scheme , using 1 - allylimidazole as the monomer ( i ) and 1 - bromobutane as the quaternising agent . the structure and properties of the thus - deposited polymer were characterised by fourier transform infrared ( ftir ) spectroscopy , x - ray photoelectron spectroscopy and electrochemical impedance spectroscopy . plasma deposition was carried out in an electrodeless cylindrical glass reactor ( volume of 480 cm 3 , base pressure of 3 × 10 − 3 mbar , and with a leak rate better than 2 × 10 − 9 mol s − 1 ), surrounded by a copper coil ( 4 mm diameter , 10 turns ) and enclosed in a faraday cage . the reactor was pumped down using a 30 l min − 1 rotary pump attached to a liquid nitrogen cold trap ; a pirani gauge was used to monitor system pressure . the output impedance of a 13 . 56 mhz radio frequency ( rf ) power supply was matched to the partially ionised gas load via an l - c circuit . prior to each deposition , the reactor was scrubbed using detergent , rinsed in propan - 2 - ol , and dried in an oven . a continuous wave air plasma was then run at 0 . 2 mbar pressure and 40 w power for 30 minutes , in order to remove any remaining trace contaminants from the reactor walls . the substrates used for coating were silicon ( 100 ) wafer pieces ( silicon valley microelectronics inc ) and polypropylene sheet pieces ( lawson mardon ltd ), with two evaporated gold electrodes ( 5 mm length and 1 . 5 mm separation ) for proton conductivity testing . 1 - allylimidazole (+ 97 %, acros organics ltd ) was loaded into a sealable glass tube and degassed using several freeze - pump - thaw cycles . monomer vapour was allowed to purge the reactor for 5 minutes at a pressure of 0 . 18 mbar prior to electrical discharge ignition . pulsed plasma deposition utilised an optimal duty cycle of 20 μs on - period and 1200 μs off - period in conjunction with a peak power of 30 w ; a polymer deposition rate of 14 nm / min was achieved . upon plasma extinction , the monomer vapour was allowed to continue to pass through the system for a further 3 minutes , and then the reactor was evacuated back down to base pressure . in order to effect quaternisation of the surface coatings , the reactor was heated to 70 ° c . and 1 - bromobutane vapour ( 99 %, sigma - aldrich ltd , degassed using several freeze - pump - thaw cycles ) was introduced at a pressure of 4 mbar for up to 4 . 5 hours . after this , the reactor was again evacuated to base pressure before venting to atmosphere . infrared spectra were acquired using an ftir spectrometer ( perkin - elmer spectrum one ™) fitted with a liquid nitrogen cooled mct detector operating at 4 cm − 1 resolution across the 700 - 4000 cm − 1 range . the instrument included a variable angle reflection - absorption accessory ( specac ™) set to a grazing angle of 66 ° for silicon wafer substrates and adjusted for p - polarisation . surface elemental compositions were determined by x - ray photoelectron spectroscopy ( xps ) using a vg escalab ™ ii electron spectrometer equipped with a non - monochromated mg kα x - ray source ( 1253 . 6 ev ) and a concentric hemispherical analyser . photoemitted electrons were collected at a take - off angle of 20 ° from the substrate normal , with electron detection in the constant analyser energy mode ( cae , pass energy = 20 ev ). experimentally determined instrument sensitivity factors were taken as c ( 1s ): n ( 1s ): br ( 3d ) equals 1 . 00 : 0 . 66 : 0 . 36 . all binding energies were referenced to the c ( 1s ) hydrocarbon peak at 285 . 0 ev . a linear background was subtracted from core level spectra and then fitted using gaussian peak shapes with a constant full - width - half - maximum ( fwhm ) [ 49 ]. film thicknesses were measured using a spectrophotometer ( nkd - 6000 , aquila instruments ltd ). transmittance - reflectance curves ( 350 - 1000 nm wavelength range ) were acquired for each sample and fitted to a cauchy material model using a modified levenberg - marquardt algorithm [ 50 ]. impedance measurements across the 10 hz - 13 mhz frequency range were carried out using an lf impedance analyser ( hewlett - packard , 4192a ) for coated polypropylene substrates . the low frequency 45 ° line in the acquired impedance plots was assigned to the warburg diffusion impedance , and a high frequency arc was fitted in order to extract the resistance of the deposited membrane layer [ 51 ]. the formula σ = 1 / rsa was used to calculate proton conductivity , where σ is the membrane conductivity , rs is the bulk membrane resistance , l is the length of the electrodes , and a is the cross - sectional area of the film [ 52 ]. humidities of 97 % and 75 % were achieved by using , respectively , saturated solutions of potassium sulphate (+ 99 %, sigma - aldrich ltd ) and sodium chloride (+ 99 . 5 %, sigma - aldrich ltd ) in water [ 53 ]. for measurements at elevated temperatures , the cell was run in a potentiostatic mode ( bio - logic ™ sp - 150 ) by applying a sinusoidal ac potential around applied dc potentials of 0 . 3 v , 0 . 5 v and 0 . 7 v respectively . this example shows how pulsed plasmachemical deposition can be used to produce thin films containing a high density of imidazole groups , which can subsequently be quaternised using vapour - phase reaction with bromobutane , as shown in fig1 . the resultant films were found to have unexpectedly high ionic conductivities , up to 93 . 6 ms cm − 1 at 100 ° c . : this is comparable to the conductivity of the widely cited benchmark , nafion ™, which is a sulphonated tetrafluoroethylene - based synthetic copolymer with ionic properties , used as a proton conductor for example in proton exchange membrane fuel cells ( see 2 . 3 below ). fourier transform infrared ( ftir ) spectroscopy of the pulsed plasma deposited poly ( 1 - allylimidazole ) films showed good structural retention when compared to the imidazole monomer . fig2 shows the ftir spectra of ( a ) the 1 - allylimidazole monomer ; ( b ) the pulsed plasma deposited poly ( 1 - allylimidazole ); and ( c ) the final quaternised poly ( ionic liquid ) product . imidazole ring stretches ( denoted by * in fig2 ) could be seen in both the monomer and the deposited films , including a c ═ c — h ring stretch at 3107 cm − 1 , a c ═ n ring stretch at 1504 cm − 1 , and an in - plane bend n ═ c — h ring vibration at 1107 cm − 1 [ 41 , 42 ]. upon quaternisation of the imidazole ring with vapour - phase bromobutane , a shift was observed in the imidazole ring vibrations to 3133 cm − 1 , 1561 cm − 1 , and 1162 cm − 1 respectively , which is consistent with the formation of an imidazolium cation [ 43 ]. the appearance of c — h stretches at 2960 cm − 1 , 2935 cm − 1 and 2873 cm − 1 , along with the out - of - plane hch deformation at 1463 cm − 1 , corresponded to the butyl chain . broad peaks at 3500 - 3100 cm − 1 and 1630 cm − 1 for both films were attributed to water stretches , which is consistent with the hydrophilic nature of imidazole - based polymers [ 41 ]. compared to previous pulsed plasma deposited poly ( 1 - allylimidazole ) films [ 41 ], there was an absence of c ≡ n stretches at 2230 cm − 1 , which can be attributed to the milder duty cycle employed in this example . x - ray photoelectron spectroscopy ( xps ) analysis of the plasma deposited poly ( 1 - allylimidazole ) layer showed two n ( 1s ) peaks at 398 . 9 ev and 400 . 7 ev , respectively corresponding to n — c and n ═ c centres [ 44 ]. fig3 shows the xps n ( 1s ) spectra of ( a ) the pulsed plasma deposited poly ( 1 - allylimidazole ) and ( b ) the final , quaternised , polymer . it can be seen that following quaternisation of the imidazole ring , the xps n ( 1s ) spectrum showed a new , larger peak at 401 . 4 ev , which denotes quaternised , positively charged nitrogen centres [ 44 ]. the xps ratio of bromine to nitrogen was measured to be 1 : 3 . 1 , which corresponds to 65 % of the imidazole rings being quaternised to imidazolium ions . vapour - phase bromobutane quaternisation also caused the film thicknesses ( initially around 950 nm ) to swell by approximately 10 %. this , along with the infrared data , indicates reaction throughout the plasma deposited polymer films . electrochemical impedance spectroscopy was used to measure the ionic conductivity of the deposited polymer films . measurements at 60 , 80 and 100 ° c . were conducted by ird fuel cells a / s ( svendborg , denmark ). control samples of pulsed plasma deposited poly ( 1 - allylimidazole ) showed no ionic conductivity , regardless of conditions . in contrast , at room temperature ( 20 ° c . ), the quaternised poly ( imidazolium ) films showed ionic conductivity of 0 . 7 ms cm − 1 at 75 . 5 % relative humidity , which increased to 1 . 0 ms cm − 1 at 97 . 6 % relative humidity . this rise in ionic conductivity with relative humidity is similar to that reported for imidazolium - based ionic liquids [ 45 ]. at higher temperatures of 60 ° c . and 80 ° c ., and 75 % relative humidity , the ionic conductivity increased further to 6 . 9 ms cm − 1 and 13 . 0 ms cm − 1 respectively . upon increasing the temperature to 100 ° c . 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