Patent Application: US-201113702106-A

Abstract:
modified carbon nanotubes are provided having carbon nanotube core covalently bound through c — c bonds to a polymer shell surrounding the carbon nanotube core . the polymer shell is a polymer having functional groups pointing outwardly from the shell . the functional groups are compatible with or able to covalently connect to another polymer . such modified carbon nanotubes are more readily dispersed in a homogeneous manner in another polymer and may be used as a reinforcing filler in a polymer matrix . the modified carbon nanotubes with a core - shell structure in which the core has a substantially unidirectional orientation within the shell are produced by reacting neutral carbon nanotubes with 4 - vinylaniline through a diazonium reaction in presence of one or more types of multifunctional monomers carrying a vinyl moiety and one or more functional groups for compatibilization with or connection to another polymer . the reaction is conducted at an elevated temperature without isolation of intermediates and without addition of any extra initiator or catalyst to form a polymer shell in situ around the carbon nanotube . the polymer shell is covalently bound to cnt sidewall through c — c bonds and has functional groups outwardly pointing from the shell for compatibilization with or connection to another polymer .

Description:
200 mg of wcpp - lv - swcnt ( bio - char ) was ground in acn ( acetonitrile ) and then transferred into a round bottom flask with magnetic stirring bar in 150 ml of odcb ( o - dichlorobenzene ). the mixture was bath - sonicated for 1 . 5 hrs . subsequently , 1 . 98 g ( 1 . 95 ml ) of va ( 4 - vinylaniline ) in 20 ml of acn ( acetonitrile ) was injected into the mixture . the mixture was bath - sonicated for 10 minutes and then 3 . 91 g ( 4 . 5 ml ) of ian ( isoamyl nitrite ) was injected under stirring . the flask was assembled with a condenser and heated up to 60 ° c . in an oil - bath for 2 hours , then to 80 ° c . for 4 hrs . afterwards the mixture was maintained at 65 ° c . overnight ( 14 hours ) and then heated up to 85 ° c . for another 4 . 5 hours the next day . after cooling down to 50 ° c ., the mixture was diluted with dmf ( dimethylformamide ) to 250 ml . the mixture was transferred into polyethylene plastic centrifuge bottles and centrifuged at 4750 rpm for 30 minutes . a deep orange - red clear solution was decanted . the yellow - greenish precipitate was transferred to a beaker with a large quantity of dmf and then washed a few times through bath - sonication centrifuge cycles . the liquid phase after centrifugation became yellow . more wash cycles were carried out with mixtures of solvents such as dmf / thf , dmf / toluene , dmf / meoh , meoh / ethanol , and ethanol / h 2 o . finally , the precipitate was filtrated with a polycarbonate membrane (& gt ; 20 μm pore size , 47 mm in diameter ) and washed with water , ethanol and methanol . the yellow - greenish solid powder was dried in air under water pump and then dried in an oven at 100 ° c . overnight , whereupon 2 . 04 g of dry sample was collected . the pure swcnt loading is calculated to be close to 10 wt %. sem images show a core - shell structure with diameter range from 60 to 310 nm and more than a few μm long ( fig1 a , 1 b ). tem images reveal that a single or a small bundle of swcnt forms the core of the structure ( fig1 c , 1 d ), which is consistent with raman signals . the sample was further characterized using scanning transmission x - ray microscopy ( stxm ), which evidenced by an oxygen - rich surface layer indicating that terminal amine groups were partially converted to hydroxyl groups due to further reaction of the amine groups on 4 - vinyl aniline with excess isoamyl nitrite . however , according to x - ray photoelectron spectroscopy ( xps ), a substantial proportion of amine groups still remain on the surface of the polymer shell . thus , the modified swcnt comprises mixed amino / hydroxyl functionalization . stxm analysis has confirmed the same with 4 - vinylaniline as reference . larger scale preparation using 50 % reduction in 4 - vinyaniline as compared to example 1a 1 . 5 g of wcpp - lv - swcnt was ground in 50 ml of acn and transferred into 600 ml of odcb in a 1 l round bottom flask having a magnetic stirring bar . while stirring , the mixture was probe - sonicated for 1 . 5 hours , and then 7 . 448 g ( 7 . 32 ml ) va was added . after mixing for a few minutes and bath - sonicating for 10 minutes , ian was added . an additional 100 ml of acn was added . the mixture was refluxed and stirred at 85 ° c . for 2 hours , after which the bath temperature was increased to 105 ° c . and the mixture refluxed and stirred for 4 hours . the mixture was then kept at 65 ° c . overnight , and then refluxed at 115 ° c . for an additional 5 hours the next day . after cooling down to 50 ° c ., the mixture was diluted with 400 ml of dmf . the diluted mixture was transferred into pe centrifuge bottles and centrifuged at 4750 rpm for 30 minutes . the deep orange red solution was discarded and the precipitate was further washed with dmf until the solution became light yellow . the precipitate was then washed with etoh and filtrated through wet - strength filter paper (& gt ; 30 μm pore size ) and subjected to washes with water , ethanol and methanol . the solid sample was dried in air and then in oven at 100 ° c . for a day . in total , 5 . 90 g was collected . the pure swcnt loading is calculated to be close to 25 . 4 wt %. sem images ( fig2 ) and the calculated loading of swcnt clearly indicate the amount of functionalized polymer coating is reduced by more than double compared with example la . the diameter range is from 40 to 110 nm . but , xps results indicate that the concentration of functional groups on the surface of the polymer remains practically unchanged . larger scale preparation using same relative amount of 4 - vinyaniline as in example 1a 2 . 81 g wcpp - lv - swcnt was ground in odcb and then transferred into 3 - neck 2 l round bottom flask equipped with mechanical stirring . the mixture in 1 . 5 litres of odcb was bath - sonicated for two hours , and then 28 g of va was added under bath - sonication for an additional hour . under vigourous mechanically stirring , 55 g of ian was injected with a syringe at room temperature . after mixing for a few minutes , the mixture was heated up to 50 ° c . with an oil - bath for 2 hours , and then stirred at room temperature overnight . the next day , the mixture was refluxed at 105 ° c . for 10 hours , then slowly cooled down to room temperature overnight , then refluxed again the next day for an additional 2 hours , and then lowered to 50 ° c . and diluted with dmf to fill up the entire 2 l flask . the diluted mixture was kept in the flask for 10 days . the mixture was centrifuged at 4750 rpm for 30 minutes . the liquid phase was discarded and the precipitate was repeatedly washed with dmf ( total volume used of about 20 litres until light yellow color ), and subsequently washed in sequence with methanol , hq water , methanol and filtrated with pc membrane . the solid sample was dried in air and then dried in an oven at 80 ° c . 22 . 68 g of dry sample was collected . the swcnt loading is calculated to be close to 12 . 4 wt %. sem images shown in fig4 indicate that the surface morphology is not as smooth as example la ( fig1 ) due to the large quantity of sample with inefficient stirring , but the core - shell structure is maintained . further surface characterization with xps analysis revealed that there is more n than o in the sample . modified swcnt of example 1b was further developed into a buckypaper and its mechanical property measured as shown in fig3 in comparison to pristine swcnt buckypaper . the results demonstrate that buckypaper produced from the modified swcnt is mechanically more resistant than the pristine buckypaper . 8 . 06 g of the greenish dry powder of the modified swcnt of example 1c was dispersed in thf ( about 3 l ) through tip and bath - sonication to form a well dispersed suspension . the suspension was concentrated by evaporating the thf by heating under stirring to about 1 litre . the concentrated suspension was then mixed with 1 . 5 l of xylene ( cas : 1330 - 20 - 7 , anachemia ) containing 192 g of ultra - high molecular weight polyethylene ( uhmwpe ) white powder in an erlenmeyer flask by mechanical stirring . the mixture was slowly heated up under vigorous mechanical stirring and nitrogen atmosphere . the remaining thf was continuously evaporated . when the evaporation of thf was nearly complete , the temperature of the mixture started to increase . when the temperature was close to the boiling point of xylene ( i . e . near 130 ° c . ), the morphology and color of the mixture became uniform to the naked eye . within about 3 to 5 minutes , the temperature reached close to 140 ° c . and the mixture became very viscous , forming one big block . at this point mechanical stirring became impractical . the heating source was quickly removed and the mixture was allowed to cool down to room temperature . free xylene was decanted and the solid was filtered with wet - strength filter paper and washed with methanol . the filtrand was dried in air with a water pump and dried at 85 ° c . in an oven overnight . the final loading of modified swcnt in the uhmwpe composite was about 4 wt % which corresponds to a final swcnt loading of about 0 . 5 wt %. 56 mg of the modified swcnt of example 1a was bath - sonicated in 100 ml of xylene in an erlenmeyer flask for 15 minutes , forming a well dispersed suspension . 495 mg of pellets of pp - g - gma ( polypropylene - g - glycidylmethacrylate , orevac oe 905 ) was added and the mixture was slowly heated under stirring to 140 ° c . ( after 120 ° c . the small white pp - g - gma pellets dissolved in solution , and xylene starts to boil at 135 ° c .) under nitrogen . the temperature was maintained at 140 ° c . for 30 minutes , and then cooled down to room temperature under continuous stirring . the mixture was heated again to 140 ° c . and refluxed for further 30 minutes , and then cooled down to room temperature . samples were taken from the cooled mixture for sem and tem measurements . the rest of the mixture was centrifuged at 9000 rpm for 30 minutes . the precipitate was washed with ethanol twice . samples were taken again for sem and tem measurements . the rest of the sample was filtered through a pc membrane ( 20 μm , 47 mm ). a fraction of the sample was used to make a paper - like sheet by hot - pressing in between two aluminum plates at 120 ° c . for an hour , and subsequently at 200 ° c . for another hour . the pressed sample became black , and one small piece was taken for sem measurement . from the sem images , the core - shell nanostructure is apparent before hot - pressing ( fig5 a ) but disappears after hot - pressing ( fig5 b ), indicating that chemical blending ( interfacial connection ) has occurred . 1 . 5 g of greenish powder of the modified swcnt of example 1 c was bath - sonicated in 1 l of thf to produce a well - dispersed suspension . the suspension was mixed with 15 g of pe - g - gma ( polyethylene - g - glycidylmethacrylate ) in 500 ml of xylene . the mixture was slowly heated up under nitrogen with magnetic stirring . when the mixture reached 100 - 110 ° c . under strong thf reflux , the pe - g - gma dissolved . the temperature was kept constant at 100 - 110 ° c . for an hour and then cooled down to room temperature . then , 22 . 5 g of uhmwpe was added with an additional 100 ml of xylene . the mixture was slowly heated again with strong stirring under nitrogen up to 130 ° c . and the temperature was maintained for 2 hrs . the mixture was then heated to 140 ° c . to the boiling point of xylene for 5 minutes . the heating source was removed and the mixture was allowed to cool down under stirring to room temperature . the supernatant xylene was decanted . the slurry was filtered through a wet - strength filter paper with a water pump . the solid was washed with methanol and dried in air with water pump suction , and then dried at 85 ° c . in an oven overnight . the loading of the modified swcnt in the final composite was calculated to be close to 4 wt %. the corresponding loading of pure swcnt is about 0 . 5 wt %. 55 mg of greenish powder of the modified swcnt of example 1a was bath - sonicated in 20 ml of thf until a well dispersed suspension formed . the suspension was then mixed with 4 . 725 g of my0510 epoxy resin . the mixture was bath - sonicated and vigorously shaken with a mechanical shaker . thereafter , the thf solvent was evaporated on a heating plate . the thf removal was completed by sparging nitrogen or air while maintaining the temperature in the 110 - 120 ° c . range . after cooling down to room temperature , a drop of the brownish liquid resin sample was viewed under raman microscope and optical images were taken as well as high magnification fluorescence microscopy to check for the quality of the dispersion ( fig6 a ). 138 . 5 mg of the brownish liquid resin was mixed with 83 . 1 mg of white powder of 4 , 4 ′- dds ( curing ratio was 100 : 60 by weight ) on a glass slide with a glass rod , and then the glass slide heated to 100 ° c . the resin mixture was mixed further in an open - air oven . the oven temperature was increased to 120 ° c . to lower the resin viscosity further . the mixture was stirred further again . the resin was spread as a thin layer on the glass slide and heated at 145 ° c . for 2 hours . then the oven temperature was increased to 160 ° c . and the sample was cured at this temperature for another 2 hours . after cooling down to room temperature , the color of the cured composite sample was dark yellow . high magnification microscopy optical images were taken and these are shown in fig6 b . tga profile of cured my0510 epoxy resin having 1 . 15 wt % loading of modified swcnt is shown in fig7 , where the lower profile has a magnified scale on the weight and temperature axes . the tga profile indicates an enhancement in thermal stability of the nanocomposite over the neat resin . 35 mg ( about 2 . 9 mmol c ) of purified plasma swcnt was placed in a round bottomed flask and was dried in an oven at 100 ° c . for 1 hour . 30 ml of odcb was added and the mixture was bath - sonicated for 1 hour to allow for dispersion . thereafter , 150 mg ( 1 . 3 mmol ) of va was dissolved in 10 ml of acn and then added to the swcnt suspension . at this point , 2 . 4 ml ( 17 . 6 mmol ) of glycidyl methacrylate was added and nitrogen gas was sparged through the suspension for 10 min . subsequently , 2 . 4 ml ( 21 . 3 mmol ) of ian was degassed and added to the suspension with a syringe . the suspension was stirred for 72 hours at 60 ° c . after cooling to room temperature , the suspension was filtered through a 0 . 22 μm polytetrafluoroethylene ( ptfe ) membrane and washed with dmf until the filtrate remained clear . the sample was dried at 80 ° c . in a vacuum oven for 1 hour and then at 100 ° c . at atmospheric pressure for 24 hours . raman spectra gave an average id / ig ratio of 0 . 421 ± 0 . 087 , indicating significant functionalization compared to the original sample . thermogravimetric analyses showed that the sample is made of 56 . 3 % swcnt and 43 . 7 % of copolymer shell (± 0 . 4 %, average of 2 runs after subtracting residual catalyst and solvent mass losses ). 20 g of polycarbonate ( pc ) was dissolved in 300 ml of thf with bath - sonication . 15 ml of the pc solution was added to 50 mg of the modified swcnt of example 4a and tip - sonicated for 30 min . the resulting black solution was poured to a mold and allowed to dry slowly overnight at room temperature . raman spectra gave an average id / ig value of 0 . 563 ± 0 . 054 . raman spectroscopy mapping of the composite showed that the composite was well dispersed compared to a composite of raw swcnt in polycarbonate , in which swcnt was used without surface functionalization . differential scanning calorimetry ( dsc ) of the composite of the present invention showed a slight decrease in the t g value versus neat polycarbonate , with the thermal stability ( by thermal gravimetric analysis ( tga )) of the composite remaining the same as neat polycarbonate . 9 . 04 g of mwcnt powder was placed in a three neck round - bottom flask in 800 ml of odcb ( o - dichlorobenzene ). the mixture was bath - sonicated for 1 hr , and then 15 g of 4 - vinylaniline in acetonitrile was added . the mixture was stirred for 10 minutes and bath - sonicated for 1 hr . under strong mechanical stirring , 29 . 5 g of isoamyl nitrite was added drop wise into the suspension over 20 minutes . after 30 minutes stirring , the mixture was warm due to the reaction . after addition , a heating mantle was applied to further increase the temperature to a gentle reflux of acetonitrile for 3 . 5 hr . after two days stirring at room temperature , the mixture was refluxed for 4 hr . then the mixture was cooled to 60 ° c . and diluted with dmf to 2 l in total in a beaker . after stirring and bath - sonication for 1 hr , the mixture was transferred into a plastic centrifuge bottle and centrifuged at 4750 rpm for 50 min . after centrifugation , the dark orange solution was discarded . the precipitate was washed with dmf for a few more cycles , and then with meoh , from which a small amount of suspension was taken for sem and tem analysis . after washing with meoh , the precipitate was filtrated through polycarbonate ( pc ) membrane and further washed with meoh . after drying in air under vacuum , and then drying in an oven at 110 ° c . for two days , the final product was collected as a black powder ( 22 . 67 g ). the dried sample was analyzed by tga - ms - ftir . the final dry sample contained 39 . 87 wt % mwcnt . tga analysis ( fig8 ) shows a single sharp decomposition of unmodified mwcnt at 592 ° c . ( fig8 a ). the modified mwcnt has three decomposition temperatures at 261 ° c ., 491 ° c . and 588 ° c . ( fig8 b ), where the lower decomposition temperatures reflect decomposition in the coating and the highest temperature represents decomposition of the carbon nanotubes themselves . tem images of mwcnt before and after modification are shown in fig9 a and fig9 b , respectively . tem images reveal that a single or a small bundle of mwcnt forms the core of a core - shell structure , which is less than 50 nm in diameter . sem images of mwcnt before and after modification are shown in fig1 a and fig1 b , respectively . sem images show that the modified mwcnt having the core - shell structure are more than a few μm long . integration of unmodified mwcnt into natural rubber ( nr ) matrix as a comparative example 2 . 72 g of the unmodified mwcnt as provided by the manufacturer as a dry powder was ground in 2 l toluene and tip - and bath - sonicated for 5 hrs . the suspension was poured into a yellow solution of 51 . 6 g of nr in 2 l toluene . natural rubber ( nr ) primarily comprises high cis - 1 , 4 - polyisoprene . the mixture was strongly stirred by mechanical stirring for two days , with occasional high shear mixing to further disperse the raw mwcnt into the nr matrix for short period of time . since high shear mixing generates heat , overheating of the rubber material should be avoided to avoid crosslinking . afterward , most of the solvent was evaporated while the mixture was continuously stirred . the residue of the mixture was then placed in a vacuum oven at 35 ° c . to remove the remaining solvent . the rubber / mwcnt composite ( fig1 a ) so formed contained 5 wt % mwcnt . the sem image of the composite is shown in fig1 a . 7 . 37 g of the modified mwcnt from example 6 as a dry powder was ground in 2 l toluene and tip - and bath - sonicated for 5 hrs . the suspension was poured into a yellow solution of 51 . 4 g of nr in 2 l toluene . the mixture was strongly stirred by mechanical stirring for two days , with occasional high shear mixing to disperse the modified mwcnt into the nr matrix for short period of time . afterward , most of the solvent was evaporated with compressed air while the mixture was continuously stirred . the residue of the mixture was then placed in a vacuum oven at 35 ° c . to remove the remaining solvent . the rubber / modified mwcnt composite ( fig1 b ) so formed contained 5 wt % neat mwcnt . the sem image of the composite is shown in fig1 b . the contents of the entirety of each of which are incorporated by this reference afzali - ardakani a , avouris p , hannon j b , klinke c . 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