Solubilizing single-walled carbon nanotubes by direct reaction with amines and alkylaryl amines

Naked single-walled nanotube carbon metals and semiconductors are dissolved in organic solutions by direct functionalization with amines or alkylaryl amines having an uninterrupted carbon chain of at least 5 and more preferably 9 carbon atoms in length.

TECHNICAL FIELD
 The present invention relates to the dissolution of single-walled carbon
 nanotubes in solutions and more particularly, to a method of dissolving
 naked single walled nanotube carbon metals and semiconductors in organic
 solutions.
 BACKGROUND OF THE INVENTION
 All previous work on carbon nanotubes (both single-walled and
 multi-walled), has been carried out on the usual intractable, insoluble
 form of this material [Yakobson, B. I.; Smalley, R. E., Fullerene
 Nanotubes: C1,000.000 and Beyond. American Scientist 1997, 85, 324-337.]
 This form of the material is not amenable to many of the processing steps
 that are necessary if the single-walled carbon nanotubes (SWNTs) are to
 reach their full potential--particularly in applications that require
 these materials in the form of polymers, copolymers, composites, ceramics
 and moldable forms.
 While present forms of the SWNTs can be heterogeneously dispersed in
 various media, the interactions between the SWNTs and host and between the
 SWNTs themselves are simply physical, and without the formation of
 chemical bonds. Thus, the advantageous properties of the SWNTs are
 unlikely to be realized on a macroscopic level. What is needed is a method
 to prepare well-dispersed forms of SWNTs perhaps by inducing them to
 exfoliate from the bundles and dissolve in organic solvents. Although long
 believed to be impossible, [Ebbesen, T. W., Cones and Tubes: Geometry in
 the Chemistry of Carbon. Acc. Chem. Res. 1998, 31, 558-566] we now teach
 such a procedure for the dissolution of SWNTs [Chen, J.; Hamon, M. A.; Hu,
 H.; Chen, Y.; Rao, A. M.; Eklund, P. C.; Haddon, R. C., Solution
 Properties of Single-Walled Carbon Nanotubes. Science 1998, 282, 95-98;
 Hamon, M. A.; Chen, J.; Hu, H.; Chen, Y.; Rao, A. M.; Eklund, P. C.;
 Haddon, R. C., Dissolution of Single-Walled Carbon Nanotubes. Adv. Mater.
 1999, 11, 834-840].
 SUMMARY OF THE INVENTION
 Accordingly, it is a primary object of the present invention to overcome
 the above-described limitations and disadvantages of the prior art by
 providing (1) a method of solubilizing single-walled carbon nanotubes; and
 (2) solutions of single-walled carbon nanotubes dissolved in an organic
 solvent. Such solutions are anticipated to be useful in determining the
 functionalization chemistry of the open ends, the exterior walls or convex
 face and the interior cavity or concave face of single-walled carbon
 nanotubes and processing useful nanotube based polymer, copolymer and
 composite products and devices for a multitude of applications in various
 industries including aerospace, battery, fuel cell and electromagnetic
 radiation shielding.
 Advantageously, as a result of the present invention, functionalization
 chemistry of the SWNTs can be determined through the study of both the
 ionic and covalent solution phase chemistry with concomitant modulation of
 the single wall nanotube band structure.
 Additional objects, advantages, and other novel features of the invention
 will be set forth in part in the description that follows and in part will
 become apparent to those skilled in the art upon examination of the
 following or may be learned with the practice of the invention. The
 objects and advantages of the invention may be realized and attained by
 means of the instrumentalities and combinations particularly pointed out
 in the appended claims.
 To achieve the foregoing and other objects, and in accordance with the
 purposes of the present invention as described herein, a novel and
 improved method of dissolving single-walled carbon nanotubes and
 semiconductors in common organic solutions is provided. The method
 comprises terminating purified single-walled carbon nanotubes with
 carboxylic acid groups, then reacting the carboxylic acid groups with an
 amine or an alkylaryl amine having a formula (1) RNH.sub.2 or (2) R.sub.1
 R.sub.2 NH.sub.1 wherein R, R.sub.1 and R.sub.2 =CH.sub.3 (CH.sub.2).sub.n
 where n=9-50 or R, R.sub.1 and R.sub.2 =(C.sub.6 H.sub.4)(CH.sub.2).sub.n
 CH.sub.3 where n=5-50 and then dissolving the reacted single-walled carbon
 nanotubes in the organic solvent.
 More specifically describing the method, the compound of formula (1)
 RNH.sub.2 is a compound selected from a group including nonylamine,
 dodecylamine, octadecylamine, pentacosylamine, tetracontylamine,
 pentacontylamine and any mixtures thereof and the alkylaryl amine compound
 of formula (2) is a compound selected from a group consisting of
 4-pentylaniline, 4-dodecylaniline, 4-tetradecylaniline,
 4-pentacosylaniline, 4-tetracontylaniline, 4-pentacontylaniline and any
 mixtures thereof. The reacting step may be further described as including
 the mixing of the single-walled carbon nanotubes with the amine or
 allkylaryl amine in an appropriate solvent (eg. toluene, chlorobenzene,
 dichlorobenzene, dimethylformamide, hexmethylphosphoramide,
 dimethylsulfoxide) or without solvent and the heating of the resulting
 mixture to a temperature between 50.degree.-200.degree. C. and more
 preferably 90.degree.-100.degree. C. Preferably, the heating is maintained
 for a least 96 hours during which the reaction is completed.
 In accordance with yet another aspect of the present invention, a novel
 solution is provided comprising single-walled carbon nanotubes dissolved
 in an organic solvent. More specifically, that organic solvent is selected
 from a group including, for example, tetrahydrofuran, chloroform, benzene,
 toluene, chlorobenzene, 1,2-dichlorobenzene, dichlorocarbene, ether and
 mixtures thereof. The single-walled carbon nanotubes dissolved in the
 organic solvent are a zwitterion having a length between 1-1000 nm and a
 diameter between 0.5-100 nm and an alkyl chain of 5 and more preferably 9
 or more carbon atoms in length.
 Advantageously, such a solution not only allows the study of the
 functionalization chemistry of the open ends, the exterior walls or convex
 face and the interior cavity or concave face of the nanotubes, but also
 processing of the nanotubes into useful products for various applications
 including as intermediates in the preparation of polymer, copolymer and
 composite materials.
 Still other objects of the present invention will become apparent to those
 skilled in this art from the following description wherein there is shown
 and described a preferred embodiment of this invention, simply by way of
 illustration of one of the modes and alternate embodiments best suited to
 carry out the invention. As it will be realized, the invention is capable
 of still other and different embodiments, and its several details are
 capable of modifications in various, obvious aspects all without departing
 from the invention. Accordingly, the drawings and descriptions will be
 regarded as illustrative in nature and not as restrictive.

Reference will now be made in detail to the present preferred embodiment of
 the invention, an example of which is illustrated in the accompanying
 drawings.
 DETAILED DESCRIPTION OF THE INVENTION
 In the novel method of the present invention, we begin with raw, as
 prepared, SWNT soot (AP-SWNTs) which may be obtained from CarboLex, Inc.
 of Lexington, Kentucky. This is prepared by use of an electric arc
 technique similar to that described by Journet, C.; Maser, W. K.; Bernier,
 P.; Loiseau, A.; Lamy de la Chappelle, M.; Lefrant, S.; Deniard, P.; Lee,
 R. and Fischer, J. E., in Large Scale Production of Single-Walled Carbon
 Nanotubes by the Electric-Arc Technique. Nature 1997, 388, 756-758. The
 estimated purity of this material is 40-60% SWNT by volume. Batches of 10
 grams may be prepared in a single run and there is considerable scope for
 further increase in scale. Thus it is possible to contemplate the very
 large-scale production of this material in the future. We describe herein
 routes to soluble SWNTs (s-SWNTs), starting from AP-SWNTs.
 In the most preferred embodiment of this procedure, the AP-SWNTs are (1)
 Purified, (2) Shortened, (3) Polished, (4) Reacted directly with an amine
 or alkylaryl amine during which the bundles are exfoliated into a mixture
 of individual SWNTs and small bundles of SWNTs. This latter material is
 soluble in a number of organic solvents and is thus suitable for further
 chemical reactions. The chemical reactions used to effect this
 transformation of the carboxylic acid functionalized SWNTs are shown
 below. The structure of the end of an SWNT after functionalization with
 octadecylamine is shown in FIG. 1.
 ##STR1##
 Purification is a desired step because the AP-SWNTs contain extraneous
 material, beside the approximately 40-60% SWNTs by volume. In particular
 the AP-SWNTs contain metal catalyst (nickel and yttrium), nanoparticles
 (carbonaceous particles sometimes containing metals), graphite, amorphous
 carbon, fullerenes and other contaminants.
 A first purification procedure is a variation of a previously published
 method [Liu, J.; Rinzler, A. G.; Dai, H.; Hafner, J. H.; Bradley, R. K.;
 Boul, P. J.; Lu, A.; Iverson, T.; Shelimov, K.; Huffman, C. B.;
 Rodriguez-Macias, F.: Shon, Y.-S.; Lee, T. R.; Colbert, D. T.; Smalley, R.
 E., Fullerenes Pipes. Science 1998, 280, 1253-1255] [Rinzler, A. G.; Liu,
 J.; Dai, H.; Nilolaev, P.; Huffman, C. B.; Rodriguez-Macias, F. J.; Boul,
 P. J.; Lu, A. H.; Heymann, D.; Colbert, D. T.; Lee, R. S.; Fischer, J. E.;
 Rao, A. M.; Eklund, P. C.; Smalley, R. E., Large-Scale Purification of
 Single-Wall Carbon Nanotubes: Process, Product and Characterization. Appl.
 Phys. A 1998, 67, 29-37].
 AP-SWNTs (40-60 vol. % of SWNTs) are refluxed in 2-3M nitric acid for about
 48 hours (200-300 ml 2-3M nitric acid per gram of AP-SWNTs). After
 centrifugation, the supernatant solution is decanted. The pH of the solid
 is adjusted to about 7 by monitoring the pH of the supernatant liquid
 through repeated cycles of washing, centrifugation and decantation.
 The resulting solid is suspended in an 0.5% aqueous solution of sodium
 dodecyl sulfate (SDS) by sonication for 2-4 hours (200-400 ml surfactant
 solution per gram of AP-SWNTs); the solution pH is then adjusted to 9-10
 by addition of sodium hydroxide. Filtration through a cotton plug gives a
 black-colored suspension.
 The resulting suspension is subjected to cross-flow filtration (CFF). The
 CFF cartridge has the following specifications: fiber diameter of 0.6 mm,
 pore size of 200 nm and surface area of 0.56 m.sup.2. The buffer solution
 is made up to contain 0.5% SDS at a pH of 9-10 (adjusted by addition of
 NaOH). Initially the filtrate is black. The CFF is halted when the
 filtrate has become light brown. HCl is added to the resulting suspension
 to terminate the open ends of the SWNTs with carboxylic acid groups
 (.about.COOH v.sub.C.dbd.O =1719 cm.sup.-1) rather than carboxylate groups
 (.about.COO.sup.-, v.sub.C.dbd.O =1620 cm.sup.-1).
 After centrifugation, the black solid is washed with distilled water and
 ethyl alcohol and dried at room temperature. The purity of the resulting
 SWNTs is around 90 vol. %, and the yield is 10-30% (based on AP-SWNTs). A
 specific example of this purification procedure is found below in Example
 1.
 EXAMPLE 1
 AP-SWNTs (6.3 g) were refluxed in 700 mL of 2 M HNO.sub.3 for 48 hrs (oil
 bath at 130.degree. C.). The mixture was centrifuged at 2000 rpm for 30
 min. The acid layer was discarded and the solid was washed with water and
 then mixed into a 0.5% wt. solution of SDS in water (1500 mL). NaOH was
 added to the solution until the pH was above 10. The mixture was sonicated
 for 10 hrs. The suspension was acidified with HCl so that the acid form of
 the SWNTs precipitated and then it was centrifuged at 2000 rpm for 30 min.
 The water layer was decanted and passed through a membrane filter, pore
 size 1.2 .mu.m. The solid slurry was then subjected to membrane
 filtration. Yield: 2.35 g.
 A second or alternative purification procedure is also a variation of a
 previously published method [Ebbesen, T. W.; Dujardin, E.; Krishnan, A.;
 Treacy, M. M. J., Purification of Single-Shell Nanotubes. Adv. Mater.
 1998, 10, 611-613]. It is simpler, but less complete than the first
 purification procedure.
 AP-SWNTs (40-60 vol. % of SWNTs) are refluxed in 70% nitric acid until the
 emission of dense brown vapors ceases (for 4 g AP-SWNTs, this usually
 takes 10-12 hours). After centrifugation, the brown-colored supernatant
 solution is decanted. The pH of the solid is adjusted to about 7 by
 monitoring the pH of the supernatant liquid through repeated cycles of
 washing, centrifugation and decantation.
 The resulting solid is washed with ethyl alcohol and dried at room
 temperature under reduced pressure. The purity of the SWNTs is around
 70-80 vol. %, and the yield is 40-50%.
 The next step is the shortening of the SWNTs. This aids in their
 dissolution in organic solvents.
 A first shortening technique is a variation of a previously published
 method. [Liu, J.; Rinzler, A. G.; Dai, H.; Hafiier, J. H.; Bradley, R. K.;
 Boul, P. J.; Lu, A.; Iverson, T.; Shelimov, K.; Huffinan, C. B.;
 Rodriguez-Macias, F.; Shon, Y.-S.; Lee, T. R.; Colbert, D. T.; Smalley, R.
 E., Fullerenes Pipes. Science 1998, 280, 1253-1255] [Rinzler, A. G.; Liu,
 J.; Dai, H.; Nilolaev, P.; Huffman, C. B.; Rodriguez-Macias, F. J.; Boul,
 P. J.; Lu, A. H.; Heymann, D.; Colbert, D. T.; Lee, R. S.; Fischer, J. E.;
 Rao, A. M.; Eklund, P. C.; Smalley, R. E., Large-Scale Purification of
 Single-Wall Carbon Nanotubes: Process, Product and Characterization. Appl.
 Phys. A 1998, 67, 29-37.] After this process the SWNTs are reduced to
 lengths in the range 100-300 nm.
 The purified SWNTs (70-80%) are sonicated in a 1:2-3 mixture of 70% nitric
 acid and 90% sulfuric acid for 24-48 hours (500-100 ml acids per gram of
 purified SWNTs). The temperature is controlled to be lower than 60.degree.
 C.
 The resulting mixture is diluted 3-4 times by pouring into distilled water
 and cooled to room temperature. The solid is isolated by membrane
 filtration (100-200 nm pore size), washed with a minimum amount of
 distilled water, and dried at room temperature under reduced pressure to
 give shortened SWNTs (40-60% yield based on purified SWNTs). A specific
 example of this shortening technique is found below in Example 2.
 EXAMPLE 2
 0.387 g of purified SWNTs were sonicated in 40 mL of 3:1 H.sub.2 SO4
 (concentrated) to HNO3 (concentrated) for 24 hours. Distilled water (200
 mL) was added to the mixture, and it was filtered (membrane pore sizes 0.2
 .mu.m), washed with water and dried. Purified, shortened SWNTs: 0.273 g.
 In accordance with a second, alternative approach, the purified SWNTs are
 stirred in a 3:1 mixture of 98% sulfuric acid and 70% nitric acid at
 60-80.degree. C. for 10-30 minutes (100 ml acid per gram of purified
 SWNTs). The resulting mixture is diluted 3-4 times by pouring into
 distilled water. After membrane filtration (200 nm pore size), the black
 solid is washed with distilled water, and dried at room temperature under
 reduced pressure.
 The black solid is probe-sonicated in 5-15% ammonium persulfate aqueous
 solution for 6-12 hours (60-120 g ammonium persulfate per gram of purified
 SWNTs). After membrane filtration (200 nm pore size), washing with
 distilled water and ethyl alcohol, drying at room temperature under
 reduced pressure, the shortened SWNTs are obtained. 30-50% yield based on
 purified SWNTs.
 The Raman spectrum of the shortened SWNTs (.omega..sub.r =161,
 .omega..sub.t =1595 cm.sup.-1, .omega..sub.r and .omega..sub.t represent
 the Raman-active radial mode and tangential mode frequencies of SWNTs) is
 close to that of raw soot (.omega..sub.r =162, .omega..sup.t =1592
 cm.sup.-1). Because the Raman radial mode of the SWNTs is sensitive to the
 diameter, but not to the symmetry of the nanotube, based on .omega..sub.r
 (cm.sup.-1)=223.75 (cm.sup.-1 nm)/d(nm), the average diameter of the
 shortened SWNTs in a typical sample is estimated to be 1.38 nm.
 Next is the polishing of the SWNTs. It is hypothesized that the polishing
 step removes polar hydroxylic functionality from the processed SWNTs.
 These hydroxylic species may be physically or chemically attached to the
 purified, shortened SWNTs. At the end of this treatment the SWNTs are less
 hydrophilic (less susceptible to forming aqueous dispersions).
 Specifically, the purified shortened SWNTs are stirred in a 4:1 mixture of
 90% sulfuric acid and 30% hydrogen peroxide at 60-80.degree. C. for 20-35
 minutes (300-500 m1 of liquid per gram of purified, shortened SWNTs).
 The resulting mixture is diluted 3-4 times by pouring into distilled water
 and cooled to room temperature. After membrane filtration (100-200 nm pore
 size), washing with distilled water and ethyl alcohol, and drying at room
 temperature under reduced pressure, the polished shortened SWNTs are
 obtained (40-50% yield based on purified, shortened SWNTs).
 A specific example of this shortening technique is found below in Example
 3.
 EXAMPLE 3
 0.42 g of purified, shortened SWNTs were heated at 70.degree. C. in 50 mL
 of 4:1 H.sub.2 SO.sub.4 (90%) to H.sub.2 O.sub.2 (30%) for 15 minutes.
 Water (300 mL) was added to the mixture, and it was filtered (membrane
 pore size 0.2 .mu.m), washed with water and dried. Mass: 0.6 g.
 The next step in the method of solubilizing is to directly react the
 carboxylic acid groups on the open ends of the shortened SWNTs with an
 amine or an alkylaryl amine having the formula RNH.sub.2 or R.sub.1
 R.sub.2 NH wherein R, R.sub.1 and R.sub.2 =CH.sub.3 (CH.sub.2).sub.n,
 where n=9-50 or R, R.sub.1 and R.sub.2 =(C.sub.6 H.sub.4)(CH.sub.2).sub.n
 CH.sub.3 where n=5-50 via the formation of a zwitterion. This is done with
 simple acid-base chemistry by mixing the shortened SWNTs with an
 appropriate quantity of amine or alkylaryl amine having the formulae just
 described either without any solvent or in an appropriate aromatic solvent
 such as toluene. Amines that may be utilized include, but are not limited
 to, nonylamine, dodecylamine octadecylamine, pentacosylamine,
 tetracontylamine, pentacontylamine and any mixtures thereof. Alkylaryl
 amines that may be utilized include 4-pentylaniline, 4-dodecylaniline,
 4-tetradecylaniline, 4-pentacosylaniline, 4-tetracontylaniline,
 4-pentacontylaniline and any mixtures thereof. Long alkyl chains of at
 least 5 and more preferably 9 carbon atoms and up to 50 carbon atoms are
 required to increase the solubility of the resulting shortened SWNTs
 product. The mixture is heated to substantially 50.degree.-200.degree. C.
 and more preferably 90-100.degree. C. for approximately 96 hours. This
 procedure advantageously results in relatively high-yields (approximately
 70-90%) of soluble shortened SWNTs. During the processing, the volume of
 the shortened SWNTs expands over time. It is hypothesized that this is due
 to exfoliation of the SWNTs bundles to give individual nanotubes.
 In sharp contrast to unprocessed shortened SWNTs of the prior art which are
 insoluble in organic solvents, the processed shortened SWNTs of the
 present invention include long alkyl chains that provide substantial
 solubility in tetrahydrofuran, chloroform and aromatic solvents such as
 benzene, toluene, chlorobenzene, 1,2 dichlorobenzene and ether. The
 black-colored or unsaturated solution of s-SWNTs is visually non
 scattering, and no precipitation is observed upon prolonged standing. Like
 fullerenes, the s-SWNTs are insoluble in water, ethanol and acetone. The
 IR spectrum of soluble s-SWNTs indicates the formation of the amide bond:
 .nu..sub.C.dbd.O =1663 cm.sup.-1 and 1642 cm.sup.-1.
 The following examples are presented to further illustrate the invention,
 but it is not to be considered as limited thereto.
 EXAMPLE 4
 Preparation of s-SWNT-COO.sup.-, .sup.+ NH.sub.3 (CH.sub.2).sub.17 CH.sub.3
 0.22 grams of shortened SWNTs were heated in excess octadecylamine (0.5 g)
 for four days. After cooling to room temperature, the excess amine was
 removed by washing with EtOH 4 times (5-10 minutes sonication). The
 remaining solid was dissolved in THF, and filtered. The black-colored
 solution was taken to dryness at room temperature on a rotary evaporator
 to give 0.14 g of solid product.
 Thus, we completed a simple acid-base reaction and produced a zwitterion.
 The resulting SWNTs were soluble in tetrahydrofuran. The near-IR of the
 s-SWNTs produced in this method (FIG. 2) show peaks at 10268, 9690, and
 9112 cm.sup.-1 (1.27, 1.20 and 1.13 eV) for the metallic band transitions,
 and a peak at 5389 cm.sup.-1 (0.67 eV) for the semi-conducting band
 transitions. The amine is associated with the SWNT via an ionic bond and
 this is reflected in the mid-IR, which shows a peak at 1579 cm.sup.-1 due
 to the carboxylate anion stretch mode. The NMR of the sample is very
 broad, with peaks at .delta.0.87 (CH.sub.3), 1.21 (CH.sub.2), and 3.49
 (.alpha.-CH.sub.2). The s-SwNT-COO.sup.-, .sup.+ NH.sub.3
 (CH.sub.2).sub.17 CH.sub.3 were found to be soluble in THF but not soluble
 in CH.sub.2 Cl.sub.2 and CS.sub.2. This may be due to the hydrogen bonding
 that can occur between THF and the primary ammonium salt.
 EXAMPLES 5-15
 The procedures of Example 4 are completed except that nonylamine,
 dodecylamine, pentacosylamine, tetracontylamine, pentacontylamine,
 4-pentylaniline, 4-dodecylaniline, 4-tetradecylaniline,
 4-pentacosylaniline, 4-tetracontylaniline or 4-pentacontylaniline is
 substituted for octadecylamine.
 EXAMPLE 16
 A mixture of polished, shortened SWNTs and excess long-chain amine was
 heated at 70-140.degree. C. for 72-240 hours. The excess long-chain amine
 was removed by repeated washing with ethyl alcohol. The remaining solid
 was dissolved in tetrahydroJuran, and after filtration, the black-colored
 filtrate was concentrated on a rotary evaporator. Ethyl alcohol was added
 to the resulting concentrated solution to precipitate the SWNTs. After
 membrane filtration, the black solid was washed with ethyl alcohol and
 dried at room temperature under reduced pressure (70-90% yield based on
 polished, shortened SWNTs).
 EXAMPLE 17
 A mixture of shortened SWNTs and excess long-chain amine was heated at
 70-140.degree. C. for 72-240 hours. The excess long-chain amine was
 removed by repeated washing with ethyl alcohol. The remaining solid was
 dissolved in tetrahydrofuran, and after filtration, the black-colored
 filtrate was concentrated on a rotary evaporator. Ethyl alcohol was added
 to the resulting concentrated solution to precipitate the SWNTs. After
 membrane filtration, the black solid was washed with ethyl alcohol and
 dried at room temperate under reduced pressure (70-90% yield, based on
 polished, shortened SWNTs).
 EXAMPLE 18
 A mixture of polished, shortened SWNTs and excess long-chain amine was
 heated at 70-140.degree. C. for 72-240 hours. The excess long-chain amine
 was removed by repeated washing with ethyl alcohol. The remaining solid
 was dissolved in tetrahydrofuran, and after filtration, the black-colored
 filtrate was concentrated on a rotary evaporator. Ethyl alcohol was added
 to the resulting concentrated solution to precipitate the SWNTs. After
 membrane filtration, the black solid was washed with ethyl alcohol and
 dried at room temperature under reduced pressure (70-90% yield, based on
 polished shortened SWNTs).
 EXAMPLE 19
 A mixture of shortened SWNTs and excess long-chain amine was heated at
 70-140.degree. C. for 72-240 hours. The excess long-chain amine was
 removed by repeated washing with ethyl alcohol. The remaining solid was
 dissolved in tetrahydrofuran, and after filtration, the black-colored
 filtrate was concentrated on a rotary evaporator. Ethyl alcohol was added
 to the resulting concentrated solution to precipitate the SWNTs. After
 membrane filtration, the black solid was washed with ethyl alcohol and
 dried at room temperature under reduced pressure (40-70% yield, based on
 polished, shortened SWNTs).
 In summary, the method of the present invention includes the preparation of
 solutions of naked carbon metals and semiconductors in organic solutions
 including both ionic (charge transfer) and covalent solution phase
 chemistry with concomitant modulation of the SWNT band structure. It is
 now possible to obtain well-characterized, highly purified SWNT materials
 which are suitable for physical property measurements. The s-SWNTs will
 have a rich chemistry at their ends, the exterior walls and the interior
 cavity. s-SWNTs are versatile precursors to copolymer materials with
 distinctive mechanical and electrical properties and as new ligands for
 metal complexation.
 The foregoing description of a preferred embodiment of the invention has
 been presented for purposes of illustration and description. It is not
 intended to be exhaustive or to limit the invention to the precise form
 disclosed. Obvious modifications or variations are possible in light of
 the above teachings. For example, while the preferred embodiment teaches
 that the SWNTs are to be purified, shortened and polished in accordance
 with the procedure for these steps set out above to increase the purity
 and yield of the desired final product, the purifying, shortening and
 polishing steps are merely preferred and not mandatory. In fact, raw SWNTs
 may be processed in accordance with the present invention. The embodiment
 was chosen and described to provide the best illustration of the
 principles of the invention and its practical application to thereby
 enable one of ordinary skill in the art to utilize the invention in
 various embodiments and with various modifications as is suited to the
 particular use contemplated. All such modifications and variations are
 within the scope of the invention as determined by the appended claims
 when interpreted in accordance with the breadth to which they are fairly,
 legally and equitably entitled.