Patent Publication Number: US-2007118937-A1

Title: Copolymerization and copolymers of aromatic polymers with carbon nanotubes and products made therefrom

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This Application is a Continuation-ln-Part of U.S. patent application Ser. No. 10/972,560, filed Oct. 25, 2004, which itself claims priority benefit to U.S. Provisional Patent Application Ser. No. 60/514,186, filed Oct. 24, 2003. Both of said Applications to which this Application relates are hereby incorporated by reference herein in their entirety-to the extent not inconsistent herewith. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates generally to carbon nanotube materials. More specifically, the invention relates to block copolymers comprising aromatic polymer blocks and short carbon nanotube blocks.  
     BACKGROUND OF THE INVENTION  
      Carbon nanotubes (CNTs), comprising multiple concentric shells and termed multi-wall carbon nanotubes (MWNTs), were discovered by lijima in 1991 [lijima,  Nature  1991, 354, 56-58]. Subsequent to this discovery, single-wall carbon nanotubes (SWNTs), comprising single graphene sheets rolled up on themselves to form cylindrical tubes with nanoscale diameters, were synthesized in an arc-discharge process using carbon electrodes doped with transition metals [lijima et al.,  Nature  1993, 363, 603-605; and Bethune et al.,  Nature  1993, 363, 605-607]. These carbon nanotubes (especially SWNTs) possess unique mechanical, electrical, thermal and optical properties, and such properties make them attractive for a wide variety of applications. See Baughman et al.,  Science,  2002, 297, 787-792.  
      The incorporation of CNTs into polymer matrices is currently an area of considerable interest, as CNTs can impart unique properties to the composite or blended material. See, e.g., Mitchell et al.,  Macromolecules,  2002, 35, 8825-8830; and Zhu et al., Nano. Lett., 2003, 3,1107-1113. In some cases, CNTs have been covalently integrated into such polymeric hosts.  
      Another area of interest is CNT-containing fibers. In some reports, such fibers comprise a polymer matrix, whereas in other cases they are largely CNTs. In such later cases, CNT fibers have been spun from CNT suspensions in poly(vinylalcohol) [Vigolo et al.,  Science,  2000, 290, 1331-1334] and intercalating acids [Zhou et al., J. Appl. Phys., 2004, 95, 649-655; and Ericson et al., Science, 2004, 305, 1447-1450].  
      In light of the above-described advances in carbon nanotube science, new polymeric systems into which CNTs have been integrated into will continue to expand the range of applications with which they can be associated.  
     BRIEF DESCRIPTION OF THE INVENTION  
      The present invention is generally directed to the block copolymerization of aromatic polymers with carbon nanotubes (CNTs). Such block copolymers, having a CNT block component and an aromatic polymer block component, are referred to herein as “nanotube block copolymers.” The present invention is also directed to fibers and other shaped articles made from these nanotube block copolymers of the present invention.  
      In some embodiments, the CNT block component is a single-wall carbon nanotube (SWNT). Typically, such SWNTs are first cut with a cutting process to provide short SWNTs, then (or simultaneously) end functionalized with moieties capable of coupling to the aromatic polymer block component. However, to the extent that suitably short SWNTs can be synthesized directly and suitably end-functionalized, such cutting is not required.  
      In some embodiments, the aromatic polymer (block) is a polybenzazole (PBZ). Block copolymers of the present invention comprising SWNTs and PBZ components are referred to herein as “SWNT/PBZ block copolymers.” In some such embodiments, the PBZ block is polybezoxazole (PBO), giving rise to “SWNT/PBO block copolymers.” 
      In some embodiments, the aromatic polymer is a aromatic polyamide. In some embodiments, the aromatic polyamide polymer is poly(p-phenylene terephthalamide) (PPTA). Block copolymers of the present invention comprising SWNTs and PPTA components are referred to herein as “SWNT/PPTA block copolymers.” 
      Such above-described aromatic polymer blocks are typically (but not necessarily) ridged rod polymers. Other suitable aromatic polymer blocks include aromatic polyimides, aromatic polyesters, and aromatic heterocyclic polymers.  
      In some embodiments, both the cutting of the SWNTs (to produce shortened SWNTs) and the coupling of the shortened SWNTs to aromatic polyamides enhances the solubility and processability of SWNTs in aprotic solvents, strong acid solvents, and other solvents. Additionally, the use of aromatic polymers, and particularly aromatic polyamides, in such block copolymers is advantageous in that it is both economical and preserves mechanical properties intrinsic to the SWNTs.  
      The foregoing has outlined rather broadly the features of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  depicts a single-wall carbon nanotube (SWNT)/polybezoxazole (PBO) copolymer, in accordance with some embodiments of the present invention;  
       FIG. 2  depicts a SWNT/poly(p-phenylene terephthalamide) (PPTA) copolymer, in accordance with some embodiments of the present invention;  
       FIG. 3  (Scheme 4) schematically depicts the preparation of p-phenylene benzobisoxazole 15 mers (15-mer PBO), in accordance with embodiments of the present invention;  
       FIG. 4  (Scheme 5) schematically depicts the preparation of p-phenylene benzobisoxazole 45 mers (45-mer PBO), in accordance with some embodiments of the present invention;  
       FIG. 5  (Scheme 6) depicts sidewall functionalization of short SWNTs with sulfanilic acid in oleum, in accordance with some embodiments of the present invention;  
       FIGS. 6A  and 6B are atomic force microscopy (AFM) images of SWNTs before (6A) and after (6B) undergoing the functionalization depicted in Scheme 6;  
       FIG. 7  (Scheme 7) schematically depicts copolymerization of short SWNTs and PBO 15 mers, in accordance with some embodiments of the present invention;  
       FIG. 8  (Scheme 8) schematically depicts the copolymerization of short functionalized SWNTs and PBO 15 mers, in accordance with some embodiments of the present invention;  
       FIG. 9  depicts Raman spectra (633 nm excitation) of SWNT/PBO copolymer films synthesized in dilute concentration, where trace (a) depicts copolymerized product (No.1, Table 1) from short SWNTs and PBO 15 mers at the weight ratio of 67/33 (0.36 wt. % concentration); and where trace (b) depicts PBO 15 mers;  
       FIG. 10  depicts Raman spectra (633 nm excitation) of SWNT/PBO copolymer film prepared in higher concentration, where trace (a) depicts copolymerized product from short SWNTs/PBO 15 mers (No. 4, Table 1); and where trace (b) depicts benzenesulfonic acid-functionalized short SWNTs/PBO 15 mers (No. 5, Table 1) at the concentration of 3.3 wt. %;  
       FIG. 11  depicts infrared (ATR-IR) spectra of variously-prepared polymer films; where trace (a) depicts benzenesulfonic acid-functionalized short SWNTs; where trace (b) depicts PBO 15 mers; and where trace (c) depicts copolymerized product (No. 5, Table 1) of benzenesulfonic acid-functionalized short SWNTs/PBO 15 mers at the concentration of 3.3 wt %;  
       FIGS. 12A-12D  are AFM images of a 2 mg sample/10 cc methanesulfonic acid (MSA) solution spun onto a silicon disk and vacuum dried at 100° C overnight; wherein  FIGS. 12A  (height) and  12 B (amplitude) are the height and amplitude images, respectively, depicting a physical mixture of functionalized short SWNTs and PBO 15 mers at weight ratio of 49/51; and wherein  FIGS. 12C  (height) and  12 D (amplitude) are the height and amplitude images, respectively, depicting a copolymerized product (No. 5, Table 1) from functionalized short SWNTs and PBO 15 mers at weight ratio of 49/51;  
       FIG. 13  (Scheme 9) schematically depicts the copolymerization of short SWNTs and PBO 45 mers, in accordance with some embodiments of the present invention;  
       FIG. 14  (Scheme 10) schematically-depicts the copolymerization of short, sidewall-functionalized SWNTs and PBO 45 mers, in accordance with some embodiments of the present invention;  
       FIG. 15  depicts Raman spectra of SWNTs/PBO copolymer film (633 nm excitation); wherein trace (a) depicts copolymerized product from PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs (No. 7, Table 2); and wherein trace (b) depicts copolymerized product from PBO 45 mers and short SWNTs (No. 6, Table 2);  
       FIG. 16  depicts Raman spectra of SWNTs/PBO copolymer film (780 nm excitation); wherein trace (a) depicts copolymerized product from PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs (No. 7, Table 2); and wherein trace (b) depicts copolymerized product from PBO 45 mers and short SWNTs (No. 6, Table 2);  
       FIG. 17  depicts Raman spectra of SWNTs/PBO copolymer films (514 nm excitation); wherein trace (a) depicts copolymerized product from PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs (No. 7, Table 2); and wherein trace (b) depicts copolymerized product from PBO 45 mers and short SWNTs (No. 6, Table 2);  
       FIG. 18  depicts a conventional dry-jet wet spinning process, in accordance with some embodiments of the present invention;  
       FIGS. 19A and 19B  are scanning electron microscopy (SEM) images of a PBO 45 mer fiber (19A) and a copolymer (No. 8, Table 2) fiber of PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs at the weight ratio of 90/10 (19B);  
       FIG. 20  depicts blending of high molecular weight PBO and copolymer of short SWNTs and PBO useful in the fiber spinning of SWNTs/PBO fibers, in accordance with some embodiments of the present invention;  
       FIG. 21  (Scheme 11) schematically depicts the synthesis of PPTA with amine groups at both ends, in accordance with some embodiments of the present invention; and  
       FIG. 22  (Scheme 12) schematically depicts the copolymerization of short SWNTs and PPTA, in accordance with some embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      In the following description, specific details are set forth such as specific quantities, sizes, etc. so as to provide a thorough understanding of embodiments of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In many cases, details concerning such considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art.  
      The present invention is generally directed to the block copolymerization of aromatic polymers with carbon nanotubes (CNTs). Such block copolymers, having a CNT block component and an aromatic polymer block component, are referred to herein as “nanotube block copolymers.” The present invention is also directed to fibers and other shaped articles made from these nanotube block copolymers of the present invention.  
      Block copolymers are polymers that comprise polymer or oligomer chains of one type of polymer that are connected with polymer or oligomer chains of one or more other types of polymers. Such polymerization leads to polymer chains having structures like that of the following di-block copolymer:
 
--AAAAAAAAAAAAAAAAA-BBBBBBBBBBBBBBBB--
 
      or tri-block copolymer:
 
--AAAAAAAAAAA-BBBBBBBBBBB-AAAAAAAAAA--,
 
      where “A” is a repeat unit (i.e., a “mer”) for a first polymer block, and “B” is a repeat unit for a second polymer block. An example of a common block copolymer is poly(styrene-butadiene-styrene), or SBS.  
      In the case of the nanotube block copolymers of the present invention, at least one of the polymer blocks is a carbon nanotube (itself an all-carbon rigid polymer) and at least one of the blocks is an organic-based aromatic polymer or oligomer. For the purposes of this discussion, oligomers are merely short polymer chains and reference to polymer block components hereinafter as polymers will be understood to include oligomers. While the block copolymers of the present invention, referred to herein as nanotube block copolymers, generally comprise at least one CNT block and at least one aromatic polymer block, they may comprise blocks of other types as well.  
      In some embodiments, because of the possibility of multiple coupling (i.e., attachment) sites on the side-walls of the CNTs and/or the CNT ends, one or both ends of the CNTs may be coupled to multiple aromatic polymer blocks.  
      CNTs, according to the present invention, include, but are not limited to, single-wall carbon nanotubes (SWNTs), multi-wall carbon nanotubes (MWNTs), double-wall carbon nanotubes (DWNTs), small-diameter (&lt;3nm) carbon nanotubes (SDCNTs), buckytubes, fullerene tubes, tubular fullerenes, graphite fibrils, and combinations thereof. Such carbon nanotubes can initially be of a variety and range of lengths, diameters, number of tube walls, chiralities (helicities), etc., and can generally be made by any known technique. The terms “carbon nanotube” and “nanotube” will be used interchangeably herein. Such CNTs are often subjected to one or more purification steps [see, e.g., Chiang et al.,  J. Phys. Chem. B,  2001, 105, 1157-1161; Chiang et al.,  J. Phys. Chem. B  2001, 105, 8297-8301]. In some embodiments, the CNTs are cut by one or more cutting techniques [see, e.g., Liu et al.,  Science,  1998, 280, 1253-1256; and Gu et al.,  Nano Lett.,  2002, 2, 1009-1013].  
      In some embodiments, the aromatic polymer blocks are polybenzazoles (PBZ) or other aromatic polymers. PBZs have the general formula:  
                 
 
      Other suitable such polymer blocks are cis- and trans-polybezoxazole (PBO):  
                 
 
 and cis- and trans- poly-p-phenylenebisbenzthiozole (PBT):  
                 
 
 and poly-2,5-(benzoxazole) (ABPBO):  
                 
 
      In some embodiments, SWNT blocks are coupled to aromatic polymer blocks via a condensation reaction to form “SWNT block copolymers.” In some embodiments, the aromatic polymer (block) is a polybenzazole (PBZ). Block copolymers of the present invention comprising SWNTs and PBZ components are referred to herein as “SWNT/PBZ block copolymers.” In some such embodiments, the PBZ block is polybezoxazole (PBO), giving rise to “SWNT/PBO block copolymers.” 
      In some embodiments, the aromatic polymer blocks are aromatic polyamides or other aromatic polymers. Such aromatic polyamides have the general formula:
 
—[—NH—Ar—NH—CO—Ar—CO—] n —or —[—NH—Ar—CO—] n —
 
 where “n” is an integer indicative of the number of respective repeat units. 
 
      For the above aromatic polyamide polymers, suitable aromatic units, -Ar-, include, but are not limited to, 1,4-phenylene; 4,4′-biphenyly; 2,6-naphthylene; 1,5-naphthylene; N,N′-piperazine; 1,3,4-oxadiazol; phenylbenzimide; 1,4-xylylene; 2,5-pyridylene; and combinations thereof. The aromatic units may comprise pendant groups such as, but not limited to, alkyl, halogen, alkoxy, cyano, acetyl, nitro, and the like. Aromatic polyamides may also comprise bridging units between the aromatic units. Suitable such bridging units include, but are not limited to, ether, sulfide, sulfone, ketone, amine, ethylene, azo, ester, diazo and other like linkages.  
      Other suitable aromatic polymer polymer blocks include aromatic polyimides, aromatic polyesters, and aromatic heterocyclic polymers.  
      As mentioned above, in some embodiments, SWNT blocks are coupled to aromatic polymer blocks via a condensation reaction to form “SWNT block copolymers.”In some such embodiments, these aromatic polymer blocks are poly(p-phenylene terephthalamide) (PPTA). Block copolymers of the present invention comprising SWNTs and PPTA components are referred to herein as “SWNT/PPTA block copolymers.” 
      In some embodiments, short SWNTs are covalently bonded to PPTA, other aromatic polyamides, or other aromatic polymers of finite length, to improve the solubility of SWNTs in aprotic solvents, mineral acids, or other solvents, and to prevent the formation of aggregates (ropes) of SWNTs.  
      In some embodiments, the spinning or casting of the above-mentioned SWNT/PBZ copolymers and/or SWNT/PPTA copolymers can be carried out from liquid crystalline solutions at higher concentrations than previously possible. This affords a more effective coagulation process and easy alignment of nanotube block copolymers during the spinning or casting process.  
      In some embodiments, the coupling of aromatic polymers (e.g., PBZ or PPTA) to short SWNTs improves the strength (“leg”) of spinning or casting solutions due to stronger interaction between polymer molecules over that of neat SWNT solutions. This can improve shaping processes and lead to shaped articles with ultra-high performance properties afforded by SWNTs.  
      In some embodiments, the present invention is directed to the synthesis of (i.e., methods of making) block copolymers comprising short SWNTs and aromatic polyamide blocks and/or other aromatic polymer blocks; fibers and other compositions containing these block copolymers; processes for making shaped articles from these block copolymers comprising aromatic polymer blocks and SWNT blocks; and shaped articles made by these processes.  
      In some embodiments, the present invention is directed toward physical blends of any of the above-described nanotube block copolymers with their corresponding homopolymers; fibers and other compositions containing these blends; processes for making shaped articles from these blends comprising blockpolymers of SWNT and aromatic polymers and the corresponding aromatic polyamide; and shaped articles made by these processes.  
      In some embodiments, methods for making nanotube block copolymers comprise a cutting and end-functionalizing of SWNTs, followed by reaction with suitably functionalized aromatic polymer blocks.  
      The synthesis of functionalized short SWNTs, according to some embodiments of the present invention, is shown below in Scheme 1:  
                 
 
      Referring to Scheme 1, SWNTs (1) are first cut in an oxidative acid (e.g., HNO 3 ) or acid mixture (e.g., piranha) to yield short SWNTs bearing carboxyl species (e.g., —COOH groups) on their open ends and/or on their side-walls (2). Such carboxyl species can then be converted to acyl chloride species (—COCI) by reaction with thionyl chloride (SOC1 2 ) to yield (3). Such above-described chemistry is known in the art. See, e.g., Liu et al.,  Science,  1998, 280, 1253-1256; and Chen et al.,  Science,  1998, 282, 95- 98   
      In some embodiments of the present invention, short SWNTs are used to enhance the solubility of the SWNT blocks in aprotic solvents such as N-methyl-2-pyrrolidone (NMP), dimethyl acetamide (DMAc), N,N-dimethylformamide (DMF), 1,3 dimethyl-2-imidazolidinone (DMI), dimethylsulfoxide (DMSO), and the like, or in strong acids such as, but not limited to, sulfuric acid, oleum (fuming sulfuric acid which is H 2 SO 4  with dissolved S03 to remove trace water), methanesulfonic acid (MSA), and the like. Similarly, the short functionalized SWNT-COOH and SWNT-COCI will have improved solubility in the above mentioned aprotic solvents or strong acids. The enhanced solubility of short SWNTs and their functionalized counterparts affords the advantage of SWNTs being processed (fibers spun or films cast) at higher SWNT concentrations in aprotic solvents or in strong acids. The shaped articles, fibers or films, will generally have greater overall mechanical strength due to the more effective process of coagulation and the enhanced orientability of SWNTs in these higher concentrated solutions.  
      As mentioned above, in some embodiments of the present invention, short SWNTs, generally with length of less than about 1000 nm, typically less than 100 nm, and more typically 5-50 nm, are used. Typically, such individual SWNTs have diameters of about 1 nm. Accordingly, some embodiments of the present invention use SWNTs with aspect ratios (defined as the length divided by diameter) of less than about 1000; typically less than 100; and more typically between 5-50. Likewise, the functionalized SWNTs have aspect ratios generally less than about 1000, typically less than 100, and more typically between 5 and 50.  
      In some embodiments, the functionalized group (i.e., chemical moiety) on the SWNT ends, shown as —COOH and/or —COCI in Scheme 1, is an electron-deficient carbon group, but can generally be any group containing a carbon atom that can react in the aprotic solvents or mineral acids with the amine moiety at the end(s) of aromatic polymers to form amide linkages between the SWNT and aromatic polymer blocks. Suitable electron-deficient groups include, but are not limited to, carboxylic acids, acid halide, metal carboxylate salts, cyano groups and trihalomethyl groups. Halogens in such electron-deficient carbon groups are typically fluorine, chlorine, or bromine, and more typically chlorine.  
      A synthesis of amine-terminated aromatic polymer blocks such as PPTA is shown below in Scheme 2, where an amide-forming moiety (4) is reacted with a species comprising an electron-deficient carbon moiety (5) to yield an amine-terminated aromatic polyamide (6), in accordance with some embodiments of the present invention.  
                 
 
      Referring to Scheme 2, suitable aromatic units, -Ar-, include, but are not limited to, 1,4-phenylene; 4-4′-biphenyl; 2,6-naphthylene; 1,5-naphthylene; N,N′-piperazine; 1,3,4-oxadiazol; phenylbenzimide; 1,4-xylylene; 2,5-pyridylene; and the like. Such aromatic units may comprise pendant groups such as, but not limited to, alkyl, halogen, alkoxy, cyano, acetyl, nitro, and the like. Aromatic polyamides may also comprise bridging units between the aromatic units. Suitable such bridging units include, but are not limited to, ether, sulfide, sulfone, ketone, amine, ethylene, azo, and other like linkages.  
      Referring again to Scheme 2, n can generally be as low as 2 and as high as practically feasible (e.g., 2000). Typically, n is about 5 to 100, and more typically between 5 and 50. In the above Scheme 2, the amide-forming moiety (4) is a p-amino-basic moiety which is bonded to an aromatic group comprising a primary amine group bonded to the aromatic group. The other reactant (5) in the above reaction comprises an electron-deficient carbon group. As mentioned above, this carbon group can be any group containing a carbon atom that can react in the aprotic solvents or mineral acid with an amino-basic moiety to form an amide. Suitable electron-deficient carbon groups include, but are not limited to, carboxylic acids, acid halides, metal carboxylate salts, cyano groups and trihalomethyl groups. Halogens in electron-deficient carbon groups are typically fluorine, chlorine, or bromine, and more typically chlorine.  
      The solvents used in the above reaction can be any aprotic solvents or mineral acid or their mixtures capable of dissolving the polymerizing reactants and aromatic polyamide polymers. The above acids and mixtures may also comprise P 2 0 5 .  
      A key aspect of the present invention is the block copolymerization of short, functionalized SWNTs (as shown in Scheme 1) with amine-terminated aromatic polymer blocks (as shown in Scheme 2) in aprotic solvents such as NMP, DMAc, etc. or in strong mineral acids capable of dissolving both reactants without any detrimental reaction or degradation of the reactants. An exemplary copolymerization reaction is shown in Scheme 3 below, where shortened functionalized SWNTs (3) are reacted with amine-terminated aromatic polyamides (6) to yield SWNT/aromatic polyamide block copolymer (7).  
                 
 
      In some such above-described embodiments, the reaction is carried out in an aprotic solvent, such as NMP with CaCI 2 , and optionally with a condensate agent. Additionally, the reaction may optionally be carried out with an excess of amine-terminated aromatic polyamide relative to the short functionalized SWNT.  
      In the above embodiments directed toward the formation of SWNT/aromatic polyamide block copolymers in aprotic solvent, the total concentration of the two reactants in the solvent (i.e., the short functionalized SWNTs and the aromatic polyamide blocks) is dependent upon the length of both of the block components. Generally, the concentration should be controlled and optimized such that the solution will have maximum concentration and minimum bulk viscosity for ease of processing, such as in fiber spinning or film casting. Dependent upon the concentration, the resultant copolymer solution can be optically isotropic or optically anisotropic, the latter of which can be liquid crystalline in form and probably nematic. Although the reaction between (3) and (6) in Scheme 3 shows the formation of an aromatic polyamide-SWNT-aromatic polyamide tri-block copolymer (7, wherein the SWNTs are themselves blocks), the reaction can be tailored to form di-block or random block copolymers of SWNT with aromatic polyamide, dependent upon the level and arrangement of —COOH, or —COCI groups on the SWNT, i.e., how many —COOH moieties are bonded to each SWNT, and which end or both ends, or even on the side-walls of the SWNTs that the —COOH moieties are bonded to, and the functionality at the ends of the aromatic polyamide reactant.  
      For the above-described SWNT/aromatic polyamide block copolymers of the present invention, the product compositions typically range from between about 5/95 SWNT/aromatic polyamide (wt/wt %) to 95/5 SWNT/aromatic polyamide (wt/wt %). In some embodiments, it is desirable to have as high a content of SWNT as possible.  
      Advantages of block copolymerizing aromatic polymers with SWNTs include minimal compromise in the resulting materials&#39; ultimate performance, as well as the economics and current understanding of aromatic polymer systems, i.e., they are relatively inexpensive, commercially available, and the fiber spinning of aromatic polymer systems like PBZ and PPTA is well known. Additionally, they are soluble in acid solvents.  
      Other aspects of the present invention are processes of shaping the above solutions/compositions (i.e., Scheme 3) into useful articles such as fibers or films. In some embodiments, fibers made by the nanotube block copolymer compositions of the present invention have superior mechanical properties; superior chemical, thermal, thermo-oxidative, and dimensional stability; ultra-light weight; and unique electrical/electro-magnetic properties suitable for structural application as the fiber component of advanced composites for aerospace and space vehicles. Other utility can be found in electronic and electrical applications, and also important utility in protective body (personal, vehicular, structural) armor. The above-mentioned properties can surpass those of state of the art organic fibers such as ZYLON (Zylon® is a registered trademark of Toyobo Co., Ltd., Osaka, Japan), KEVLAR (Kevlar® is a registered trademark of E.l. du Pont de Nemours and Co., Wilmington, Del.), and TWARON (Twaron® is a registered trademark of Teijin Twaron B.V. Ltd., Arnhem, Netherlands) for example, or other advanced carbon fibers currently being used in the above-mentioned applications.  
      The current art of spinning fibers of neat SWNTs (with indiscriminate lengths) or casting neat SWNT films has had limited success with regard to fully realizing the potential of SWNTs [Ericson et al.,  Science,  2004, 304, 1447-1450]This is partly due to the low solubility of SWNTs in common organic or mineral acid solvents, and the intractability of SWNT ropes, i.e., aggregates of individual SWNT, readily formed during or before the dissolution process. Also, the current art of spinning composite SWNT fibers from solutions of physical mixtures of SWNTs of indiscriminate lengths (as opposed to the cut, shortened SWNTs used in some embodiments of the present invention) with other polymers, including PBO and PPTA, has had limited success due to the relatively low level of dispersability of SWNTs in these polymers.  
      The present invention teaches, in part, the covalently bonding of short (e.g., shortened) SWNTs with aromatic polymers of finite length. The shorter length improves the solubility of SWNTs in aprotic solvents, mineral acids, and other solvents, and minimizes the formation of aggregates (ropes) of SWNTs. Furthermore, aromatic polymers like PBZ and PPTA are readily soluble in such above-described aprotic solvents and acids and can impart the short SWNTs with increased solubility (and processability) when covalently attached to the short SWNTs in the form of a block copolymer. Consequently, the spinning or casting of SWNT-based nanotube block copolymers can be carried out with liquid crystalline solutions at higher concentrations which afford a more effective coagulation process and easy alignment of, e.g., SWNT/aromatic polyamide copolymers during the spinning process. Also, in some embodiments, the incorporation of aromatic polyamide with SWNT can improve the strength (“leg”) of the spinning or casting solutions due to stronger interaction between molecules. This generally improves the shaping process and generally leads to shaped articles with ultra-high performance properties afforded by SWNT.  
      The following examples are provided to more fully illustrate some of the embodiments of the present invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follows represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute exemplary modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.  
     EXAMPLE 1  
      While not intending to be bound by theory, this Example serves to illustrate, by virtue of Halpin-Tsai equations, the reinforcing efficiency and therefore, the benefit of incorporating short SWNTs into aromatic polymer block copolymer materials. For:  
               E   c     =       ⁢       (       (     1   +     a   ⁢           ⁢     μυ   f         )     /     (     1   -     μυ   f       )       )     ⁢     E   m                       ⁢     a   ∼     2   ⁢     (     l   /   d     )                     μ   =       ⁢       (         E   f     /     E   m       -   1     )     /     (         E   f     /     E   m       +   a     )                 
 
      Where:  
      Ec=Young&#39;s modulus of composite fiber  
      Em=Young&#39;s modulus of matrix (e.g., PPTA)  
      Ef=Young&#39;s Modulus of SWNT  
      I=length of SWNT, d=diameter of SWNT  
      a=2*(aspect ratio of SWNT)  
      νf=volume fraction of SWNT  
      νm=volume fraction of PPTA.  
      The reinforcement efficiency of SWNT is defined as: RE=E c /(E f ν f +E m ν m ) and (E f ν f +E m ν m ) represents the ultimate linear rule-of-mixture modulus of a uniaxially oriented composite. Thus, for a 50/50 v/v % SWNT/PPTA composite fiber, the calculated RE, using the above equations, is 1 (or 100% reinforcement efficiency) for SWNTs with aspect ratio of 32 and E f /E m  of 10. On the other hand, when a softer matrix is used, e.g., E f /E m =50, it would require the aspect ratio of SWNTs to be at least 200 in order to achieve 95% of reinforcement efficiency. This simply means that with a rigid matrix such as PPTA, very short SWNTs can be utilized as reinforcement without any degradation in reinforcement efficiency.  
     EXAMPLE 2  
      This Example serves to illustrate the preparation of p-phenylene benzobisoxazole 15 mers, in accordance with some embodiments of the present invention.  
      Referring to Scheme 4 ( FIG. 3 ), 4.4765 g (21.01 mmol) of diaminoresorcinol dihydrochloride and 4.0 g (19.70 mmol) terephthaloyl chloride were added to a solvent mixture of 33.1529 g of polyphosphoric acid (84.5% as P 2 0 5 ) and 0.4331 9 of P 2 0 5  (total P 2 0 5  content in mixture =84.7 wt. %) to yield a reaction mixture. The reaction mixture underwent a dehydrochlorination step at 45° C. for 16 hours; whereas an oligomerization step was carried out at 95° C. for 8 hours, 150° C for 16 hours, and 190° C. for 24 hours. This yielded a p-phenylene benzobisoxazole oligomer with an inherent viscosity of 1.96 dL/g.  
     EXAMPLE 3  
      This Example serves to illustrate the preparation of p-phenylene benzobisoxazole 45 mers, in accordance with some embodiments of the present invention.  
      Referring to Scheme 5 ( FIG. 4 ), 6.5 g (30.51 mmol) of diaminoresorcinol dihydrochloride and 6.0593 g (29.85 mmol) terephthaloyl chloride were added to a solvent mixture of 48.9445 g of polyphosphoric acid (84.5% as P 2 0 5 ) and 0.64 g of P 2 0 5  (total P 2 0 5  content in mixture =84.7 wt. %) to yield a reaction mixture. The reaction mixture underwent a dehydrochlorination step at 45° C. for 16 hours; whereas an oligomerization step was carried out at 95° C. for 8 hours, 150° C. for 16 hours, and 190° C. for 24 hours. This yielded a p-phenylene benzobisoxazole oligomer (45 mer) with an inherent viscosity of 7.06 dL/g.  
     EXAMPLE 4  
      This Example serves to illustrate sidewall functionalization of short SWNTs with sulfanilic acid in oleum, in accordance with some embodiments of the present invention. Such functionalization is generally described in the following commonly-assigned international patent application: Tour et al., “Functionalization of Carbon Nanotubes in Acidic Media,” Serial No. PCT/US05/09677 (Publication No. W02005113434), filed Mar. 24, 2005.  
      Referring to Scheme 6 ( FIG. 5 ), 250 mg (20.81 mmol) of short (ca. 60 nm) SWNTs were reacted with 14.4163 g (20.81×4 mmol) of sulfanilic acid in a reaction mixture comprising 100 mL H 2 SO 4  (fuming, 20% free S0 3 ), 5.7436 g (20.81×4 mmol) sodium nitrite, and 683 mg (20.81×0.2 mol) 2,2′-azobisisobutyronitrile (AIBN). This yielded water-soluble, sidewall-functionalized short SWNTs, as shown in Scheme 6.  
      The sidewall-functionalized short SWNTs were characterized by UV-vis spectroscopy as being devoid of van Hove singularities  FIGS. 6A and 6B  are atomic force microscopy (AFM) images of the short SWNTs before ( FIG. 6A ) and after ( FIG. 6B ) the above-described functionalization. The AFM images show that the short SWNTs were exofoliated into individuals and small bundles by the sidewall-functionalization.  
     EXAMPLE 5  
      This Example serves to illustrate the copolymerization of short SWNTs and PBO 15 mers, in accordance with some embodiments of the present invention.  
      Referring to Scheme 7 ( FIG. 7 ), 0.2 g of a polyphosphoric acid (PPA) solution of p-phenylene benzobisoxazole 15 mer (the solution comprising 25 mg of PBO 15 mer) was combined with a suspension comprising 50 mg of short (ca. 60 nm) SWNTs, 10 g MSA, 10 g PPA (84.5% as P 2 0 5 ), and 0.15 g of P 2 0 5 . This was allowed to react at 100° C. for 3 days to yield a SWNT/PBO 15 mer block copolymer, as depicted in Scheme 7.  
     EXAMPLE 6  
      This Example serves to illustrate the copolymerization of short sidewall-functionalized SWNTs and PBO 15 mers, in accordance with some embodiments of the present invention.  
      Referring to Scheme 8 ( FIG. 8 ), 0.4 g of a PPA solution of p-phenylene benzobisoxazole 15 mer (comprising 50 mg of PBO 15 mer) was combined with 36 mg of short (ca. 60 nm) benzenesulfonic acid-functionalized SWNTs (see, e.g., EXAMPLE 4) in a reaction mixture further comprising 10 g of MSA, 10 g PPA, and 1.0 g P 2 O 5 . The reaction mixture was then heated at 100° C for 3 days to yield short sidewall-functionalized SWNT/PBO 15 mer block copolymers, as depicted in Scheme 8.  
     EXAMPLE 7  
      This Example serves to illustrate Raman and infrared (IR) spectroscopic analysis and AFM analysis of a series of SWNT/PBO 15 mer block copolymers prepared under a variety of conditions.  
      Table 1 details a variety of SWNT/PBO 15 mer block copolymers prepared via copolymerization of short SWNTs and PBO 15 mers carried out in a mixed solvent of PPA/MSA with P 2 O 5  for 3 days.  
                                       TABLE 1                                      Wt ratio of PBO   Molar ratio of                       15 mers and short   PBO 15 mers   Wt ratio of   Temp   Concentration (wt %)                                             No.   SWNTs   to short SWNTs   PPA and MSA   (° C.)   PBO/SWNTs a     PBO   SWNTs a                                                       1   67/33   16   50/50   100   0.36   0.12   0.24       2   33/67   64   50/50   100   0.36   0.24   0.12       3   33/67 b     64   50/50   100   0.36   0.24   0.12       4   33/67   64   17/83   150   3.3   2.2   1.1       5   33/67 b     64   17/83   150   3.3   2.2   1.1                   a Calculated based on SWNTs weight for benzenesulfonic acid short SWNTs.              b Benzenesulfonic acid functionalized short SWNTs were used.             
 
       FIG. 9  depicts the Raman spectra (633 nm excitation) of SWNT/PBO copolymer film synthesized in dilute concentration, wherein trace (a) depicts copolymerized product No. 1 (see Table 1) prepared from short SWNTs and PBO 15 mers at the weight ratio of 67/33 (0.36 wt. % concentration), and wherein trace (b) depicts PBO 15 mers. This confirms that the SWNTs are indeed incorporated within the SWNT/PBO copolymer, as the PBO alone shows no characteristic Raman bands in this region of the spectrum.  
       FIG. 10  depicts the Raman spectra (633 nm excitation) of SWNT/PBO copolymer film prepared in higher concentration, wherein trace (a) depicts copolymerized product No. 4 (see Table 1), and wherein trace (b) depicts benzenesulfonic acid-functionalized short SWNT/PBO 15 mers (copolymerized product No.  5 , Table 1). The copolymerized functionalized SWNT/PBO indeed shows the characteristic functionalized SWNT Raman bands, confirming the functionalized SWNTs are incorporated in the copolymer, i.e., it is not merely PBO alone.  
       FIG. 11  depicts attenuated total reflectance-infrared (ATR-IR) spectra of benzenesulfonic acid-functionalized short SWNTs (trace a), PBO 15 mers (trace b), and the copolymerized product (No. 5, Table 1) of benzenesulfonic acid-functionalized short SWNT/PBO 15 mers at the concentration of 3.3 wt. %. The SWNT/PBO copolymer spectrum is a composite (near summation) spectrum of the independent SWNT and the independent PBO spectra, therefore confirming the presence of both components in the copolymer.  
      Shown in  FIGS. 12A-12D  are AFM images of a 2 mg sample/10 cc MSA solution spun onto a silicon wafer and vacuum dried at 100° C. overnight.  FIGS. 12A  (height) and  12 B (amplitude) depict a physical mixture of functionalized short SWNTs and PBO 15 mers at a weight ratio of 49/51 as height and amplitude scans, respectively.  FIGS. 12C  (height) and  12 D (amplitude) depict copolymerized product (No. 5, Table 1) from functionalized short SWNTs and PBO 15 mers at a weight ratio of 49/51 as height and amplitude scans, respectively. The physical mixture is clearly different, at the nanoscale level, than the copolymerization product. The latter ( FIGS. 12C and 12D ) have a thicker appearance, due to the covalently-appended oligomers, which further keeps the SWNT portions primarily as individuals, i.e., they do not tend to bundle into longer structures.  
     EXAMPLE 8  
      This Example serves to illustrate the copolymerization of short SWNTs and PBO 45 mers, in accordance with some embodiments of the present invention.  
      Referring to Scheme 9 ( FIG. 13 ), p-phenylene benzobisoxazole 45 mer was synthesized and then block copolymerized with short (ca. 60 nm) SWNTs, the short SWNTs comprising carboxylic acid (—COOH) groups on the ends. The copolymerization was carried out in a reaction mixture comprising 250 mg of short SWNTs, 2.0 g of a PPA solution of PBO 45 mer (comprising 250 mg of PBO 45 mer), 15 g methanesulfonic acid, and 1.5 g P 2 0 5 . The copolymerization was allowed to proceed at a temperature of 150° C. for a period of 3 days to yield a SWNT/PBO 45 mer block copolymer, as depicted in Scheme 9.  
     EXAMPLE 9  
      This Example serves to illustrate the copolymerization of short sidewall-functionalized SWNTs and PBO 45 mers, in accordance with some embodiments of the present invention.  
      Referring to Scheme 10 ( FIG. 14 ), p-phenylene benzobisoxazole 45 mer was synthesized and then block copolymerized with short (ca. 60 nm) benzenesulfonic acid-functionalized SWNTs, the short SWNTs comprising carboxylic acid (-COOH) groups on the ends and benzene sulfonic acid groups on their sidewalls. The copolymerization was carried out in a reaction mixture comprising 356 mg of the short benzenesulfonic acid-functionalized SWNTs, 2.0 g of a PPA solution of PBO 45 mer (comprising 250 mg of PBO 45 mer), 15 g MSA, and 1.5 g P 2 0 5 . The copolymerization was allowed to proceed at a temperature of 150° C. for a period of 3 days to yield a sidewall-functionalized SWNT/PBO 45 mer block copolymer, as depicted in Scheme 10.  
     EXAMPLE 10  
      This Example serves to illustrate Raman spectroscopic analysis, at a variety of excitation wavelengths, for a series of SWNT/PBO 45 mer block copolymers prepared under a variety of conditions.  
      Table 2 details a variety of SWNT/PBO 45 mer block copolymers prepared via copolymerization of short SWNTs and PBO 45 mers carried out in a mixed solvent of PPA/MSA with P 2 0 5  for 3 days.  
                                   TABLE 2                                      Wt ratio of PBO   Molar ratio of                   45 mers and short   PBO 45 mers   Wt ratio of   Concentration (wt %)                                         No.   SWNTs   to short SWNTs   PPA and MSA   PBO/SWNTs a     PBO   SWNTs a                                                   6   50/50   11   10/90   2.6   1.3   1.3       7   50/50 b     11   10/90   2.6   1.3   1.3       8   90/10 b     100   33/67   4.7   4.2   0.5                   a Calculated based on SWNTs weight for benzenesulfonic acid short SWNTs.              b Benzenesulfonic acid functionalized short SWNTs were used.             
 
      Various areas of the copolymer films were examined with 514 nm, 633 nm and 780 nm excitation.  FIG. 15  depicts Raman spectroscopic analysis (633 nm excitation) of SWNT/PBO 45 mer copolymer film, wherein trace (a) depicts copolymerized product from PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs (No. 7, Table 2), and wherein trace (b) depicts copolymerized product from PBO 45 mers and short SWNTs (No. 6, Table 2).  FIG. 16 . depicts Raman spectroscopic analysis (780 nm excitation) of SWNT/PBO 45 mer copolymer film, wherein trace (a) depicts copolymerized product from PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs (No. 7, Table 2), and wherein trace (b) depicts copolymerized product from PBO 45 mers and short SWNTs (No. 6, Table 2).  FIG. 17  depicts Raman spectroscopic analysis (514 nm excitation) of SWNT/PBO 45 mer copolymer film, wherein trace (a) depicts copolymerized product from PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs (No. 7, Table 2), and wherein trace (b) depicts copolymerized product from PBO 45 mers and short SWNTs (No. 6, Table 2).  
      Regarding  FIG. 16 , both traces (a) and (b) show that the copolymers do indeed exhibit the expected presence of the SWNTs. However, trace (a) shows an expected larger D-band to G-band ratio than trace (b), due to the arylsulfonic acid sidewall functionalization, further confirming that the sidewall functionalization survives the copolymerization conditions.  
      Regarding  FIG. 17 , both trace (a) and trace (b) show that the copolymers do indeed exhibit the expected presence of the SWNTs. Again, however, trace (a) shows the expected larger D-band to G-band ratio than trace (b), due to the arylsulfonic acid sidewall functionalization, further confirming that the sidewall functionalization survives the copolymerization conditions. Note that the intensity of trace (a) is depressed because of the lack of resonant Raman enhancement seen in functionalized SWNTs, and also because it is further diluted with respect to there being a longer PBO (45 mer) segment.  
     EXAMPLE 11  
      This Example serves to illustrate a conventional dry-jet wet spinning process useful for spinning fibers of nanotube block copolymers, in accordance with some embodiments of the present invention.  
      Referring to  FIG. 18 , such a spinning process typically involves a spinning apparatus 1800 coupled with the steps of: (a) degassing of a nanotube block copolymer solution; (b) extrusion of the degassed copolymer solution through a spinneret 1804 to form a fiber; (c) coagulation of the fiber in a coagulation bath 1801 (directed by idle roll 1803); take-up of the fiber by take-up drum 1802; (d) washing the spun fiber; (e) drying the spun fiber; and (f) various optional post treatments.  
       FIGS. 19A and 19B  are scanning electron microscopy images contrasting a PBO 45 mer fiber ( FIG. 19A ) with a copolymer (No. 8, Table 2) of PBO 45 mers and benzenesulfonic acid-functionalized short SWNTs at the weight ratio of 90/10 ( FIG. 19B ).  
      In the above or other embodiments, to enhance or modulate the properties of the fibers produced, the nanotube block copolymers can be blended with PBO homopolymers (or other aromatic polymer), as depicted in  FIG. 20 .  
     EXAMPLE 12  
      This Example serves to illustrate the copolymerization of short SWNTs and poly(p-phenylene terephthalamide) (PPTA).  
      First, PPTA, comprising amine groups at both ends, is synthesized as shown in Scheme 11 ( FIG. 21 ). Then, as depicted in Scheme 12 ( FIG. 22 ), this PPTA is then copolymerized with short SWNTs in a reaction mixture comprising NMP, CaCI 2 , and triphenyl phosphate/pyridine (condensate reagent).  
      All patents and publications referenced herein are hereby incorporated by reference to the extent not inconsistent herewith. It will be understood that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, it will be understood that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention as defined by the appended claims.