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Reexamination Certificate
1999-06-29
2002-07-30
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C423S44500R, C428S357000, C428S375000, C428S378000, C428S395000
Reexamination Certificate
active
06426134
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to single-wall carbon nanotube/polymer composites, a process for the production of such, and their use as fibers, films and articles.
TECHNICAL BACKGROUND
Carbon nanotubes were first reported in 1991 by Sumio Iijima who produced multilayer tubules by evaporating carbon in an arc discharge. These linear fullerenes are attracting increasing interest as constituents of novel nanoscale materials and device structures. Defect-free nanotubes are expected to have remarkable mechanical, electronic and magnetic properties that will be tunable by varying the diameter, number of concentric shells, and chirality of the tube.
In 1993, Iijima's group and an IBM team headed by D. S. Bethune independently discovered that a single-wall nanotube could be made by vaporizing carbon together with a transition metal such as iron or cobalt in an arc generator (see Iijima, et al., Nature, Vol. 363, p. 603, (1993); D. S. Bethune et al., Nature 363 (1993) 605 and U.S. Pat. No. 5,424,054). These syntheses produced low yields of non-uniform nanotubes mixed with large amounts of soot and metal particles.
Richard Smalley et al. in Chem. Phys. Letters, Vol. 243 (1995) 49-54 disclose a process for making single-wall nanotubes having diameters of about 1 nm and lengths of several microns. The nanotubes aggregated into “ropes” in which many tubes were held together by van der Waals forces. The nanotubes produced were remarkably uniform in diameter.
In later work published in Science, Vol. 273 (1996) 483-487, Smalley et al. discuss the addition of a second laser to their process which gives a pulse 50 nanoseconds after the pulse of the first laser. This raised the yield of nanotubes to an estimated range of 70 to 90% and seemingly favored the 10, 10 configuration (a chain of 10 hexagons around the circumference of the nanotube). The product consisted of fibers approximately 10 to 20 nm in diameter and many micrometers long comprising randomly oriented single-wall nanotubes, each nanotube having a diameter of about 1.38 nm.
J. Liu et al. in “Fullerene Pipes”, Science, Vol. 280 (1998) 1253 discusses single-wall fullerene nanotubes that are converted from nearly endless, highly tangled ropes into short, open-ended pipes that behave as individual macromolecules. Also described therein is the termination of the open ends of the nanotubes with carboxylic acid groups after treatment in acid. This is followed by reaction with SOCl
2
at room temperature to form the corresponding acid chloride.
Because of their unique electronic and mechanical properties, further progress toward new uses of single-wall nanotubes is desirable.
SUMMARY OF THE INVENTION
The present invention relates to a single wall carbon nanotube/polymer composite, comprising a single wall carbon nanotube having at least one end chemically bonded to a polymer.
The present invention also relates to a process for producing a single wall carbon nanotube/polymer composite, comprising the steps of:
(a) contacting single wall carbon nanotubes with an acid, wherein at least a portion of said carbon nanotubes form acid derivatized nanotubes, each of said acid derivatized nanotubes having at least one carboxylic acid attached to at least one end of the nanotube;
(b) contacting the product of step (a) with one or more polymer precursors to form a pre-polymer product; and
(c) polymerizing the pre-polymer product of step (b) to form a single wall carbon nanotube/polymer composite.
The present invention further provides a fiber comprising the single wall carbon nanotube/polymer composite described above.
The present invention also provides an article comprising the single wall carbon nanotube/polymer composite described above.
The present invention also provides a film comprising the single wall carbon nanotube/polymer composite described above.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with a first embodiment of the present invention, there is provided a single wall carbon nanotube/polymer composite. The present composite comprises a nanotube component and a polymer component. The nanotube component comprises single wall carbon nanotubes each individually having a length ranging from about 10 to about 300 nm and each nanotube having a diameter ranging from about 1 to about 2 nm. At least one end of a portion of the nanotubes present within the composite is derivatized and chemically bonded to or within one or more chains of a polymer of the polymer component via one or more chemical bonds. Thus, there can be a derivatized nanotube bearing a carboxyl group at one end that can serve as a chain-terminating group of a polymer chain of the polymer component. A nanotube bearing carboxyl groups at both ends is capable of copolymerization and can reside at the end of or within the polymer chain. Thus, the derivatized nanotubes can reside at the end of polymer chains, within the polymer chains, or both. The composites of the present invention can be described as block copolymers in which the nanotubes are the hard segment.
As used herein a single wall carbon nanotube refers to a hollow carbon fiber having a wall consisting essentially of a single layer of carbon atoms. Single wall carbon nanotubes can be made by the processes disclosed in lijima et al., Nature, Vol. 363, p. 603 (1993); D. S. Bethune et al., Nature 63 (1993) 060, U.S. Pat. No. 5,424,054, R. Smalley et al, Chem. Phys. Letters, Vol. 243 (1995) 49-54 and Science Vol. 273 (1996) 483-487.
The polymer component of the present composite comprises polymers, including copolymers, capable of chemically bonding to a derivatized end of a single wall carbon nanotube or those polymers that can be prepared from one or more monomer precursors capable of bonding with a derivatized end of a single wall carbon nanotube either prior to or during polymerization. Representative examples of polymers comprising the polymer component of the present invention include linear and branched polyamides, polyesters, polyimides and polyurethanes. Preferred polyamides include but are not limited to nylon 6; nylon 6,6; and nylon 6,12. Preferred polyesters include but are not limited to poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(trimethylene naphthalate).
In accordance with the present invention, there is provided a process for preparing a single wall carbon nanotube/polymer composite. The process comprises the steps of preparing an acid derivatized nanotube, contacting the derivatized nanotube with one or more polymer precursors to form a pre-polymer product and polymerizing the pre-polymer product to form the single wall carbon nanotube/polymer composite.
Prior to forming the acid derivatized nanotube, it may be necessary to cut the nanotubes and optionally purify them. Highly tangled ropes of nanotubes currently available or produced by the methods referenced above can be cut into short lengths of open tubes of about 10 to 300 nm in length. The cut tubes can then be suspended, sorted, and manipulated as individual macromolecules (see Liu et al., Science, Vol. 280, 1253-1256, 1998).
Since the nanotubes produced by the methods currently available may contain impurities, such as bucky onions, spheroidal fullerenes, amorphous carbon, and other material, that are difficult to separate from the nanotubes once they have been cut, it is preferable to purify the nanotube material before cutting. A suitable purification method comprises refluxing in 2.6 M nitric acid and resuspending the nanotubes in pH 10 water with surfactant, such as sodium lauryl sulfate, followed by filtration with a cross-flow filtration system. The resultant purified single wall nanotube suspension can be passed through a polytetrafluoroethylene filter to produce a freestanding mat of tangled single wall nanotube ropes. Preferably, the ropes are not allowed to dry since that can make redispersion more difficult.
Alternatively, purified single wall nanotubes in aqueous suspension can be purchased from Tubes@Rice, MS-100, P.O. Box 1892, Houston Tex. 77251-1892 or Carbolex Inc., ASTe
Lavin John Gerard
Samuelson Harry Vaughn
E. I. du Pont de Nemours and Company
Le Hoa T.
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