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Description  |
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FIELD OF INVENTION
This invention relates generally to conducting polymers, and more
particularly relates to electrically conductive, shaped articles such as
parts, containers, fibers, tapes, films and coatings of colored
polyaniline and to methods of forming and use of same conductive articles.
BACKGROUND OF THE INVENTION
Electrically conductive, thermoplastic polymer compounds are of increased
practical interest, for instance, for packaging electronic instruments and
parts, and to solve a wide range of static decay, static shielding and
electromagnetic shielding problems. Often such compounds are made by
mixing, for example, carbon black, stainless steel fibers, silver or
aluminum flakes or Nickel-coated fibers with insulating bulk
thermoplastics such as polystyrene, polyolefins, nylons, polycarbonate,
acrylonitrile butene styrene (ABS) copolymers, etc. These filled compounds
are subsequently processed into the desired shapes and articles by
extrusion, injection or blow molding and the like. Major problems
associated with the above filled thermoplastic compounds are that
processing of these materials is not trivial, is often associated with
excessive machine wear and that their colorability is difficult due to the
mechanical and optical properties of the fillers, respectively. For
example, it is virtually impossible to produce carbon black filled
polymers having a high electrical conductivity that are not black. The
importance of colorability of conductive compounds derives from
applications of these materials in, for instance, the carpet and fashion
industry where product appearance is critical, and for color coding of
films, containers, housings and enclosures.
More recently, there has been an increased interest in replacing the carbon
black or metal filled compounds with intrinsically electrically conductive
polymers and their blends with common insulating polymers. The latter
systems are believed to be more cost competitive, easier to process and to
exhibit desirable mechanical properties. Among the various conductive
polymers, the polyanilines have attracted particular attention because of
their excellent environmental stability and their low production costs.
Polyaniline is well known in the art, and the preparation of the
electrically conductive form of this polymer based on, for example,
contacting polyanilines with protonic acids has been disclosed. Green, A.
G., and Woodhead, A. E., "Aniline-black and Allied Compounds, Part 1, "J.
Chem. Soc., Vol. 101, pp. 1117 (1912); Kobayashi, et al., Electrochemical
Reactions . . . of Polyaniline Film-Coated Electrodes," J. Electroanl.
Chem., Vol. 177, pp. 281-91 (1984); U.S. Pat. Nos. 3,963,498, 4,025,463
and 4,983,322; U.S. patent application Ser. No. 714,165. Typical examples
of such disclosed protonic acids are HCl, H.sub.2 SO.sub.4, sulfonic acids
of the type R.sub.1 -SO.sub.3 H, phosphoric acids, etc. Chiang, J. -C. and
MacDiarmid, Alan G., "Polyaniline: Protonic Acid Doping of the Emeraldine
Form to the Metallic Regime", Synthetic Metals, Vol. 13, p. 196 (1986);
Salaneck, W. R. et al., "A Two-Dimensional-Surface "State" Diagram for
Polyaniline" Synthetic Metals, Vol. 13, p. 297 (1986). Such acids form
complexes with polyaniline, which, generally, exhibit electrical
conductivities of 10.sup.-3 S/cm or more. Thus, the electrical properties
make these so-called "doped" polyanilines and their blends and compounds
with common insulating bulk polymers suitable for a variety of the
anti-static and shielding applications that are currently served by metal
or carbon black filled systems. Indeed, certain polyaniline-based systems
may be conveniently processed using standard polymer processing techniques
without machine wear and exhibit excellent mechanical properties.
However, invariably the polyanilines in the art in their conducting form
show very strong absorptions around 300-400 nm (which corresponds to about
3.2 eV) and from 600 nm upwards (which corresponds to 2.0 eV downwards) in
the visible spectral range, giving the polymers an intense, dark,
black/green/blue appearance; cf. the absorption spectrum in FIGS. 1
through 6.
This very dark blue/green/black color of conventional conductive
polyanilines is well recognized. (See, for example the text of Examples 2
and 8 of Patent Cooperation Treaty patent application serial number WO
90/10297.) Polyaniline rendered conductive through protonation with
commonly used protonic acids exhibit about the same absorption spectrum,
and, hence, the same blue/green/black color. Examples of conductive
acid-doped polyanilines which will exhibit this characteristic
blue/green/black color are those based on the following dopants:
______________________________________
DOPANT REFERENCE
______________________________________
p-toluene sulfonic acid
WO '297-text Example 8;
S. K. Dhawan et al., Polym.
International, 25, 1, 55
(1991).
1,5-naphthalenedisulfonic
WO '297 - text Example 2.
acid, tetrahydrate
benzene sulfonic acid
S. K. Dhawan et al., Polym.
International, 25, 1, 55
(1991).
sulfosalicylic acid
K. Tzou et al., Synthetic
Metals, 53, 365 (1993)
HCl M. G. Roe et al. Physical
Review Letters, 60, 2789
(1988); P. M. McManus et al.,
J. Physical Chemistry,
91, 744 (1987); K. Tzou et al,
Synthetic Metals, 53,
365 (1993)
H.sub.2 SO.sub.4 E. M. Genies et al., J.
Electroanal. Chem., 220,
647 (1987)
HClO.sub.4 M. Enoue et al., Synthetic
Metals, 30, 199 (1989)
HNO.sub.3 Y. Li et al., Synthetic
Metals, 25, 79 (1988)
acetic acid A. Ray et al., Synthetic
Metals, 29, E141 (1989)
camphor sulfonic acid (CSA)
See FIGS. 2 and 3
dodecylbenzene sulfonic
See FIG. 3 "PANI-DBSA"
acid
1,5-naphthalenedisulfonic
See FIG. 4
acid
butylsulfamic acid
See FIG. 4
hydroxyaminosulfonic acid
See FIG. 4
4-nitrotoluene-2-sulfonic
See FIG. 5
acid
m-xylene-4-sulfonic acid
See FIG. 5
2-acrylamido-2-methyl-1-
See FIG. 5
propanesulfonic acid
2-naphthalene sulfonic acid
See FIG. 6
4-hydroxy-3-nitroso-1-
See FIG. 6
naphthalene sulfonic acid
2-sulfobenzoic acid
See FIG. 6
sulfoacetic acid See FIG. 6
2-hydroxy-4-methoxy-
See FIG. 7
benzophenone-5-sulfonic
acid
p-chlorobenzene sulfonic
See FIG. 7
acid
phenylhydrazine-p-sulfonic
See FIG. 7
acid
______________________________________
The conductive polyanilines disclosed by Cameron in U.S. Pat. No. 4,935,163
and by Tamura et al in U.S. Pat. No. 4,556,623 employ dopants which are
chemically so similar to these materials that they would yield very
similar absorptions and hence similar blue/green/black colors.
From the spectra provided herein as FIGS. 2 through 7 it may be readily
seen that the protonated polyanilines of the art are characterized by two
strong absorptions, one around 350-400 nm and one from about 600 nm
upwards. It can also be seen that the absorption at 400 nm generally is
about as strong as that at 850 nm.
Clearly, selection of specific protonic acids to yield conducting
polyanilines characterized by distinctly different absorption spectra in
the visible range, and therefore colors which range outside of the dark
blue/green/black palette of the past, would be desirable. Due to the
relatively low conductivity of doped polyaniline, in comparison with
silver, steel and other metals, often large amounts of the polymer are
needed in compounds or blends with insulating polymers to impart
sufficient conductivity for the desired shielding and antistatic
applications. Thus, much like the metal and carbon black filled
thermoplastic compounds, the colorability of the polyaniline-based systems
is believed to be poor and problematic. Clearly, a need exists for methods
to fabricate colored, electrically conductive compounds and articles.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to overcome the
aforementioned disadvantages of the prior art and to provide colored,
electrically conductive compounds and articles comprising polyaniline and
one or more protonic acids that are functionalized to simultaneously or
independently
(i) form an electrically conductive complex with the polyaniline, and
(ii) provide an absorption in the near infrared, visible or ultraviolet
range.
It is additionally an object of the present invention to provide colored,
electrically conductive compounds and articles comprising polyaniline and
one or more protonic acids that are functionalized to simultaneously or
independently
(i) forman electrically conductive complex with the polyaniline,
(ii) provide an absorption in the near infrared, visible or ultraviolet
range, and
(iii) induce processibility of the polyaniline.
It is additionally an object of the present invention to provide colored,
electrically conductive compounds and articles comprising polyaniline and
one or more protonic acids that are functionalized to simultaneously or
independently
(i) form an electrically conductive complex with the polyaniline,
(ii) provide an absorption in the near infrared, visible or ultraviolet
range, and
(iii) induce processibility of the polyaniline to form intimate admixtures
(solutions or the like) with a substrate material.
The terms "substrate" or "substrate polymer" is used herein to indicate a
range of insulating (i.e. conductivity of about 10.sup.-9 S/cm or less)
and semiconducting (conductivity greater than 10.sup.-9 S/cm such as in
the range from about 10.sup.-8 to .about.10.sup.-1 S/cm) solvents and
polymers. "Polymers" include solids, melts and pre-polymers (oligomers).
It is additionally an object of the present invention to provide shaped
articles, fibers, coatings, films, tapes and the like from colored,
electrically conductive polyaniline and blends of electrically conductive
polyaniline with bulk polymer and pre-polymer substrates.
Additional objects, advantages and novel features of the invention will be
set forth in part in the description which follows, and in part will
become apparent to those skilled in the art on examination of the
following, or may be learned by 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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the absorption spectrum of a conducting polyaniline
(PANi)-xylenol blue complex cast from m-cresol.
FIG. 2 shows the absorption spectrum of a PANi-camphor sulfonic acid (CSA)
complex of the art in solution in m-cresol. FIGS. 3 through 7 show
absorption spectra for additional conducting polyaniline compositions of
the art which spectra are consistent with the classic blue/green/black
color exhibited by such materials.
FIG. 8 compares solid-state absorption spectra of a blend of xylenol blue
and poly(methylmethacrylate) (PMMA); a blend composed of a PANi-xylenol
blue complex and PMMA; and a blend of a PANi-xylenol blue-CSA complex and
PMMA; represented by, respectively, the mixed dashed, dashed and solid
lines in the graph.
DETAILED DESCRIPTION OF THE INVENTION
The colored compositions of this invention typically include two or three
types of ingredients.
(i) One or more substituted or unsubstituted polyanilines; and
(ii) One or more functionalized protonic acid solutes in which the
counter-ion(s) have been functionalized so as to simultaneously or
independently impart a conductivity to the composition greater than about
10.sup.-11 S/cm, absorbance in the spectral range from 200 to 800 nm, and
especially in the visual spectral range of from about 350 nm to about 800
nm, and compatibility with an optional organic substrate phase (iii) are
always present;
(iii) One or more substrate phases are optionally present. This phase is
insulating or semiconducting organic material and can be an organic liquid
such as a solvent or a pre-polymer. It can also be an organic solid or
semisolid which is meltable during compounding or mixing with (i) and (ii)
and/or during shaping into the colored conductive article, such as melted
or softened polymer. It can be mixtures of two or more of these materials.
The substrate, when a solvent, may be present during fabrication and
removed at least partially in the final product or article.
Surprisingly, it has been discovered that, unlike the electrically
conductive compositions described in the prior art, materials can be
prepared comprising polyaniline that display a wide variety of intense
attractive colors and cover a very broad range of conductivities.
The Polyaniline
One ingredient in the present materials is substituted or unsubstituted
polyaniline homopolymer or a polyaniline copolymer as described in U.S.
patent application Ser. No. 714,165 and U.S. Pat. No. 4,983,322. Both of
these documents are incorporated herein by reference. When the term
"polyaniline" is used in this application, it is used generically to
include substituted and unsubstituted polyanilines and polyaniline
copolymers, unless the context is clear that only the specific
nonsubstituted form is intended.
Particularly preferred for the use in the practice of this invention are
polyanilines derived from unsubstituted aniline.
In general, the polyanilines useful in the practice of this invention are
those which are of sufficient molecular weight to exhibit high electrical
conductivity, i.e. having a number average molecular weight of more than
1,000 daltons. In general substituted and unsubstituted polyanilines and
polyaniline copolymers will be of at least 8 repeat units. In the
preferred embodiments of the invention, the number of repeat units is at
least about 10, and in the most preferred embodiments, the number of
repeat units is at least about 15.
The polyaniline can be conveniently used in the practice of this invention
in any of its physical forms. Illustrative of useful forms are those
described in U.S. patent application Ser. No. 714,165 and U.S. Pat. No.
4,983,322. For unsubstituted polyaniline, useful forms include
leucoemeraldine, protoemeraldine, emeraldine, nigraniline and
toluprotoemeraldine forms. Useful polyanilines can be prepared through the
use of chemical and electrochemical synthetic procedures referred to, for
example, in the above references.
The Functionalized Protonic Acid
A second ingredient of the colored compositions of the present invention is
one or more "functionalized protonic acids" in which the counter-ion(s)
have been functionalized so as to simultaneously or independently impart a
conductivity to the composition, impart a "coloring" absorbance in the
spectral range from 200 to 800 nm to the composition and exhibit
compatibility with an optional organic substrate phase.
As used herein, the terms "colored" or "coloring," when referencing the
property of an electrically conductive polyaniline compound, composition,
or article, shall mean that the compound, composition, or article has a
substantial absorbance in the near infrared, visible or near ultraviolet
wavelengths, preferably maximum (peak) absorbance in the spectral range of
200 to 800 nm which is at least 0.1 times its absorbance at 850 nm.
(Polyanilines have a strong absorbance at 850 nm.) Preferably "colored" or
"coloring" refers to the property of a polyaniline complex of this
invention of presenting a substantial absorbance in the visible
wavelengths and particularly a maximum (peak) absorbance in the spectral
range of from about 350 nm to about 800 nm (and especially 350 nm to 750
nm) which is at least 0.1, more suitably at least 0.5, especially at least
1, more preferably at least 2 and, in the best embodiments, at least 10
times its absorbance at 850 nm.
As used herein, a "protonic acid" is an acid that protonates the
polyaniline to form a complex with said polyaniline which has a
conductivity greater than about 10.sup.-11 S/cm. Preferred protonic acids
are those that protonate the polyaniline to form a complex, said complex
having an electrical conductivity of greater than about 10.sup.-6 S/cm,
and particularly preferred protonic acids are those that form a complex
with the polyaniline having a conductivity of greater than about 10.sup.-3
S/cm. Amongst these particularly preferred embodiments, most preferred are
those protonic acids which form a polyaniline complex having a
conductivity of greater than 0.1 S/cm.
Protonic acids are well known as dopants in the conductive polymer art as
shown by the reference to J. -C. Chiang and Alan G. MacDiarmid; and the
reference to W. R. Salaneck et al., noted above. They can be compatible
with insulating or semi-conducting substrates, but not necessarily are,
and do not necessarily display absorbance in the spectral range from 200
to 800 nm. As used herein, a "functionalized" protonic acid is an acid
that protonates the polyaniline to form a complex with said polyaniline,
which complex has a conductivity equal to or greater than about 10.sup.-11
S/cm; which has absorbance in the spectral range from 200 to 800 nm such
that the ratio of the maximum absorbance in said range to the absorbance
at 850 nm, is greater than 0.1; and which simultaneously or independently
has been functionalized to be miscible with, or soluble in the substrate
which makes up the third component of these products. Preferred
"functionalized" protonic acids are those which meet these values and
which form a complex with polyaniline presenting a substantial absorbance
in the visible wavelengths and particularly a maximum (peak) absorbance in
the spectral range of from about 350 nm to about 800 nm (and especially
350 nm to 750 nm) which is at least 0.1, more suitably at least 0.5,
especially at least 1, more preferably at least 2 and, in the best
embodiments, at least 10 times its absorbance at 850 nm.
Functionalized protonic acids that form an electrically conductive complex
with polyaniline which has a coloring absorbance in the spectral range
from 200 to 800 nm such that the ratio of the maximum absorbance in said
range to the absorbance at 850 nm, is greater than 0.1, generally for use
in the invention are those of Formula I:
A.sub.n -D.sub.1 I
wherein:
n is an integer from 1 to 5 inclusive
A is the same or different at each occurrence and is an acid functionality
such as sulfonic acid, selenic acid, phosphonic acid, boric acid or a
carboxylic acid group; or hydrogen sulfate, hydrogen selenate, hydrogen
phosphate, and the like; and
D.sub.1 is an organic moiety covalently bonded to A that imparts to the
compound of Formula I a coloring absorption in the spectral range from 200
to 800 nm. Such moieties generally are aromatic structures and are
well-known as chromophores in the stain, dye and colorant arts.
Many of such useful functionalized protonic acids which include both the A
and D.sub.1 groups are commercially available, such as those tabulated in
"the Sigma-Aldrich Handbook of Stains, Dyes and Indicators", by Floyd J.
Green, Aldrich Chemical Company, Inc. (Milwaukee, Wis.) 1990;
"Lambdachrome Laser-grade Dyes" by Ulrich Brackmann, Lambda Physik GmbH
(G.sub.-- ttingen, Germany) 1986; and in "Kodak, Laboratory Chemicals",
Catalog No. 54, pp. 895-901 (1990). These references are incorporated
herein by-reference. Illustrative examples of useful functionalized
protonic acids of Formula I are pyrogallol red, pyrocatechol violet,
cresol red, phenol red, xylenol blue, xylenol orange, sulforhodamine 640,
sulforhodamine 620, and the like. The selection of the functionalized
protonic acid naturally will depend on the desired color and absorption
spectrum. This selection can readily be made by those skilled in the art,
because the latter spectra are readily available and are generally
supplied by the manufacturers.
Particularly preferred for use in the present invention are functionalized
protonic acids that forman electrically conductive complex with
polyaniline having an absorbance in the spectral range from 200 to 800 nm,
and especially 350 to 800 nm and more particularly 350 to 750 nm, such
that the ratio of the maximum absorbance in said range to the absorbance
at 850 nm, is greater than 0.5. Amongst the particularly preferred
embodiments, most preferred for use in the practice of this invention are
functionalized protonic acids that forman electrically conductive complex
with polyaniline and have absorbance in the spectral range from 200 to 800
nm, and especially 350 to 800 nm and more particularly 350 to 750 nm, such
that the ratio of the maximum absorbance in said range to the absorbance
at 850 nm, is greater than 1. In the most preferred embodiments of this
invention, functionalized protonic acids are used that form an
electrically conductive complex with polyaniline and have absorbance in
the spectral range from 200 to 800 nm, and especially 350 to 800 nm and
more particularly 350 to 750 nm, such that the ratio of the maximum
absorbance in said range to the absorbance at 850 nm, is greater than 10.
The functionalized protonic acids employed of the compositions of the
present invention are acids that form an electrically conductive complex
with the polyaniline, which complex has a conductivity equal to or greater
than about 10.sup.-11 S/cm; which have absorbance in the spectral range
from 200 to 800 nm, and especially 350 to 800 nm and more particularly 350
to 750 nm, such that the ratio of the maximum absorbance in said range to
the absorbance at 850 nm, is greater than 0.1, more suitable at least 0.5,
especially at least 1, more preferably at least 2 and, in the best
embodiments, at least 10; and which preferably have been functionalized to
simultaneously or independently be miscible with, or soluble in a
substrate, which makes up the optional third insulating or semiconducting
component of these products. The requirements for the latter phenomenon to
occur have been disclosed in U.S. patent application Ser. No. 714,165.
This functionalization allows the colored, conductive polyaniline complex
to be homogenized into the substrate through solubilization intimate
mixing and the like. This dissolving and/or intimate mixing leads to the
formation of an essentially continuous network of the conductive species
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