U.S. patent application number 09/822936 was filed with the patent office on 2001-08-09 for direct method for preparing doped polyaniline, product prepared thereby and resinous articles containing said product.
Invention is credited to Chandra, Subhas, Dhawan, Sundeep Kumar, Fishburn, James Ross, Gopal, Erode Subramanium Raja, Rodriques, David Ernest, Singh, Navjot, Todt, Michael Leslie.
Application Number | 20010012884 09/822936 |
Document ID | / |
Family ID | 23747783 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012884 |
Kind Code |
A1 |
Dhawan, Sundeep Kumar ; et
al. |
August 9, 2001 |
Direct method for preparing doped polyaniline, product prepared
thereby and resinous articles containing said product
Abstract
Doped polyanilines are prepared by contacting aniline with an
oxidizing agent such as ammonium peroxydisulfate in aqueous
solution at a temperature of at most about 10.degree. C. in the
presence of at least one organic sulfonic acid, preferably an
alkylbenzenesulfonic acid such as dodecylbenzenesulfonic acid. The
products may be blended with thermoplastic resins such as
polystyrene to produce blends having excellent static discharge
properties
Inventors: |
Dhawan, Sundeep Kumar;
(Delhi, IN) ; Chandra, Subhas; (Delhi, IN)
; Gopal, Erode Subramanium Raja; (Bangalore, IN) ;
Singh, Navjot; (Clifton Park, NY) ; Rodriques, David
Ernest; (Malta, NY) ; Todt, Michael Leslie;
(Schenectady, NY) ; Fishburn, James Ross;
(Menands, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY
CRD PATENT DOCKET ROOM 4A59
P O BOX 8
BUILDING K 1 SALAMONE
SCHENECTADY
NY
12301
US
|
Family ID: |
23747783 |
Appl. No.: |
09/822936 |
Filed: |
March 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09822936 |
Mar 30, 2001 |
|
|
|
09440186 |
Nov 15, 1999 |
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Current U.S.
Class: |
528/422 ;
524/745; 524/800 |
Current CPC
Class: |
C08G 73/0266 20130101;
H01B 1/128 20130101 |
Class at
Publication: |
528/422 ;
524/745; 524/800 |
International
Class: |
C08G 073/00; C08K
005/42; C08L 079/00 |
Claims
What is claimed is:
1. A method for preparing an electrically conductive polyaniline
which comprises contacting aniline with an oxidizing agent in
aqueous solution at a temperature of at most about 10.degree. C. in
the presence of at least one organic sulfonic acid.
2. A method according to claim 1 wherein the oxidizing agent is
ammonium peroxydisulfate.
3. A method according to claim 2 wherein the sulfonic acid is an
alkylbenzenesulfonic acid.
4. A method according to claim 3 wherein the alkylbenzenesulfonic
acid is dodecylbenzenesulfonic acid.
5. A method for preparing an electrically conductive polyaniline
which comprises contacting aniline with ammonium peroxydisulfate in
aqueous solution at a temperature in the range of about
0-10.degree. C. in the presence of at least one
alkylbenzenesulfonic acid, the molar ratio of said ammonium
peroxydisulfate to said aniline being in the range of about
1.0-1.2:1 and the sulfonic acid being present in the amount of
about 5-10 ml per gram of aniline.
6. A method according to claim 5 wherein the alkylbenzenesulfonic
acid is dodecylbenzenesulfonic acid.
7. A sulfonic acid-doped polyaniline prepared by the method of
claim 1.
8. A sulfonic acid-doped polyaniline prepared by the method of
claim 3.
9. A sulfonic acid-doped polyaniline prepared by the method of
claim 4.
10. A sulfonic acid-doped polyaniline prepared by the method of
claim 5.
11. A sulfonic acid-doped polyaniline prepared by the method of
claim 6.
12. A method of isolating polyaniline doped with at least one
organic sulfonic acid which comprises precipitating said doped
polyaniline from aqueous solution by combination with a mixture of
water and a C.sub.1-4 water-miscible alkanol and separating the
precipitated polyaniline from said solution.
13. A method according to claim 12 wherein the alkanol-water
mixture contains an amount up to about 95% by weight water with the
balance being alkanol.
14. A method according to claim 12 wherein the sulfonic acid is an
alkylbenzenesulfonic acid.
15. A method according to claim 14 wherein the alkylbenzenesulfonic
acid is dodecylbenzenesulfonic acid.
16. A method according to claim 12 wherein the alkanol is
2-propanol.
17. A conductive resinous composition comprising at least one
thermoplastic resin and a sulfonic acid-doped polyaniline according
to claim 7.
18. A composition according to claim 17 wherein the thermoplastic
resin is selected from the group consisting of olefin polymers,
diene polymers, alkenylaromatic polymers other than diene polymers,
vinyl halide polymers, vinyl ester and alcohol polymers, acrylic
polymers, polycarbonates, polyesters, polyphenylene ethers,
polyarylene sulfides, polyetherimides and polyethersulfones.
19. A composition according to claim 18 wherein the thermoplastic
resin is polystyrene.
20. A composition according to claim 18 comprising about 60-99% by
weight of said thermoplastic resin and correspondingly about 1-40%
of said doped polyaniline.
21. A conductive resinous composition comprising about 60-99% by
weight of polystyrene and correspondingly about 1-40% of a
dodecylbenzenesulfonic acid-doped polyaniline according to claim
11.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to conductive polymers, and more
particularly to conductive doped polyanilines and compositions
containing them
[0002] The use of conductive materials as additives for plastics is
of considerable interest since increased conductivity is desirable
for many applications, including electrostatic painting and
dissipation of static charges. For the latter purpose, especially,
a very short static decay time, on the order of 0.02 second, is
desirable.
[0003] Among the conductive additives which have been employed are
conductive carbon black and conductive carbon fiber. At high
loadings, however, carbon black tends to accumulate at the surface
of a plastic part and subsequently slough off the plastic part.
Carbon fiber is expensive and can decrease impact resistance of the
part.
[0004] It is also possible to coat the surfaces of particulate
non-conductive fillers such as mica, glass fibers or glass spheres
with a conductive metal or compound thereof such as copper, silver
or antimony-doped tin oxide. This, however, can cause problems
including high cost, insufficient adhesion to the base resin and
loss in conductivity as a result of oxidation of the metal
coating.
[0005] Many of these problems can be alleviated by employing a
conductive polymer as the additive. A particularly advantageous
conductive polymer is polyaniline, which may be prepared by
electrochemical methods or chemically by the oxidation of aniline
in the presence of a mineral acid under relatively mild
conditions.
[0006] These preparation methods typically afford the polyaniline
as a partially oxidized and partially reduced material, with the
reduced portion comprising --C.sub.6H.sub.4NH-- structural units
and the oxidized portion comprising alternating quinone and
phenylene moieties separated by trivalent nitrogen atoms. This
partially oxidized and partially reduced polyaniline is known as
"emeraldine". It can be readily converted to the fully oxidized
state, known as "pernigraniline", or to the fully reduced state,
known as "leucoemeraldine". It can also be handled in the
protonated state, known as "protonated emeraldine".
[0007] Polyaniline prepared by known methods, including the
above-described chemical method, has, however, various problems
which detract from its utility as a conductive polymer. As a single
example of such a problem, such polyaniline is often contaminated
with by-products such as the virulently carcinogenic benzidine.
[0008] PCT application 95/06,685 provides a summary of the state of
the art of conductive polyaniline production and processing as of
1994, including the doping of polyaniline with such materials as
alkylbenzenesulfonic acids. It also discloses a process in which
doped polyaniline is combined with a polymer and a
"solvent-plasticizer" to form a processable composition. Such a
process requires a first step of preparing the polyaniline, a
second step of doping it and a third step of combining the doped
material with a polymer and a solvent-plasticizer.
[0009] It remains of interest, therefore, to prepare a polyaniline
which is not contaminated with harmful by-products and which can be
prepared in a minimum of steps and then blended with plastic
materials to produce a processable conductive material.
SUMMARY OF THE INVENTION
[0010] The present invention provides a single-step direct method
for preparing doped polyaniline and a method for separating the
product from the reaction system I which it was prepared. The
product of said method is benzidine-free and has a static decay
time which is substantially shorter than that of doped polyaniline
prepared by other methods. Said product can be combined in a single
blending operation with thermoplastic polymers to afford
processable conductive resinous compositions.
[0011] In one of its aspects, the invention is a method for
preparing an electrically conductive polyaniline which comprises
contacting aniline with an oxidizing agent in aqueous solution at a
temperature of at most about 10.degree. C. in the presence of at
least one organic sulfonic acid. Another aspect of the invention is
sulfonic acid-doped polyanilines prepared by this method.
[0012] A further aspect is conductive resinous compositions
comprising at least one thermoplastic resin and the sulfonic
acid-doped polyaniline.
[0013] A still further aspect is a method of isolating polyaniline
doped with at least one organic sulfonic acid which comprises
precipitating said doped polyaniline from aqueous solution by
combination with a mixture of water and a C.sub.1-4 water-miscible
alkanol and separating the precipitated polyaniline from said
solution.
DETAILED DESCRIPTION; PREFERRED EMBODIMENTS
[0014] In the method of the invention for polyaniline preparation,
aniline is contacted with an oxidizing agent suitable for its
conversion to polyaniline. Suitable oxidizing agents are, in
general, mild ones and their identities are known in the art. The
preferred oxidizing agent, for most purposes, is ammonium
peroxydisulfate, (NH.sub.4).sub.2S.sub.2O.sub.- 8.
[0015] Also employed is at least one organic sulfonic acid. It may
be an aliphatic, aromatic or heterocyclic sulfonic acid;
illustrative acids are methanesulfonic acid, benzenesulfonic acid,
p-toluenesulfonic acid, 3-carboxy-4-hydroxybenzenesulfonic acid and
8-hydroxyquinoline-5-sulfonic acid. The preferred acids are the
alkylbenzenesulfonic acids, most preferably those in which the
alkyl groups contain about 4-20 carbon atoms; examples are
2-n-octylbenzenesulfonic acid and 4-n-dodecylbenzenesulfonic acid,
the latter often being especially preferred.
[0016] Polyaniline preparation is effected by simply bringing the
aniline into contact with the oxidizing agent and sulfonic acid at
a temperature of at most about 10.degree. C. at which the oxidation
reaction takes place, the preferred temperature range being about
0-10.degree. C. An aqueous medium is preferred. When the oxidizing
agent is a peroxydisulfate such as ammonium peroxydisulfate, it is
used in at least an equimolar amount with respect to the aniline,
preferably in a molar ratio in the range of about 1.0-1.2:1. The
sulfonic acid is preferably used in the amount of about 5-10 ml per
gram of aniline. Most often, the oxidizing agent is added gradually
or portionwise to a mixture of water, aniline and sulfonic acid,
and the resulting mixture is agitated to facilitate polyaniline
formation.
[0017] The polyaniline obtained according to the invention is
already doped with sulfonic acid and is generally in the form of a
suspension in the aqueous medium, said suspension being difficult
to filter since the polyaniline particles tend to clog filters of
pore size less than about 200 microns or pass through filters with
larger pore sizes. According to the polyaniline isolation method of
the invention, the suspension is combined with a mixture of water
and a C.sub.1-4 water-miscible alkanol such as methanol, ethanol,
1-propanol, 2-propanol or 2-methyl-2-propanol. The preferred
alkanol in most instances is 2-propanol, by reason of its
particular suitability, availability and low cost.
[0018] Combination of the aqueous reaction mixture with the
alkanol-water mixture is ordinarily effected under ambient
conditions including temperatures in the range of about
20-30.degree. C. Said alkanol-water mixture typically contains an
amount up to about 95% by weight water with the balance being
alkanol. Upon such combination, the doped polyaniline precipitates
as a fine powder which may be easily removed by filtration. After
drying, typically in vacuum, it is ready for use.
[0019] The entire process of polyaniline preparation and isolation
according to the invention is most often completed in a period of
6-8 hours. This is in contrast to the prior art method employing a
mineral acid, which may require up to 10 hours for completion.
[0020] Sulfonic acid-doped polyanilines prepared and, preferably,
isolated by the method of this invention are conductive and may be
used in the same way as other conductive polymers. In particular,
it may be employed to form a conductive coating on fillers and
reinforcing agents of high aspect ratio, such as glass fibers,
which may then be incorporated in thermoplastic resins to increase
their conductivity.
[0021] The doped polyaniline may also be used directly as a
conductive additive for thermoplastic resins. Illustrative resins
include addition polymers, exemplified by olefin polymers such as
polyethylene and polypropylene; diene polymers such as
polybutadiene, polyisoprene, high impact styrene-diene copolymers
and acrylonitrile-butadiene-styrene copolymers; alkenylaromatic
polymers other than diene polymers, such as homo- and
copolystyrenes; vinyl halide polymers; vinyl ester and alcohol
polymers; acrylic polymers including polyacrylonitrile,
potyacrylamide and poly(alkyl acrylates) and poly(alkyl
methacrylates) such as poly(methyl methacrylate). Also included are
condensation polymers, exemplified by polycarbonates such as
bisphenol A polycarbonate, polyesters such as poly(ethylene
terephthalate) and poly(1,4-butylene terephthalate); polyphenylene
ethers such as poly(2,6-dimethyl-1,4-phenyl- ene ether);
polyarylene sulfides; polyetherimides such as the condensation
product of 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane
dianhydride with at least one of p- and m-phenylenediamine; and
polyethersulfones. For many purposes, polystyrene is a preferred
thermoplastic resin. The resinous blends of the invention most
often contain about 60-99% by weight of the thermoplastic resin and
correspondingly about 1-40% of the doped polyaniline.
[0022] The invention is illustrated by the following examples.
EXAMPLE 1
[0023] A beaker was charged with 3,000 ml of water, 18.2 g of
aniline and 90 ml of dodecylbenzenesulfonic acid. The mixture was
cooled in an ice bath to 10.degree. C. and a solution of 45.2 g of
ammonium peroxydisulfate in 200 ml of water was added dropwise over
1.5 hours, with stirring. The reaction mixture was stirred for
about 7 hours.
[0024] The product was an aqueous suspension of
dodecylbenzenesulfonic acid-doped polyaniline which was found by
gas chromatography-mass spectroscopy to be free from benzidine. By
contrast, a control polyaniline reaction mixture prepared similarly
using hydrochloric acid in place of the sulfonic acid was found to
contain a trace of benzidine.
EXAMPLE 2
[0025] A 400-g portion of the aqueous polyaniline suspension
prepared in Example 1 was mixed with 400 g of water and 400 g of
2-propanol. A precipitate formed which was easily removable from
the aqueous medium by filtration through a filter with 1-micron
pores. The filtration residue was the desired
dodecylbenzenesulfonic acid-doped polyaniline (11.11 g).
EXAMPLES 3-5
[0026] Blends of dodecylbenzenesulfonic acid-doped polyaniline,
prepared and isolated by the method of Examples 1-2, and a
commercially available polystyrene were prepared by mixing the
resins in a Brabender mixer at 220.degree. C. for 5 minutes. The
static decay times of the resulting blend samples were determined
by applying 5,000-volt positive charges thereto and measuring the
time required for the charge to decrease to 500 volts. Three
applications of positive charge were made to each sample at
5-second intervals, followed by three similar applications of
negative charge.
[0027] The average positive and negative charge dissipation times
for each sample are reported in the following table. Comparison is
made with two controls similarly prepared from the control
polyaniline of Example 1; i.e., the polyaniline prepared using
hydrochloric acid and subsequently doped with
dodecylbenzenesulfonic acid.
1 Avg. Avg. positive negative dissipation dissipation Example
Polystyrene, % Polyaniline, % time, V time, V 1 98 2 0.02 0.02 2 95
5 0.01 0.01 3 90 10 0.01 0.01 Control 1 98 2 6.56 2.37 Control 2 95
5 6.29 2.40
[0028] The results in the table clearly demonstrate the superior
conductivity of the doped polyaniline prepared by the method of the
invention, as compared with polyaniline prepared conventionally and
subsequently doped.
* * * * *