Note: Descriptions are shown in the official language in which they were submitted.
CA 02309194 2000-OS-OS
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Conductive Polymer Compositions
This invention relates to conductive polymer
compositions and more particularly to fluid compositions
based on polyaniline from which conductive fibres, films and
coatings can be made.
The emeraldine base form of polyaniline, doped with a
sulfonic acid, is now well-established as a useful air-stable
conductive polymer (and the leuco base form may also be
useful), but conventional fluid compositions only form good
films if their solids content is rather small, and even then
the films do not draw well. The present invention provides
compositions which are capable of use in a wet-spinning
process for the manufacture of drawn fibres; they are also
useful for the manufacture of drawable films and of coatings
by processes in which a competitive solvent is used to
achieve solidification faster than is possible by solvent
evaporation alone.
The polymer composition in accordance with the invention
is the reaction product of:
(a) a polyaniline in base form;
(b) an aliphatic sulfonic acid wholly free of ring
structures and having in addition to at least one sulfonic
acid group a second hydrogen-bonding functional group; and
(c) an acid solvent having a pKa in aqueous solution at 25°C
less than 5 but substantially higher (more positive) than
that of the sulfonic acid.
While the invention does not depend on any theory and
the applicants do not intend to be bound by theory, it is
thought that the sulfonic acid not only acts as a dopant to
make the polyaniline conductive but also as a solvating agent
to increase the "solubility" of the polymer (the word has
been put in inverted commas because the mixtures are
sometimes considered to be, at least partly, stable
dispersions rather than true (fully solvated) solutions: a
homogenising step will usually be required in forming them).
It is also thought that aliphatic sulfonic acids are less
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CA 02309194 2000-OS-OS
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liable than the bulky sulfonic acids currently in general use
(dodecyl benzene sulfonic acid and camphor-10-sulfonic acid)
to inhibit the alignment of polyaniline molecules that is
presumably desirable for both drawability and conductivity.
The polyaniline is preferably as free of branching and
other defects as possible, and polyanilines of the kind
showing only two substantial peaks in their 13C NMR spectra in
the leuco base form, in accordance with W095/23822, are
preferred. For making fibres and drawn film, high molecular
weight is normally also desirable, but this may not always be
so if the mixture is for use in making coatings.
Preferably the polyaniline is in its emeraldine base
form; alternatively it is possible to use the Ieuco base
form, though for most applications this will eventually need
to be oxidised to the emeraldine form.
The aliphatic sulfonic acid is preferably free of bulky
substituents. Polymerised or polymerisable aliphatic sulfonic
acids have the advantage that they are less likely to migrate
away from the polyaniline, and may therefore be preferred.
High molecular weights are undesirable. Preferred functional
groups are carbonyl, amido, amino and hydroxy, especially
amido and carbonyl.
Specific aliphatic sulfonic acids that appear to be
commercially available and are considered suitable are:
2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)
[HZC=CH-CO-NH-C(CH3)2-CHZ-S03H](the hydrogenated derivative of
this acid can also be used);
N-(2-acetamido)-2-aminoethanesulfonic acid (ACES)
[HZN-CO-CHZ-NH-CHZ-CHz-S03H] ;
N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES)
[ ( HO-CH2-CHZ- ) 2 N-CH2-CHZ-S03H ] ;
3-(amidinothio)-1-propanesulfonic acid
[ H2N- ( C=NH ) -S- ( CHZ ) 3 -S03H ]
3-[bis(2-hydroxyethyl)amino]-2-hydroxy-1-propanesulfonic acid
[ ( HOCHZ-CHZ- ) 2 N-CHZ-CH ( OH ) -CHZS03H ] and
-, -
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CA 02309194 2000-OS-OS
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3-[(l,l-dimethyl-2-hydroxyethyl)amino]-2-hydroxy-
1-propanesulfonic acid
[ HOCHZ-C ( CH3 ) 2 -NH-CHZ-CH ( OH ) -CH2S03H ] .
Of these, ACES and most especially AMPSA (and its oligomers)
are preferred.
The pKa values of aliphatic sulfonic acids are difficult
to measure and not readily accessible, but it may be assumed
that they all have pKa values lower than 1, and in many cases
below 0.
l0 The proportion of sulfonic acid in the mixture may vary
in the usual ranges; mostly a proportion in the range from
0.3 to 1.0 calculated by reference to the number of nitrogen
atoms in the polyaniline will be suitable.
Preferably the acid solvent has a pKa not greater than 4
IS and more especially not greater than 3 or better still 2 or
even 1.5; preferably it is at least 0.5 units larger (more
positive) than that of the sulfonic acid. We prefer to use
carboxylic acids that meet these criteria and especially
those with halogeno- substituents (meaning -C1, -F or -CN).
20 Acid solvents that are liquid at ambient temperature, or not
far above, are preferred. Most preferred is dichloroacetic
acid (pKa = 1.48, melting point 11°C). Other representative
acid solvents and their pKa's (and melting points) are:
acid solvent pKa m. pt (C)
bromoacetic acid 2.69 51
chloroacetic acid 2.85 64
cyanoacetic acid 2.45 68
pyruvic acid 2.39 12
2-chloropropionic acid 2.83 #
2-ketobutyric acid 2.5 34
2-chlorobutyric acid 2.86 #
2-oxo-3-methylpentanoic acid 2.3 14
phosphorous acid 1.3 #
formic acid 3.75 8
CA 02309194 2000-OS-OS
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acrylic acid 4.2 13
acetic acid 4.7 17
melting points noL reaaily avallaxle
The mixtures in accordance with the invention may
include more than one such acid solvent; they may also
include additional solvents (diluents) and/or host polymers
that may become incorporated into the fibres, films or
coatings; we prefer that they do not contain lithium chloride
(or any inorganic electrolytes). The fluid mixtures in
accordance with the invention are green, indicating
protonation of the polyaniline.
l0 The invention includes processes for making fibres,
films and coatings characterised by the step of removing the
acid solvent from the mixtures described by exposing the
mixture to the action of a competitive solvent, by which is
meant a liquid in which the acid solvent in the mixture is
readily soluble but polyaniline is substantially insoluble.
We have found that selected esters and ketones,
including in particular acetone, methylisobutyl ketone and
butyl acetate are effective and suitable competitive
solvents. Water may be too effective for some processes, as
it is usually desirable for some of the acid solvent to
remain as an aid to subsequent drawing (a plasticiser) and
over-rapid solidification may not be conducive to optimum
structure; but aqueous solutions of alcohols, ketones and
esters may prove usable.
Thus the invention includes
l.a process for the manufacture of polyaniline fibre which is
a wet-spinning process in which the mixture described is
caused to pass through the openings) of a spinneret into a
bath of competitive solvent and the resulting filament
optionally drawn simultaneously or subsequently;
2.a process for the manufacture of a polyaniline-coated
substrate in which the mixture described is applied in at
least one layer on the surface of the substrate, the layer,
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CA 02309194 2000-OS-OS
or each layer in turn, is exposed to competitive solvent,
and the coating is subsequently dried; and
3.processes for manufacture of polyaniline film in which a
coating made as just outlined is freed from the substrate
5 (before or after drying) and optionally uniaxially or
biaxially drawn.
Both fibres and films can be cold-drawn (at room
temperature) or drawn at elevated temperatures, up to about
150°C. At present we prefer to draw at temperatures in the
range from 80 to 120, and more especially 90-100°C for fibres
and 100-110°C for films and most especially at the higher end
of each of these last two ranges.
EXAMPLES
The polyaniline starting material for these examples is
an emeraldine base prepared according to the teaching of
W095/23822 and having a molecular weight (MP) measured as
described in that application of about 150,000 Daltons.
Example 1
Polyaniline (3.4678) was ground by a pestle and mortar with
2o AMPSA (4.5338, 57 molecules per hundred nitrogen atoms in the
polyaniline) using a glove box with dry nitrogen atmosphere
to avoid gelation. The ground mixture was added to
dichloroacetic acid (92.08) to give a mixture with a solids
content of 8% by weight (or about l2ow/v, as the acid has a
specific gravity of about 1.5). The mixture was homogenised
for 10 minutes in a Ultraturrax homogeniser running at
20,000 rpm. The homogenisation/protonation is appreciably
exothermic. A portion of the resulting dark green mixture was
cast onto a 125 mm diameter polished silicon wafer and dried
in an oven at 80°C for about 24 hours. The dried film was
peeled from the substrate and found to be 0.202 ~ 0.004 mm
thick; its electrical conductivity was measured using a 4-
wire probe and found to be 177~6 S/cm. A dumbbell with a bar
section 25 mm long and 4.0 mm wide was die-cut from this film
and clamped in a stretching rig; it was heated to 110°C and
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CA 02309194 2000-OS-OS
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then stretched slowly until the applied force reached 6.0 N.
The bar portion of the sample was then 58 mm long (elongation
130%), 0.114 ~ 0.004 mm thick and 2.7 mm wide; its
longitudinal conductivity was 540 S/cm.
Example 2
Polyaniline (0.632 g) was ground with AMPSA (0.868 g, 60
molecules per hundred nitrogen atoms) and added to
dichloroacetic acid (28.5 g) and homogenised, using the same
procedure as before but under ambient atmosphere as the
solids content was only 50, at which level gelation is not
experienced. The solution was cast onto a silicon wafer as
before but then immersed in acetone at room temperature for
ten minutes to "coagulate" the coating by dissolving part of
the dichloroacetic acid. It was dried overnight in the 80°C
oven before peeling from the substrate and cutting dumbbells
as before. The as-cast film had a conductivity of
168 ~ 13 S/cm. A sample with an initial cross-section 4 mm by
0.16 mm was stretched at room temperature at a rate of about
1 mm/min without the load exceeding 5.5 N; in a few minutes,
an elongation of 1150, retracting reversibly to 1000 on
removal of the tension, was obtained. The cross-section after
stretching was 3 mm by 0.11 mm and longitudinal conductivity
344 ~ 35 S/cm. The sample was returned to the stretch rig and
held under a tension of 5.5 N at 110°C; after 10 minutes, the
conductivity was foand to be 408 ~ 40 5/cm, after an hour
459 ~ 40 S/cm and after 3 hours 450 ~ 40 S/cm. The cross-
section at 1150 extension was now 2.7 mm by 0.10 mm. It is
assumed that residual solvent was lost during this annealing
process; there was an appreciable loss of elasticity.
Unstretched samples were also annealed at 110° (for an
hour); this was found to produce a steady decline in
conductivity.
Example 3
Polyaniline (1.517 g) was ground with AMPSA (2.083 g,
60 molecules per hundred nitrogen atoms) and then added under
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CA 02309194 2000-OS-OS
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nitrogen to dichloroacetic acid (36.4 g) over a 5-minute
period while homogenising at 20,000 rpm, generally as in the
preceding examples. Homogenising was continued for a further
minutes to obtain a 9~-solids mixture (by weight - about
5 15o w/v). The mixture was transferred immediately, without
cooling, to a cylindrical dope-pot 25 mm in diameter having
at its bottom end a 140-micrometre filter and a spinneret
consisting of a single hole with a diameter of 150~m. The pot
was removed from the glove box and promptly connected at its
10 top end to a nitrogen gas supply. An electric heating tape
was wrapped round the pot to enable it to be brought to and
held at a temperature of 50 ~ 5°C, and its bottom end was
dipped into two litres of cold butyl acetate in a measuring
cylinder. The nitrogen pressure in the pot was raised to
0.7 MPa (100 psi) to spin a continuous filament, which was
left in the butyl acetate for up to 10 minutes and then dried
in air.
The filament was measured with a micrometer and found to
have a diameter of 0.30 ~ 0.01 mm, and examination with a
scanning electron microscope (including examination of a
surface formed by fracture at liquid nitrogen temperature)
showed it to be smoothly cylindrical and without apparent
voids or granules. Longitudinal conductivity of the filament
was 70 ~ 9 S/cm.
A ten-millimetre length of the filament was stretched at
room temperature at a rate of about lOmm/sec, and was thus
elongated into a fibre 50 mm long and with a uniform cross-
section of 0.10 ~ 0.01 mm. Its conductivity was
810 ~ 200 S/cm and tensile strength at break about 45 MPa
(breaking load 0.4 N) .
Example 4
This was substantially the same as Example 3 except that
the butyl acetate was replaced by acetone.
The filament diameter (as formed) was 0.26 ~ 0.01 mm and
its longitudinal conductivity 90 ~ 8 S/cm.
~ L;',.z:
CA 02309194 2000-OS-OS
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A ten-millimetre length of the filament was stretched as
before and thus elongated into a fibre 80 mm long and with a
uniform cross-section of 0.09 ~ 0.01 mm. Its conductivity was
then 1014 ~ 200 S/cm and tensile strength at break about
60 MPa (breaking load 0.41 N).
Example 5
A filament was made by the same procedure as in
Example 4 but in this case the diameter of the filament as
formed (which is very sensitive to precise conditions) was
found to be 0.15 mm; its conductivity was still about
90 S/cm.
A 29-mm length of this filament was heated to 90°C and
drawn at a uniform rate to achieve a length of 185 mm over a
ten-minute period. This resulted in a fibre 0.059 ~ 0.02 mm
in diameter with a conductivity in a longitudinal direction
of 1950 ~ 180 S/cm.
Example 6
A solution was made using the same procedure as before with
the same polyaniline emeraldine base, AMPSA and
dichloroacetic acid, but in proportions to give 50 molecules
of AMPSA per hundred nitrogen atoms in the polyaniline and a
solids content of only 1.5% by weight and using a 5-minute
homogenisation step followed by centrifuging for 30 minutes
in a typical laboratory centrifuge at 4,500 rpm. Flat glass
substrates were coated with enough of this solution to cover
the surface and spun, using a commercial spin coater, at 1700
rpm about an axis normal to the coated surface and through
its centre and while spinning heated to 120°C using an infra-
red heat lamp until dry (around 3 minutes) to obtain a coating
0.07~m thick, as measured with an ""-step" profilometer. The
film had a conductivity of 60 S/cm, a sheet resistance of 800
ohms per square and an optical transmission of 95% at 550 nm.
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