Preparation of the thermally stable conducting polymer PEDOT - Sulfonated poly(imide)

Article abstract of DOI:10.1016/j.polymer.2010.01.048

We describe the template polymerization of EDOT with sulfonated poly(amic acid) (SPAA), resulting in a stable conducting polymer aqueous dispersion, PEDOT-SPAA, with particle size ca. 63?nm. In films of PEDOT-SPAA, the sulfonated poly(amic acid) template undergoes imidization within 10?min at temperatures greater than 150?°C, resulting in PEDOT-sulfonated poly(imide) (PEDOT-SPI) with 10-fold conductivity enhancement. This material is highly thermally stable as compared to PEDOT-PSS. Thermal stability is necessary for many processing applications of conducting polymers, including annealing for OPVs and melt-processing of polycarbonate for device encasement. Isothermal TGA experiments were run at 300?°C for PEDOT-PSS and PEDOT-SPAA and we found that PEDOT-SPAA had a smaller slope for degradation. Annealing of films at 300?°C for 10?min caused the conductivity of PEDOT-PSS films to be unmeasurable (<1?×?10^-5?S/cm), while those of PEDOT-SPAA increased 6-fold. Secondary doping of the PEDOT-SPAA system with additives commonly used for PEDOT-PSS was also investigated.

Full text of DOI:10.1016/j.polymer.2010.01.048

Polymer 51 (2010) 1231–1236
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Preparation of the thermally stable conducting polymer
PEDOT – Sulfonated poly(imide)
,
,
Bongkoch Somboonsub a 1, Michael A. Invernale b 1, Supakanok Thongyai a, Piyasan Praserthdam a,
Daniel A. Scola b, Gregory A. Sotzing b
,
*
a Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University,
Bangkok 10330, Thailand
b University of Connecticut, Department of Chemistry and the Polymer Program, 97 North Eagleville Road U-3136, Storrs, CT 06269-3136, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
We describe the template polymerization of EDOT with sulfonated poly(amic acid) (SPAA), resulting in
a stable conducting polymer aqueous dispersion, PEDOT-SPAA, with particle size ca. 63 nm. In films of
PEDOT-SPAA, the sulfonated poly(amic acid) template undergoes imidization within 10 min at tempera-
tures greater than 150 ꢀC, resulting in PEDOT-sulfonated poly(imide) (PEDOT-SPI) with 10-fold conductivity
enhancement. This material is highly thermally stable as compared to PEDOT-PSS. Thermal stability is
necessary for many processing applications of conducting polymers, including annealing for OPVs and
melt-processing of polycarbonate for device encasement. Isothermal TGA experiments were run at 300 ꢀC
for PEDOT-PSS and PEDOT-SPAA and we found that PEDOT-SPAA had a smaller slope for degradation.
Annealing of films at 300 ꢀC for 10 min caused the conductivity of PEDOT-PSS films to be unmeasurable
(<1 ꢁ 10ꢂ5 S/cm), while those of PEDOT-SPAA increased 6-fold. Secondary doping of the PEDOT-SPAA
system with additives commonly used for PEDOT-PSS was also investigated.
Received 18 November 2009
Received in revised form
19 January 2010
Accepted 23 January 2010
Available online 1 February 2010
Keywords:
Conducting polymers
Template polymerization
Thermal stability
Published by Elsevier Ltd.
1. Introduction
the p-doped form [10], high conductivity [11], good film formation
[12], and excellent transparency in the doped state [13]. PEDOT-PSS
Conducting polymers such as polypyrroles, polythiophenes,
polyanilines, and poly(para-phenylene-vinylenes) have attracted
much attention due to their light weight [1], high conductivities,
electrochromic properties [2], and use in a wide variety of appli-
cations such as organic light emitting diodes (OLEDs) [3], organic
photovoltaic devices (OPVs) [4], capacitors [5], and sensors [6].
Poly(3,4-ethylenedioxythiophene) (PEDOT) is among the most
popular conducting polymers, having achieved commercialization
in the form of a colloidal dispersion in water, PEDOT-PSS. It has
shown good conductivities, ranging from 10ꢂ2 to 10ꢂ5 S/cm for
OLED grade [7]. However, PEDOT alone is an insoluble polymer in
common solvents. This issue was solved by template polymeriza-
tion with a polyanion, poly(styrene sulfonic acid) (PSSA). PSSA is
a charge-balancing dopant during polymerization in water which
allows for the formation of a colloidal dispersion of poly(3,4-
ethylenedioxythiophene)-poly(styrenesulfonic acid) or PEDOT-
PSS [8,9]. This material has achieved popularity for applications
due to its many advantageous properties, such as high stability in
dispersed in water can easily be spin-coated (among other
methods) [14], resulting in transparent films that have relatively
high electrical conductivity (0.05–10 S/cm) [10]. PEDOT-PSS has
been used as a transparent electrode for electrochromic devices as
well as a hole-injection layer for solar cells [15–17].
However, the thermal stability of PEDOT-PSS has hindered its
use for high-temperature processing or applications. It is stable up
to 200 ꢀC [18], however annealing beyond this temperature causes
a marked decrease in conductivity [19]. Electrochemically prepared
PEDOT is stable up to 300 ꢀC, based on our own TGA measurements.
It is therefore possible that the use of a new template may allow for
higher thermal stability of the conducting polymer. It is not likely
that devices using PEDOT-PSS will ever be subjected to operating
temperatures approaching these degradation limits [20], yet
a variety of processing steps may easily exceed them. For example,
annealing with secondary dopants or additives is a common prac-
tice, but again, above 200 ꢀC (or for prolonged periods at 180 ꢀC),
conductivity will suffer instead of improve. Melt-processing of
polycarbonate to create ballistic-type coatings (temperatures ca.
220 ꢀC) might be a viable processing step for an electrochromic
device or a photovoltaic, as well. This would also create problems
for PEDOT-PSS, being above the desired thermal range for the
* Corresponding author. Tel.: þ1 860 486 4619; fax: þ1 860 486 4745.
E-mail address: sotzing@mail.ims.uconn.edu (G.A. Sotzing).
1
Equally contributing authors.
0032-3861/$ – see front matter Published by Elsevier Ltd.
doi:10.1016/j.polymer.2010.01.048

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B. Somboonsub et al. / Polymer 51 (2010) 1231–1236
polymer. With these obstacles in mind, a different template was
conceived for the preparation of PEDOT-based conductors.
films, without secondary dopants. These films exhibited higher
thermal stability without the loss of conductivity (up to 300 ꢀC).
Poly(3,4-ethylenedioxythiophene)-sulfonated poly(imide) films
can resist higher temperatures than PEDOT-PSS and still maintain
their conductivity.
Faure and coworkers found the first sulfonated five-membered
ring polyimides from 4,40-oxydiphthalic anhydride (O-DPDA),
which were practically tested in fuel cell systems [21]. A major
application of condensation polyimides is as thin films in elec-
tronics packaging, wire insulation, and gas separator membranes
[22]. It is well-known that polyimides have found wide applications
in many industrial fields due to their excellent thermal stability
[23], high mechanical strength [24], good film forming ability, and
superior chemical resistance [25]. They have also been used as
dielectric materials for circuitry applications [26]. The creation of
a conducting polymer–polyimide complex, using the precursor
poly(amic acid) as a new template, represents a significant step
towards the development of highly conductive and highly ther-
mally stable polymeric systems. Further, such a composite should
exhibit better adhesion to a polyimide dielectric material, partic-
ularly upon heat treatment.
Some applications for which these conducting polymer disper-
sions are suitable require high conductivity, as well. Conductivity in
polymer systems has previously been improved by so-called
secondary doping [27]. The addition of a dopant such as glycerol
[11,28,29], sorbitol [10,11,30], or a mixture of sorbitol, N-methyl-
pyrrolidone (NMP), and isopropanol, dimethyl sulfoxide (DMSO)
[31], N,N-dimethylformamide (DMF), tetrahydrofuran (THF) to
improve conductivity have been investigated. The morphological
changes induced by the presence of the dopants are important
factors in the increased conductivity for doped films. The addition
of a polar solvent, such as dimethyl sulfoxide (DMSO) to PEDOT-PSS
was found to increase the conductivity by a factor of 100, attributed
to the screening effect. Furthermore, Winter et al. [32] found that
sustained heating at 150 ꢀC causes irreversible structural changes in
the PEDOT main chain and further shows that electrical properties
of conducting polymers are strongly dependent on film
morphology and chemical and physical structure. These properties
are in turn affected by the annealing temperature.
2. Experimental
2.1. Materials
4,40-Diaminodiphenyl ether (4,40-ODA), 4,40-oxydiphthalic
anhydride (O-DPDA), triethylamine (Et3N), m-cresol, fuming
sulfuric acid (SO3, 20%), poly(styrene sulfonic acid) (18 wt.% in
water), iron (III) p-toluene sulfonate hexahydrate, 3,4-ethyl-
enedioxythiophene (EDOT), lithium trifluoromethane sulfonate,
and N,N-dimethylformamide (DMF) were purchased from Sigma–
Aldrich. EDOT was distilled before use. Concentrated sulfuric acid
(95%), sodium hydroxide (NaOH), hydrochloric acid (HCl), and
acetone were purchased from Fisher Scientific and were used as
received. SurfynolÒ 2502 surfactant was purchased from Air
Products, Inc.
D-Sorbitol 97% and ion-exchange resin DOWEX
50WX8 50–100 mesh were purchased from Acros Organics. Dialysis
tubes (Molecular weight cut off [MWCO] ¼ 3.5 to 5 kDa) were
purchased from Spectrum Laboratories Inc.
2.2. Preparation of monomer and poly(amic acid) (SPAA)
2.2.1. Synthesis of 4,40-diaminodiphenyl ether-2,20-disulfonic
acid (4,40-ODADS)
To a 100 mL three-neck flask with a stirring device was added
2.00 g (10.0 mmol) of 4,40-diaminodiphenyl ether (4,40-ODA). The
flask was cooledin an ice bath, and then 1.7 mL of concentrated (95%)
sulfuric acid was slowly added with stirring. After 4,40-ODA was
completely dissolved, 10.5 mL of fuming (SO3 20%) sulfuric acid was
slowlyadded to the flask. The reaction mixture was stirred at 0 ꢀC for
2 h and then slowly heated to 80 ꢀC and kept at this temperature for
an additional 3 h. After cooling to room temperature, the slurry
solution mixture was carefully poured onto 20 g of crushed ice. The
resulting white precipitate was filtered off and then redissolved in
a sodium hydroxide solution. The basic solutionwas filtered, and the
filtrate was acidified with concentrated hydrochloric acid. The solid
was filtered off, washed with water and methanol successively, and
dried at 80 ꢀC in vacuum oven overnight [34].
Herein, the use of a sulfonated poly(amic acid) for the template
polymerization of PEDOT is accomplished, resulting in a stable
colloidal dispersion in water, PEDOT-SPAA, shown in Scheme 1. The
dispersions obtained are comparable to PEDOT-PSS in terms of
particle size, film forming properties, and, most importantly,
conductivity. This system, PEDOT-SPAA, undergoes a conversion to
the poly(imide) form (PEDOT-SPI) upon heating (Scheme 1),
confirmed by FTIR measurements [33]. The innovativeness of this
work is that unlike templates formerly used for PEDOT, this
template undergoes a chemical transformation in the annealing
process that can have an effect on the resulting morphology of the
films. Imidization causes a 10-fold increase in conductivity for the
2.2.2. Synthesis of sulfonated poly(amic acid) (SPAA)
To a 100 mL three-neck flask with N2 inlet and outlet was added
0.5467 g (1.5171 mmol) of 4,40-ODADS, 6 mL of m-cresol, and
0.3617 g (3.5745 mmol) of triethylamine. After 4,40-ODADS was
Scheme 1. Representation of water-dispersible PEDOT-SPAA undergoing conversion to the thermally stable PEDOT-SPI.

B. Somboonsub et al. / Polymer 51 (2010) 1231–1236
1233
completely dissolved, 0.4706 g (1.5171 mmol) of O-DPDA was
added and then stirred at room temperature for 24 h. When the
reaction was complete, the reaction mixture was decanted into
acetone (75 mL), filtered, washed with acetone (25 mL, 2 times),
and dried at 50 ꢀC in a vacuum oven overnight (0.8511 g, 83.66%
yield).
performed by a Perkin–Elmer TGA 7 series analysis system at
a heating rate of 20 ꢀC/min under air at a flow rate of 60 mL/min.
Gel Permeation Chromatography (GPC) was done using a millipore
model 150-C GPC system; DMAC was used as the mobile phase. The
results were calibrated by standards of poly(methyl methacrylate).
Nuclear Magnetic Resonance (NMR) 1H NMR spectra were recorded
on a Bruker DMX-500 NMR Spectrometer. Elemental analysis was
performed using a Vario Micro Elementar CHNS system. The
PEDOT-PSS and PEDOT-SPAA particles were imaged using JEOL
2010 Fas and Philips EM420 transmission electron microscope.
Conductivities were measured using a four-line collinear array
utilizing a Keithley Instruments 224 constant current source and
a 2700 Multimeter. The polymer was coated on the glass substrate
having four gold coated leads on the surface across the entire width
of the polymer and 0.25 cm apart from each other. The current was
applied across the outer leads and voltage was measured across the
inner leads.
2.2.3. Purification
The sulfonated poly(amic acid) was purified via dialysis tube.
SPAA dissolved in water was loaded inside the dialysis tube and
soaked in DI water for 24 h, changing the water twice (2 times at
12 h each).
2.2.4. Ion exchange
The purified SPAA salt form was changed to SPAA acid form with
an ion exchange resin of strong acid type DOWEX 50WX8 (cation
exchange). The SPAA salt form was stirred in DI water with the ion
exchange resin (Hþ) for 1 h to convert it to the free acid form
(SO3H); it was centrifuged and filtered in a crucible filter (pH ca. 1),
and then dried at 50 ꢀC in vacuum oven overnight. Elemental
analysis of sulfonated poly(amic acid) (SPAA) was (Theoretical/
Found); %C (50.152/49.411), %H (2.705/4.190), %N (4.177/4.763),
%S (9.564/7.871). Molecular weight and molecular weight distri-
butions of SPAA were Mn ¼ 20,769, Mw ¼ 35,502, PDI ¼ 1.71.
3. Results and discussion
3.1. Monomer synthesis and polymerization
4,40-Diaminodiphenyl ether-2,20-disulfonic acid (4,40-ODADS)
was synthesized by direct sulfonation of the 4,40-diaminodiphenyl
ether (4,40-ODA). Fuming sulfuric acid was used as a sulfonating
agent. First, 4,40-ODA was reacted with concentrated sulfuric acid
(H2SO4) to form the sulfuric acid salt of 4,40-ODA. Second, SO3 in
fuming sulfuric acid reacted with 4,40-ODA at 80 ꢀC. The monomer
structure was confirmed by 1H NMR and FTIR. The FTIR spectrum
shows absorptions at a) 1031.8 and b) 1088.3 cmꢂ1 for the sulfonic
acid group, and at c) 3481.7 cmꢂ1 assigned to NH2 of the diamime.
The sulfonation primarily occurred at the meta position.
2.3. Template polymerization of EDOT and poly(styrenesulfonic
acid) (PEDOT-PSS)
To a 25 mL one neck flask, 51.12 mg (0.36 mmol) of EDOT and
0.697 g of 18 wt.% PSSA aqueous solution were added. To this
suspension 257.53 mg of iron (III) p-toluene sulfonate hexahydrate
was added. The total mass of all the reactants was adjusted to 10 g
by adding an appropriate amount of de-ionized water. The reaction
mixture was stirred vigorously for 24 h at room temperature
leading to a dark blue dispersion, purified according to literature
procedure [35,36].
Sulfonated poly(amic acid) polymerization of O-DPDA and 4,40-
ODADS was carried out in m-cresol medium in the presence of
triethylamine (Et3N). The poor solubility of 4,40-ODADS in
m-cresol was improved by the addition of Et3N. The reaction was
carried out at room temperature to prevent any imidization from
occurring at this stage. The poly(amic acid) polymerization is an
exothermic reaction [37]; if the reaction was carried out at
a higher temperature, hydrolysis would have occurred, producing
lower molecular weight and unstable polymers. The poly(amic
acid)s in the salt form were converted to the free acid form (Hþ) by
using a strong acid ion exchange resin. The structure of poly(amic
acid) in acid form was confirmed with FTIR. The broad absorption
band at 3476.9 cmꢂ1 is assigned to the absorbed water in the
sample (the sulfonic acid groups are highly hydrophilic). The
strong absorption bands around 1719.7 cmꢂ1 are assigned to
the symmetric imide C]O stretching, however this peak did not
indicate complete imidization. Complete imidization will occur
after heating at 180 ꢀC, wherein two molecules of water will be
liberated from the poly(amic acid) backbone and result in cycli-
zation to the polyimide. The peak at 1663.3 cmꢂ1 indicate the
absorption bands of carbonyl group (CONH) and peak at ca. 2500–
3500 cmꢂ1 indicate the absorption bands of the carboxylic acid
2.4. Template polymerization of EDOT and sulfonated
poly(amic acid) (PEDOT-SPAA)
To a 25 mL one neck flask, 21.30 mg (0.15 mmol) of EDOT and
0.200 g of SPAA were added. To this suspension 103.2 mg of iron (III)
p-toluene sulfonate hexahydrate was added. The total mass of all
the reactants was adjusted to 10 g by adding appropriate amount of
de-ionized water. The reaction mixture was stirred vigorously for
7 days at room temperature leading to a dark blue dispersion,
purified according to literature procedure [35,36].
2.5. Preparation of PEDOT-PSS and PEDOT-SPAA films
Films were prepared by spin coating, for 60 s at 3000 rpm,
PEDOT-PSS, PEDOT-SPAA and doped PEDOT-SPAA onto glass slides
at room temperature. The films were annealed at 180 ꢀC for 10 or
90 min, and 300 ꢀC for 10 min for improving conductivities with
thermal treatment. Separate films of each material were evaluated
for conductivity at room temperature after annealing. PEDOT-SPAA
(COOH). The sulfonic acid groups (SO3H) appear at 1029.0 cmꢂ1
,
which confirmed formation of the prepared poly(amic acid).
films were also prepared with 5 wt.% of D-sorbitol, 0.1 wt.% DMF,
0.1 wt.% SurfynolÒ 2502, and with all three components.
3.2. Conductivity
2.6. Measurements
Conductivity for PEDOT-PSS and PEDOT-SPAA films was
measured via the four-point probe technique. We observed
a successful increase in conductivity by heat treatment at 180 ꢀC for
10 min of the PEDOT-SPAA, resulting in PEDOT-SPI. Without the
addition of dopants, conductivities for the PEDOT-SPI were found to
be 10-fold greater, while those of PEDOT-PSS showed no change.
Fourier transform infrared spectroscopy (FTIR) was performed
using a MAGNA-IR560. Spectra was taken on ground powder in
a KBr matrix with a scanning range of 500–4000 cmꢂ1, 64 scans at
a resolution of 4 cmꢂ1. Thermogravimetric Analysis (TGA) was

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B. Somboonsub et al. / Polymer 51 (2010) 1231–1236
Table 1
This increase is attributed to the imidization reaction which occurs
at this temperature. This imidization was confirmed by FTIR
measurements, as shown in Fig. 1. The conversion of the SPAA
template to SPI is shown in Fig. 1 I, while the conversion of
PEDOT-SPAA to PEDOT-SPI is shown in Fig. 1 II. In both cases, the
peaks at 1778.6 cmꢂ1 and 1718.6 cmꢂ1 correspond to the imide
form and the amide form, respectively. This confirmed that
imidization takes place during the relatively short curing process.
After heat treatment, the chain alignment in thin polymer films
often changes with temperature, leading to modified morphol-
ogies. The peak at 1191.7 cmꢂ1 in Fig. 1 II indicated stretching in the
ethylenedioxy group in structure which is differential peak from SPI
and SPAA. The other peaks at 1515, 1473, 1388, 1311 cmꢂ1 indicate
the C]C and CeC bonds in thiophene.
Films were also prepared and annealed for 90 min at 180 ꢀC. It is
known that films of PEDOT-PSS can be heated in air at 100 ꢀC for up
to 1000 h with no change in conductivity [13]. However, at this
temperature for this time, PEDOT-PSS was reduced to 84% of its
conductivity, while PEDOT-SPI films exhibited a 3-fold improve-
ment over the PEDOT-SPAA. Annealing at 300 ꢀC for 10 min resulted
in PEDOT-PSS samples that could no longer be measured
(<1 ꢁ 10ꢂ5 S/cm) whereas PEDOT-SPI films showed a 6-fold
increase in conductivity. These conductivities are summarized in
Table 1.
Conductivities of PEDOT-PSS (in-house) and PEDOT-SPAA. Upon annealing, PEDOT-
SPAA imidizes to PEDOT-SPI.
Processing
temperature
20 ꢀC
PEDOT-PSS
PEDOT-SPAA
Conductivity (S/cm)
Std. Dev.
Conductivity (S/cm)
Std. Dev.
Conductivity (S/cm)
Std. Dev.
3.15 ꢁ 10ꢂ4
4.03 ꢁ 10ꢂ5
2.65 ꢁ 10ꢂ4
3.32 ꢁ 10ꢂ5
<1 ꢁ 10ꢂ5
<1 ꢁ 10ꢂ5
1.12 ꢁ 10ꢂ4
8.69 ꢁ 10ꢂ6
2.96 ꢁ 10ꢂ4
5.49 ꢁ 10ꢂ6
6.06 ꢁ 10ꢂ4
4.84 ꢁ 10ꢂ5
180 ꢀC (90 min)
300 ꢀC (10 min)
a combination of all three dopants. Conductivity was measured at
room temperature (PEDOT-SPAA) and after annealing at 180 ꢀC and
300 ꢀC (PEDOT-SPI). The conductivity values for this series of
experiments are listed in Table 2. It was found that, upon annealing,
films of PEDOT-SPI doped with D-sorbitol or DMF were observed to
have a 100-fold increase in their conductivity. The values observed
were comparable to commercially available PEDOT-PSS
dispersions.
3.3. Thermal stability of PEDOT-PSS and PEDOT-SPAA films
The effect of secondary dopants on the PEDOT-SPAA/PEDOT-SPI
system was also investigated. Films were prepared using pristine,
5 wt.%
The thermal properties of PEDOT-SPAA and PEDOT-PSS, in an air
atmosphere, were investigated (details in Supporting Information).
Isothermal TGA analyses were run at a variety of temperatures for
5 h in order to assess the long term thermal stability of these
systems. At 300 ꢀC, the thermal stability of PEDOT-SPI was higher
than that of PEDOT-PSS; the slope of degradation was more
pronounced for PEDOT-PSS (Fig. 2). The overall mass loss for
PEDOT-SPAA is 10.7% after heating at 300 ꢀC for 300 min. By
comparison, PEDOT-PSS lost 33.2% of its mass under the same
conditions.
D
-sorbitol, 0.1 wt.% DMF, 0.1 wt.% SurfynolÒ 2502, and
3.4. Particle size of colloidal dispersions
The particle size of the colloidal dispersions PEDOT-PSS and
PEDOT-SPAA were investigated by TEM, as shown in Fig. 3. Fig. 3a
shows the particle sizes for a sample of PEDOT-SPAA, averaging ca.
63 nm. Fig. 3b shows the particle sizes for PEDOT-PSS, averaging ca.
137 nm.
Table 2
Conductivities of secondary-doped PEDOT-SPAA at various processing tempera-
tures. Upon annealing, PEDOT-SPAA imidizes to PEDOT-SPI.
Processing
PEDOT-SPAA
DMF 0.1 wt.%
temperature
20 ꢀC
Conductivity (S/cm)
Std. Dev.
Conductivity (S/cm)
Std. Dev.
Conductivity (S/cm)
Std. Dev.
2.04 ꢁ 10ꢂ4
3.42 ꢁ 10ꢂ3
5.83 ꢁ 10ꢂ3
1.18 ꢁ 10ꢂ3
6.47 ꢁ 10ꢂ4
3.73 ꢁ 10ꢂ5
5.76 ꢁ 10ꢂ4
6.09 ꢁ 10ꢂ5
8.99 ꢁ 10ꢂ2
8.28 ꢁ 10ꢂ2
4.25 ꢁ 10ꢂ2
2.03 ꢁ 10ꢂ2
180 ꢀC (10 min)
300 ꢀC (10 min)
Processing
Surfynol
D
-sorbitol
Combination
temperature
0.1 wt.%
5 wt.%
20 ꢀC
Conductivity
(S/cm)
Std. Dev.
Conductivity
(S/cm)
Std. Dev.
Conductivity
(S/cm)
1.82 ꢁ 10ꢂ4
4.22 ꢁ 10ꢂ2
3.78 ꢁ 10ꢂ4
2.51 ꢁ 10ꢂ5
3.33 ꢁ 10ꢂ4
5.84 ꢁ 10ꢂ3
2.00 ꢁ 10ꢂ2
9.33 ꢁ 10ꢂ5
4.34 ꢁ 10ꢂ3
180 ꢀC (10 min)
300 ꢀC (10 min)
3.59 ꢁ 10ꢂ5
5.68 ꢁ 10ꢂ3
3.51 ꢁ 10ꢂ3
6.56 ꢁ 10ꢂ3
8.54 ꢁ 10ꢂ4
3.74 ꢁ 10ꢂ3
Fig. 1. (I) FTIR spectrum of a) SPI, b) SPAA. (II) FTIR spectrum of a) PEDOT-SPI, attained
after annealing b) PEDOT-SPAA. In each case, the peak at 1778.6 cmꢂ1 indicates
imidization. The peak at 1191.7 cmꢂ1 corresponds to the ethylenedioxy bonds in
PEDOT [38].
Std. Dev.
1.48 ꢁ 10ꢂ3
1.50 ꢁ 10ꢂ3
1.13 ꢁ 10ꢂ3

B. Somboonsub et al. / Polymer 51 (2010) 1231–1236
1235
4. Conclusion
The use of a sulfonated poly(amic acid) for the template poly-
merization of PEDOT was accomplished, resulting in PEDOT-SPAA.
This offers an alternative route for the preparation of PEDOT
while using a template which can be chemically changed to a poly-
(imide) that imparts greater thermal stability to the system. By
polymerizing 3,4-ethylenedioxythiophene (EDOT) in the presence
of a sulfonated poly(amic acid) in water, a stable colloidal dispersion
was prepared. Thermal treatment of this material at 180 ꢀC (form-
ing PEDOT-SPI) was shown to boost conductivities, even without
the addition of dopants (10-fold increase). The use of D-sorbitol,
DMF, and a surfynol to increase the properties of the dispersion
resulted in conductivities which more closely match those of
in-house prepared PEDOT-PSS. The thermal stability of PEDOT-
SPAA (and the corresponding PEDOT-SPI) was a large improve-
ment over PEDOT-PSS. PEDOT-SPI displayed an increase in
conductivity at 300 ꢀC while PEDOT-PSS dropped below the
measurable limit (<1 ꢁ 10ꢂ5 S/cm). The dopants used were those
commonly associated with PEDOT-PSS, however these materials
(particularly alcohols, sugars, and low-boiling solvents) are not
amenable to high temperature applications. We are currently
investigating the use of more appropriate small-molecule additives
that can withstand the high temperatures used and more favorably
associate with the amic acid and imide backbones. This conductive
dispersion is a promising step towards highly conductive and highly
thermally stable materials. Its use in applications or processing
steps which require temperatures greater than 180 ꢀC would relieve
the property losses observed in PEDOT-PSS at these temperatures.
Fig. 2. Isothermal TGA at 300 ꢀC for PEDOT-SPAA (solid line) and PEDOT-PSS (dashed
line). Samples were dried for 30 min at 75 ꢀC before mass loss measurements were
taken.
Acknowledgements
Dr. Sotzing and Dr. Scola wish to thank the Institute of Materials
Science and the Polymer Program at the University of Connecticut.
Dr. Thongyai and Dr. Praserthdam wish to thank the Chulalongkorn
University Dutsadi Phiphat Fund.
Appendix. Supporting information
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.polymer.2010.01.048.
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