Highly conductive polyaniline copolymers with dual-functional hydrophilic dioxyethylene side chains

Article abstract of DOI:10.1016/j.polymer.2011.07.052

We investigated new highly conductive polyaniline copolymers bearing a small amount of dual-functional hydrophilic dioxyethylene side chains, which can act as a stabilizer in a heterogeneous dispersion medium in polymerization and a reactive dispersant in polar solvents. Compared to the unsubstituted polyaniline, new polyaniline copolymers maintained their high electrical conductivity of 485 S/cm with camphorsulfonic acid dopant in m-cresol. Moreover, in the alcoholic butoxyethanol solvent with a dodecylbenzenesulfonic acid dopant, new polyaniline copolymers showed enhanced dispersion abilities with very small particle sizes of <10 nm and exhibited a high electrical conductivity of 13 S/cm, which is significantly higher than polyanilines in an organic aliphatic alcoholic solvent (10^-6～1 S/cm). Therefore, new polyaniline copolymers are very interesting materials for electronic applications.

Full text of DOI:10.1016/j.polymer.2011.07.052

Polymer 52 (2011) 4451e4455
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Highly conductive polyaniline copolymers with dual-functional hydrophilic
dioxyethylene side chains
1
*
Eun-Mi Kim , Chan-Keun Jung, Eun-Young Choi, Chunji Gao, Sang-Wook Kim, Suck-Hyun Lee ,
O-Pil Kwon
*
Department of Molecular Science and Technology, Ajou University, Suwon 443-739, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
We investigated new highly conductive polyaniline copolymers bearing a small amount of dual-
functional hydrophilic dioxyethylene side chains, which can act as a stabilizer in a heterogeneous
dispersion medium in polymerization and a reactive dispersant in polar solvents. Compared to the
unsubstituted polyaniline, new polyaniline copolymers maintained their high electrical conductivity of
485 S/cm with camphorsulfonic acid dopant in m-cresol. Moreover, in the alcoholic butoxyethanol
solvent with a dodecylbenzenesulfonic acid dopant, new polyaniline copolymers showed enhanced
dispersion abilities with very small particle sizes of <10 nm and exhibited a high electrical conductivity
of 13 S/cm, which is significantly higher than polyanilines in an organic aliphatic alcoholic solvent
(10ꢀ6w1 S/cm). Therefore, new polyaniline copolymers are very interesting materials for electronic
applications.
Received 22 March 2011
Received in revised form
22 July 2011
Accepted 30 July 2011
Available online 8 August 2011
Keywords:
Conducting polymers
Polyanilines
Nanoparticles
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
polyaniline [6e9]. Even with an optimized dopant and good solvent
system, in many cases, the substituted polyanilines exhibit low
Conducting polymers have attracted considerable interest for
applications, such as organic electrodes for electronic devices
including organic photovoltaics and organic light emitting diodes,
sensors, anti-corrosion coating, and EMI shielding [1,2]. In partic-
ular, polyaniline with high electrical conductivity has been widely
investigated [3,4]. However, the low processability of conducting
polyaniline in common organic solvents due to its low dispersion
ability (or low solubility), has limited these practical applications
[3]. Many approaches have investigated improvement of the
processability of polyanilines including the introduction of highly
soluble substituted groups, such as alkyl, alkoxy and fluorine
groups and oxyethylene groups (or polyethylene glycol)by chemical
modification of the aniline monomer or post-modification of the
emeraldine base (EB) form of the polyanilines [5e9] and graft-
copolymerization of polyanilines onto highly soluble polymers,
polystyrene sulfonic acid [10]. However, the chemical substitution
of polyaniline results in a dramatic decrease in its electrical
conductivity in organic solvents compared to unsubstituted
electrical conductivity of 10ꢀ6w20 S/cm [5e10].
Here, we report new highly conductive polyaniline copolymers
with a small amount of dual-functional hydrophilic dioxyethylene
side chains (see Fig. 1a), which can act as
a stabilizer in
a heterogeneous dispersion medium during polymerization, as
well as a reactive dispersant in polar solvents. Compared to
unsubstituted polyaniline, new polyaniline copolymers S2 main-
tained their high electrical conductivity of 485 S/cm with cam-
phorsulfonic acid (CSA) dopant in m-cresol. Moreover, in alcoholic
butoxyethanol solvent with
a dodecylbenzenesulfonic acid
(DBSA) dopant, new polyaniline copolymers showed enhanced
dispersion abilities with very small particle sizes of <10 nm and
exhibited a high electrical conductivity of 13 S/cm, which is
significantly higher than conventional polyanilines in an organic
aliphatic alcoholic solvent.
2. Experimental section
The chemicals used were obtained from mainly SigmaeAldrich
(aniline, ammonium persulfate, 2-aminophenol, diethyleneglycol
monomethyl ether, p-toluene sulfonic chloride, sodium hydride
(60% dispersion in mineral oil), tetrahydrofuran (99.9%), (1S)-
(þ)-10-camphorsulfonic acid), Shinyo Pure Chemicals (sodium
* Corresponding authors. Tel.: þ82 31 219 2462; fax: þ82 31 219 1610.
E-mail addresses: hyja@ajou.ac.kr (S.-H. Lee), opilkwon@ajou.ac.kr (O.-P. Kwon).
Present address: ELPANI, BiBong, Yangnori 732-6, Hwasung 445-842, Republic
1
of Korea.
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.07.052

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E.-M. Kim et al. / Polymer 52 (2011) 4451e4455
Scheme 1. Synthetic route for aniline monomer M2 with a dual-functional dioxy-
ethylene side chain.
solid. (Yield ¼ 82%). 1H-NMR (CDCl3,
d): 8.145 (s, 1H, eNH),
7.095e6.845 (m, 4H, Ar), 6.675 (s, 1H, eOH), 1.530 (s, C(CH3)3).
2-(2-Methoxyethoxy)ethyl 4-methylbenzenesulfonate: Diethylene-
glycol monomethyl ether (12 g, 0.12 mol) with 4-toluenesulfonyl
chloride (TsCl:19 g, 0.1 mol) was dissolved in THF (200 ml). The
NaH (5.5 g, 0.12 mol) was then added slowly to the resulting solution
and stirred for 3 h. The resulting light-purple solution was filtered to
remove the remaining sodium hydride. The yellow solution was
extracted by dichloromethane. (Yield ¼ 84%), 1H-NMR (CDCl3,
d):
7.793, 7.772 (d, 2H, Ar), 7.341, 7.321 (d, 2H, Ar), 4.176e4.152 (m,
2H, eCH2), 3.697e3.674 (m, 2H, eCH2), 3.586e3.575 (m, 2H, eCH2),
3.571e3.356 (m, 2H, eCH2), 3.347 (s, eCH3), 2.448 (s, eCH3, Ar).
tert-Butyl 2-(2-(2-methoxyethoxy)ethoxy)phenylcarbamate: tert-
Butyl 2-hydroxyphenylcarbamate (10.45 g, 0.05 mol) with potassium
tert-butoxide (6.1 g, 0.055 mol) was dissolved inTHF (200 mL) and the
mixturestirred at40 ꢁC undera N2 atmosphere. 2-(2-Methoxyethoxy)
ethyl 4-methylbenzenesulfonate (15.07 g, 0.055 mol) in THF (50 mL)
was then added drop wise for 30 min using a dropping funnel. The
mixture was stirred for 3 days and the resulting brown solution was
filtered to remove the remaining potassium-tert-butoxide. The brown
solution was then separated by ethyl acetate and water. (Yield ¼ 62%).
1H-NMR (CDCl3, d): 8.064 (s, eNH), 7.803,7.782 (d,1H Ar), 7.342, 7.321
(d, 1H Ar), 6.971e6.859 (m, 4H Ar), 4.204e4.151 (m, CH2),
3.866e3.842 (m, CH2), 3.731e3.715 ((m, CH2), 3.614e3.572 (m, CH2),
3.439 (s, eCH3), 1.582 (s, C(CH3)3).
2-(2-(2-Methoxyethoxy)ethoxy)benzenamine (M2): tert-Butyl
2-(2-(2-methoxyethoxy) ethoxy) phenylcarbamate (6.24 g,
0.02 mol) with trifluoroacetic acid (TFA: 4.56 g, 0.04 mol) in
dichloromethane (40 mL) was stirred at 40 ꢁC for 3 h. The NaHCO3
was added to neutralize the trifluoroacetic acid, and the product
was extracted with dichloromethane and water. (Yield ¼ 71%). 1H-
Fig. 1. (a) Chemical structure of the LE form of the S2 polyaniline copolymer with
a dioxyethylene side chain. (b) Schematic diagram of self-stabilized effect of dual-
functional monomers in the SSDP method. (c) SEM images of the as-synthesized S2-
2 (upper) and unsubstituted PANI (lower) emeraldine salt (ES) particles at a reaction
temperature of 0 ꢁC.
NMR (CDCl3, d): 6.809e6.697 (m, 4H Ar), 4.173e4.148 (m, CH2),
3.869e3.844 (m, CH2), 3.724e3.708 (m, CH2), 3.701e3.573 (m,
CH2), 3.596 (s, eCH3).
bicarbonate), TCI (potassium-tert-butoxide), Samjung (trifluoro-
2.2. Synthesis of new polyaniline copolymers
acetic acid), and Samchun (35% HCl, NH4OH, H2SO4 (95%)).
New polyaniline copolymers S2 with a hydrophilic side chain
and unsubstituted polyanilines PANI were synthesized by the
chemical oxidation of aniline with ammonium persulfate (APS) as
the oxidant [11]. An example synthesis of the S2-2 copolymer
follows: the reactor was cooled to 0 ꢁC with an HCl solution and
chloroform and kept at that temperature for 30 min. Purified
aniline and new synthesizing monomer M2 were added to the
solution (aniline: M2 monomer ¼ 100:2 in molar ratio) and the
ammonium persulfate (APS) dissolved in HCl was added drop wise.
The solution color changed from brown to blue after 3 h. Poly-
merization was performed for 12 h. The polymer powders were
filtered and washed with dichloromethane and acetone and dried
in a vacuum oven. Dried polyaniline (ES form) was dedoped to the
emeraldine base (EB) form using ammonium hydroxide for 24 h.
This EB powder was dried for 48 h in a vacuum oven. IR: quinoid
2.1. Synthesis of monomer
An aniline monomer 2-(2-(2-methoxyethoxy)ethoxy)benzen-
amine (M2) with a dual-functional dioxyethylene side chain was
prepared using the following procedure (see Scheme 1). The 1H-
NMR spectra were recorded on a Varian 400 MHz and the chemical
shifts reported in ppm (d) relative to (CH3)4Si.
tert-Butyl 2-hydroxyphenylcarbamate: 2-Aminophenol (10.9 g,
0.1 mol) dissolved in THF (250 mL) was mixed with NaHCO3 (8.8 g,
0.15 mol) dissolved in deionized water (250 mL). Di-tert-butyl
dicarbonate (t-BOC: 22.7 g, 0.1 mol) was then added to the resulting
solution and stirred for 10 h. The resulting brown solution was
evaporated to remove the THF solvent and produce a light brown

E.-M. Kim et al. / Polymer 52 (2011) 4451e4455
4453
ring (1592w1578 cmꢀ1), benzoid ring (1535w1495 cmꢀ1), C]N
stretching (1310w1290 cmꢀ1), aromatic CeH in-plane bending
(1170w1000 cmꢀ1), CeH out-of-plane bending (830 cmꢀ1), CeO
stretching (1300e1000 cmꢀ1).
solvent, its dual-functional polar side chain can act as a self-
dispersion agent in the organic polar solvent, which lead to
enhanced processability. Since the electrical conductivity of the
substituted polyaniline decreased dramatically with increasing side
chain length [6], as short as possible polar side chain with suffi-
ciently high hydrophilicity (two -(CH2CH2O)- units) were thus
introduced.
2.3. Elemental analysis of S2 copolymers
Fig. 1a shows the chemical structure of the new polyaniline
copolymer (S2) with a dioxyethylene side chain in the leucoemer-
aldine (LE) base form. The dual-functional aniline monomer M2
was synthesized by a reaction of 2-aminophenol with dieth-
yleneglycol monomethyl ether (see Scheme 1). Large amounts of
substituted aniline monomers in the copolymer lead to a decrease
in electrical conductivity [5e10]. Therefore, only a small amount of
dual-functional aniline monomer M2 was used for copolymeriza-
tion. The S2-2 and S2-10 copolymers stand for feeding aniline: M2
molar ratio ¼ 100:2 and 100:10, respectively. For polymerization,
the SSDP method with ammonium persulfate oxidant in a non-
polar chloroform/polar water biphasic system was used, as repor-
Based on elemental analysis (EA) for C, H, and N in the EB form of
the S2 copolymers, the molar ratio of the dual-functional monomer
M2 with a hydrophilic dioxyethylene group to the unsubstituted
aniline monomer was calculated. The EA for S2-2 polymerized at
0
ꢁC was C 74.47%, H 4.99% and N 14.02%. As shown in the figure
below, when x:y ¼ 1 : 5.7, the experimental results were well agree
with those calculated C 74.47%, H 4.96% and N 14.02%, corresponding
to that the molar ratio of M2 monomer to unsubstituted aniline
monomer (M2:aniline ¼ 3.9:100 (molar ratio)). The S2-2 and S2-10
polymerized at ꢀ10 ꢁC, with a final molar ratio of M2 monomer to
unsubstituted aniline monomer of M2:aniline ¼ 3.7:100 and
18.3:100, respectively.
O
O
2CH3
H
N
H
N
H
N
H
N
N
N
N
N
x
y
2.4. Sample preparation and electrical conductivity measurements
ted in Ref. [11,12]. For comparison, unsubstituted polyaniline
(henceforth, noted PANI) was synthesized under identical experi-
mental conditions.
To form the conducting emeraldine salt (ES), the non-
conducting emeraldine base (EB) of S2 copolymers and unsub-
stituted polyaniline (PANI) were first grinded with a dopant for
30 min and slowly added to corresponding solvent: m-cresol for
camphorsulfonic acid (CSA) (aniline: CSA ¼ 2:1 molar ratio) and
butoxyethanol (BuEtOH) for dodecylbenzenesulfonic acid (DBSA)
(aniline: DBSA ¼ 2 : 1.5 molar ratio). The conducting thick films
were casted onto slide glass at 50 ꢁC from the prepared solution.
The electrical conductivity of the substituted and unsubstituted
polyaniline ES films, with sample widths of 1 mm and thicknesses
In polyaniline, these physical properties and electrical conduc-
tivity show wide variations depending on the polymerization
temperature [15]. First, the effect of the polymerization tempera-
ture was examined on a small scale in a 1L reactor. Similar exper-
imental conditions, such as amount of reagents and solvents,
reaction time, impeller shape, stirring speed and reactor, were used
to eliminate the influence of other experimental parameters. To
screen the polymerization temperature for S2 copolymers with
high electrical conductivity, S2 copolymers were polymerized with
different reaction temperatures for a reaction time of 12 h. Con-
ducting S2 copolymer films were prepared using the synthesized
S2 EB copolymers doped with camphorsulfonic acid (CSA) in
m-cresol (aniline: CSA ¼ 2:1 in molar ratio). The dopant/solvent
(CSA/m-cresol) system used for the polyaniline was reported to
produce the highest electrical conductivity due to the primary and
from few micrometers to 30
mm was measured by a four-line
method at room temperature with a Keithley 237 picoamper-
ometer. The distance between each electrodes was 1 mm. To reduce
contact resistance between the polyaniline film and gold wire
electrode, graphite glue was used.
secondary doping effects [3,11]. Fig.
2 shows the electrical
3. Results and discussion
conductivity measured using a four-line method [12] as a function
of the reaction temperature for S2-2 and S2-10. The inherent
viscosity relative to the molecular weight was measured using an
Ubbelohde viscometer with S2 EB copolymers in sulfuric acid at
30 ꢁC and plotted together with the electrical conductivity, as
shown in Fig. 2.
In unsubstituted PANI, the highest conductivity was obtained at
a reaction temperature of ꢀ25 ꢁC, despite the low reaction rate [11].
However, the S2 copolymers were not polymerized at this reaction
temperature due to steric hindrance of the dioxyethylene side-
chains. The electrical conductivity of the S2 copolymers as a func-
tion of the reaction temperature showed similar trends to their
inherent conductivity; the electrical conductivity decreased with
decreasing inherent viscosity as shown in Fig. 2. The S2-2 copoly-
mers showed approximately one order of magnitude higher elec-
trical conductivity than the S2-10 copolymers. Moreover, the S2
copolymers synthesized at a polymerization temperature of 0 ꢁC
exhibit the highest electrical conductivity. It was attributed that the
polymerization temperature of 0 ꢁC may be lowest temperature
Recently, a new polymerization method, self-stabilized disper-
sion polymerization (SSDP) method [11] based on a heterogeneous
solvent system without a stabilizer, was developed. The resulting
polyaniline exhibited high electrical conductivity and metallic
transporting properties [12]. The self-stabilizing effect of the
monomer anilinium chloride on the interface of the biphasic
organic/aqueous solvent system [12] lead to a lower degree of
chemical structural defects (i.e., lower ortho-linked defects) [13].
Here, an aniline analogous monomer 2-(2-(2-methoxyethoxy)
ethoxy)benzenamine (M2) [14] with a dual-functional dioxy-
ethylene side chain was used to enhance the self-stabilizing effects
of the monomer during polymerization (see Fig. 1). Owing to the
high hydrophilicity of the dioxyethylene groups, the polar side-
chains could enhance the self-stabilizing effects of the anilinium
monomer during polymerization in a heterogeneous biphasic non-
polar chloroform/polar water solvent system, as shown in Fig. 1b.
Moreover, when the polyaniline copolymer polymerized using M2
monomer is conducting emeraldine salt (ES) form in an organic

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E.-M. Kim et al. / Polymer 52 (2011) 4451e4455
having moderated molecular weight to overcome the steric
hindrance of the dioxyethylene side-chains. Therefore, the S2-2
copolymer synthesized with smaller amounts of the dual-
functional monomer at a polymerization temperature of 0 ꢁC was
further investigated.
copolymers, the higher molar ratio of the M2 monomer than the
feeding ratio is related to the higher hydrophilicity of the M2
monomer with dioxyethylene groups compared to that of unsub-
stituted aniline monomer. In the SSDP method, the anilinium salts
were polymerized dominantly in the interfaces between the water
and chloroform phases [11,12]. The higher hydrophilicity of the M2
monomer enhanced the self-stabilizing effect during biphasic
polymerization, and consequently the M2 monomers participated
more in the polymerization process at the interface between the
water and chloroform phases.
SEM confirmed the enhancing self-stabilizing effect of the M2
monomer bearing a dioxyethylene side chain. Fig. 1c shows the
SEM images of the as-synthesized S2-2 (upper) and PANI (lower)
emeraldine salt (ES) particles, which were doped with HCl. The S2-
2 copolymers formed much thinner skins compared to that of PANI,
S2-2 copolymers were polymerized at 0 ꢁC in a relatively large-
scale reactor with a 5-L capacity. The EB form of the S2-2 copolymer
showed a molecular weight of Mn ¼ 69,600 and Mw ¼ 215,000,
confirmed by gel permeation chromatography (GPC) in N-methyl-
pyrrolidone (NMP) and an inherent viscosity of 1.04 in sulfuric acid
at 30 ꢁC. Unsubstituted PANI polymerized at 0 ꢁC under identical
conditions, such as amount of reagents and solvents, reaction time,
stirring speed and reactor as described above, showed a similar
molecular weight of Mn ¼ 71,000 and Mw ¼ 266,100 and a similar
inherent viscosity of 1.05.
Scanning electron microscopy (SEM) and elemental analysis
(EA) were performed to examine the self-stabilizing effects of the
anilinium chloride M2 monomer at the interface of a biphasic
non-polar chloroform/polar water solvent system in the SSDP
method (see Fig. 1b). Based on EA for C, H, and N in the EB form,
the molar ratio of the dual-functional monomer M2 with hydro-
philic dioxyethylene group to unsubstituted aniline monomer
in the S2-2 copolymer was M2:aniline ¼ 3.9:100 (molar ratio),
which was higher than the feeding ratio in polymerization
(M2:aniline ¼ 2:100 (molar ratio)). This higher ratio of M2 than
feeding ratio in polymerization was also observed in the S2-10
copolymer (see Experimental section). In the synthesized S2
with a thickness of w200 nm and w3
mm for S2-2 and PANI,
respectively. The S2-2 polymers were polymerized mainly at the
interfaces between the water and chloroform phases. The thinner
skin of the S2-2 morphology can more readily assist in the
dispersion process with small particle sizes than the thicker skin of
the PANI.
Although the stabilizing effects of the M2 monomer and the
thinner skin morphology of the S2-2 copolymers were enhanced,
they showed an electronic structure similar to PANI. As shown in
Fig. 3, the absorption spectra of the EB form in N-methyl-
pyrrolidone (NMP) and ES doped with CSA in m-cresol of both S2-2
and PANI were similar. Both the S2-2 and PANI conducting ES forms
showed a well-developed “free-carrier tail” in the near-infrared
region, which is characteristic of highly conducting materials
[3b]. As expected in the linear absorption properties, the S2-2
copolymers bearing side-chains exhibited high electrical conduc-
tivity: at a polymerization temperature of 0 ꢁC and doped with CSA
in the m-cresol system, S2-2 and unsubstituted PANI films had
a conductivity of 485 and 160 S/cm, respectively. Therefore, the S2-
2 copolymers bearing hydrophilic side-chains maintained the high
electrical conductivity of unsubstituted PANI and exhibit signifi-
cantly higher electrical conductivity than other substituted poly-
anilines (10ꢀ6w20 S/cm) [5e10].
In order to examine the dispersion ability of the S2-2 polymers
in common organic solvents, the dispersion solution in aliphatic
alcoholic solvent was prepared by stirring and milling. The S2-2
copolymer doped with dodecylbenzenesulfonic acid (DBSA) was
added to butoxyethanol (BuEtOH) (aniline : DBSA ¼ 2:1.5 M
ratio). The S2-2/DBSA/butoxyethanol solution exhibited high
dispersion abilities and a high solid content: the solid content in
the solution was 1.6 wt% and 0.8 wt% after 5.0 and 1.2 mm PTFE
filtration, respectively. Fig. 4a and b show transmission electron
Fig. 2. Electrical conductivity with CSA/m-cresol and the inherent viscosity of the EB
form as a function of the reaction temperature for a reaction time of 12 h for (a) S2-2
and (b) S2-10.
Fig. 3. Absorption spectra of the emeraldine base (EB) and emeraldine salt (ES) of the
S2-2 copolymer and PANI.

E.-M. Kim et al. / Polymer 52 (2011) 4451e4455
4455
particle sizes (<10 nm) in alcoholic solvent leads to high electrical
conductivity.
4. Conclusion
We have investigated new highly conductive polyaniline
copolymers S2 that bear a small amount of dual-functional
hydrophilic dioxyethylene side chains, which act both as a stabi-
lizer in a heterogeneous dispersion medium in polymerization and
a reactive dispersant in polar solvents. Compared to unsubstituted
polyaniline PANI, the new polyaniline copolymers S2 maintain their
high electrical conductivity, but showed enhanced dispersion
abilities in organic alcoholic solvents with very small particle sizes
of <10 nm. Therefore, polyaniline copolymers S2 are very inter-
esting materials for electronic applications.
Acknowledgments
This work has been supported by a grant from the Fundamental
R&D Program for Core Technology of Materials funded by the
Ministry of Commerce, Industry and Energy, Republic of Korea,
Priority Research Centers Program through the NRF of Korea funded
by the Ministry of Education, Science and Technology (2010-
0028294) and an Ajou University research fellowship of 2010 (S-
2010-G0001-00057).
Fig. 4. S2-2 ES polyaniline nanoparticles in a butoxyethanol solution: (a) TEM image,
(b) SEM image of the nanoparticles spin-coated on a silicon wafer, (c) schematic
diagram of well-dispersed S2-2 nanoparticles in a polar organic solvent.
microscopy (TEM) and SEM images of S2-2 polyaniline nano-
particles after 1.2 mm filtration. The samples for the SEM image
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