ELSEVIER
Synthetic
Metals 84 (1997)
129-130
In situ polymerization of aniline within lightly sulfonated polystyrene
Yueping Fu, R. A. Weiss
Polymer Science Program and Department of Chemical Engineering
University of Connecticut, Storm, CT 06269-3136, LX4
Abstract
Highly conductive polyaniline/sulfonated
polystyrene (PANI/HSPS)
composites were synthesized by in situ polymerization
of aniline within HSPS matrixes. The amount of polyaniline, the conductivity and the morphology of the composite films depend
on the sulfonation level of HSPS and the immersion time in the aniline solution. A maximum conductivity of 0.1 S/cm and high
transmittance of 80% (at 460-680 nm) have been achieved.
Keywords:
1.
Polyaniline,
sulfonated
polystyrene,
UV-Vis-NIR
Introduction
composite
3. Results
As an important
member of the conducting
polymer
family, polyaniline
shows very promising industrial application because of its good environmental
stability and facile
synthesis [l]. PANI/PE
and PANI/PET
composites were
prepared by consecutively soaking PE or PET films in pure
aniline and oxidant solution or vapor [2, 31. The diffusion of
aniline monomer and oxidant can cause nonhomgeneous
distribution of PANI within the polymer matrix: the PANI is
mainly restricted on the surface layer.
In this paper, we report the chemical synthesis of PAN1
within lightly sulfonated polystyrene. The randomly distributed sulfonic acid groups on the polystyrene main chain form
ionic domains and act as templates to protonate aniline to
form the aniline salt. Polymerization
of aniline is initiated
within these fixed ionic domains of the matrix by diffusion of
an oxidant. The resulting composites show improved compositional uniformity throughout the ionomer matrix.
2.
absorption,
and
discussions
Polymerization of aniline within HSPS matrix is expected
to be a diffusion controlled process. FeC13 was used as an
oxidant for all the synthesis instead of the commonly used
ammonium peroxydisulfate (APS). This is because of the poor
wetability
and diffusion of APS within polymers, which
results in nonuniformity
of PAN1 /HSPS films. The diffusion
of aniline in HSPS is much faster then in PE or PET because of
the acid-base interaction, This protonation is also important
for the following polymerization
because anilinium ions are
required for head-tail chain growth [5]. Sulfonic acid groups on
HSPS also protonate the resulting PANI backbone along with
chloride anion. The polymerization
time was held constant in
all experiments and we assume that it was sufficiently long so
that the FeC13 can access all of the aniline monomer within
the films.
30 4
Experimental
Polystyrene
(Mn = 100,000, M,
= 280,000)
was
sulfonated to 5.3 mol % and 13.5 mol % in dichloroethane at
50 OC with acetyl sulfate following
the procedure
of
Makowski et al [4]. Thin films with thickness of l-5 urn were
spin cast from 10% THF solution, Films with thickness of ca.
0.2 mm were compression molded at 175 OC.
The HSPS films were immersed in 0.35 M aniline aqueous
solution at room temperature for various times (5 min to 240
min). They were then washed with distilled water. Then they
were immersed in 1.0 M aqueous FeC13 solution for a fixed
time of 5 h to initiate polymerization.
Green films were
washed with 1.0 M HCl solution and water, and dried in vacuum
for 24 h. LJV-Vis-NIR
spectra were recorded on Perkin-Elmer
Lambda 900 spectrophotometer.
The conductivity
of PAN1
composite films was measured by, a standard four-point probe
method. SEM was done with an AMR model 1200B
microscope with an EDAX detector.
0379-6779/97/%17.00
Q 1997 Elsevier
PII SO379-6779(96)038694
Science S.A All rights reserved
00
0
5
Timeli2;~i”~/2
Fig. 1. PANI content as function
(+) and 13.5 % (*)HSPS.
)15
of immersion
2o
time in 5.3 %
Fig. 1 shows the weight increase of PANI [(W-WO)/Wo ]
in the HSPS with 5.3 % and 13.5 % sulfonation level as a
function of immersion time in the aniline solution. The PAN1
Y. Fu, R.A. Weiss/Synthetic
130
Met&
84 (1997)
129-130
0.50’
*’ ”
’ m”
’ w* ”
”
”
”
”
_
0.40:
0.30s
0.2E
O.lG
00
0.0’
5Timel/Z;;i,1/2)15
0
2o
Fig. 2. Linear region of Fig, 1.
, , , , , , , , , , , , , , , , , , , , , 500
1000
1500
2000
2500
Wavelength
(nm)
Fig. 4. UV-Vis-NIR
of PANUHSPS
thin film.
weight increased with the square root of immersion time in
aniline solution, and leveled off beyond 100 min. For the
same immersion time, the PANI content is higher in 13.5 mol
% HSPS than in 5.3 mol % HSPS because of the more favorable
adsorption of aniline monomer with higher sulfonic acid
content of the ionomers. As shown in Fig. 2, a linear relationship of PAN1 content vs. square root of immersion time was
found for the early immersion
stage. This indicates that
diffusion of aniline monomer within HSPS is Fickian.
l.OE+O 3
o.oo:, , , , , , , , , , , , , , , , , , , , ,:
l.OE-1 T
500
550
Wavelength
l.OE-2;
Fig. 5. Transmittance
l.OE-3;
1 .OE-4
of PANI/HSPS
600
(nm)
650
at 460-680 nm.
/%
, , , , , , , , , , , , , , ,
0
Fig. 3. Conductivity of composites vs. immersion
% (+) and 13.5 % (0) HSPS.
time in 5.3
Fig. Sshows the conductivity of PANI/HSPS composites
increased with the immersion time. This is because the amount
of adsorbed aniline monomer increased with time,
Fig. 4 shows the UV-Vis-NIR
spectra of PANI/HSPS (5.3
% sulfonation level) thin film. The absorption peak at 870 nm
is characteristic of the polaron band transition from conducting
PANI. The transmittance at 460-680 nm is above 70% (Fig. 5).
SEM and X-ray microanalysis on the cross section of
PANI/HSPS composites shows that PAN1 is initially deposited
on the surface layer for short immersion time, but penetrates
throughout the film as the immersion time is increased beyond
1 hour [6].
Acknowledgment
We gratefully acknowledge Connecticut Innovations, Inc.
for financial support for this work and Yacob Ghebremeskel
for providing the 13.5 % HSPS material,
References
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[2]
[3]
[4]
[5]
[6]
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