American Journal of Analyt ical Chemistry, 2011, 2, 182-193
doi:10.4236/ajac.2011.22021 Published Online May 2011 (http://www.SciRP.org/journal/ajac)
Copyright © 2011 SciRes. AJAC
In Situ UV–Vis Spectroelectrochemical Studies on the
Copolymerization of Diphenylamine and
o-Phenylenediamine
Lei Zhang, Baoqin Hou, Qiuhua Lang
Department of Chemistry, College of Life and Environment Sciences,
Shanghai Normal University, Shanghai, China
E-mail: chemzl@shnu.edu.cn
Received August 23, 2010; revised January 10, 2011; accepted March 1, 2011
Abstract
The in situ ultraviolet-visible (UV-Vis) spectroelectrochemical study on the copolymerization of diphenyl-
amine (DPA) and o-phenylenediamine (OPD) has been performed at a constant potential of 0.8 V using in-
dium tin oxide (ITO)-coated glass electrodes as working electrode. And also, as a comparison, the electro-
chemical homopolymerizations of DPA and OPD have been investigated by using the in situ spectroelectro-
chemical technique. The intermediate species generated during the electrochemical homopolymerization of
DPA and OPD, and the copolymerization of DPA with OPD have been identified by using the in situ spec-
troelectrochemical procedure. The results reveal the formation of an intermediate in the initial stage of co-
polymerization through the cross-reaction of the cation radicals of DPA and OPD, and the absorption peak
located at 538 nm in the UV–Vis spectra is assigned to this intermediate. To further investigate the copoly-
merization of DPA with OPD, cyclic voltammetry (CV) has been used to study the electrochemical ho- mo-
polymerization of DPA and OPD and also the copolymerization of DPA and OPD with different concen-
tration ratios in solution. The different voltammetric characteristics between the homopolymerization and
copolymerization processes exhibit the occurrence of the copolymerization, and the difference between the
copolymerization of DPA and OPD with different concentration ratios shows the dependence of the copoly-
merization on the concentrations of DPA and OPD. The copolymer has also been characterized by Fourier
transform infrared spectroscopy (FT-IR).
Keywords: o-Phenylenediamine, Diphenylamine, Copolymerization, In Situ UV-Vis Spectroelectrochemistry
1. Introduction
Electronically conducting polyaniline (PANI) has at-
tracted significant attention owing to its environmental
stability and its electrical, optical and electrochemical
properties [1-3]. However, the insolubility of PANI in
common organic solvents and its limited electrochemical
activity in media with pH 4 make its applications dif-
ficult. To extend its application in practice, several stud-
ies have been made toward the improvement of solubility
and processability of PANI. The typical procedures are
as the following: preparation of the substituted PANI
through post-treatment of the base form of PANI [4];
electrochemical or chemical homopolymerization of ani-
line derivatives [5-7]; and the electrochemical or chemi-
cal copolymerization of aniline with different kinds of
ring or N-alkyl substituted aniline derivatives [8-10]. The
improved processability, electrochromism and other
properties over PANI have been noticed for the polymers
derived from the various benzene ring substituted and
N-substituted aniline derivatives. This means that co-
polymerization can provide an alternative and easy ap-
proach to modify the structure of PANI, thus, it becomes
possible to tune the electrochemical and electronic prop-
erties by altering the conditions of copolymerization.
The N-substituted derivatives exhibit an additional pro-
perty of the comparable conductivity to that of PANI. In
comparison with PANI, the copolymers of aniline with
phenyl-substituted or N-substituted aniline derivatives
show better solubility, decreased conductivity, disor-
dered structure, and enhanced electrochemical stability
[10-13]. The polymer of diphenylamine (DPA), a N-aryl
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
183
substituted aniline derivative, possesses the properties
between PANI and poly (p-phenylene). DPA has been
polymerized by Comisso et al. [14] in a mixture of 4 M
H2SO4 and ethanol, in which ethanol was used as
co-solvent to lead to the dissolution of oligomeric prod-
ucts and to hinder the growth of poly(diphenylamine)
(PDPA) on electrode surface. Also, some reports can be
available on the polymerization of N-alkyl diphenyl-
amine, 3-methoxy diphenylamine and 3-chlorodiphenyl-
amine [15,16]. The obtained polymers have been found
to have the C-C phenyl-phenyl coupling in their back-
bone. Recently, Wu et al. [17] have reported the electro-
chemical copolymerization of DPA with anthranilic acid
and used X-ray photon spectroscopy to confirm the for-
mation of the copolymer. Poly(DPA-co-aniline) [18] has
been synthesized by pulse potentiostatic technique and a
possible growth scheme has been proposed correlating
the conditions of copolymerization with the charge asso-
ciated with film deposition. Santhosh and coworkers [19]
have studied the electrochemical copolymerization of
DPA with m-toluidine (MT), and found that the elec-
tronic transitions as noticed from the in situ UV-Vis
spectra recorded during electropolymerization with dif-
ferent molar feed concentration ratios of DPA depend on
molar compositions of DPA and MT units in the co- po-
lymer. Also, the electrochemical copolymerization of
DPA with 2,5-diaminobenzene sulphonic acid (DABSA)
has been reported, the intermediates formed during the
electrochemical copolymerization have been followed
through the in situ UV–visible studies [20]. And, Wu’s
research group [21] have reported the formation of the
short-lived intermediates, showing the absorption peaks
at 310 nm and 500 nm in the UV–Vis regions for their
electronic states, during the electrochemical oxidation of
DPA in 2 M H2SO4 medium by using the in situ spec-
troelectrochemical procedure.
Due to the potential applications of poly (o-pheny- le-
nediamine) (POPD) in the fields of electrochromism [22],
sensors [23-25], rechargeable batteries [26] and corro-
sion protection [27], etc, the copolymers of OPD and
other aniline derivatives have been widely studied in
order to improve the properties of homopolymers. Re-
cently, Holze et al. [28,29] have reported the electro-
chemical copolymerization of OPD with o-toluidine (OT)
and MT, respectively, both being substituted anilines,
with various concentrations of OPD in the feed. The ob-
tained homo-/co-polymers had been characterized using
CV and in situ conductivity measurements, and it was
found that the copolymers showed an extended electrode
potential range of redox activity and good redox re-
sponses at higher pH-values in comparison with the ho-
mopolymers of POPD, poly(o-toluidine) (POT) and poly
(m-toluidine) (PMT) as well as good electrochemical sta-
bility. Also, Holze et al. [30] have studied the initial stages
of the copolymerization of OPD with MT, monitored
with in situ UV–vis spectroscopy, using an ITO-coated
glass electrode in solutions with a constant concentration
of MT and varying OPD concentrations. The formation
of aniline type mixed intermediates as a result of the
cross-reaction between the cation radicals of OPD and
MT was proposed from the presence of the band at 497
nm during the electro-polymerization of OPD and MT.
Since the intermediates formed during the polymerize-
tion of aniline and other aniline derivatives are short-
lived, it is difficult to detect these intermediates by using
electrochemical techniques only. While, as an effective
and useful tool for following the short-lived intermedi-
ates generated during the early stages of the electro-
oxidation of aniline and its derivatives, the in situ
UV-Vis spectroscopy has been widely used to study the
homopolymerization of aniline and its derivatives, and
the copolymerization of aniline with its derivative. For
example, Gopalan et al. [17,31-34] have used CV and in
situ UV-Vis spectroscopy to study the copolymerization
of DPA with some aniline derivatives and explained the
copolymer formation through a plausible mechanism.
And, the electrochemical copolymerization of DPA with
OT in 4 M H2SO4 medium has also been studied by
Santhosh et al. using electrochemical and spectroelec-
trochemical methods [35]. The composition of the two
monomers in the obtained copolymer and the reactivity
ratios of DPA and OT had been determined, and a possi-
ble copolymer model for explaining the changes in elec-
trochemical and spectroelectrochemical characteristics
was proposed. Recently, Zhang et al. [36] have studied
the homopolymerization of o-toluidine (OT) and p-pheny-
lenediamine (PPDA) and also the electrocopolymeriza-
tion of OT with PPDA on an ITO conductive glass elec-
trode at 0.7 V, 0.8 V, and 0.9 V using in situ UV–vis
spectrometry in 0.5 mol/L sulfuric acid media. The spec-
tral results indicated that the electrocopolymerization of
OT and PPDA did happen. Also, Zhang et al. [37] have
reported the electrochemical copolymerization of MT
with PPDA using in situ UV–vis spectrometry procedure,
and indicated that PPDA might react with MT to yield
some more active intermediates, which can promote the
electropolymerization.
In this study, the electrochemical copolymerization of
DPA with OPD in 4 M H2SO4 medium has been investi-
gated using the techniques of cyclic voltammetry and in
situ UV-Vis spectroscopy. The course of electropolyme-
rization has been followed by in situ UV-Vis spectros-
copy to provide an insight about the intermediates formed
during copolymerization and the mechanism of copoly-
mer formation. The obtained copolymer has also been
characterized by FT-IR spectroscopy.
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
184
2. Experimental
2.1. Reagents and Solutions
DPA (Sigma) and OPD (Sigma) were used without any
further purification. Other chemicals were used as re-
ceived. All reagents were prepared with ultrapure water,
and freshly prepared solutions were used throughout the
experiment. All chemicals were of analytical grade.
2.2. Apparatus and Procedures
2.2.1. Electrochemical Homo-/Co-Polymerization
Electrochemical synthesis and cyclic voltammetric stud-
ies were performed using a CHI 660B electrochemical
workstation (CH instruments, USA). Ultrapure water
was used for the preparation of electrolyte solutions con-
taining 4.0 M H2SO4. A three-electrode cell was used
with a platinum foil (1 × 1 cm2) as working electrode, an
Ag/AgCl electrode as reference, and a platinum wire
serving as counter electrode. Electrochemical copoly-
merization of DPA with OPD was carried out by poten-
tial scanning between –0.2 - 1.2 V at 100 mV/s. Electro-
chemical homopolymerizations of DPA and OPD had
also been performed using the same procedure as that of
the copolymerization.
2.2.2. In Situ Spectroelectr ochemistry
The in situ UV–Vis spectra were recorded by using a
UV-1800 UV-Vis spectrophotometer (Shimadzu). Elec-
trochemical copolymerization was carried out by apply-
ing a constant potential of 0.8 V for the binary mixture of
DPA and OPD with different feed ratios. The homo-
polymerizations of DPA and OPD were also performed
using the same procedure as that of the above copoly-
merization. The UV–Vis spectra were collected simulta-
neously while potentiostatic electrolysis was performed.
Spectroelectrochemical experiments were made in a
quartz curvet of 1 cm path length by placing an in- di-
um-doped tin oxide (ITO) coated glass electrode (with a
specific surface resistance of 10 /cm2) installed per-
pendicular to the light path. A platinum wire was used as
counter electrode and Ag/AgCl was used as reference
electrode. For each experiment, a fresh ITO-coated glass
electrode was used, which had been degreased with ace-
tone and rinsed with plenty of ultrapure water. In the
reference channel of spectrometer, a quartz curvet con-
taining 4.0 M H2SO4 aqueous solution was inserted. All
the spectra recorded are background-corrected.
2.2.3. Fouri er T r ansf o rm Infrared Spectroscopy
FT-IR spectra were recorded on a KBr disk containing
about 1% sample by weight using a Nicolet Avatar 370
DTGS (USA) spectrophotometer. For each sample, a
total of 120 scans at a resolution of 4 cm–1 was used.
3. Results and Discussion
3.1. Electrochemical Homo-/Co-Polymerization
To investigate the electrochemical behaviors of the ho-
mo-/co-polymerization of DPA and OPD, the cyclic vol-
tammograms (CVs) have been recorded during the elec-
trochemical homopolymerization of DPA and OPD, and
the copolymerization of DPA with OPD with different
concentration ratios (R = 1:1, 1:2, and 2:1) in 4.0 M
H2SO4 by scanning the potentials in the limits -0.2-1.2 V
for 20 cycles (Figure 1). Figure 1(a) shows the CVs
recorded for the homopolymerization of DPA. As can be
seen, in the first cycle, an irreversible oxidation peak is
observed at 0.49 V, which could be assigned to the elec-
trooxidation of DPA to generate the diphenylamine ca-
tion radicals (DPACRs), and after the first potential
scanning, another anodic peak was observed at 0.27 V.
This peak is caused by the products that could be identi-
fied as the DPA dimer, which is shown to be able to
grow into the final polymer during electrochemical de
position [38]. On the other hand, one can note that the
peak current for the oxidation peak located at 0.27 V
increased gradually with the continuous potential scan-
ning, while, for the wave at 0.49 V, the peak current de-
creased gradually with the continuous potential scanning.
This is because that, after the formation of the DPACRs,
they will react each other or with the DPA monomers in
solution to generate the DPA dimer, thus, with the con-
tinuous formation of the DPA dimer, the amount of
DPACRs in solution will decrease gradually, and the
amount of DPA dimer will show a corresponding in-
crease. This will, thus, lead to the decrease for the oxida-
tion current of the peak at 0.49 V and the increase for the
peak current of the oxidation wave at 0.27 V. And, for
the reduction wave at 0.21 V, the peak current increases
gradually with the con- tinuous electrolysis. These elec-
trochemical behaviors are the typical characteristics for
the polymerization of compound. Finally, a dark green
PDPA film was deposited on the electrode surface. Fig-
ure 1(b) shows the CVs obtained during the elec-
tro-oxidation of OPD from a solution containing 0.002 M
OPD. As can be seen, in the first anodic sweep, the oxi-
dation peak, corresponding to the oxidation of OPD at
0.80 V, indicates formation of the OPD cation radicals
(OPDCRs) from the reduced leucoemeraldine. And, dur-
ing the subsequent potential cycling, another anodic peak
at 0.13 V can be noticed. This peak can be assigned to the
further oxidation reaction of OPDCRs to dications. The
anodic peak at 0.80 V shows a decrease in peak current
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
185
with increase in the number of cycles, while the current
response for the oxidation peak at 0.13 V increases
gradually with continuous potential cycling. This is due
to the conversion of OPDCRs into their dications. As for
the reduction wave at 0.02 V and 0.26 V, the peak cur-
rent increase gradually with the continuous electrolysis.
These electrochemical properties indicate the polymeri-
zation of OPD on electrode surface. A bronze-brown
film was finally obtained on the working electrode.
Figure 1(c-e) show the CVs for the electrochemical
copolymerization of DPA and OPD with different con-
centration ratios (c: R = 1:1; d: R = 1:2; e: R = 2:1).
Firstly, it can be seen that the electrochemical behaviors
of the copolymerization of DPA with OPD are appar-
ently different from that of the homopolymerizations of
DPA (Figure 1(a)) and OPD (Figure 1(b)). This dem-
onstrates that the copolymerization of DPA and OPD do
occur during the electrolysis of their binary mixture. Se-
condly, the different growth characteristics can be ob-
served for the copolymers synthesized with different
concentration ratios of DPA and OPD. It can be seen
from Figure 1(c) (R = 1:1) that, during the first anodic
scan of potential on the copolymerization of DPA with
OPD, an anodic peak is observed at 0.98 V, which could
be due to the formation of the electroactive species gen-
erated from the oxidation of both DPA and OPD that can
ultimately result in the oligomer/polymer formation [35].
This is justifiable by the fact that when the anodic poten-
tial is beyond 0.70 V, both DPA and OPD could be si-
multaneously oxidized to generate their cation radicals,
diphenylamine cation radical (DPACR) and o-pheny-
lenediamine cation radical (OPDCR) [35, 39]. And after
the first cycle of potential scanning, three anodic peaks
were observed in the CVs at 0.07 V, 0.78 V, and 0.98 V,
respectively, which distinctly differs from the CVs with
the two anodic peaks during the copolymerization of
DPA and OPD with the concentration ratios of 1:2 and
2:1. The peaks located at 0.07 V and 0.78 V could be
assigned to the oligomers/ polymers generated by the
cross-reaction between the intermediate species of
DPACR and OPDCR. Thirdly, apart from the different
anodic and cathodic peak potentials shown in Figures
1(c), 1(d) and 1(e), the peak currents for the copoly- me-
rization of DPA and OPD with R = 1:2 and R = 2:1
(Figures 1(d) and 1(e)) are higher than those shown in
Figure 1(c) for the copolymerization of DPA and OPD
(a) (b) (c)
(d) (e)
Figure 1. (a): CVs of the electrochemical polymerization of 0.001 M DPA in 4 M H2SO4; (b): CVs of the electrochemical po-
lymerization of 0.002 M OPD in 4 M H2SO4; (c-e): CVs recorded during the electrochemical copolymerization of DPA with
OPD (c: R = 1:1; d: R = 1:2; e: R = 2:1) in 4 M H2SO4. Scan rate = 100 mV/s.
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
186
with concentration ratio of 1:1. This may be because that
the surface bound polymer film deposited on electrode
surface exhibits different redox characteristics as a result
of the incorporation of DPA or OPD in different extent.
Finally, a dark golden-brown film can be observed on
electrode surface. These results not only show that the
copolymerization of DPA and OPD do happen using the
proposed electrochemical procedure, but also indicate
that the copolymerization process is related to the con-
centration ratio of DPA and OPD in the feed.
3.2. In-Situ Spectroelectrochemistry
3.2.1. In-Situ Spectroelectrochemistry of the
Homopolymerization of DPA
Figures 2(a) and 2(b) show the in situ UV–Vis spectra
for the homopolymerization of DPA with different con-
centrations (0.001 M and 0.005 M) in 4.0 M H2SO4
(a)
(b)
Figure 2. (a and b): UV–Vis spectra obtained at different
time intervals (in minutes) after applying a potential of 0.80
V in solutions containing different concentr ations of DPA (a:
0.001 M; b: 0.005 M).
aqueous solution at a potential of 0.80 V. Typically, three
absorption bands at around 380 - 410 nm, 500 nm and >
600 nm are noticed during the homopolymerization of
DPA. And, the absorption peaks at about 430 nm, 500 nm
and > 600 nm have also been reported for the homopoly-
merization of DPA by earlier workers [34,40]. Based on
the literature [34], the band at 380 - 410 nm is assigned to
the aniline type cation radical and/or oxidized benzidine
type dimer generated in the backbone. The other two
bands at 500 nm and >600 nm are assigned to the genera-
tion of diphenyl benzidine type oligomer cation radical
(DPB+) and N’, N-diphenyl benzidine type dication radi-
cal (DPB2+) of the oligomer (Scheme 1), respectively.
Both of the peaks grow in intensity gradually during the
electrooxidation of DPA with the time going on. This is
because that with the continuous electrolysis, more and
more intermediates are formed.
The assignment of these peaks to the intermediates
could be supported by the results of the spectral studies
after switching off the applied potential. Figure 3 illus-
trates the UV–Vis spectra obtained at different time in-
tervals (1 - 6 min) after interruption of 10 min electroly-
sis of 0.005 M DPA. As can be seen, the intensity of the
absorption bands at about 500 nm and > 600 nm show a
significant decrease with the time going on, and the in-
tensity of the absorption band at > 600 nm decreases
more quickly than that of the absorption peak at 500 nm.
This is because that, after interruption of electrolysis, the
intermediates of DPB+ and DPB2+ of the oligomers
would not be generated any more. While, although the
potential electrolysis is ended, the DPB2+ intermediates
would keep reacting each other as before. Thus, the con-
tent of DPB2+ intermediates in solution becomes less and
less, which would lead to the significant decrease of the
absorption intensity. On the other hand, one can note that,
with the time going on, the absorption peak at about 500
nm shifts negatively gradually. This may be attributed to
the transformation of intermediates into the end product.
3.2.2. In Situ Spectroelectr ochemistry of the
Homopolymerization of OPD
Figure 4 displays the UV–vis spectra recorded at various
time intervals for initial stages of the polymerization of
OPD (0.002 M) in 4.0 M H2SO4 aqueous solution at an
applied potential of 0.8 V versus Ag/AgCl. As can be
seen, two absorption bands located at λ = 460 nm and λ =
490 nm can be firstly found in the UV–Vis spectra. How-
ever, with the time increasing, another weak absotption
peak at 550 nm can be observed. It has been reported that
there are three absorptive bands located at 420 nm, 462
nm and 492 nm, respectively, in its UV-Vis spectrum
[30]. This difference may be resulted from the different
medium used. It has been known that there are two
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
187
Scheme 1. Copolymerization of DPA and OPD.
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
188
Figure 3. UV–Vis spectra obtained at different time inter-
vals (1-6 minutes) after interruption of the electrolysis of
0.005 M DPA performed for 10 min.
Figure 4. UV–Vis spectra obtained at different time inter-
vals (in minutes) after applying a potential of 0.80 V in so-
lutions containing 0.002 M OPD. Inset: plots of the intensi-
ties of the absorptive peaks at 460 nm (red line) and 490 nm
(black line) with time.
different kinds of structure for poly(o-phenylenediamine)
(POPD), they are the phenazine-type structure [26,41]
and the PANI-like backbone structure [22,42], respect-
tively. The absorbance transient located at 460 nm is
assigned to the intermediate of the phenazine-type dim-
mer/oligomer or the OPD cation radicals. The dimer and
oligomer containing the phenazine-type have been re-
ported to give the absorption bands at 420 nm and 451
nm, respectively [43,44]. The transients at 490 nm and
550 nm can be ascribed to the PANI-like dimer and oli-
gomer intermediates, as shown in Scheme 1. The ab-
sorption intensity of these two bands increase with con-
tinuous electro-oxidation of OPD, but the intensity of the
absorption at 460 nm grows more quickly than that of the
other absorption band at 490 nm (Figure 4, inset) and
gradually becomes predominant in the later stages of
polymerization. This is because that the generation rate
of the intermediate of phenazine type dimmer/oligomer
or OPD cation radicals is significantly quicker than that
of the PANI-like dimer intermediates in 4 M H2SO4
aqueous solution at the potential of 0.8 V.
3.2.3. In Situ Spectroelectr ochemistry of the
Copolymerization of DPA with OPD
The UV–Vis spectra recorded during constant potential
copolymerization at 0.8 V of DPA and OPD with differ-
ent concentration ratios (R = 1:1, 1:2, and 2:1) are shown
in Figure 5. It can be seen from Figure 5 that there is
great difference between the absorption bands for the
copolymerization of DPA with OPD and those for the
homopolymerization of DPA and OPD. On the one hand,
in Figure 5(a), there are three bands, which are located
at 400 nm, 493 - 500 nm, and 538 nm, respectively; and
in Figures 5(b) and 5(c), the absorption bands are lo-
cated at 400 nm, 493 nm and 538 nm, and 400 nm,
507-514 nm and 538 nm, respectively. Compare to the
spectra obtained during the homopolymerization of DPA
or OPD alone, a new band appeared at 538 nm in the
UV-Vis spectra for the copolymerization of DPA and
OPD. Under the applied potential of 0.80 V, DPA and
OPD can be oxidized to get their corresponding cation
radicals (DPACR and OPDCR), which undergo cross-
reaction to result in the dimers/oligomers (Scheme 1). The
existence of the absorption peak at 538 nm in the
UV-Vis spectra for the copolymerization is attributed to
the formation of these intermediates (dimers/oligomers)
as a result of the cross-reaction between DPACR and
OPDCR (Scheme 1). Besides, one can also notice from
Figure 5 that the intensity ratio for these absorption
peaks is different when the concentration ratio of DPA to
OPD in the feed is altered. On the other hand, for the
copolymerization of DPA and OPD, the bands at around
490-510 nm which correspond to the generation of di-
phenyl benzidine type oligomer cation radical (DPB+)
and the PANI-like dimer intermediates show shifts while
changing the concentration ratio of DPA and OPD in the
feed. This demonstrates that the concentration changes of
DPA and OPD in the solution produce copolymers with
different amounts of DPA or OPD in it. And, the absorp-
tion peak assigned for the aniline type cation radical,
observed at around 380 - 410 nm in the case of DPA
polymerization, appeared at 400 nm for the copolymeri-
zation of DPA and OPD. Obviously, the incorporation of
OPD units in the backbone of copolymer does happen
when electrolysis is performed in the mixture of DPA
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
189
(a) (b)
(c) (d)
(e) (f)
Figure 5. (ac): UV–Vis spectra obtained at different time intervals (in minutes) after applying a potential of 0.80 V in solu-
tions containing DPA and OPD with different molar ratios (a: R = 1:1; b: R = 1:2; c: R = 2:1). (df): the time dependenc e of
the absorbance at 500 nm and 538 nm, respectively (d: R = 1:1; e: R = 1:2; f: R = 2:1).
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
190
and OPD.
To further investigate the spectroelectrochemical be-
haviors of these absorption bands at different time inter-
vals, the growth of absorbance of these bands in solu-
tions containing different concentration ratios of DPA
and OPD are illustrated in Figure 5(d) (R = 1:1), 5(e) (R
= 1:2), and 5(f) (R = 2:1), respectively. As can be seen,
the absorption intensity of these three bands all increase
with continuous electro-oxidation in various concentra-
tion ratios, but the intensity of the absorption at 500 nm
grow more quickly than that of the absorption at 538 nm.
This accounts for the high activity of the DPA cation
radical, it can react with other cation radicals or/and
OPD monomers in solution.
To investigate the different characteristics of the vari-
ous intermediates generated during the copolymerization
of DPA and OPD, the UV–Vis spectra recorded at dif-
ferent time intervals after interruption of 10 min elec-
trolysis of the mixed solution (R = 1:2) is illustrated in
Figure 6. As can be seen, the absorption bands at 500
nm and 538 nm decrease in intensity with prolonged time.
The absorbance value of the band at 538 nm, assigned to
the dimers/oligomers resulting from the cross reaction of
DPACR and OPDCR, shows less decrease in absorbance
in comparison with the neighboring band at 500 nm. This
is because that the intermediates continue to react each
other and form the end product after interruption of elec-
trolysis, which leads to the continuous decrease of the
amount of the intermediates.
3.3. FT-IR Spectroscopy
To confirm the formation of the copolymer of DPA and
OPD, the FT-IR spectrum of the copolymer (R = 1:1) is
Figure 6. UV–Vis spectra at different time intervals (in mi-
nutes) after interruption of the electrolysis in the mixed
solution (R = 1:2) performed for 10 min.
presented in Figure 7(a). As a comparison, the FT-IR
spectra of PDPA and POPD have also been shown in
Figures 7(b) and 7(c), respectively. It can be seen from
Figure 7(a) that, the absorption bands at 3500 cm–1 cor-
responds to the N-H stretching vibration. The absorption
(a)
(b)
(c)
Figure 7. FT-IR spectra of the copolymer of DPA with OPD
(a), PDPA (b), and POPD (c).
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
191
band at 1509 cm–1 is the characteristic of C–C multiple
bond stretching modes of benzene ring [6]. The strong
absorption band at 1670 cm–1 is assigned to the bending
mode of aromatic secondary amine [7]. And, the band at
1310 cm–1 is assigned to the stretching vibration of C-N
groups with partially double bonds characteristics. In the
lower frequency region, the peak at 1123 cm–1 is due to
the C-H in-plane deformation, which is used to evaluate
the electron delocalization in polymers [45]. Therefore,
the enhanced IR absorption at this location indicates that
the copolymers have good conductivity, this agrees well
with the strong absorption by free electrons in the region
4000 - 2000 cm–1. While, the bands at 1068-1064, 885
and 850 cm–1 suggests the presence of phenazine struc-
tures in the copolymer backbone [46]. These structures
could be due to the presence of the OPD units, which
also appears in the spectrum of POPD. The bands at
1249 and 1117 cm-1 indicate the presence of the
–C–NH–C– units as a consequence of the linking of NH2
group of OPD with the phenyl carbon atom of DPA [9],
which does not appear in the spectrum of PDPA. Thus,
the FT-IR spectrum of the copolymer reveals the pres-
ence of both OPD and DPA monomer units in the co-
polymer backbone, as well as the structural differences
between the homo- and co- polymers.
4. Conclusions
The electrochemical copolymerization of DPA and OPD
has been investigated by using electrochemical and in
situ spectroelectrochemical techniques. Compare to the
CVs for electrochemical homopolymerization of DPA
and OPD, the different characteristics in the CVs for the
electrooxidation of the mixture of DPA and OPD indi-
cate the occurrence of the copolymerization of DPA with
OPD. And, the in situ UV–Vis spectroelectrochemical
studies on the copolymerization of DPA with OPD
demonstrate that the spectral characteristics for the co-
polymerization are different from those of the polymeri-
zation of DPA and OPD alone. The new absorption peak
observed at 538 nm in the spectrum reveals the formation
of the dimers/oligomers intermediates as a result of the
cross- reaction between DPACRs and OPDCRs. FT-IR
spectrum of the copolymer reveals the presence of both
monomer units in the copolymer backbone, as well as the
structural differences between homopolymers and co-
polymer.
5. Acknowledgements
This work was supported by the Innovation Program of
Shanghai Municipal Education Commission (09YZ161)
and Natural Science Foundation of Shanghai (09ZR-
1423500).
6. References
[1] E. M. Genis, A. Boyle, M. Lapkwoski and C. Tsintavis,
“Polyaniline: A Historical Survey,” Synthetic Metals, Vol.
36, No. 2, June 1990, pp. 139-182.
doi:10.1016/0379-6779(90)90050-U
[2] D. Zhang and Y. Wang, “Synthesis and Applications of
One-Dimensional Nano-Structured Polyaniline: An
Overview,” Materials Science and Engineering, B, Vol.
134, No. 1, September 2006, pp. 9-19.
doi:10.1016/j.mseb.2006.07.037
[3] A. G. MacDiarmid and A. J. Epstein, “The Concept of
Secondary Doping as Applied to Polyaniline,” Synthetic
Metals, Vol. 65, No. 2-3, August 1994, pp. 103-116.
doi:10.1016/0379-6779(94)90171-6
[4] N. Kuramoto and A. Tomita, “Aqueous Polyaniline Sus-
pensions: Chemical Oxidative Polymerization of Dode
cylbenzene-Sulfonic Acid Aniline Salt,” Polymer, Vol.
38, No. 12, June 1997, pp. 3055-3058.
doi:10.1016/S0032-3861(96)00861-0
[5] Y. Wei, G. E. Wnek, A. G. MacDiarmid, A. Ray and W.
W. Foke, “Synthesis and Electrochemistry of Alkyl Ring-
Substituted Polyanilines,” Journal of Physical Chemistry,
Vol. 93, No. 1, January 1989, pp. 495-499.
doi:10.1021/j100338a095
[6] A. Watanabe, A. Lwabuchi, Y. Lwasaki, O. Ito, K. Mori
and Y. Nakamura, “Electrochemical Polymerization of
Aniline and N-alkylanilines,” Macromolecules, Vol. 22,
No. 9, September 1989, pp. 3521-3525.
doi:10.1021/ma00199a003
[7] C. DeArmitt, S. P. Armes, J. Winter, F. A. Uribe, S. Got-
tesfeld and C. Mombourguette, “A Novel N-substituted
Polyaniline Derivative,” Polymer, Vol. 34, No. 1, January
1993, pp. 158-162. doi:10.1016/0032-3861(93)90299-P
[8] H. S. O. Chan, S. C. Ng, W. S. Sim, K. L. Tan and B. T.
G. Tan, “Preparation and Characterization of Electrically
Conducting Copolymers of Aniline and Anthranilic Acid:
Evidence for Self-Doping by X-Ray Photoelectron Spec-
troscopy,” Macromolecules, Vol. 25, No. 22, October
1992, pp. 6029-6034. doi:10.1021/ma00048a026
[9] A. A. Karyakin, A. K. Strakhova and A. K. Yatsimirsky,
“Self-Doped Polyanilines Electrochemically Active in
Neutral and Basic Aqueous Solutions: Electropolymeri-
zation of Substituted Anilines,” Journal of Electroana-
lytical Chemistry, Vol. 371, No. 1-2, June 1994, pp. 259-
265. doi:10.1016/0022-0728(93)03244-J
[10] M. T. Nguyen and A. F. Diaz, “Water-Soluble Poly (ani-
line-co-o-anthranilic acid) Copolymers,” Macromolecules,
Vol. 28, No. 9, April 1995, pp. 3411-3415.
doi:10.1021/ma00113a047
[11] A. Ito, K. Ota, K. Tanaka and T. Yamabe, “n-Alkyl Group-
Substituted Poly (m-aniline)s: Syntheses and Magnetic
Properties,” Macromolecules, Vol. 28, No. 16, July 1995,
pp. 5618-5625. doi:10.1021/ma00120a029
[12] S. K. Dhawan and D. C. Trivedi, “Influence of Polym-
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
192
erization Conditions on the Properties of Poly (2-methy-
laniline) and Its Copolymer with Aniline,” Synthetic met-
als, Vol. 60, No. 1, January 1993, pp. 63-66.
doi:10.1016/0379-6779(93)91185-5
[13] A. Bagheri, M. R. Nateghi and A. Massoumi, “Electro-
chemical Synthesis of Highly Electroactive Polydipheny-
lamine/Polybenzidine Copolymer in Aqueous Solutions,”
Synthetic Metals, Vol. 97, No. 2, September 1998, pp.
85-89. doi:10.1016/S0379-6779(98)00090-3
[14] N. Comisso, S. Daolio, G. Zotti, S. Zecchin, R. Salmaso
and G. Mengoli, “Chemical and Electrochemical Synthe-
sis and Characterization of Polydiphenylamine and Poly-
N-methylaniline,” Journal of Electroanalytical Chemistry,
Vol. 255, No. 1-2, November 1988, pp. 97-110.
doi:10.1016/0022-0728(88)80007-X
[15] M. T. Nguyen and L. H. Dao, “Synthesis, Characteriza-
tion and Properties of Poly (3-Methyldiphenylamine) and
Poly(3-Methoxydiphenylamine),” Journal of Electroana-
lytical Chemistry, Vol. 289, No. 1-2, August 1990, pp.
37-53. doi:10.1016/0022-0728(90)87205-X
[16] M. T. Nguyen, R. Paynter and L. H. Dao, “Polymeriza-
tion and Properties of Poly (3-Chlorodiphenylamine): A
Soluble Electrochromic Conducting Polymer,” Polymer,
Vol. 33, No. 1, January 1992, pp. 214-216.
doi:10.1016/0032-3861(92)90589-O
[17] M. S. Wu, T. C. Wen and A. Gopalan, “Electrochemical
Copolymerization of Diphenylamine and Anthranilic Acid
with Various Feed Ratios,” Journal of The Electroche-
mical Society, Vol. 148, No. 5, May 2001, pp. D65-D73.
doi:10.1149/1.1366625
[18] V. Rajendran, A. Gopalan, T. Vasudevan and T. C. Wen,
“Electrochemical Copolymerization of Diphenylamine
with Aniline by a Pulse Potentiostatic Method,” Journal
of the Electrochemical Society, Vol. 147, No. 8, August
2000, pp. 3014-3020. doi:10.1149/1.1393641
[19] P. Santhosh, M. Sankarasubramanian, M. Thanneermalai,
A. Gopalan and T. Vasudevan, “Electrochemical, Spec-
troelectrochemical and Spectroscopic Evidences for Co-
polymer Formation between Diphenylamine and
m-Toluidine,” Materials Chemistry and Physics, Vol. 85,
No. 2-3, June 2004, pp. 316-328.
doi:10.1016/j.matchemphys.2004.01.021
[20] C. F. Chang, W. C. Chen, T. C. Wen and A. Gopalan,
“Electrochemical and Spectroelectrochemical Studies on
Copolymerization of Diphenylamine with 2, 5-Diamino-
benzenesulfonic Acid,” Journal of the Electrochemical
Society, Vol. 149, No. 8, July 2002, pp. E298-E305.
doi:10.1149/1.1491984
[21] M. S. Wu, T. C. Wen and A. Gopalan, “In Situ UV-Visi-
ble Spectroelectrochemical Studies on the Copolymeriza-
tion of Diphenylamine with Anthranilic Acid,” Materials
Chemistry and Physics, Vol. 74, No. 1, February 2002, pp.
58-65. doi:10.1016/S0254-0584(01)00406-0
[22] J. Yano, “Electrochemical and Structural Studies on So-
luble and Conducting Polymer from o-Phenylenedia-
mine,” Journal of Polymer Science Part A: Polymer
Chemistry, Vol. 33, No. 1, January 1995, pp. 2435-2441.
doi:10.1002/pola.1995.080331416
[23] K. Ogura, M. Kokura and M. Nakayama, “A Conductive
and Humidity-Sensitive Composite Film Derived from
Poly (o-phenylenediamine) and Polyvinyl Alcohol,” Jour-
nal of the Electrochemical Society, Vol. 142, No. 9, Sep-
tember 1995, pp. L152-L153. doi:10.1149/1.2048730
[24] J. Yano, A. Shimoyama and K. Ogura, “Poly (o-pheny-
lenediamine)-Film-Coated Electrode Having a Permse-
lective Response to Halogenide Ions,” Journal of The
Electrochemical Society, Vol. 139, No. 5, May 1992, pp.
L52-L53. doi:10.1149/1.2069443
[25] Q. Deng and S. Dong, “Mediatorless Hydrogen Peroxide
Electrode Based on Horseradish Peroxidase Entrapped in
Poly(o-phenylenediamine),” Journal of Electroanalytical
Chemistry, Vol. 377, No. 1-2, October 1994, pp. 91-195.
doi:10.1016/0022-0728(94)03465-6
[26] S. R. Sivakkumar and R. Saraswathi, “Application of
Poly (o-Phenylenediamine) in Rechargeable Cells,” Jour-
nal of Applied Electrochemistry, Vol. 34, No. 11, Novem-
ber 2004, pp. 1147-1152.
[27] L. F. D. Elia, R. L. Ortiz, O. P. Marquez, J. Marquez and
Y. Martinez, “Electrochemical Deposition of Poly
(o-phenylenediamine) Films on Type 304 Stainless Steel,”
Journal of The Electrochemical Society, Vol. 148, No. 4,
April 2001, pp. C297-C300. doi:10.1149/1.1354619
[28] S. Bilal and R. Holze, “Electrochemical Copolymeriza-
tion of o-Toluidine and o-Phenylenediamine,” Journal of
Electroanalytical Chemistry, Vol. 592, No. 1, July 2006,
pp. 1-13. doi:10.1016/j.jelechem.2006.03.039
[29] S. Bilal and R. Holze, “Electrochemical Copolymeriza-
tion of m-Toluidine and o-Phenylenediamine,” Electro-
chimica Acta, Vol. 52, No. 3, November 2006, pp. 1247-
1257. doi:10.1016/j.electacta.2006.07.024
[30] S. Bilal and R. Holze. “In situ UV–vis Spectroelectro-
chemistry of Poly(o-phenylenediamine-co-m-toluidine),”
Electrochimica Acta, Vol. 52, No. 17, May 2007, pp.
5346-5356. doi:10.1016/j.electacta.2007.02.034
[31] P. Santhosh, T. Vasudevan and A. Gopalan, “In Situ
UV–visible Spectroelectrochemical Studies on the Co-
polymerization of Diphenylamine with ortho-Methoxy
Aniline,” Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy, Vol. 59, No. 7, May 2003,
pp. 1427-1439. doi:10.1016/S1386-1425(02)00284-6
[32] M. Thaneermalai, T. Jeyaraman, C. Sivakumar, A. Go-
palan, T. Vasudevan and T. C. Wen, “In Situ UV–visible
Spectroelectrochemical Evidences for Conducting Co-
polymer Formation between Diphenylamine and m-Me-
thoxyaniline,” Spectrochimica Acta, Vol. 59, No. 9, July
2003, pp. 1937-1950.
doi:10.1016/S1386-1425(02)00441-9
[33] C. Y. Chung, T. C. Wen and A. Gopalan, “Identification
of Electrochromic Sites in Poly(diphenylamine) Using a
Novel Absorbance–Potential–Wavelength Profile,” Elec-
trochimica Acta, Vol. 47, No. 3, October 2001, pp. 423-
431. doi:10.1016/S0013-4686(01)00742-3
[34] W. C. Chen, T. C. Wen and A. Gopalan, “Electrochemi-
cal and Spectroelectrochemical Evidences for Copolymer
Formation between 2-Aminodiphenylamine and Aniline,”
Journal of the Electrochemical Society, Vol. 148, No. 11,
L. ZHANG ET AL.
Copyright © 2011 SciRes. AJAC
193
September 2001, pp. E427-E434. doi:10.1149/1.1405519
[35] P. Santhosh, A. Gopalan, T. Vasudevan and T. C. Wen,
“Studies on Monitoring the Composition of the Copoly-
mer by Cyclic Voltammetry and In Situ Spectroelectro-
chemical Analysis,” European Polymer Journal, Vol. 41,
No. 1, January 2005, pp. 97-105.
doi:10.1016/j.eurpolymj.2004.08.003
[36] G. R. Zhang, A. J. Zhang, X. L. Liu, et al., “Investigation
of the Electropolymerization of o-Toluldine and p-Phe-
ny-lenediamine and Their Electrocopolymerization by In
Situ Ultraviolet-Visible Spectroelectrochemistry,” Jour-
nal of Applied Polymer Science, Vol. 115, No. 5, May
2010, pp. 2635-2647. doi:10.1002/app.29597
[37] G. R. Zhang, J. B. Zhang, L. P. Xiao, S. F. Zhao and J. X.
Lu, “In Situ UV-Vis Spectroelectrochemistry for Elec-
tropolymerization of m-Toluidine and Electrocopoly-
merization of m-Toluidine with p-Phenylenediamine,”
Acta Chimica Sinica, Vol. 67, No. 7, July 2009, pp. 657-
664
[38] Y. B. Shim, M. S. Won and S. M. Park, “Electrochemis-
try of Conductive Polymers. VIII. In Situ Spectroelectro-
chemical Studies of Polyaniline Growth Mechanisms,”
Journal of The Electrochemical Society, Vol. 137, No. 2,
February 1990, pp. 538-544. doi:10.1149/1.2086494
[39] T. C. Wen, C. Sivakumar and A. Gopalan, “In-Situ Spec-
troelectrochemical Evidences for the Copolymerization of
o-Toluidine with Diphenylamine-4-sulphonic Acid by
UV-Visible Spectroscopy,” Spectrochimica Acta, Vol. 58,
No. 1, January 2002, pp. 167-177.
doi:10.1016/S1386-1425(01)00529-7
[40] M. S. Wu, T. C. Wen and A. Gopalan, “In Situ UV–visi-
ble Spectroelectrochemical Studies on the Copolymeriza-
tion of Diphenylamine with Anthranilic Acid,” Materials
Chemistry and Physics, Vol. 74, No. 1, February 2002, pp.
58-65. doi:10.1016/S0254-0584(01)00406-0
[41] A. Malinauskas, M. Bron and R. Holze, “Electrochemical
and Raman Spectroscopic Studies of Electrosynthesized
Copolymers and Bilayer Structures of Polyaniline and
Poly(o-phenylenediamine),” Synthetic Metals, Vol. 92,
No. 2, January 1998, pp. 127-137.
doi:10.1016/S0379-6779(98)80102-1
[42] K. Chiba, T. Ohsaka, Y. Ohnuki and N. Oyama, “Elec-
trochemical Preparation of a Ladder Polymer Containing
Phenazine Rings,” Journal of Electroanalytical Chemi-
stry, Vol. 219, No. 1-2, March 1987, pp. 117-124.
doi:10.1016/0022-0728(87)85034-9
[43] A. H. Premasiri, W. B. Euler and Macromol, “Syntheses
and Characterization of Poly(aminophenazines),” Mac-
romolecular Chemistry and Physics, Vol. 196, No. 11,
November 1995, pp. 3655-3666.
doi:10.1002/macp.1995.021961118
[44] M. A. D. Valle, F. R. Diaz, M. E. Bodini, G. Alfonso and
G. M. Soto, E. D. Borrego, “Electrosynthesis and Char-
acterization of o-Phenylenediamine Oligomers”, Poly-
mer International, Vol. 54, No. 3, March 2005, pp. 526-
532. doi:10.1002/pi.1700
[45] J. C. Chiangn and A. G. Macdiarmid, “Polyaniline: Pro-
tonic Acid Doping of the Emeraldine Form to the Metal-
lic Regime,” Synthetic Metals, Vol. 13, No. 1-3, January
1986, pp. 193-205. doi:10.1016/0379-6779(86)90070-6
[46] M. R. Huang, X. G. Li and W. Duan, “Synthesis and
Properties of a Functional Copolymer from N-ethylani-
line and Aniline by an Emulsion Polymerization,” Poly-
mer, Vol. 46, No. 5, February 2005, pp. 1523-1533.
doi:10.1016/j.polymer.2004.12.021