chemical synthesis and characterization of poly...
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CHAPTER IV
CHEMICAL SYNTHESIS AND CHARACTERIZATION OF POLY
(DIPHENYLAMINE-co-4, 4′-DIAMINODIPHENYL SULFONE)
Chemical copolymerization of diphenylamine (DPA) with different
concentrations of 4,4′-diaminodiphenyl sulfone (DADPS) were carried out using
potassium perdisulfate as oxidizing agent. The characterizations of copolymer obtained
by various techniques and their electrochromic behaviour are presented in this chapter.
4. 1. INTRODUCTION
Copolymerization is a simple way of preparation for new polymers which greatly
increases the scope of tailor-making materials with specifically desired properties [1].
Polydiphenylamine (PDPA) is reported to be a new conducting polymer with
intermediate properties between PANI and poly(paraphenylene). This is mainly due to
the difference in the mechanism of polymerization between ANI and DPA. In the
formation of PANI and its ring-substituted derivatives, polymerization proceeds through
head to tail addition of monomer units to result C-N coupled structure in the polymer.
But, for DPA, the polymerization takes place through 4-4′ coupling which results PDPA
having C-C coupled structures. Hence, the copolymerization of DPA with other
derivatives of aniline would proceed through a mechanism, which may comprise of
C-C and C-N coupled intermediates.
Chemical syntheses for polymerizing aniline and dimethylaminoaniline have
already been developed [2, 3]. Recently the chemical synthesis of poly(methylene blue)
(PMB) and poly(methylene green) (PMG) were carried out [4] and their electrocatalytic
applications are studied. A series of polystyrene graft palmitic acid (PA) copolymers as
novel polymeric solid–solid phase change materials (PCMs) were synthesized [5] and
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characterized by FTIR and other techniques. The poly (p-phenylendiamine-co-o-amino
phenol) has been synthesised by chemical and electrochemical polymerisation method
for corrosion protection of mild steel (MS) in acidic medium [6]. The copolymer
structure was confirmed by 1H NMR, FT-IR spectroscopy and its thermal stability was
observed by TGA. A star copolymer based on poly(propylene imine) (PPI) dendrimer
core (generations 1–4) and polypyrrole (PPy) shell was prepared [7]. The resulting star
copolymer, called poly(propylene imine)-co-polypyrrole (PPI-co-PPy) was characterized
using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spec-
troscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy
(SEM), X-ray diffraction (XRD).
A simple mechanochemical route for the synthesis of high quality inorganic
anion doped polydiphenylamines (PDPAs) is reported [8] and characterized.
Polydiphenylamine/single walled carbon nanotube (PDPA/SWNT) composites were
synthesized aiming at their application as active electrode materials for rechargeable
lithium batteries [9]. Kinetics of chemical oxidative polymerization of 4-
aminodiphenylamine (4ADPA) was followed in aqueous 1 M p-toluene sulfonic acid (p-
TSA) using silver nitrate (AgNO3) as an oxidant by UV-visible spectroscopy [10].
Usage of materials with biological importance for the preparation of newer nano
polymeric compounds assumes importance in the present environment [11]. Aligned or
ordered, otherwise called poled polyurea sulfone thin films having excellent transparency
from near UV to visible region were prepared by carrying out additional polymerization
of 1,4-phenylene diisocyanate and 4,4′-diaminodiphenyl sulfone simultaneously.
Electrochemically synthesized copolymer of aniline (ANI) and 4,4′-diaminodiphenyl
sulfone (DADPS) [12] exhibited novel electrochromic properties.
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Electrochromic (EC) materials exhibited different color as a function of applied
potential. Both inorganic and organic materials have been used as EC materials. But
there is still a lot of scope for further improvement in terms of switching speeds,
stability, contrast and ease of synthesis and processing. Conducting or conjugated
polymers have been found to be more promising as EC materials because of their better
stability, faster switching speeds and easy processing compared to the inorganic EC
materials. Electrochromic materials are highly desirable, as they are the potential
candidates for applications in display devices [13].
Two electrochromic devices, using polypyrrole and polythiophene derivatives as
electrochromic materials, deposited on optically transparent plastic electrodes assembled
under atmospheric conditions [14]. To quantitatively compare the electrochromism of
organic polymers to each other and to classically studied inorganic materials (WOx,
IrO2), a general method for measuring the efficiency of color change with respect to
structure was developed [15].
A family of poly(3,4-alkylenedioxythiophenes) was employed to measure their
composite coloration efficiency and to understand more fully the reasons why different
polymers possess varying coloration efficiencies. The copolymer, 2-[(3-
thienylcarbonyl)oxy]ethyl-3-thiophene carboxylate (TOET) was synthesized [16]. The
copolymer exhibited multi-color changes from a pale red in the neutral state, an orange,
and finally a bluish-gray upon oxidation, and a long-term switching stability up to 450
double switches.
Copolymer of 1-(4-nitrophenyl)-2,5-di(2-thienyl)-1H-pyrrole (NTP) with 3,4-
ethylene dioxythiophene (EDOT) was synthesized and characterized [17]. Resulting
copolymer film has distinct electrochromic properties. It has five different colors (light
red, red, light grey, green, and blue).
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The electrochemical synthesis of poly(diphenylamine-co-4,4′-diaminodiphenyl
sulfone), characterization and electrochromic responses of this copolymer films were
presented in the previous chapter. In this chapter, the chemical copolymerization of
diphenylamine (DPA) with 4,4′-diaminodiphenyl sulfone (DADPS) is presented.
Solubility of the copolymers in various organic solvents and conductivities were studied.
Cyclic voltammetric behavior, FTIR, 1H NMR,
13C NMR, UV-visible spectral studies,
XRD, SEM studies were carried out. The electrochromic properties of this copolymer
were analyzed and the results are discussed.
4. 2. EXPERIMENTAL
Reagent grade diphenylamine (E-Merck) and potassium persulphate (E-Merck)
were used as received. The monomer, 4,4′-diaminodiphenyl sulfone (DADPS) was
synthesized [18] by reacting thionyl chloride (reagent grade obtained from Zigma-
Aldrich) with acetanilide (reagent grade obtained from Zigma-Aldrich), followed by
oxidation to the sulfone with CrO3 (reagent grade obtained from Zigma-Aldrich).
DADPS was then recrystallized to white crystals (m.p. 178 - 179oC) using ethanol. All
solutions were prepared using ultra pure water obtained from a TAK-LAB water system.
4.2.1. Chemical Polymerization
Diphenylamine with various concentrations of DADPS was polymerized by
chemical oxidative method, using potassium persulphate as oxidizing agent in 4 M
H2SO4 and ethanol medium. Diphenylamine of 0.01 M with 0.005, 0.01, and 0.015 M of
DADPS in 250 ml of 4 M H2SO4 and ethanol having 15 g of potassium persulphate were
stirred for 30 min in an ice bath by controlling the temperature between 0 ± 5oC. After
stirring for 10 hrs at room temperature, the polymer was precipitated with ammonia,
centrifuged repeatedly, washed with ultrapure water and dried in vacuum at about 45oC
for more than 12 hrs.
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4.2.2. Characterization of Chemically Synthesized Homo and Copolymers
The surface of glassy carbon electrode (GCE) was coated with a thin film of the
chemically synthesized copolymers of poly(DPA-co-DADPS) and dried. Then the cyclic
voltammograms (CVs) were recorded in the potential range of 0 to 1.3 V in a scan rate of
50 mV s-1
using CH 460, Electrochemical Workstation (CH Instruments Inc., USA) with
a three electrode system viz. glassy carbon working electrode (GCE), platinum (Pt)
counter electrode, and saturated calomel reference electrode (SCE).
Spectroelectrochemical studies were performed in a quartz cuvette with a path
length of 1 cm utilizing an optically transparent working electrode, an indium-tin oxide
(ITO) plate (4-8 /cm2), a Pt counter electrode, an Ag/Ag
+ reference electrode and a
computer controlled JASCO V-530, UV-visible spectrophotometer. The synthesized
copolymer was characterized by FTIR spectral data recorded using KBr-copolymer
pellets on a SHIMADZU 8400S spectrophotometer. The polymers also characterized by
1H NMR data obtained using BRUKER 400 MHz NMR spectrometer. The
13C NMR
spectra of the polymers were obtained using BRUKER 100 MHz NMR spectrometer.
The surface morphology of the polymer films was studied utilizing SEM images
obtained from a Hitachi S3000 H SEM instrument. The grain size of the copolymer was
measured using XRD data obtained from an XRERT PRO PANALYTICAL instrument
using Cu K radiation with = 1.5418 Å.
4. 3. RESULTS AND DISCUSSION
4.3.1. Solubility of Copolymers
The solubility of the three different copolymers was tested with various organic
solvents. The results are given in table 4. 1. The different copolymers, poly (DPA-co-
DADPS) showed more solubility in dimethyl sulfoxide (DMSO), N,N-dimethyl
formamide (DMF) and moderate solubility in tetrahydro furan (THF). They were
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insoluble in other organic solvents tested. The presence of sulphone group in the polymer
renders higher polarity and this in turn enhances the solubility of the polymer only in
high polar solvents. The percentage of solubility for the three copolymers in DMSO were
compared and presented in table 4.2. The copolymer prepared from mixtures of
monomer with higher proportion of DADPS incorporated exhibited more solubility due
to the presence of more number of sulphone units in the back-bone of polymer.
4. 3. 2. Conductivity Studies of Copolymers
The electrical conductivity of copolymer was measured, through four-point
conductivity meter and the results were summarized in table 4. 3. It is observed that the
electrical conductivity is strongly influenced by the DADPS incorporation. Compared to
the conductivity of polydiphenylamine, slightly higher values are found for copolymers.
As the feed concentration of DADPS increased, the conductivity reaches maximum
value for the copolymer obtained from equal concentrations of monomers and then
slowly decreased. Similar variations were reported by many researchers [19]. This might
be caused by the increased separation of the polymer chain due to the presence of side
groups.
4. 3. 3. Cyclic Voltammetric Behavior of Copolymers
The copolymers obtained from the different concentration of monomers were
coated as thin film on the surface of glassy carbon electrode and the cyclic voltammetric
behaviour of the copolymers was studied (Fig. 4.1). The volatammogram was cycled
between 0 and 1.3 V in 0.1 M H2SO4 at scan rate 50 mV s-1
. The cyclic voltammmogram
of copolymer obtained from 0.01 M DPA and 0.005 M DADPS (Figure 4.1a) exhibited
two-oxidation peaks at 0.62 and 1.1 V and one reduction peak around 0.42 V. The first
oxidation peak is due to PDPA unit and the latter one might be due to PDADPS units of
polymer back-bone. The reduction peak might be due to that of copolymer. When the
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concentration of DADPS increases to 0.01 M (Figure. 4.1b), the voltammogram
exhibited the same behavior near the oxidation and reduction peak of 0.62 and 0.42 V
respectively as in 4.1a. But the behavior near oxidation peak 1.1 V was different as this
peak shifted towards 0.98 V revealed the extent of copolymerization increases at this
concentration as compared to the previous concentrations. The cyclic voltammaogram
obtained from the monomers of 0.01 M of DPA and 0.015 M of DADPS represented in
Figure 4.1c exhibited an intense oxidation and reduction peaks at 0.88 and 0.4 V
respectively. These peaks are similar to those obtained during the electrochemical
polymerization of 0.01 M DPA and 0.01 M DADPS (figure 3.9) evidenced that the
effective copolymerization between these two monomers take place either in equal
concentrations or slightly excess concentration of DADPS than DPA.
4. 3. 4. FTIR Spectral Behavior of Copolymers
FTIR spectral studies of the copolymers were carried out and sample spectra are
presented in figure 4.2. The influence of DADPS concentration was studied during
copolymerization through FTIR spectra. Figure 4.2a & 2b represents the FTIR spectrum
of chemically synthesized homopolymers of PDPA and PDADPS respectively. The
FTIR spectrum of copolymer obtained from 0.01 M diphenylamine and 0.005 M DADPS
is presented in figure 4.2c exhibited a series of small peaks between 3250 and 3450 cm-1
may be due to the various N-H stretching vibrations of monomer units, oligomers and
copolymers. This revealed that there may be an incomplete copolymerization took place
at this concentration even though the (N-H)b, (S=O)s, (C-N)s, (C-H)b-in plane, (C-H)b-
out of plane and (S=O)b frequencies were seen at 1628, 1288, 1170, 1070, 852, 667 and
580 cm-1
respectively.
The figures 4.2d and 4.2e represent the FTIR spectra of copolymers obtained
from the monomers of 0.01 M DPA with 0.01 M DADPS and 0.015 M DADPS
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respectively. The figure 4.2d showed peaks at 3404, 1597, 1312, 1178, 1068, 851, 678
and 554 cm-1
corresponding to (N-H)s, (C=C)s, (S=O)s, (C-N)s, (C-H)b-in plane, (C-H)b-
out of plane and (S=O)b vibrations respectively. Similarly in figure 4.2e also the same
vibrations were noticed at 3439, 1560, 1308, 1161, 1068, 851, 679 and 577 cm-1
respectively. In these two figures 4.2d and 4.2e the (N-H)b vibrations are observed at
1560 and 1628 cm-1
respectively. The comparison of various vibrational frequencies of
homopolymers, PDADPS and PDPA with respect to the copolymers P(DPA-co-DADPS)
obtained from the three different concentrations of DADPS revealed that there was
almost a slight shift in all the vibrations. These facts confirmed the presence of both
DPA and DADPS units in the copolymers formed. The table 4.4 shows the various
vibrational frequencies of homopolymers and copolymers.
From the table it was understood that the most of vibrational frequencies are
shifted in copolymers as compared to the homopolymers. As an increase in the
incorporation of DADPS, the intensity of almost all bands increased suggesting the
formation copolymers with more units of DADPS.
4. 3. 5. 1H NMR Spectral Studies of Copolymers
The proton NMR spectra for copolymers dissolved in DMSO-d6 are presented in
figure 4.3. The spectrum of poly(DPA-co-DADPS) obtained from 0.01 M DPA with
0.005, 0.01 and 0.015 M DADPS are given as A, B and C respectively in figure 4.3. The
corresponding expanded spectrum in the region of about 6.4 to 8 ppm are also given as a,
b and c in the figure 4.3. Common peaks at 2.5 and 3.5 ppm are noticed in all the spectra
and these peaks may be assigned to the residual protons of DMSO-d6 and water in the
solvent respectively.
The spectrum A showed two doublets at 7.596-7.576 and 6.823-6.805 ppm which
is characteristic of differently, para-disubstituted benzene. The former peak peak may be
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assigned to the ortho protons of benzene ring with respect to -SO2- group of DADPS
units in which the deshielding occurs due to the electron withdrawing SO2 group. The
later peak may be due to meta- protons of benzene ring to SO2 group in which shielding
occurs due to ortho NH protons present. The coupling constant (J) for these two doublets
are found to be 8 and 7.2 Hz respectively. These coupling constant (J) values are
corresponding to the spin-spin coupling between the ortho protons of the para
disubstituted benzene rings. Thus it showed the presence of at least two types of para
substituted benzene rings in the polymer and these benzene units could be obtained from
both monomers during copolymerization. Further there were a few small peaks seen
between 7.4 and 7.1 ppm. These peaks may be due to various aromatic protons of DPA
and DADPS units present in the copolymer. But the low intensity of these peaks may be
due to poor copolymerization at this molar ratio of monomers.
The spectra B and C are almost identical and showed distinct aromatic peaks for
the copolymers. This fact revealed that the extent of copolymerization took place at these
mole ratio of monomers were excellent. The spectrum B noticed a series of six doublets
corresponding to various para substituted aromatic protons of both DPA and DADPS
units as given in scheme 4.1. The strong doublet appeared at 7.558-7.540 ppm was
assigned to the ortho protons of benzene ring with respect to -SO2- group of DADPS
units in the copolymer. The next doublet noticed at 7.482-7.466 ppm may be due to
protons of aromatic benzene ring meta with respect to -SO2- group and ortho with
respect -NH- group of DADPS units of copolymer. The peak for protons of DPA unit’s
benzene ring ortho with respect to -NH- group of DADPS unit was observed as a doublet
at 7.218-7.200 ppm. The doublet seen at 7.110-7.090 ppm was assigned to ortho protons
of benzene ring with respect to –NH+= group of DPA units in the copolymer. The peak
for ortho protons of DPA unit’s quininoidal ring with respect to –NH+= group was
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appeared as a strong doublet at 6.792-6.774 ppm. The sixth doublet appeared at 7.074-
7.057 ppm may be assigned to ortho protons of benzene ring of DADPS unit with respect
to –NH+= group.
Further a small peak seen at 7.32 ppm of spectrum B may be assigned to the
protons of end aromatic units of monomers. The protons of various NH, NH+ groups
may be overlapped with the above peaks discussed. The coupling constant values
calculated from the above chemical shift values are existed between J = 6.4 and 8 Hz.
This fact clearly indicated that all the doublets appeared here are due to the ortho
couplings between the protons of para substituted benzene molecules in the polymer.
Therefore it was followed that the polymerization between DADPS and DPA molecules
take place by head to tail interaction between these two monomers. i.e. the -NH2 unit of
DADPS may interact with the para position of benzene ring with respect to -NH- group
of DPA unit and the structure assigned to the copolymer, poly(DPA-co-DADPS) in the
previous chapter was strengthened to be correct. The spectrum C of copolymer was
identical to B except an additional peak observed at 6.98 ppm and this may be due to
aromatic protons of end monomer units.
4. 3. 6. 13
C NMR Spectral Studies of Copolymers
The 13
C NMR spectra for copolymers dissolved in DMSO-d6 are presented in
figure 4.4. The spectrum of poly(DPA-co-DADPS) obtained from 0.01 M DPA with
0.005, 0.01 and 0.015 M DADPS are given as A, B and C respectively in figure 4.4. The
spectrum B and C are identical while the spectrum A is slightly different and the peaks
are less intense than B and C. The 13
C chemical shift values for various C atoms of both
monomers and copolymers are given in table 4.5. The entire spectrums displayed in
figure 4.4 shows an intense peak at 39 ppm, which correspond to the carbon atoms of
solvent DMSO.
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The 13
C chemical shift value for ipso carbon atom having primary amino group in
DADPS is 152.38 ppm. Similarly the chemical shift value for ipso carbon atom haqving
secondary amino group in DPA is 143.17 ppm. But these carbon atoms showed peaks at
150 and 148.46 ppm respectively in copolymers.
Likewise the chemical shift for ortho protons of benzene ring in DADPS with
respect to sulfone (-SO2-) group is 128.22 ppm. The chemical shift for meta protons of
benzene ring in DPA with respect to secondary amino (-NH-) group is 129.30 ppm. But
in copolymers these carbon atom showed peaks at 130.16 and 130.99 ppm.
Similarly the chemical shift for meta protons of benzene ring in DADPS with
respect to sulfone (-SO2-) group is 112.59 ppm. The chemical shift for ortho protons of
benzene ring in DPA with respect to secondary amino (-NH-) group is 117.88 ppm. But
in copolymers these carbon atom showed peaks at 115.31 and 115.98 ppm.
These facts discussed above clearly indicated that copolymers were formed
between these two monomers. It was more interesting to note that the 13
C chemical shift
for para carbon atom of benzene ring in diphenylamine with respect to secondary amino
group is 120.96 ppm. This peak not at all appeared in any of the copolymers formed
evidenced that the para C atom of DPA interacts with primary amino group of DADPS to
form a copolymer via C – N linkage. The 13
C NMR peak for this C atom may be
appeared at 148.66 or 150 ppm.
The remaining peaks observed at 129.21 and 126.47 (spectrum A alone) in
spectra of figure 4.4 were assigned to ortho C atoms of phenyl ring in DADPS with
respect to sulfone group of terminal unit and ortho C atoms of phenyl ring in DPA with
respect to secondary amino group of terminal unit respectively. The peak seen at 117.10
ppm of copolymers were due to ortho and meta C atoms of quininoidal ring with respect
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to iminium =NH+- group of DPA unit in the polymeric backbone. The
13C chemical shift
values of various carbon atoms for the copolymer are represented in scheme 4.2.
4. 3. 7. XRD Studies of Copolymers
The crystalline regions in the copolymers are shown by the presence of relatively
sharp peaks. The amorphous regions are visible by the broad low intensity peaks. X-ray
diffraction profile of the homopolymers and copolymers are shown in figure 4.5. The
homopolymers, PDPA (Figure 4.5a) and PDADPS (Figure 4.5b) showed amorphous and
lesser crystalline natures respectively. The copolymers obtained during the
copolymerization of 0.01 M DPA with 0.005, 0.01 and 0.015 M DADPS represent in
figures 4.5c, 4.5d and 4.5e respectively. These XRD patterns indicated substantial
increase in degree of crystallinity as the concentration of DADPS increases. The base
form of the copolymer with low DADPS was found to have less crystallinity, compared
to the highly doped form. The particle size of homopolymers and copolymers were
calculated from XRD studies using the Scherrer’s formula as follows.
Grain size =
cosFW
K
Where K is the shape factor of the average particle (expected to be 0.94), is the
wave length (usually 1.5418 Å), is the peak position and FW is the full width at half
maximum. Using this formula the grain sizes of PDPA, PDADPS, P(DPA-co-DADPS)
obtained from the molar concentrations of 0.01 M DPA with 0.005, 0.01 and 0.015 M
DADPS were found to be 28, 34, 42, 47 and 48 nm respectively. These facts evidenced
the presence of nano structured copolymers.
4. 3. 8. SEM Behaviour of Copolymers
Chemically copolymerized materials were characterized by scanning electron
microscopic (SEM) analysis. The material exhibited the influence of DADPS during
chemical copolymerization. SEM photographs of chemically synthesized homopolymers,
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PDPA and PDADPS are presented in figures 4.6A and 4.6B respectively. The SEM
image of PDPA showed a spongy like structure while that of PDADPS showed leave-
like structure in the nano scale. The copolymer formed from 0.01 M diphenylamine and
0.005 M DADPS given in figure 4.6C showed scales-like arrangements with granular
spongy like structures embedded in it. This irregular structure confirmed the formation of
copolymer. When the concentration of DADPS increased to 0.01 and 0.015 M, the
resulting copolymers exhibited (Figures 4.6D and 4.6E) almost similar structures in the
form of three dimensional scales like arrangements. The effective copolymerization took
place only in these two concentrations of 0.01 and 0.015 M DADPS with 0.01 M DPA as
compared to the previous one (0.01 M DADPS with 0.01 M DPA) and this may be
responsible for the identical SEM behavior of figures 4.6D and 4.6E with more
homogeneous scales like arrangements in nano scale level.
4. 3. 9. UV-visible Spectra of Copolymers
The UV-visible spectral studies were carried out for homopolymers, (PDADPS &
PDPA) and all copolymers, poly(DPA-co-DADPS) in DMSO and the spectra are shown
in figure 4.7. The figures 4.7a, b, c, d and e represent the spectrum of PDADPS, PDPA,
poly(DPA-co-DADPS) of 0.01 M DPA with DADPS concentrations of 0.005, 0.01 and
0.015 M respectively. Peaks with wavelength maximum at 310 and 360 nm were
observed for all copolymers in DMSO. For homopolymer, PDADPS (a) broad peak was
observed at 360 and another peak seen at 280 nm. In homopolymer PDPA (b) one peak
was seen at 380 nm. These peaks may be associated with * transition and
conjugated benzenoid rings. This confirmed the presence of benzene rings in poly (DPA-
co-DADPS) as in diphenylamine and 4,4′-diaminodiphenyl sulfone. Hence it is
confirmed indirectly the polymerization between diphenylamine and DADPS through
amino group. Another absorption band observed at 570 nm in copolymers (Figure 4.6c &
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4.6d) resulted from 0.005 and 0.01 M DADPS with 0.01 M DPA was due to the polaron
band transition. The band at 680 nm for the copolymer obtained from 0.015 M of
DADPS with 0.01 M DPA was due to bipolarons and this band may be responsible for
the green color of the copolymer. As more amounts of DADPS were incorporated, the
copolymer exhibited high percentage of absorption value (Fig. 4.7c - e).
Further attempts were made to analyze the molar composition of these two
monomers (DPA and DADPS) in the copolymer P(DPA-co-DADPS) using UV-visible
spectroscopy. Ramelow and Baysal [20] developed a spectrophotometric method for the
analysis of the copolymer composition by UV-visible spectroscopy. The mole fraction
X1 of monomer 1 (DADPS) in the copolymers has been determined by
X1 =
.
Where 12, 1 and 2 are the specific extinction coefficient of the copolymer
P(DPA-co-DADPS), homopolymers 1 (PDADPS) and 2 (PDPA) respectively. Similar
procedure was adopted to determine the mole fraction X2 of monomer 2 (DPA) in the
copolymers.
Spectra were recorded for the copolymers prepared with different feed ratio of
DPA and DADPS. Figure 4.7 shows the UV-visible spectra recorded for the copolymer
of DADPS with DPA in different feed ratios. By taking spectra of poly(DADPS) and
poly(DPA) the specific extinction coefficients were found to be DADPS = 12.3 10-3
l/mg
at max = 280 nm and DPA = 19.02 10-3
l/mg at max = 380 nm respectively. Using the
spectra recorded for the copolymer synthesized with different molar compositions of
DPA or DADPS, the molar extinction coefficient 12 was calculated for the copolymers
at max = 360 nm and the values are listed in table 4.6. These values of molar extinction
coefficients of copolymers are used to determine the copolymer compositions using the
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above equation and the compositions are also given in table 4.6. Thus it was clear that
the composition of DPA or DADPS in the copolymer varied with the feed composition
of the two monomers employed in the polymerization as given in table 4.6. From the
UV-visible spectra it was also concluded that as the concentration of DADPS increases
during copolymerization and more amounts of DADPS units are incorporated into the
backbone of polymers.
The copolymer with more amounts of DADPS exhibited higher percentage of
absorption as shown in figure 4.7. The monomer reactivity ratios, r1 and r2 (1 correspond
to DADPS and 2 correspond to DPA), were calculated using the simplified Fineman-
Ross equation [20].
= r1
- r2, where F and f are the molar ratio values of monomers 1
and 2 in initial monomer feeds and in copolymers respectively. The plot of
against
denoted in Figure 4.8 is linear. The values of r1 and r2 are determined from the
slope and intercept of the straight line. Thus the reactivity of DADPS and DPA are found
to be 0.55 and 0.63 respectively. These values indicated that the DPA monomer was
slightly more reactive during copolymerization than DADPS.
4. 3. 10. Spectroelectrochemical Behavior of Copolymers
Insitu UV-visible spectroelectrochemical studies of the chemically prepared
copolymer were carried out. The copolymer film was coated on an ITO glass plate. The
spectra of the dark blue color adhered film on ITO plate were recorded at various applied
potentials in 0.1 M H2SO4 medium. Since all the three copolymer films were blue in their
oxidized state, each was subsequently reduced to determine whether there was a direct
correlation between monomer compositions and electrochromic response. As an
illustration, the in situ UV-visible spectra of the copolymer film obtained from 0.01 M
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diphenylamine with 0.005, 0.01 and 0.015 M DADPS at various applied potentials are
presented in figures 4.9, 4.10 and 4.11 respectively.
The figure 4.9 corresponding to the copolymer obtained from 0.01 M DPA with
0.005 DADPS shows comparatively lesser electrochromic behavior due to low
concentration of DADPS. In this case as the applied potentials changed from –0.2 to 1.2
V, the spectrum exhibited absorption bands at 305 nm, which might be due to *
transition band. As the applied potential increased to oxidation side, the film color
changed from orange-brown to blue. Apart from these bands, an additional broad band
was observed in the visible region. The wavelength maxima of this band depended on the
applied potentials. When the applied potential changed from –0.2 to 0.6 V, an absorption
band was obtained between 450 to 475 nm exhibiting orange-brown colour due to the
formation of cation radical (polaronic forms). As the potential varied from 0.8 to 1.2 V,
the absorption band shifted to lower energy side i.e. a bathochromic shift was observed.
The absorption band between 550 to 600 nm may be due to the formation of bipolarons.
The copolymer film was a conducting blue-violet color film. And this absorption band
disappeared when the applied potential was varied from 1.2 to 1.4 V. The less
conducting blue-violet film may be because of the fully oxidized copolymer. Slightly
different behavior was observed in other copolymer films.
The copolymers obtained from 0.01 M DPA with 0.01and 0.015 M DADPS are
shown in figures 4.10 and 4.11 shows almost similar electrochromic behavior. As the
potential was changed from 0.3 to 0.2 V, absorption band appeared at 550 nm
exhibiting reddish brown color. This may be due to the formation of polaronic forms.
Further increase of potential from 0.4 to 1.2 V caused for an absorption band at 625 nm
resulting bluish green color. This may be due to the formation of bipolaronic forms.
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While the film was switched between the reduced and oxidized states of the
copolymers, the percentage transmittance at max of 550 was monitored as a function of
time for the copolymers obtained from the monomer concentrations of 0.01 M DPA with
0.005 M DADPS. Similarly the percentage transmittance at max of 625 nm was
monitored as a function of time for the copolymers obtained from the monomer
concentrations of 0.01 M DPA with 0.01 and 0.015 M DADPS. The contrast is
determined as the difference between the reduced and oxidized states and reported as
%T and the results are presented in table 4.7. The controlled potential coulometry was
employed to evaluate the coloration efficiency and response time and the results are
presented in table 4.7. Employing of cyclic voltammetry tested the stability of copolymer
films. The potential cycling between 0 to 1.3 V at scan rate of 50 mV s-1 was carried out
and the changes were observed in the redox responses. The copolymer film exhibited no
significant change in the redox behavior up to 500 cycles. This suggested that the
stability of the copolymer films is excellent.
4.4. CONCLUSION
The effect of co monomer feed compositions and polymerization conditions on
the conducting copolymers of diphenylamine (DPA) and 4,4′diaminodiphenyl sulphone
(DADPS) synthesized using oxidizing agent have been studied. Characterization of the
copolymers by a host of techniques supports their copolymerization. These copolymers
exhibited conductivity as well as solubility in some organic solvents. The redox behavior
of the formed copolymers was understood from cyclic voltammetric studies. The
electrochromic effect was found out through insitu spectroelectrochemical studies. The
composition of monomers in the copolymer was determined using UV-visible
spectroscopy and the influence of DADPS during copolymerization also studied using
Fineman-Ross plots. The copolymer formation and characteristics of functional groups
110
were confirmed through FTIR and proton NMR spectral studies. The surface
morphology and grain size (100 nm) were understood from SEM experiments. The XRD
studies also evidenced the formation of nano sized copolymers.
111
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113
Table 4.1: The solubility of chemically prepared copolymers in various organic solvents
S. No. Organic solvents Solubility
1 DMF ( Merck-AR) Soluble
2 DMSO (Merck-AR) Soluble
3 Tetra Hydro Furan (Merck-AR) Soluble
4 Chloroform (Ranchem-AR) Insoluble
5 Trichloroethylene (Qualigens) Insoluble
6 Hexane (Merck-AR) Insoluble
7 Xylene (Merck-AR) Insoluble
8 Acetone (Ranchem-AR) Insoluble
9 Carbon tetra Chloride (Merck-AR) Insoluble
10 Acetonitrile (Merck-AR) Insoluble
Table 4.2: The percentage of solubility for the copolymers in DMSO
S. No. DPA (M) DADPS (M) Percentage of Solubility
1 0.01 0.005 84
2 0.01 0.01 93
3 0.01 0.015 95
114
Table 4.3: Conductivity and yield of copolymers
Conc. of DPA (M) Conc. of DADPS (M) Conductivity S cm-1
% Yield
0.01 0.005 2.61 10–2
65
0.01 0.01 2.74 10–2
74
0.01 0.015 2.66 10–2
72
Table 4.4: FTIR Spectral data of PDADPS, PDPA, P(DPA-co-DADPS) of 0.01
M DPA & 0.005M DADPS, P(DPA-co-DADPS) of 0.01 M DPA & 0.01M DADPS and
P(DPA-co-DADPS) of 0.01 M DPA & 0.015M DADPS.
Vibrations
Wave number (cm-1
)
Homopolymers
Copolymers of 0.01 M DPA
with
PDADPS PDPA
0.005 M
DADPS
0.01 M
DADPS
0.015 M
DADPS
(N-H)s 3377 3385 3238 3404 3439
(N-H)b 1628 1560 1628
(C=C)s
1593
1402
1593
1417
1597
1421
1560
1421
(S=O)s 1304 1288 1312 1308
(C-N)s 1153 1171 1170 1178 1161
(C-H) in plane bending 1105 1070 1070 1068 1068
(C-H) out of plane
bending
842
689
824
692
852
667
851
678
851
679
(S=O)b 555 580 554 577
115
Table 4.5: The 13
C chemical shift values for various C atoms of DADPS and
DPA monomers and P(DPA-co-DADPS) copolymers
Nature of Carbon
13C Chemical Shift (ppm)
Monomers Copolymers
DADPS DPA
Copolymer of
0.01 M DPA with
0.005 M DADPS
Copolymer of
0.01 M DPA with
0.01 and 0.15 M
DADPS
Sulfonyl “C” 127.93 128.61 128.67
“C” ortho to -SO2-
group
128.22 130.16 130.99
“C” meta to -NH-
group
129.30 130.16 130.99
“C” meta to -SO2-
group
112.59 115.31 115.98
“C” ortho to -NH-
group
117.88 115.31 115.98
1o amino (ipso) “C” 152.38 150 148.46
2o amino (ipso) “C” 143.17 150 148.66
“C” para to -NH-
group
120.96 150 148.66
116
Table 4.6: Molar composition of DPA and DAPDS in poly(DPA-co-DADPS) by UV –
Visible Spectroscopy
Feed ratio
(mM)
Concentration of
Copolymer
( 10-4
mg/l)
Average
( 10-3
l/mg)
Molar Composition of
Copolymer
DPA DADPS DPA DADPS
10 5
2.5
14.6 0.66 0.34
1.5
10 10
2.5
15.6 0.51 0.49
1.5
10 15
2.5
18.1 0.14 0.86
1.5
Table 4.7: Electrochromic parameters of chemically prepared copolymers,
Poly(DPA-co-DADPS) 0.01 M DPA with 0.005, 0.01 & 0.015 M DADPS
Applied
Potential
Range
(V)
DADPS
(M) Color
Wavelength
( in nm)
Coloration
Efficiency
( in cm2/C)
Response Time
( in sec) Optical
Contrast
(∆%T) Coloring Bleaching
-0.3-0.2 0.005
Violet/
Blue
550 436 12 16 48
0.4-1.2
0.01
&
0.015
Blue/
Green
625 578 18 21 59
117
Scheme 4.1: The assignment 1H NMR chemical shift values of poly(DPA-co-DADPS)
in DMSO-d6.
Scheme 4.2: 13
C chemical shift values for various carbon atoms in DPA and DADPS
monomers.
Scheme 4.3: The assignment 13
C NMR chemical shift values of poly(DPA-co-DADPS)
in DMSO-d6.
118
Figure 4.1: The cyclic voltammetric behavior of copolymers obtained from 0.01 M DPA
with (a) 0.005 M DADPS, (b) 0.01 M DADPS and (c) 0.015 M DADPS cycled between
0 to 1.3 V in 0.1 M H2SO4 at a scan rate of 50 mV s-1
.
119
Figure 4.2: FTIR spectrum of (a) PDPA, (b) PDADPS, Poly(DPA-co-DADPS) obtained
from 0.01 M DPA with (c) 0.005 M DADPS, (d) 0.01 M DADPS and
(e) 0.015 M DADPS
120
Figure 4.3:
1H NMR spectrum of Poly(DPA-co-DADPS) obtained from 0.01 M DPA
with (A) 0.005 M DADPS, (B) 0.01 M DADPS and (C) 0.015 M DADPS. The
corresponding expanded spectra are shown as a, b and c respectively.
121
Figure 4.4:
13C NMR spectrum of Poly(DPA-co-DADPS) obtained from 0.01 M DPA
with (A) 0.005 M DADPS, (B) 0.01 M DADPS and (C) 0.015 M DADPS
122
Figure 4.5: XRD diffraction patterns of (a) PDPA, (b) PDADPS, Poly(DPA-co-DADPS)
obtained from 0.01 M DPA with (c) 0.005 M DADPS, (d) 0.01 M DADPS and
(e) 0.015 M DADPS
123
Figure 4.6: SEM images of (A) PDPA, (B) PDADPS, Poly(DPA-co-DADPS) obtained
from 0.01 M DPA with (C) 0.005 M DADPS, (D) 0.01 M DADPS and
(E) 0.015 M DADPS
124
Figure 4.7: UV Spectrum of homopolymers (a) PDADPS, (b) PDPA,
Poly(DPA-co-DADPS) obtained from 0.01 M DPA with (c) 0.005 M DADPS,
(d) 0.01 M DADPS and (e) 0.015 M DADPS in DMSO.
Figure 4.8: Plot of F(f-1)/f versus F
2/f (Simplified Fineman-Ross Equation).
125
Figure 4.9: Spectroelectrochemical behavior of Poly(DPA-co-DADPS) obtained from
0.01 M DPA with 0.005 M DADPS in 0.1 M H2SO4 medium at various applied potential.
Figure 4.10: Spectroelectrochemical behavior of Poly(DPA-co-DADPS) obtained from
0.01 M DPA with 0.01M DADPS in 0.1 M H2SO4 medium at various applied potential.
126
Figure 4.11: Spectroelectrochemical behavior of Poly(DPA-co-DADPS) obtained from
0.01 M DPA with 0.015 M DADPS in 0.1 M H2SO4 medium at various applied potential.