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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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112

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873.

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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.