O. MELAD, M. JAROUR: COPOLYMERIZATION OF POLY (O-PHENYLENEDIAMINE-CO-O/P-TOLUIDINE) VIA ...
283–288
COPOLYMERIZATION OF POLY
(O-PHENYLENEDIAMINE-CO-O/P-TOLUIDINE) VIA THE
CHEMICAL OXIDATIVE TECHNIQUE: SYNTHESIS AND
CHARACTERIZATION
KOPOLIMERIZACIJA POLI
(O-FENILENDIAMINA-CO-O/P-TOLUIDINA) S TEHNIKO
KEMIJSKE OKSIDACIJE: SINTEZA IN KARAKTERIZACIJA
Omar Melad, Mariam Jarour
Al-Azhar University Gaza, Chemistry Department, P.O.Box 1277, Gaza, Palestine
omarmelad@yahoo.com
Prejem rokopisa – received: 2016-01-23; sprejem za objavo – accepted for publication: 2016-03-16
doi:10.17222/mit.2016.023
Chemical oxidative copolymerization of o-phenylenediamine -co-o/p-toluidine at different molar ratios of monomer was
performed using potassium dichromate as an oxidant. The resulting copolymers were investigated using Fourier transform
infrared spectroscopy (FTIR) and UV-visible spectroscopy. In the copolymer, the intensity of the band at 1005 cm–1 is
substantially decreased due to the -CH3 bending vibrations. A hyposochromic shift is observed in UV-visible spectroscopy. The
electrical-conductivity values obtained for the o-toluidine copolymers are higher than those for the p-toluidine copolymers.
Keywords: o-phenylenediamine, o-toluidine, p-toluidine, conductivity, chemical oxidativeness, FTIR
Izvedena je bila kemijska oksidativna kopolimerizacija o-fenilendiamina-co-o/p-toluidina pri razli~nih molarnih razmerjih
monomera, z uporabo kalijevega dikromata kot oksidanta. Nastali kopolimeri so bili preiskovani z uporabo infrarde~e
spektroskopije s Fourierjevo transformacijo (FTIR) in UV-vidno spektroskopijo. V kopolimeru je intenziteta pasu pri 1005 cm–1
ob~utno zmanj{ana zaradi upogibnih vibracij -CH3. V UV vidnem spektru je opa`en zamik v spektralnem pasu. Vrednosti
elektri~ne prevodnosti dobljene pri o-toluidin kopolimerih so vi{je kot pri p-toluidin kopolimerih.
Klju~ne besede: o-fenilendiamin, o-toluidin, p-toluidin, prevodnost, kemijska oksidativnost, FTIR
1 INTRODUCTION
Intrinsically conductive polymers have become an
efficient alternative to inorganic conductors in many
practical applications in the recent decade.1 Polyaniline,
poly toluidine, polypyrrole, poly aminopyridine, poly-
thiophene and poly phenylenediamine are examples of
conductive polymers, showing high conductivity. Poly-
aniline is an important member of the intrinsically con-
ductive polymers because of the ease of its preparation,
an excellent environmental stability, interchangeable oxi-
dation states, electrical and optical properties, economic
costs,2–4 and because they can be used for chemical
sensors,5,6 electromagnetic shielding,7 electrochemical
and corrosion devices.8–9 Polymerization of a conducting
polymer may be performed with chemical10 or electro-
chemical11 methods. Different chemical oxidizing agents
such as potassium dichromate,12–14 potassium iodate,15
hydrogen peroxide,16 ferric chloride or ammonium per-
sulphate17 can be used. The application of polyaniline is
limited because of its poor processability,18 which is true
for most conducting polymers.
A good method to obtain soluble conductive poly-
mers is the polymerization of aniline derivatives. Poly
phenylenediamine homopolymer has attracted attention
because it has been reported to be a high aromatic
polymer containing a 2,3-diamino phenazine or quino-
xaline repeat unit and exhibiting an unusually high
thermostability.19–21 In recent years, copolymerization
has been developed as one of the most essential and
alternative strategies for modifying physical and chemi-
cal properties of conducting polymers. These copoly-
mers show characteristics reasonably different from
those of the homo polymer.22,23 Thus, copolymerization
can be a convenient synthetic method and a process for
preparing new conducting materials with improved
properties. However, the conductivity and solubility of
the phenylenediamine homopolymer are low.19–21 Co-
polymerization of o-phenylenediamine with o/p toluidine
might be one of the best methods. A close analysis of the
literature shows a large number of reports on the chemi-
cal and electrochemical synthesis of polytoluidine and its
copolymer with aniline and other substituted anili-
nes.24–33 Electrochemical copolymerization of o-pheny-
lenediamine with o-toluidine has been reported.34 So far,
there has been no report on copolymerization of o-phe-
nylenediamine with o/p toluidine using the chemical
oxidative method. Toluidines are derivatives of aniline
where a – CH3 group is substituted in the aromatic ring
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Materiali in tehnologije / Materials and technology 51 (2017) 2, 283–288 283
UDK 67.017:620.1:66.095.26 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)283(2017)
at the o-, m- or p- positions. In this work, a chemical
oxidative copolymerization of o-phenylenediamine with
o/p toluidine at different molar ratios of monomer was
synthesized and characterized using FTIR, UV-visible
spectroscopy and conductivity measurements.
2 EXPERIMENTAL PART
2.1 Materials
o-phenylenediamine (o-PD), o-touidine (oT), p-tolui-
dine (pT) (ADWIC, Egypt), potassium dichromate
(K2Cr2O7), ammonium persulfate ((NH4)2S2O3) (Merk,
Germany), hydrochloric acid (HCl 32 %), formic acid
(HCOOH 98 %) and glacial acetic acid (CH3COOH 99.5 %)
(Merk-Germany), dimethylsulfoxide (DMSO) and
N,N-dimethylformamide (DMF) were used for the
UV-visible and conductivity measurements, respectively.
All the chemicals, acids and solvents were used as
received without any further purification.
2.2 Measurements
The FTIR spectra were recorded with a FTIR
8201PC (SHIMADZU) instrument using KBr pellets
techniques. For measuring the UV-visible absorption
spectra, a spectrophotometer (UV-1601 SHIMADZU)
was used. Conductivity measurements were made at
room temperature using a conductivity meter (CM-30V).
2.3 Synthesis of poly (o-phenylenediamine – Co –o/p-
toluidine)copolymer
2.3.1 Synthesis of poly o-phenylenediamine
The polymer of o-phenylenediamine was synthesized
by dissolving 1.622 g of o-phenylenediamine in 100 mL
of 0.1M HCL in a stirred ice bath to produce a homo-
genous solution. 4.413 g of potassium dichromate was
dissolved in 50 mL of 0.1M HCL and added to the first
solution for 30 min while being constantly stirred, then it
was left at room temperature for 24 h. After this the
solution was filtered, washed with acetone and distilled
water and the polymer was left to dry in an oven at 60 °C
for 24 h.
2.3.2 Synthesis of poly o- and p- toluidine
Poly (o- and p- toluidine) were synthesized with che-
mical oxidative polymerization of o- and p- toluidine in
an acidic media. 5 mL of oT was dissolved in 300 mL of
1M formic acid and kept at 0 °C; 11.4 g of K2Cr2O7 was
dissolved in 200 mL of 1M formic acid also at 0 °C and
added dropwise under constant stirring to the
(oT/HCOOH) solution over a period of 20 min. The
resulting dark green solution was maintained under con-
stant stirring for 24 h. The solution was filtered and then
washed with distilled water; the black powder of poly
o-toluidine was left to dry in air for one week, while 2.5
mL of pT was dissolved in 150 mL of 1M HCL and kept
at 0 °C; 5.7 g of K2Cr2O7 was also dissolved in 100 mL
of 1M HCL at 0 °C and added dropwise under constant
stirring to the (pT/HCL) solution over a period of
20 min. The resulting dark red solution was maintained
under constant stirring for 24 h. The solution was filtered
and then washed with distilled water, and the black red
powder of poly p-toluidine was left to dry in air for one
week.
2.3.3 Synthesis of poly (o-phenylenediamine – Co –
o-/p- toluidine)copolymer
1.54 g oPD and 0.5133 mL oT/pT were added to
150 mL of 1M glacial acetic acid in a 500 mL single-
neck glass flask at 40 °C . 13.68 g ((NH4)2S2O8) was
dissolved separately in 14 mL distilled water to prepare
an oxidant solution. The monomer solution was then
stirred and treated with the oxidant solution added
dropwise at an adding rate of one drop every three
seconds for 30 min at 40 °C. Immediately after the first
few drops, the reaction solution turned violet in the case
of oT and blackish green in the case of pT. After 1 h, the
copolymer acetate was isolated from the reaction mixture
with filtration and washed with the excess of distilled
water to remove the oxidant and oligomers. A whitish
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Figure 1: Scheme of copolymerization mechanism of poly
(o-phenylenediamine-Co-o-toluidine) copolymer
Slika 1: Shema mehanizma kopolimerizacije poli ( o-fenilendiamin in
o-toluidin) kopolimera
violet solid powder and a greenish brown solid powder
for oT and p-T copolymers, respectively, were left to dry
in the oven at 118 °C for 48 h and then dry in air for one
week. The above procedure was repeated at various
molar ratios of the monomers oT and pT at the feeds of
0.50 and 0.25 molar of oPD, respectively.
3 RESULTS AND DISCUSSION
3.1 Synthesis of poly (o-phenylenediamine – Co – o-/p-
toluidine)copolymer
Toluidines are derivatives of aniline where a –CH3
group is substituted in the aromatic ring at the o-, m- or
p- positions. Schemes in Figures 1 and 2 represent the
copolymerization mechanism of poly (o-phenylen-
ediamine-Co-o-/p-toluidine)copolymer, respectively.
3.2 FTIR spectra of poly (o-phenylenediamine – Co - o
/ p- toluidine) copolymer
Figure 3 shows the FTIR spectra of poly o-phenylen-
ediamine, poly o-toluidine and poly p-toluidine, respec-
tively.
A weak band is observed at 3326–3391 cm–1 cha-
racteristic of the –NH2 and N-H stretching, another one
is observed at 1640–1525 cm–1 assigned to the quinoid
and benzenoid phenyl ring for poly o-phenylenediamine
(Figure 3 (A), the signal due to the C-H in-plane
bending vibratio is observed at 1161 cm–1. Figure 3 (B
and C) shows the frequency peaks at (2917, 1638, 1450,
1301, 1207, 1157, 920) cm–1 that are attributed to the
C-H stretching of the substituent methyl group, C=C
stretching vibrations of quinoid rings, C=C stretching
vibrations of benzoid rings, C-N stretching vibrations of
quinoid rings, C-N stretching vibrations of benzoid
rings, C-H in-plane bending vibrations and 1, 2, 4- tri
substituted aromatic rings, respectively. The signal at
567 cm–1 is due to the C-H out-of-plane bending vibra-
tion. The peak at 3063 cm–1 in Figure 3 (B and C) is
caused by the C-H stretch modes of the substituent
methyl group. Figure 4 shows the FTIR spectra of poly
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Figure 4: FTIR spectra of poly (oPD-Co-oT) copolymer with
different molar ratios of oPD: A) 0.25, B) 0.50, C) 0.75
Slika 4: FTIR-spektri poli (oPD in oT) kopolimera z razli~nimi
molskimi razmerji oPD: A) 0,25, B) 0,50, C) 0, 75
Figure 2: Scheme of copolymerization mechanism of poly
(o-phenylenediamine-Co-p-toluidine) copolymer
Slika 2: Shema mehanizma kopolimerizacije poli ( o-fenilendiamin in
p-toluidin) kopolimera
Figure 3: FTIR spectra of: A) poly o-phenylenediamine, B) poly
o-toluidine and C) poly p-toluidine
Slika 3: FTIR-spekter: A) poli o-fenilendiamina, B) poli o-toluidina
in C) poli p-toluidina
(oPD-Co-oT) copolymer with different molar ratios of
oPD.
Most of the bands show variations in the intensity
and position. The spectra of the copolymer show the
main bands corresponding to the N-H stretching vibra-
tions and ring stretching vibrations of quinoid and
benzeoid structures. The intensity of the N-H stretching
vibrations in the region between 3470–3010 cm–1 in-
creases with the increasing oPD feed concentration,
indicating an increase in the number of primary and
secondary amino groups in the copolymer structure. The
band at 1590 cm–1 (Figure 3 (B)) and the band at 1627
cm–1 (Figure 3 (C)) correspond to the C=C stretching
vibrations of the aromatic rings. This signal is shifted to
1630 cm–1 in the copolymer, Figure 4. The intensity of
the two bands centered at 1497 cm–1 and 600 cm–1
greatly increases with the increasing oPD feed concen-
tration (Figure 4), while the 1497 cm–1 band in the copo-
lymer indicates the presence of phenazine-type structures
in the copolymer backbone. These cyclic structures in
the copolymer are either due to the presence of oPD
blocks or may result from the cyclization of the adjacent
oPD and oT units in the copolymer chain. On the other
hand, the intensity of the band at 1005 cm–1, due to the
–CH3 bending vibrations, substantially decreases in the
copolymer. This is indicative of a gradual decrease in the
oT units in the copolymer structure with the increasing
oPD feed concentration.
Figure 5 shows the FTIR spectra of poly(oPD-
Co-pT) copolymer with different molar ratios of oPD.
In general, with some exceptions, the spectral charac-
teristics of the copolymers are very similar to those of
PoPD. The intensity of the broad band, in the region of
3000–3353 cm–1 increases with the increasing oPD feed
concentration. The band corresponding to the quinoid
stretching vibrations occurs at 1616 cm–1 for the
copolymer. The intensity of this band was also found to
increase with the increasing oPD feed concentration. The
incorporation of the p-toluidine moiety in the copolymer
was indicated by the appearance of the characteristic
C-H stretching of the substituent methyl group, which
was observed as a very weak band at 2917 cm–1. As in
o-toluidine, the intensity of the band at 1029 cm–1, due to
the -CH3 bending vibrations, substantially decreases in
the copolymer.
3.3 UV-visible spectra of poly (o-phenylenediamine –
Co - o / p- toluidine) copolymer
Figure 6 shows the UV-visible spectra of poly
o-phenylenediamine, poly o-toluidine and poly
p-toluidine, respectively.
Figures 7 and 8 show the UV-visible spectra of poly
(oPD-Co-oT) and poly (oPD-Co-pT)copolymers, respec-
tively, with different molar ratios of oPD. In Figures 6, 7
and 8, for UV-visible spectra of homopolymers and
copolymers, two characteristic absorption peaks were
found at around 290 nm and in a range of 417–563 nm
corresponding to the benzene -* electronic transition
and n-* electronic transition. A hyposochromic shift
from 550 nm in the o-toluidine copolymer to 450 nm in
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Figure 6: UV-VIS spectra of: A) poly o-phenylenediamine, B) poly
o-toluidine and C) p-toluidine
Slika 6: UV-VIS spektri: A) poli o-fenilendiamin, B) poli o-toluidin in
C) p-toluidin
Figure 5: FTIR spectra of poly (oPD-Co-PT) copolymer with
different molar ratios of oPD: A) 0.25, B) 0.50, C) 0.75
Slika 5: FTIR-spektri poli (oPD in PT) kopolimera z razli~nimi
molskimi razmerji oPD: A) 0,25, B) 0,50 in C) 0,75
Figure 7: UV-VIS spectra of poly (oPD-Co-oT) copolymer with
different molar ratios of oPD: A) 0.25, B) 0.50 and C) 0.75
Slika 7: UV-VIS spektri poli (oPD in oT) kopolimera z razli~nimi
molskimi razmerji oPD: A) 0,25, B) 0,50 in C) 0,75
the p-toluidine copolymer implies a decrease in the
extent of conjugation and an increase in the band gap.
These bands correspond to the excitation transition of the
quinoid rings. It can be observed that these bands
increase when the o-phenylenediamine in the copolymer
is increased. This blue shift with the increasing o-phenyl-
enediamine in the copolymer is due to the steric effect of
the substituents, indicating a successful copolymeri-
zation.
3.4 Electrical conductivity
Table 1: shows electrical conductivity of poly (o-phenylenediamine
–Co-o/p-toluidine) copolymer at room temperature in DMF
Tabela 1: Elektri~na prevodnost poli (o-fenilendiamina in
o/p-toluidin) kopolimera pri sobni temperaturi v DMF
Polymer Conductivity (S/cm)
PoPD 2.23
PoT 1.43
PpT 2.04
P(oPD-Co-oT)25 3.39
P(oPD-Co-oT)50 3.42
P(oPD-Co-oT)75 4.65
P(oPD-Co-pT)25 1.615
P(oPD-Co-pT)50 1.878
P(oPD-Co-pT)75 1.898
It can be seen that the conductivity increases as the
amount of o-phenylenediamine increases in the copoly-
mers. In general, o-isomer gives higher conductivity
values than the other isomers; the small values of the
conductivity in the case of poly (o-phenylenedia-
mine–Co-p-toluidine) copolymer compared with the
conductivity value of o-phenylenediamine may indicate
that p-toluidine is not a good enough polymer to make a
copolymer with o-phenylenediamine.
5 CONCLUSION
The synthesis of the copolymerization of o-pheny-
lenediamine with o / p-toluidine was characterized using
FTIR and UV-Vis spectroscopy. The intensity of the
band at 1005 cm–1 that is due to the -CH3 bending
vibrations, substantially decreases in the copolymer. A
hypsochromic shift from 550 nm in the o-toluidine
copolymer to 450 nm in the p-toluidine copolymer
implies a decrease in the extent of conjugation and an
increase in the band gap. In general, ortho-isomers give
higher conductivity values than the other isomers; so the
obtained conductivity values that are higher for the
o-toluidine copolymer than for the p-toluidine copo-
lymer, indicate that p-toluidine is not a good enough
polymer able to make a copolymer with o-phenylen-
ediamine.
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