Polyvinyl chloride modification with sodium salt of 2-thiobenzimidazole

Article abstract of DOI:10.1134/S1070363214090266

Polymer analogous reaction has been used to partially substitute chlorine atoms of polyvinyl chloride with 2-thiobenzimidazole fragments. ¹³C NMR and IR spectroscopy studies have shown that the vinylene units are present in the modified polymer

Full text of DOI:10.1134/S1070363214090266

ISSN 1070-3632, Russian Journal of General Chemistry, 2014, Vol. 84, No. 9, pp. 1799–1802. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © N.S. Shaglaeva, V.V. Bayandin, P.V. Multuev, K.A. Abzaeva, M.G. Voronkov, 2014, published in Zhurnal Obshchei Khimii, 2014,
Vol. 84, No. 9, pp. 1563–1566.
Polyvinyl Chloride Modification with Sodium Salt
of 2-Thiobenzimidazole
N. S. Shaglaevaa, V. V. Bayandina, P. V. Multueva, K. A. Abzaevab, and M. G. Voronkovb†
a Irkutsk State Technical University, ul. Lermontova 83, Irkutsk, 664074 Russia
e-mail: ShaglaevaNS@yandex.ru
b Favorskii Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia
Received May 5, 2014
Abstract—Polymer analogous reaction has been used to partially substitute chlorine atoms of polyvinyl
chloride with 2-thiobenzimidazole fragments. 13C NMR and IR spectroscopy studies have shown that the
vinylene units are present in the modified polymer. The copolymer product has been used to prepare the
membrane with proton conductivity of 1 × 10–2 to 0.04 S/cm at 25–195°C.
Keywords: poly(vinyl chloride), 2-thiobenzimidazole sodium salt, membrane, proton conductivity
DOI: 10.1134/S1070363214090266
Polyvinyl chloride PVC is among the most im-
portant large-scale industrial polymers. The high
content of chlorine in PVC, 56.8 wt %, causes its
major advantages and drawbacks. In particular, PVC is
1.5 times cheaper than polyethylene, possess high
durability and stability in contact with common acids,
oxidizers, and solvents; furthermore, PVC is an
excellent electric insulator. However, PVC melts are
highly viscous and thermally unstable under the
processing conditions. Hydrogen chloride evolving at
heating PVC is known to catalyze further degradation
of the polymer. The softening temperature of PVC is
higher than the degradation temperature; hence, PVC
cannot be melt-processed. PVC processing is generally
performed after its plasticization with low-molecular
compounds [1]. Another possible route of PVC
properties modification is its polymer analogous
reaction with nucleophiles [2, 3]. Polymers with new
valuable properties have been prepared as a result of
PVC chemical modification [4, 5]. As chlorine
substitution in PVC is of undoubtful practical im-
portance, the search for the new nucleophiles capable
of the interaction with PVC and elaborating the
optimal process conditions are of remarkable interest.
fragments and the formation of proton-conductive
membranes based on the reaction products.
Nucleophilic substitution of PVC chlorine with 2-
thiobenzimidazole sodium salt was performed in the
cyclohexanone medium at 80–120°С (Table 1). The
presence of nitrogen and sulfur in the product con-
firmed that the substitution reaction occurred. The
amounts of vinyl chloride in the copolymer product as
calculated from the content of the residual chlorine and
from the nitrogen content were different (Table 1),
pointing at the side reaction of dehydrochlorination.
The deviation between the two calculated values
reflected the degree of the elimination reaction.
IR spectra of the modified PVC specimens con-
tained the absorption bands of the polymer backbone
methylene and methine groups (1420, 1320, and
960 cm–1) as well as those assigned to 2-thiobenz-
imidazole fragments (a group of bands at 1520–
1400 cm–1); moreover, the band appeared at about
1640 cm–1 typical of vinylene units.
The presence of the ~СН=СН~ fragments in the
copolymer products was confirmed by the 13С NMR
spectra that contained the signals of carbons of the
unreacted vinyl chloride units [58.0–64.0 ppm (CHCl)
and 46.0–48.4 ppm (CH2)], the broadened signals of 2-
thiobenzimidazole units[110–118 (С4,7), 122 and 126
(С5,6), ≈140 (С8,9), and 142–150 (С2) ppm], and the
This work aimed at PVC modification via nucleo-
philic substitution of chlorine with benzimidazole
†
Deceased.
1799

1800
SHAGLAEVA et al.
Table 1. Conditions of PVC modification with 2-thiobenz-
imidazole sodium salt
Table 2. Composition of the products of PVC modification
with 2-thiobenzimidazol sodium salt
Elemental analysis of the
Duration,
Units in the copolymer, mol %
Exp.
product, wt %
Exp. no. Т, °C
h
no.a
N
S
Cl
unmodified units units modified with vinylene units
~CH2–CHCl~ 2-thiobenzimidazole ~CH=CH~
1
2
3
4
5
6
80
100
100
100
100
120
8
2
4
6
8
8
7.52
10.02
25.02
8.21
8.47
9.95
10.10
11.00
11.65
11.68
20.92
17.62
15.12
13.62
13.90
1
2
3
4
5
6
68.93
62.19
55.85
50.53
47.06
47.68
27.22
28.75
29.74
35.29
41.03
36.12
3.85
9.06
9.65
14.41
14.18
11.91
16.20
10.86
9.30
highly overlapped strong signals at 128–127 ppm
assigned to the ~СН=СН~ groups.
a The exp. numbers correspond to those in Table 1.
Content of the vinylene fragments (V) in the
modified PVC was calculated as follows.
product (Table 2, Exp. 1, 2, and 6). The highest
fraction of the ~СН=СН~ units was 16.20 mol %;
however, the product was still soluble in the reaction
mixture (Table 2, Exp. 6). Hence, no crosslinking via
the double bonds of vinylene units occurred under the
conditions of nucleophilic substitution.
V = 100 – (VC + BI).
In the equation, VC stands for the amount of vinyl
chloride units calculated from the chloride content and
BI is the amount of 2-thiobenzimidazole fragments
calculated from the nitrogen content.
Basing on the obtained data, we derived the follow-
ing scheme of the PVC modification.
Increase of the studied reaction temperature led to
higher fraction of the vinylene units in the copolymer
N
+
N
H
SNa
z
n
n
y
Cl
Cl
S
N
H
N
The presence of strongly basic nitrogen atoms in
the product could afford significant proton con-
ductivity of the produced modified PVC, when doped
with acids. The model membrane was prepared from
the product with the highest 2-thiobenzimidazole
fragments fraction (Table 2, Exp. 5). The 0.3 mm thick
membrane was obtained from the 10 wt % solution in
DMF via the casting–evaporation procedure. The total
exchange capacity of the membrane was of 1 mmol/g.
acid during 24 h. The proton conductivity of the
membrane as a function of temperature is shown in the
figure.
The proton conductivity was 1.0 × 10–2 S/cm at 45°C.
Upon further heating, the membrane proton conduc-
tivity was up to 3.8 × 10–2 S/cm, the effective active-
tion energy being of 26±1 kJ/mol. The membrane did
not lose the mechanical integrity under the
experimental conditions.
Proton conductivity of the membrane was measured
The low-temperature (20–50°С) proton conduc-
tivity of the membrane based on the modified PVC
was lower than those of the membranes prepared from
by impedance spectroscopy (two-point method, 10–3
×
106 Hz) after doping with concentrated phosphoric
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 9 2014

POLYVINYL CHLORIDE MODIFICATION WITH SODIUM SALT
1801
polybenzimidazole or Nafion. However, upon heating
log σ, S/cm
up to 200°С the conductivity of the membrane prepared
in this work, about 0.04 S/cm, was close to that of
polybenzimidazole-based membranes. The proton
conductivity could be expected to further increase after
modification of the membrane with certain inorganic
and organic doping agents, similarly to [6, 7].
–1.4
–1.5
–1.6
–1.7
–1.8
The major advantage of the reported PVC-based
membrane is the simplicity of preparation. The
membrane can be potentially used for fuel cells and
separation devices involving ion-exchange membranes
assemblies.
–1.9
–2.0
–2.1
2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4
1000/T, K–1
EXPERIMENTAL
The Arrhenius plot of proton conductivity of the membrane
We used the emulsion-polymerized PVC soluble in
dimethylformamide, cyclohexanone, and (partially) in
dimethylsulfoxide. The polymer parameters were as
follows: the Fikentscher K-value 62–63, the
decomposition temperature 120°C, and the specific
surface area 1.81 cm2/g. 2-Thiobenzimidazole (Fluka,
“analytically pure” grade) was purified by recrystal-
lization from the 1 : 1 aqueous ethanol; mp 304–305°С.
Cyclohexanone and dimethylformamide were purified
via the usual procedures [8].
based on the modified PVC.
current bridge at 10 Hz to 600 kHz and at 20–100°С.
Ionic conductivity of the membrane at each
temperature was determined by the impedance
extrapolation onto the active resistance axis.
2-Thiobenzimidazole sodium salt. 0.1 mol of 2-
thiobenzimidazole was dissolved in 100 mL of ethanol,
and 0.1 mol of NaOH was added in the form of
aqueous solution. The reaction mixture was left
standing during 3 h at room temperature. After the
solvents elimination, the salt formed was washed with
ethanol and dried in a vacuum dessicator over Р2О5.
The salt purity was determined by potentiometric
titration.
Elemental analysis of the products was performed
using the ThermoFinnigan gas analyzer. IR spectra
(KBr pellets or mineral oil suspension) were recorded
using the Specord IR-75 and Bruker IFS-25 spectro-
meters. 13С NMR spectra of the copolymers solutions
in DMSO-d6 were recorded using the VXR-500S
Varian spectrometer (125.5 MHz).
The membrane was prepared via solution casting
and the solvent evaporation from the copolymer 10 wt %
solution in dimethylformamide; the membrane thick-
ness was measured using the Mitutoyo digital micro-
meter with the accuracy ±1 µm.
PVC modification. Equimolar amount of 2-
thiobenzimidazole sodium salt was added by portions
to the 4 wt % solution of PVC in cyclohexanone. In all
cases, the modified PVC was soluble in the reaction
mixture. The products were isolated via dialysis or
precipitation into water followed by filtration. The so
obtained copolymer was dried in a vacuum drying
cabinet. Other preparation conditions are collected in
Table 1.
The membrane exchange capacity was measured by
potentiometric titration of the copolymer specimens
(0.0453 g) immersed into the NaCl (0.1 mol/L)
solution with aqueous HCl (0.01 mol/L). pH of the
solution was measured with the Ekoniks-Ekspert 001
voltmeter equipped with the Mettler Toledo combined
pH electrodes. The pH value was automatically
recorded each 3 s. The experiment was performed till
the stationary state of the ion exchange was attained.
ACKNOWLEDGMENTS
This work was financially supported by Russian
Foundation for Basic Research (project code 12-08-
00115-a) and by Ministry of Education and Science in
the frame of basic part of the Governmental contract
(no. 37).
Resistivity of the membrane was measured in
contact with deionized water using the 2V-1 alternated
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 84 No. 9 2014

1802
SHAGLAEVA et al.
Russ. J. Appl. Chem., 2013, vol. 86, no. 10, p. 1576.
DOI: 10.1134/S1070427213100182.
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