Modification of Poly(vinyl chloride) by N -Phenyl Itaconimides for the Improvement of Its Thermal Stability

Article abstract of DOI:10.1155/2019/4782745

Poly(vinyl chloride) (PVC) is modified by N-phenyl itaconimide derivatives (N-(RPh)IM) as modifying agents or graft comonomers. The resulting modified polymers or graft copolymers were characterized using FTIR and UV/Vis spectrophotometry. The thermal pro

Full text of DOI:10.1155/2019/4782745

Hindawi
Journal of Chemistry
Volume 2019, Article ID 4782745, 8 pages
https://doi.org/10.1155/2019/4782745
Research Article
Modification of Poly(vinyl chloride) by N-Phenyl Itaconimides for
the Improvement of Its Thermal Stability
Asma M. Elsharif , Azza A. Al-Ghamdi, and Abir S. Abdel-Naby
Chemistry Department, College of Science, Imam Abdulrahman Bin Faisal University, P.O. Box 1982,
31441 Dammam, Saudi Arabia
Correspondence should be addressed to Abir S. Abdel-Naby; aabdelnaby@iau.edu.sa
Received 2 April 2019; Revised 7 June 2019; Accepted 24 June 2019; Published 15 July 2019
Academic Editor: Marinos Pitsikalis
Copyright © 2019 Asma M. Elsharif et al. +is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Poly(vinyl chloride) (PVC) is modified by N-phenyl itaconimide derivatives (N-(RPh)IM) as modifying agents or graft co-
monomers. +e resulting modified polymers or graft copolymers were characterized using FTIR and UV/Vis spectrophotometry.
+e thermal properties of the modified polymers were investigated using thermogravimetry (TGA), which revealed that the
synthesized polymers exhibited high thermal stability, as shown from the value of their initial decomposition temperatures and the
percentage of weight loss at high temperatures. +e polymer modified by 4-bromo itaconimide exhibited the most thermal
stability. A mechanism for the modification reaction and the graft copolymerization of PVC was suggested.
free from labile sites and capable of withstanding high
temperatures.
1. Introduction
Poly(vinyl chloride) (PVC) is one of the most produced
polymers. It is mainly used in various plastic applications.
Despite possessing the advantage of being a low-cost
polymer, PVC suffers from poor heat stability. While the
molding temperature needed for most PVC products exceeds
180°C, the polymer starts to degrade at 120°C. +us, the
polymer should be thermally stabilized before the molding
process. +e thermal degradation leads to the evaluation of
HCl gas and formation of conjugated polyenes [1], causing
discoloration of the polymer. +us, labile sites, tertiary and
allyl chlorine atoms, should be replaced by more stable groups
before the molding process. +is occurs through chemical
modification [2, 3], graft copolymerization [2, 4, 5], or simply
adding various thermal stable compounds [6, 7].
Itaconimide derivatives were previously used as thermal
additives for PVC [8, 9], but the additives technique is not
considered as an effective method for the stabilization since
the stable additives act as a physical protector on the surface
layer of the polymer only. It does not prevent the formation
of HCl and the polyenes inside the polymeric matrix.
In the present work, chemical modification and graft
copolymerization are used to synthesize stable PVC,
2. Materials and Methods
2.1. Materials and Chemicals. Poly(vinyl chloride) (PVC)
was obtained from the Sabic company with a k value of 67
and itaconic anhydride 98% from Acros. Freshly distilled
tetrahydrofuran (THF) was used, and cyclohexanone (99.8%)
was purchased from Acros.
2.2. Synthesis of Itaconimide Derivatives. All N-(substituted
phenyl)itaconimide derivatives (N-(RPh)IM) were prepared by
two steps described by Adam [6]. In the first step, 1 mol of
itaconic anhydride was dissolved in dry diethyl ether and then,
1 mol of the primary amine dissolved in the same solvent was
slowly added to the itaconic anhydride at 0–5°C for 3 hours.
+e resulted acid N-(substituted phenyl)itaconic acid was fil-
tered, washed, and dried. +e following step was cyclization
which occurred by adding acetic acid anhydride and fused
sodium acetate in a steam bath for 30 minutes. +e resulted
monomer was crystallized from aqueous ethanol. Table 1
shows the melting points of prepared itaconimide derivatives.

2
Journal of Chemistry
Table 1: Melting points of various N-(halo phenyl)itaconimides.
2.8. 5ermogravimetry (TG). TG data were obtained by
Shimadzu TGA-50H under the N2 atmosphere at a heating
rate of 10°C/min from room temperature to 500°C.
Melting
N-(phenyl)itaconimide derivatives
point (°C)
N-(phenyl)itaconimide [N-Ph IM]
N-(4-chloro phenyl)itaconimide [N-(4-ClPh)IM]
N-(4-bromo phenyl)itaconimide [N-(4-BrPh)IM]
112-113
131-132
134-135
3. Results and Discussion
3.1. Characterization of the Modified Copolymer
3.1.1. UV/Vis Spectroscopy. Figure 1 shows the UV/Vis
spectrum of modified PVC by N-(4-BrPh)IM. +e spectrum
displayed new two peaks around 330 nm and 390 nm. Since
PVC does not absorb in the UV/Vis region, these two peaks
confirmed the modification of the polymer by the suggested
comonomers.
2.3. Preparation of Modified Polymers. +e modified poly-
mer was prepared according to the Abdel Naby method
[2, 3]. 64 mmol of PVC was dissolved in 1 L of cyclohexa-
none. 50 mmol of the itaconimide was added to PVC so-
lution stirred, at 60°C, under the nitrogen atmosphere. +e
resulted polymer was obtained by precipitating the polymer
mixture in cold methanol, filtered, and then purified by the
Soxhelt system using hot methanol. +e polymer was dried
under vacuum.
3.1.2. IR Spectroscopy. Figure 2 shows the IR spectroscopy of
modified PVC by 4-(BrPh)IM. +e IR spectrum showed the
following peaks:
−1
2.4. Preparation of Graft Copolymer. +e graft copolymer
was prepared by adding benzoyl peroxide (initiator) to the
dissolved PVC solution in THF, at 50°C, under the nitrogen
atmosphere for 10 minutes. Afterwards, the monomer so-
lution was injected to the reaction medium, allowing the
grafting process to occur for two hours. +e product was
precipitated in cold ethanol, purified using the Soxhlet
system, and then dried in vacuum oven at 40°C [2, 9]. +e
graft percentage was investigated by the following equation:
(i) +e C�C stretching band at 1637 cm corre-
sponding to the stabilizer moieties.
(ii) +e peak corresponding to C�O stretching appears
−1
at 1709 cm . +is peak was shifted to the lower
wavenumber as a result of the delocalization of
electrons between double bond and carbonyl groups
((Scheme 1), equation 1(a), structure A).
(iii) Broad peak at 3400 cm−1 indicating the formation of
enolic form of stabilizer moieties (Scheme 1 (A)).
Wg − Wo
%G �
× 100,
(1)
ꢀ
ꢁ
Figure 3 displays the IR spectra of modified PVC before
and after 2 hours of exposure to molding temperature 180°C
in air. +e result revealed the following observations:
Wo
where Wo is the weight of native PVC and Wg is the weight
of polymer after the graft process.
(i) Absence of ethylenic bond C�C which indicated the
participation of the double bond in the stabilization
process
2.5. Preparation of the Poly(vinyl chloride) Films. 1 g of the
polymer sample was dissolved in THF and poured onto a dry
Petri dish, and then the resulted film was dried, in vacuum
oven, at 70°C.
−1
(ii) Also, the presence of the C�O peak at 1728 cm ,
unshifted to the lower wavenumber as in case of the
ungrafted copolymer, confirmed the consumption of
the ethylenic bond in the stabilization reaction which
prohibited the conjugation of double bond with the
carbonyl group
2.6. Evaluation of the Degradation Process. Evaluation of the
stabilizing efficiency was carried out by measuring the rate of
dehydrochlorination by the continuous potentiometric de-
termination of the hydrogen chloride evolved at 180°C in air.
A detailed description of this method was given by Vymazal
et al. [10].
Moreover, the disappearance of the broad peak at
3400 cm−1 confirmed the absence of enol form as a result of
the participation of the C�C bond in the stabilization process.
Following up the discoloration of the modified polymer
(PVC/4(BrPh)IM) with the degradation time, at 180°C,
gradual increase in the discoloration of the sample occurred
with thermal degradation time, till 35 minutes. Conversely,
increasing the time of degradation (>35 min) lightness of the
degraded sample coloration occurred (Table 2) which
confirmed the possibility of the occurrence of the Diels–
Alder reaction (Scheme 1, equation 1(b)).
A digital pH meter (potentiometer), Type HI 9321 PH
(HANNA Instruments, Germany), of accuracy 1 digit
1⁄40.1 mV was used. It was connected to a silver electrode for
the potentiometric measurements. +e results reported are
the average of three replicates in each case.
2.7. Investigation of the Discoloration of the 5ermally De-
graded Samples. UV/visible spectrophotometry was used to
determine the formation of polyenes (extent of discolor-
ation) as indication of the degradation process. A Perki-
nElmer Lamda 4 device was used. Constant concentration
solutions in all samples were prepared.
3.2. 5ermal Gravimetry (TG) of Modified PVC. Regardless of
the molding process, an essential target of this work was to
produce PVC capable to withstand high temperature. To
investigate the thermal behavior of the synthesized modified

Journal of Chemistry
3
0.25
0.2
polymer, the graft copolymerization was used. Before un-
dergoing the graft copolymerization of PVC with the sug-
gested itaconimide derivatives, the grafting parameters were
studied to determine the optimum conditions for the
grafting process.
0.15
0.1
3.4. Factors Affecting Graft Copolymerization
3.4.1. Effect of Initiator Concentration. +e study of the
effect of initiator concentration on the percentage of graft
showed that the percentage of graft increased with the in-
crease in the initiator concentration up to 1.5 ×10−2 mol/L,
followed by remarkable decrease in the G% (Figure 5). +is
might be attributed to termination reactions of growing
radicals by excess free radicals produced from initiator
molecules [11, 12].
0.05
0
250
350
450
nm
550
650
Figure 1: UV spectrum of PVC modified by N-(4-BrPh)IM.
3.4.2. Effect of Monomer Concentration. Figure 6 indicates
that increasing monomer concentration up to 3 ×10−1 mol/
L led to an increase in the percentage of graft (17%) fol-
lowed by slightly decrease in %G (15%) for 6 ×10−1 mol/L,
and this might be attributed to the formation of the ho-
mopolymer [11].
(a)
(b)
3.4.3. Effect of Temperature. +e study of the effect of
temperature on %G showed that increasing reaction tem-
perature led to slight gradual increase in %G till 50°C and
then a sudden increase occurred up to %G � 22%; then, a
constant percentage of graft was observed for the range 58°C
to 68°C followed by a sharp decrease. +is could be at-
tributed to increase the chain termination reactions between
monomer molecules and grafted chains or chain transfer
reactions [12, 13] (Figure 7).
3.5. Characterization of the Grafted PVC Copolymer
(c)
3.5.1. IR Spectroscopy. +e IR spectroscopy was the main
tool used to characterize the structure of the graft co-
polymer. Figure 8 shows the IR spectrum of PVC-g-4(BrPh)
IM. +e spectrum involved the following:
4000
3500
3000
2500
2000
1500
)
1000
350
Wavenumber (cm–1
(i) Disappearance of the stretching band of C�C,
−1
corresponding to stabilizer moieties at 1660 cm :
Figure 2: FTIR spectra of PVC modified by N-(4-BrPh)IM (c) as
compared to N-(4-BrPh)IM monomer (b) and PVC (a).
this is attributed to the incorporation of double
bond of comonomer in the graft process.
polymer, at high temperature (up to 500°C), TG technique
was used.
(ii) Appearance of the strong band referred to the
carbonyl group at 1713 cm−1 as compared to that of
pure stabilizer: this is due to absence of resonance
between C�O and ethylenic bond which was con-
sumed in graft copolymerization.
Figure 4 and Table 3 show the thermal behavior of the
modified copolymers. PVC/4-(BrPh)IM exhibited the highest
thermal stability, as shown from T0 values (T0 � 294°C) and
the total weight loss, at 500°C (59%). PVC/4-(ClPh)IM
exhibited less T0 value 283°C but still exhibited higher thermal
stability than unmodified polymer (T0 � 247°C).
(iii) Appearance of the bending peak according to the
−1
aromatic ring (bending out of plane) at 820 cm .
(iv) In addition, Table 4 shows the effect of the thermal
degradation at 180°C, in air, on the discoloration
of PVC which was modified or grafted by 4-(BrPh)
IM as compared to that of PVC. +is deepness
in color could be explained by consuming the
3.3. Stabilization of PVC through Graft Copolymerization.
In order to build a stabilizer polymeric in nature through the
polymeric matrix to increase the thermal stability of the

4
Journal of Chemistry
Before thermal degradation
After thermal degradation
(Active hydrogen)
H
CH2 CH
Cl
CH2 CH2 CH
CH
O
CH
CH2 CH
Cl
CH2 CH2 CH
CH
CH
Cl
+
O
O
N
N
R
+
O
CH2
R
CH2
Cl
CH
CH2
–HCl
CH2 CH
CH2 CH2 CH
CH CH
H
Cl
Equation 1(b)
O
O
N
R
CH2
CH
Cl
CH2
CH2
CH
CH CH
O
Equation 1(a)
Keto-enol toutomerism
N
O
R
CH2 CH
Cl
CH2 CH2 CH
CH CH
CH2
CH2
OH
O
N
Cl
CH
CH2
R
(A)
Scheme 1: Suggested reaction mechanism representing the modification of poly(vinyl chloride) by N-phenyl itaconimide derivatives, before
and after exposure to molding temperature 180°C, in air.
(a)
(b)
4000
3500
3000
2500
2000
1500
)
1000
350
Wavenumber (cm–1
Figure 3: FTIR spectra of PVC modified by N-(4-BrPh)IM (a) before thermal degradation and (b) after thermal degradation, at 180°C, in air.

Journal of Chemistry
5
Table 2: Effect of thermal degradation at 180°C, in air, on the
discoloration of the films of PVC modified by N-(4-BrPh)IM as
compared to that of PVC.
Table 3: Initial decomposition (T0) and total weight loss per-
centage at 500°C of PVC and modified PVC by various itaconimide
derivatives, under the nitrogen atmosphere.
Time of
degradation
(min)
PVC
modified by
N-(4-BrPh)IM
Polymeric
sample
PVC
N-(4-BrPh)
IM
N-(4-ClPh)
IM
N-PhIM
N-(4-
MeOPh)IM
Initial decomposition
Total weight loss
(%) at 500°C
PVC
temperature T0 (°C)
247
−78
294
−59
283
255
264
−61
−70
−67
0
14
12
10
8
10
35
6
4
135
2
0
0
0.5
1
1.5
2
2.5
)
3
Initiator concentration (mol/L × 10–2
Figure 5: Effect of initiator concentration on the degree of grafting
on PVC by N-PhIM. Monomer concentration (3 mol/L × 10−1) at
60°C for 17 h.
120
100
80
18
16
14
12
10
8
60
40
6
20
4
0
0
2
50 100 150 200 250 300 350 400 450 500
Temperature (°C)
0
0
1
2
3
4
5
6
7
PVC
N-(4-MeOPh)IM
N-PhIM
N-(4-ClPh)IM
N-(4-BrPh)IM
Monomer concentration (mol/L × 10–1
)
Figure 6: Effect of monomer concentration on the degree of grafting
−2
on PVC by N-PhIM. Initiator concentration of 1.5 mol/L × 10 at
Figure 4: +ermal gravimetric analysis of PVC modified by various
itaconimide derivatives as compared to PVC.
60°C for 17 h.

6
Journal of Chemistry
Table 4: Effect of thermal degradation at 180°C, in air, on the
discoloration of the PVC modified and grafted by N-(4BrPh)IM as
compared to PVC.
25
20
15
10
5
PVC
modified
by N-(4-BrPh)
IM
PVC
grafted
Time of
degradation
(min)
PVC
by
N-(4BrPh)IM
0
0
0
20
40
60
Temperature (°C)
Figure 7: Effect of temperature on the degree of grafting on PVC by
N-PhIM. Monomer concentration of 3 mol/L × 10−1; initiator
−2
concentration of 1.5 mol/L × 10 for 17 h.
10
35
(a)
(b)
135
for PVC-g-4-(-ClPh)IM as compared to that of pure PVC
(78%) (Figure 9).
Table 5 shows the initial decomposition temperature (T0)
and total weight loss percentage, at 500°C, of grafted and
modified PVC samples as compared to PVC. +e
data clarified that the graft copolymerization gave the poly-
mer extra heat stability than the simply modification process.
+e extra thermal stability of the grafted copolymers was
observed from the higher T0 value and lower weight loss
percentage (Table 5). +is might be due to the ability of the
grafted branches which possessed the ability to wrap around
the main chains, protecting them from the heat effect.
4000
3500
3000
2500
2000
1500
1000
350
Wavenumber (cm–1
)
Figure 8: FTIR spectra of PVC stabilized by N-(4-BrPh)IM
through (a) chemical modification and (b) graft copolymerization.
3.5.3. Determination of the Extent of Discoloration.
Comparison between the extent of discoloration of the
thermally degraded grafted copolymer and that of the
modified polymer is illustrated in Figure 10. All samples
were degraded for 2 hours in air at 180°C. +e results in-
dicated that graft and modification techniques could be used
to inhibit the discoloration of PVC. +e modified polymer
(PVC/4(BrPh)IM) sample showed slight improvement as
compared to the PVC grafted with the same monomer. +is
referred to the ability of the modified samples performing
the Diels–Alder reaction through the ethylenic double
bonds, while the graft copolymer could not since the double
bonds were consumed in the graft copolymerization.
ethylenic bonds C�C by the grafting process;
thus, no Diels–Alder reaction with polyene formed
(Scheme 2).
3.5.2. 5ermal Gravimetry (TG) of Grafted Copolymers.
To compare the thermal behavior of the graft copolymer and
PVC, the TG analysis was used. +e results of the initial
decomposition temperature values revealed that PVC-g-4-
(-BrPh)IM possessed higher thermal stability (T0 � 313°C)
than PVC-g-4-(-ClPh)IM (T0 � 278°C).
In addition, the values of total weight loss of grafted
samples decreased to 50% for PVC-g-4-(-BrPh)IM and 57%

Journal of Chemistry
7
CH2 CH
Cl
CH2 CH2 CH
CH
CH
Cl
CH2
O
O
N
I
H2C
CH
Cl
CH2 CH2 CH
CH
CH CH2
CH2 CH2
CH2
O
CH2
N
O
N
O
O
R
R
Scheme 2: Suggested reaction mechanism representing the grafting of N-phenyl itaconimide onto poly(vinyl chloride) chains.
120
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
100
80
60
40
20
0
(a)
(c)
0
50 100 150 200 250 300 350 400 450 500
Temperature (°C)
(b)
350
PVC
N-(4-ClPh)IM
N-(4-BrPh)IM
250
450
550
650
N-PhIM
Wavelength (nm)
Figure 9: +ermal gravimetric analysis of PVC grafted by various
itaconimide derivatives as compared to PVC. % of graft for samples
2–2.5%.
Figure 10: UV spectra of degraded (a) parent PVC, (b) PVC
grafted by N-(4-BrPh)IM, and (c) PVC modified by N-(4-BrPh)IM
−1
samples, dissolved in THF (concentration 0.02 g·l ), at 180°C for
2 hours in air.
Table 5: Initial decomposition (T0) and total weight loss per-
centage, at 500°C, of grafted and modified PVC as compared to
PVC, under the nitrogen atmosphere.
4. Conclusions
Polymeric
sample
PVC
N-(4-BrPh)IM
(modify)
N-(4-BrPh)IM
(graft)
Initial decomposition
Total weight loss
(%) at 500°C
In order to improve thermal stability of PVC, itaconimide
derivatives were used to prepare modified polymer and graft
copolymers. +e resulting products were characterized using
IR and UV/Vis spectroscopy. Both techniques, modification
reaction and graft copolymerization, led to thermally stable
polymers as shown from their initial decomposition tem-
peratures and weight loss percentages.
Moreover, both the grafted copolymers and modified
polymers exhibited less degree of discoloration than parent
PVC. Mechanisms for both modification and grafting co-
polymerization reactions confirmed that the modification
reaction did not occur through the ethylenic bond, and they
are consumed in the grafting process. +e modified PVC by
temperature T0 (°C)
247
−78
294
−59
313
283
298
−50
−61
−57
N-(4-ClPh)IM
(modify)
N-(4-ClPh)IM
(graft)
N-PhIM
255
278
−70
−60
(modify)
N-PhIM (graft)

8
Journal of Chemistry
Cd stearate,” Journal of Applied Polymer Science, vol. 18, no. 9,
pp. 2861–2863, 1974.
[11] U. K. Saroop, K. K. Sharma, M. Saroop, K. K. Jain, A. Misra,
and S. N. Maiti, “Grafting of poly(vinyl chloride) with methyl
methacrylate-I: synthesis and characterization,” European
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[12] P. Lakshmi, K. Vijayalakshmi, and P. N. Sudha, “Synthesis and
characterization of graft copolymers of nylon 6 with maleic
anhydride and methylmethacrylate,” Archives of Applied
Science Research, vol. 3, no. 6, pp. 351–363, 2011.
4-bromoitaconimide exhibited the highest thermal stability.
+us, it is highly recommended to modify PVC using ita-
conimide derivatives, by chemical reactions or graft co-
polymerization, prior to the molding process.
Data Availability
+e data used to support the findings of this study are
available from the corresponding author upon request.
[13] A. S. Singha and A. K. Rana, “Kinetics of graft co-
polymerization of acrylic acid onto Cannabis indica fibre,”
Iranian Polymer Journal, vol. 20, no. 1, pp. 913–929, 2011.
Conflicts of Interest
+e authors declare that they have no conflicts of interest.
Acknowledgments
+e authors gratefully acknowledge the use of the services
and facilities of the Basic and Applied Scientific Research
Center at Imam Abdulrahman Bin Faisal University and the
support given by DSR for project no. 2013-133.
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