Materials Sciences and Applicatio ns, 2010, 1, 358-368
doi:10.4236/msa.2010.16052 Published Online December 2010 (http://www.scirp.org/journal/msa)
Plasticization Effect on the Photodegradation of
Poly (4-Chlorostyrene) and Poly (4-Bromostyrene)
Films
Khalid E. Al Ani1, Afrah Essa Ramadhan2
1Department of Petroleum Engineering, The British University of Science and Technology, Irbil, Iraq; 2Department of Industrial
Chemistry, Institute of Technology, Baghdad, Iraq.
Received September 15th, 2010; revised October 16th, 2010; accepted November 19th, 2010.
ABSTRACT
The photodegradation of thin films of poly (4-chlorostyrene) and poly (4-bromostyrene) with 265 nm radiation in the
presence of oxygen and as a function of irradiation time has been studied mainly using fluorescence, FT-IR, and
UV-VIS spectroscopic techniques. The influence of phthalate and terephthalate plasticizers on photo-oxidative degra-
dation was also investigated. Phthalate and terephthalate-plasticizers were found to increase the photodegradation
processes in polymeric chains. On the other hand, the intensity of absorption was also found to increase with irradia-
tion time and in the intensity of a new absorption band at longer wavelength. The appearance of new fluorescence
bands in the irrad iated polymer films can well indicate a possibility o f photodegradation of po lymer films. In addition,
the observed increase in the intensities of the carbonyl and hydroxyl regions of the FT-IR spectra, providing evidence
for the photodegradation as well as the photo-oxidation of polymeric chains. The increase in the analyzed ranges was
attributed to the forma tion of alcohols, aliphatic keton es and to the increase in the number of (C=C) that resulted from
hydrogen abstraction during chains-scission.
Keywords: Excimer Fluorescence, Poly (4-Bromostyrene), Poly (4-Chlorostyrene), Photodegradation Kinetics,
Phthalate Plasticizers
1. Introduction
The study of degradation and stabilization of polymers is
significant for both practical and theoritical viewpoints
[1]. The thermal behaviour of halogenated polymers re-
ceived a considerable attention, owing mainly to the in-
dustrial importance of these polymers [2-6]. Indeed
thermal degradation behavior of poly (4-bromostyrene)
(PBS), and Poly (4-chlorostyrene) (PCS), has been found
to be closely analogous to that of polystyrene (PS) [7]. A
blend of PBS with poly (methyl methacrylate) showed
some interaction during degradation resulting in some
stabilization of the PBS. Thus, bromonation and chlrori-
nation in polymer chromophore, losse the backbone
helide as hydrogen helide at high temperature or during
irradiation. The resulting unsaturation in the polymer
backbone provides points of weakness for chain scission,
which occurs at lower temperature than for polystyrene
[8]. Ring-brominated polystyrene is less stable than ring
chlorinated polystyrene, as it lacks the backbone haloge-
nations which are unavoidable in the ring chlorination in
polystyrene. The halogenated polystyrenes have fairly
similar thermal stability to polystyrene and degrade in
essentially the same way giving mainly the monomer, as
well as styrene and hydrogen halide [2].
The knowledge of photodegradation process in poly-
mers is quite essential from a practical point of view, es-
pecially when it comes to its outdoor applications. Weath-
ering of polymer materials which involves physical and
chemical changes during the exposure of polymer to light
and heat [9-11] is often investigated in accelerated condi-
tions, though they can significantly differ from that in a
natural environment [12]. It should be indicated that irra-
diated polymeric materials undergo a series of oxidative
reactions that lead to photochemical degradation [13-15]
with consequences like brittleness, loss of brightness, and
color changes. Besides the cross-linking processes, a
number of other changes may take place in polymeric
chains during photodegradation [16,17].

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 359
Many investigations concerning the photodegradation
of polystyrene [18-20] and substituted polystyrene [21]
have been carried out. It has been reported that photode-
gradation in PS films occurs when irradiated with
UV-radiation; under atmospheric oxygen. Hence the ini-
tiation of photo-oxidation is expected to result from the
absorption by polymeric chromophores. From the latter
process, a number of different photoproducts were re-
ported. More specifically, hydro peroxides, carbonyl and
hydroxyl compounds were the main products that re-
sulted from the photo-oxidation of PS films [22-25].
On the other hand polymeric additives were found to
accelerate the radiation-induced degradation of PS and
poly (4-substituted styrene) films (SPS) [20]. It was also
found that the photo-stability of PS was reduced by the
addition of bromine-containing flame retardants, and
appeared to depend upon the chemical structure of the
polymeric additive [19]. It was reported that the photo-
degradation of the PS containing carbonyl group was
increased with the increase in the time of irradiation. The
changes in the average molecular weight in photo-oxi-
dized PS were produced as a consequence of chain dis-
sociation by the Norrish Type II reaction [26].
The aim of this work is to examine the photostability
of pure and blended PBS and PCS films, which contain a
small amount of doped dimethyl terephthalate, diethyl
terephthalate, dioctyl terephthalate, dibutyl phthalate and
dioctyl phthalate plasticizers upon UV-irradiation. The
present study also seeks to check if plasticization affects
the photostability of these polymers in solid films, and to
investigate the effect of the bulkiness of plasticizer
molecules on the photodegradation processes of PBS and
PCS in films.
The photodegradation processes of the irradiated
polymer have been characterized by UV-visible, fluo-
rescence, and FT-IR spectroscopic techniques. The effi-
ciency of photodegradation of PCS and PBS is compared
to that of blended polystyrene with polymeric additives.
2. Experimental Part
2.1. Materials
The samples of PCS and PBS were supplied by Across-
Organics with high purity, PCS, (Mw = 65,000, Mn =
31,000), and PBS, (Mw = 7,500, Mn = 3,300) [27].
Spectroscopic-quality, dichloroethane was found to give
no detectable absorption in the range 250-400 nm, and
was used in preparation of solid films. It was purchased
from Fluka GMBH and was used as received. The used
plasticizes were dimethyl terephthalate (DMT), diethyl
terephthalate (DET), dioctyl terephthalate (DOT), dibutyl
phthalate (DBP), and dioctyl phthalate (DOP), were of
high-purity of 99.8% which was purchased from Across-
Organics. They were also found to give no detectable
absorption or emission in the range 265-400 nm.
2.2. Preparation of Plasticized Polymeric Solid
Films
PCS and PBS thin films with thickness of approximately
0.02 mm were prepared by solution casting of 20 wt.%
polymer in dichloroethane solvent (DCE) on a spectro-
scopic window (quartz plate of 1.0 mm × 20 mm diame-
ter). Moreover, about 0.02 mm thick PCS and PBS- plas-
ticizer films, containing different wt.% plasticizers were
prepared by solution casting of a 20 wt.% polymer +
added plasticizer, in DCE solvent. All solid films were
dried in a vacuum oven at 300 K for 6 hrs, as to ensure
the complete removal of solvent traces [27].
2.3. Absorption and Fluorescence Spectra
Measurements
Fluorescence spectra were recorded on JASCO FP 6500
Spectrofluorometer for each of the prepared samples.
The parameters were constant for all measurements, and
the excitation wavelength was 265 nm. The emission
wavelength range was 270-500 nm, and all fluorescence
spectra of the solid films were obtained using a thermo-
stated solid sample holder at 298 K.
The UV absorption spectra for PCS and PBS solid
films were recorded before and immediately after UV
irradiation with a Cary 100 Bio UV-visible Spectropho-
tometer at 298 K.
2.4. Irradiation of Polymeric Films
PCS and PBS solid films were exposed to UV-radiation
for different intervals of time, from (0.0-4.0 hrs), using a
JASCO spectrometer with a built in Hydrogen-Xenon
lamp (6808-J007A model number ESC-333). It is sup-
ported with monochromator of holographic grating with
1800 grooves/mm. Each film was irradiated for different
interval of time with a monochromatic light of 265 nm in a
thermostated solid sample holder in presence of air. The
intensity of incident radiation was (4.9 mW/cm2), and the
distance between light source and samples was (5 cm).
2.5. FT-IR Spectroscopy
The FT-IR-spectroscopy system that was employed in this
work was NICOLET-MAGNA-IR-560 spectrometer, while
the transmission mode was employed in these measure-
ments. The FT-IR spectra were recorded for the irradiated
and the non-irradiated films, whereas the transmittance
was plotted as function of the wavenumbers.
2.6. Calculation of Io
[PH-PH]*/I[PH-PH]* Ratios
In an earlier work, an equation was invented to calculate
the fluorescence quenching effect and the photo quench-
ing rate constant as function of increase in exposure time

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 360
[37]. The ratio of Io
[PH-PH]*/I[PH-PH]* was found to increase
by the increase in irradiation time to polymeric films. Io
[PH-PH]* is the intensity of excimer fluorescence of pure or
doped polymer at zero time of irradiation, whereas,
I[PH-PH]* is the intensity of excimer emission of pure or
doped polymer at different intervals of exposure time to
UV - irradiation.
[][]
()
()
**
1'
oPQ
PH PHPH PH
I
IkA
−−
=+× ×t
(1)
[][]
() **
1
oPQ
PH PHPH PH
I
Ik
−−
=+ ×t
)
=
(2)
where [A] = number of (photons/s) absorbed by poly-
meric chromophores.
t = time of irradiation in s.
(
'
PQ PQ
kkA=×photo-quenching rate constant.
In the photo-quenching processes, if we assume that
the number of photons released from the light source and
absorbed by solid films is constant (A), then, according
to Equation (2), we can plot Io[PH-PH]*/I[PH-PH]* – values
against the time of irradiations. From the plot, which is
similar to that of Stern-Volmer plot, we can evaluate the
photo-quenching rate constant (kPQ).
3. Results and Discussion
3.1. Effect of UV-Irradiation on Absorption
Spectra of Pure and Blended PCS and
PBS Films
The effect of UV-light irradiation on the efficiency of
photochemical processes in films of pure PCS and PBS
as well as in blended polymers films with 1-4% of
phthalates or terephthalate plasticizers were studied by
their absorption spectra. The absorption spectra of irradi-
ated PCS and PBS films for different exposure time
show that the absorbance increases markedly at wave-
length above 295 nm for PCS and above 290 nm for PBS,
as shown in Figure 1 for PCS, and Figure 2 for PBS.
As in the case of many vinyl polymers, the chromo-
phoric units, which are responsible for UV-light energy
absorption, are the basic backbone structure of the poly-
mer [13], whereas in PBS and PCS, the para-substituted
styrene groups, are the chromophoric units that are re-
sponsible for absorption of the 265 nm radiation, and of
course is affected by the chemical structure of the con-
stituents. The effect of the irradiation on the absorption
spectra of both PCS and PBS films, in presence of air
resulted in a gradual increase in the intensity of the ab-
sorption spectra with the increase in exposure time, as
shown in Figure 1(a), and Figure 2(a) for PCS and PBS,
respectively. The irradiated films of blended PCS and
PBS showed a higher increase in the intensity of absorp-
tion spectra as shown in Figure 1(b) and Figure 2(b)
respectively. The increase in the absorption intensity
after irradiation for 2 hours, with the increase in added
DOT, suggests that added plasticizers is either enhancing
the photochemical degradation of PCS and PBS films, or
interact with the excited polymeric chromophores. More-
over, the increase of absorption of DOT doped polymer
films, with the increase in irradiation time; suggest that
photo-oxidation and photodegradation processes are the
main dominating processes in the irradiated PCS and
PBS solid films [28].
3.2. Effect of UV-Irradiation Time on
Fluorescence Spectra of Pure and
Blended PCS and PBS Films
A number of studies have provided information about
photodegradation of para-substituted polystyrenes [29,30],
but none of these have dealt with the photodegradation of
plasticized PCS and PBS in solid films. It is well known
that irradiation of para substituted polystyrene leads to
the generation of aromatic free radicals that can initiate
photodegradation of polymeric chains [31,32]. The ef-
fects of light energy on the stability of pure and blended
PCS and PBS were studied by measuring their emission
spectra before and after irradiation. The fluorescence
spectra of PCS, before and after the exposure of solid films
(a)
(b)
Figure 1. Absorption spectra of PCS, (a) pure polymer film,
and (b) blended PBSwith 4.0% DOT, irradiated at 0.0, 1.0,
2.0, and 4.0 hrs at λext = 265 nm.

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 361
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
260 290 320 350 380
Absorption Intensity (a. u.)
Wavelength in (nm)
(a)
0
0.04
0.08
0.12
260 290 320 350 380
Wavelen
g
th in (nm)
Absorption Intensitry (a. u.)
(b)
Figure 2. Absorption spectra of PBS, (a) pure polymer film,
and (b) blended PBSwith 4.0% DOT, irradiated at 0.0, 2.0,
and 4.0 hrs, at λext = 265 nm.
to UV-radiation for different intervals of time are pre-
sented in Figure 3.
It can be noticed from the fluorescence spectra of irra-
diated pure PCS that the increase in the time of
UV-exposure causing an increase in the intensity of two
new fluorescence bands at maxima of about 362 nm and
378 nm. This process was accompanied by the decrease
in the intensity of the excimer fluorescence band. Al-
though the two new fluorescence bands are not identified,
one can conclude that the increase in the time of irradia-
tion caused an increase the photodegradation of the
polymeric chains, as shown in Figure 3(a). On the other
hand, the fluorescence spectra of blended PCS films,
showed different characteristics in comparison with that
of irradiated pure PCS films. That is, addition of phtha-
lates and terephthalate plasticizers caused quenching to
the excimer fluorescence without the formation of exci-
plex emission [33,34]. As can be seen in Figures 3(b,c),
for the blended PCS with 2.0% and 4.0% DBP, the in-
crease in exposure time of blended PCS films caused a
decrease in the excimer fluorescence band λmax = 312 nm
and an increase in the intensity of a new broad bands at
λmax = 362, 380, 452, and 471 nm. The intensity of the
fluorescence bands were also found to increase with in-
creasing in the exposure irradiation time. From the changes
in the fluorescence spectra of blended PCS films, one can
conclude that irradiation of blended PCS films may initiate
a photochemical reaction between plasticizer molecules
and polymeric chromophores as well as photodegradation
of polymeric chains that can be initiated by free radical
formation.films, showed different characteristics in com-
parison with that of irradiated pure PCS films. That is, ad-
dition of phthalates and terephthalate plasticizers caused
0
200
400
600
800
Fluorescence Intensity (a u)
1000
270 300 400
Wavelength [nm]
450 350 500
(a)
0
600
200
400
Fluorescence Intensity (a u)
270 300 400 450 350 50
0
Wavelength [nm]
(b)
0
100
200
300
400
270 300 400
Wavelength [nm]
450
350 500
Fluorescence Intensity (a u)
(c)
Figure 3. Effect of irradiation time on excimer fluorescence
intensity of PCS, non-irradiated film (dotted line), and ir-
radiated films (solid lines). (a) Pure PCS film, (b) PCS film
blended with 2.0% DBP, and (c) PCS film blended with 4.0%
DBP at (0.0, 10, 15, 20, 30, 40, 60. 80 and 100 min), from top
to bottom.

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 362
quenching to the excimer fluorescence without the for-
mation of exciplex emission [33,34]. As can be seen in
Figures 3(b,c), for the blended PCS with 2.0% and 4.0%
DBP, the increase in exposure time of blended PCS films
caused a decrease in the excimer fluorescence band λmax
= 312 nm and an increase in the intensity of a new broad
bands at λmax = 362, 380, 452, and 471 nm. The intensity
of the fluorescence bands were also found to increase
with increasing in the exposure irradiation time. From
the changes in the fluorescence spectra of blended PCS
films, one can conclude that irradiation of blended PCS
films may initiate a photochemical reaction between
plasticizer molecules and polymeric chromophores as
well as photodegradation of polymeric chains that can be
initiated by free radical formation.
Furthermore, blending of PCS films with DBP or with
DOP plasticizer caused higher excimer fluorescence
quenching effect than that observed with blending with
DMT, DET and DOT plasticizers.
The same observations were observed in the irradia-
tion of PBS film at different intervals of exposure time.
This process was also accompanied by the decrease in
the intensity of the excimer fluorescence band as shown
in Figure 4(a).
As shown in Figures 4(b,c), for the blended PBS with
2.0% and 4.0% DOT, the increase in exposure time of
blended PBS films caused a decrease in the excimer
fluorescence band at λmax = 304 nm, and an increase in
the intensity of a new broad bands at λmax = 353, and 420
nm. The intensity of the latter fluorescence bands were
also found to increase by increasing the exposure time of
irradiation.
Almost the same observations were noticed in blend-
ing of PBS with DMT, DET, DBP and DOP plasticizers.
The structure in the fluorescence spectra at longer wave-
length is considered to be a noise, as the quantum yield
of PBS fluorescence is low, which was reported to be
(0.023) [35].
Based on the reported works by Torikai et al. [19] and
Geuskens et al. [36] on photo-irradiated polystyrene, the
emission bands of 362, 425, and 477 nm corresponded to
polyene unit structures and were defined by n = 1, 2, and
3 respectively. As shown in Figures (3,4), although the
formation of the new emission bands have no clear
maxima, the position of these bands were closed to that
reported by Geuskens et al. [36] indicating the possibility
of formation of polyene structure units.
The kinetic treatments to the fluorescence quenching of
PCS by the increase in the amount of added DBP, DMT
and DET, plasticizers are shown in Figures 5 (a-c).
The fluorescence quenching of PBS by the added
DMT, DET and DOP by the increase in the amount of
added plasticizers are shown in Figures 6 (a-c).
50
100
150
-100
270
500
300400
Wavelength [nm]
450350
Fluorescence Intensity (a u)
(a)
130
50
100
270 500
300400
Wavelength [nm]
450350
Fluorescence Intensity (a u)
(b)
0
120
50
100
270 500
300 400
Wavelength [nm]
450350
Fluorescence Intensity (a u)
(c)
Figure 4. Effect of added mass percent of, (a) DBP, (b)
DMT, and (c) DET, on excimer fluorescence quenching of
PCS films at different irradiation time.
As can be observed in Figures 5 (a-c), for blended PCS
with, the increase in the amount of added DBP, DMT, and
DET plasticizers resulted in a decrease in the ratio of Io
[PH-PH]*/
I[PH-PH]*, and increased with increasing the exposure time.
The increase in this ratio with time of irradiation indicates
that the irradiation process may be accompanied by pho-
tochemical reactions in the polymeric chains. Chain scis-
sions and photo-oxidation processes that were interpreted
as a reaction involving benzene ring-opening photo-oxi-
dation were the processes that resulted from irradiation of
PS in the presence of polymeric additives [29,30]. It has
been reported that the photodegradation of polystyrene
films was reduced by blending with polymeric additives,
as to depend on the chemical structure of the additive. Wu

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 363
0
1
2
3
4
5
6
0 2040 60 80 100
Irradiation Time in (min)
PCS + 0.0%DBP
PCS + 1.0%DBP
PCS + 3.0%DBP
PCS + 2.0%DBP
PCS + 4.0%DBP
I
oEX
/
I
EX
(a)
0
1
2
3
4
5
6
020 406080 100
Irradiation Time in (min)
PCS+ 0.0% DMT
PCS+ 1.0% DMT
PCS+ 3.0% DMT
PCS+ 4.0% DMT
IoEX / IEX
(b)
0
1
2
3
4
5
020406080 100
Irradiation Time in (min)
I
oEX
/
I
EX
PCS + 0.0% DET
PCS + 1.0% DET
PCS + 3.0% DET
PCS + 2.0% DET
PCS + 4.0% DET
(c)
Figure 5. Effect of added mass percent of, (a) DBP, (b)
DMT, and (c) DET, on excimer fluorescence quenching of
PCS films at different irradiation time.
et al. [38] also studied the photo-oxidation of polystyrene
by fluorescence spectra, and proposed that photo-quen-
ching of polystyrene fluorescence was attributed to the
quenching effect of peroxides formed during polymer ir-
radiation. PCS and PBS showed lower photo- stability in
comparison with other substituted polystyrene like, poly
(4-methoxystyrene), Poly (4-methylstyrene) and poly (4-
tert-butylstyrene) in solutions [39].
Similarly, as can be observed in Figures 6(a-c), for
PBS, the increase in the amount of added DMT, DET,
and DOP plasticizers resulted in a decrease in the ratio of
Io
[PH-PH]*/I[PH-PH]*, and increased with increasing the ex-
posure time.
The efficiency of photo-quenching for plasticized poly-
mer showed a lower value than that for pure polymer,
and was also found to increase with the increase in the
bulkiness of plasticizer molecules.
0.5
1
1.5
2
2.5
02040 60 80 100
Irradiation Time in (min)
PBS + 0.0% DMT
PBS + 1.0% DMT
PBS + 2.0% DMT
PBS + 3.0% DMT
PBS + 4.0% DMT
I
oEX
/
I
EX
(a)
0
0.5
1
1.5
2
2.5
0204060 80 100
Irradiation Time in (min)
PBS + 0.0% DET
PBS + 1.0% DET
PBS + 2.0% DET
PBS + 3.0% DET
PBS + 4.0% DET
I
oEX
/
I
E
X
(b)
0.5
1
1.5
2
2.5
02040 60 80 100
Irradiation Time in (min)
PBS + 0%DOP
PBS + 1%DOP
PBS + 2%DOP
PBS + 3%DOP
PBS + 4%DOP
I
oEX
/
I
EX
(c)
Figure 6. Effect of added mass percent of, (a) 4.0% DMT,
(b) 4.0% DET, and (c) 4.0 % DOP on excimer fluorescence
quenching of PBS films at different irradiation time, at (λ =
265 nm).
From Figures 5 and 6, where the ratio Io
[PH-PH]*/I[PH-PH]*
was plotted against different intervals of the exposure
time, from the slope of the obtained lines, kPQ values
were calculated for PCS and PBS plasticized with 4.0%
of DMT, DET, DOT, DBP, and DOP, and are presented
in Table 1.
As can be observed from Figures 5 and 6, and Table
1, the photo-quenching rate constant kPQ values, were
found to increase with the increase in molar mass of the
used plasticizer. Phthalate plasticizers, on the other hand,
displayed a higher efficiency of photo-quenching than
that which was observed by terephthalate plasticizers.
This fact also correlates well with the thermal quenching
of the polymers excimer fluorescence. In other words the

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 364
Table 1. Relative Intensities of the ratio (Io
EX/IEX) and kPQ
values for the excimer fluorescence spectra of pure and
blended irradiated PMXS films.
kPQ
(IoEX/I EX)
Irradiated
Time
(min)
Plasticizer
& %
λ (emis)
(nm)
(max)
Polymer
0.0473.85 90 DMT 0.0 316 PCS
0.0434.02 90 DMT 1.0 318 PCS
0.0404.60 90 DMT 3.0 321 PCS
0.0345.05 90 DMT 4.0 323 PCS
0.0324.25 90 DET 0.0321 PCS
0.0193.04 90 DET 4.0323 PCS
0.0383.05 90 DOT 0.0320 PCS
0.0263.64 90 DOT 4.0321 PCS
0.0444.90 90 DBP 0.0322 PCS
0.0263.66 90 DBP 4.0322 PCS
0.0344.37 90 DOP 0.0320 PCS
0.0283.86 90 DOP 4.0322 PCS
0.0112.5 90 DMT 0.0 305 PBS
0.0081.48 90 DMT 3.0 307 PBS
0.0101.96 90 DET 0.0306 PBS
0.0031.30 90 DET 4.0306 PBS
0.0091.65 90 DOT 0.0305 PBS
0.0061.44 90 DOT 4.0307 PBS
0.0102.55 90 DBP 0.0306 PBS
0.0042.04 90 DBP 4.0307 PBS
0.0122.05 90 DOP 0.0304 PBS
0.0071.48 90 DOP 3.0306 PBS
photo-oxidation mechanism of SPS is largely similar to
the mechanism of thermo-oxidation [34].
Phthalate plasticizers, on the other hand, displayed a
higher efficiency of photo-quenching than that which
was observed by terephthalate plasticizers. This fact also
correlates well with the thermal quenching of the poly-
mers excimer fluorescence. In other words the photo-
oxidation mechanism of SPS is largely similar to the
mechanism of thermo-oxidation [34].
Numerous mechanisms for polystyrene photodegrada-
tion under UV-irradiation have been proposed by many
authors [40-43], but a totally consistent theory is yet to
be agreed upon due to the complexity of the kinetics and
the formation of different photodegradation products,
The mechanism of photodegradation of PCS and PBS
was prepared in a similar basis and according to the re-
sults obtained from the changes in the UV-vis, fluores-
cence and FT-IR spectra of irradiated pure and blended
PCS and PBS films, as seen in Scheme 1.
In order to describe the photodegradation processes,
particular attention has been paid to the reaction steps
and to the physical aspects of the degradation processes.
The first step in the mechanism of photo-oxidation of
PCS and PBS (Scheme 1) is a hydrogen abstraction from
the polymeric backbone, which causes the formation of
Scheme 1. Photodegradation processes in the irradiated
PCS and PBS films.
free radicals (Equation (3)) which in the presence of at-
mospheric oxygen, leads to the formation of peroxyradi-
cal (Equation (4)). After that, peroxyradical abstracts a
hydrogen atom from the macromolecular chain to form
hydroperoxide (Equation (5)). The latter was photolyzed
into an alkoxy radical, which leads to chain scission with
the formation of shorter chain polymer radicals and car-

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 365
bonyl species (Equation (6)). The formed polymer free
radical reacts with the hydroxyl radical to form polymer
hydroxide (Equation (7)). The benzyl radical then reacts
with hydroxyl radical to form alcoholic structure com-
pound (Equation (8)). The mechanism also shows that
during irradiation of polymeric chains beside chain scis-
sion, conjugated alkenes form in the aliphatic portion of
polymeric chains through stable polyene radical interme-
diates (Equation (9)). It was reported that the formation
of polyene structure in the photodegradation of polysty-
rene, was the major factor in yellowing in the degrada-
tion processes [22]. Random chain scission (Equation
(10)) forms two macro radicals, one of which is a pri-
mary radical which is more stable then the secondary
radical. The latter gives as product the substituted styrene
in the first propagation step (Equation (11)).
The degradation mechanism shows that the major
photo-products resulting from oxidation processes are
carbonyl, hydroxyl, hydroperoxide, and conjugated al-
kenes. In addition to these photo-products, the benzyl
radicals generated by UV-irradiation can combine with
each others to result in cross-linking of polymeric chains.
A more detailed discussion on the processes involved
in the oxidative degradation in a polymer film has been
reported by Rabek [16]. Photo-oxidative degradation is a
free radical chain mechanism which occurs when the
polymer is exposed to UV-radiation in presence of oxy-
gen. Chemical modifications have been attributed to
scission of the polymer chains, and to the cross- linkages.
The obtained values for the rate constant of photo-
quenching process for PBS are much higher than that
obtained with PCS solid films. These behaviors may in-
dicate that the stability of PBS polymer chains is much
lower than that of PCS polymer chains upon irradiation
with UV light. On the other hand, the stability of the col-
lision energy transfer complex of (terephthalate-PCS)* is
higher than that of (phthalate-PBS)* complex towards
UV-irradiation. It is more likely that the bulkiness of
blended plasticizer molecules can lower the stability of
the formed energy transfer complex, and also to the ex-
ciplex activation energy for exciplex formation of the
charge transfer character.
3.3. Effect of Irradiation Time on FT-IR Spectra
of Pure and Blended PCS and PBS Films
The photodegradation mechanism is further supported by
FT-IR analysis of both (PCS, PBS) and irradiated (PCS,
PBS) samples. FT-IR spectra of pure PCS film as well as
irradiated polymer film for 2 hrs were obtained, and pre-
sented in Figure 7(a). The FT-IR spectra for blended
PCS with 4% DOT as well as the irradiated blended
polymer film with 4% DOT are shown in Figure 7(b).
FT-IR spectra of pure PBS film as well as irradiated
polymer film for 2 hrs were obtained and shown in Fig-
ure 8(a). The FT-IR spectra for blended PBS with 4%
DOT, as well as the irradiated blended film with 4%
DOT are shown in Figure 8(b).
As seen in Figures 7 and 8, chemical changes were
assessed by FT-IR spectra for photo-irradiated of blended
and pure PCS and PBS solid films. Both changes show
typical functional group in the hydroxyl 3800-3000 cm-1;
C-H stretching vibration in the aliphatic chain and in
aromatic rings 2800-3100 cm-1; carboxyl stretching vi-
bration 1800-1600 cm-1; and deformation vibration 1400-
600 cm-1 regions.
The hydroxyl stretching vibration region showed the
growth of a broad band between 3300 and 3500 cm-1
centered at 3445 cm-1, corresponding to hydroxyl groups
associated with carboxylic acids. Aliphatic hydroperox-
ide, absorbed in the 3300-3500 cm-1 region, are also re-
sponsible for the formation of this broad band. Moreover
the law intensity band at 3550-3700 cm-1 can be seen in
blended PCS and PBS as shown in Figures 7 and 8, is
resulting from the presence of –OH functional groups.
545
825.
1010
1092
1409
1489
1633
2842
2924
3445
538
822
1011
1092
1412
1489
1645
1707
2847
2923
3446
3738
92
94
96
98
100
%Transmittance
3851
(A)
(B)
Wavenumbers (cm
-1
)
94
96
98
100
538
8201011
1091
1412
1490
1645
1716 2925
3444
3743 543
825
1014
1490
1715
2847
2919
3445
3851
3000 4000 2000 1000
2849
3012
Figure 7. FT-IR spectra of (a) PCS solid film (bold) and
irradiated PCS solid film for 2 hrs (fade), and (b) blended
PCS with 4% DOT (bold), blended PCS with 4% DOT ir-
radiated for 2 hrs at 298 K. (λext = 265 nm)

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 366
539
1484
1589
2851
2923
3021
3446
3861
1072
11 87
1483
1643
1889
2847
3026
3436
3753
95.0
96.0
97.0
98.0
99.0
100.0
1000 2000 3000
819
820
1073
1007
% Transmitt ance
4000
Wavenumbers (cm
-1
)
(a)
541
711
820
1008
1073
1110
1274
1403
1483
1644
1723
1889
2852
2924
3445
3748
819
1630
1723
2924
3445
93.0
94.0
95.0
96.0
97.0
98.0
99.0
100.0
% Transmittanc
e
1000
2000
3000
3021
3860
Wavenumbers (c
m
-1
)
4000
(b)
Figure 8. FT-IR spectra of (a) PBS solid film (bold) and irra-
diated PBS solid film for 2 hrs (fade), and (b) blended PBS
with 4% DOT (bold), and blended PBS with 4% DOT irra-
diated for 2 hrs at 298 K. (λext = 265 nm)
The appearance of the 3851 and 3743 cm-1 in the irradi-
ated blended PCS film Figure 7(b) and 3860 and 3748
cm-1 in the irradiated blended PBS film Figure 8(b), pro-
vides evidence for photo-oxidation processes occurring as
a result of irradiation of polymeric films. The region 2800-
3100 cm-1 shows three main bands at 3012, 2923, 2842
cm-1, and is attributed to the deformation and skeletal vi-
bration of C-H in PCS and blended PCS. The intensity of
these bands increased with blending of the polymer chains
(which is similar to the bands observed in pure PCS with
small red shift), indicating a less stability of the blended
polymer. The same observation was noticed in case of
photo-irradiated polystyrene films [44].
Photo-oxidation of irradiated PCS and PBS films leads
to increase the intensity of absorbance in the bands
(comparing to PCS and PBS films), at 1889, 1707, 1645,
1489, 1412 cm-1 in irradiated PCS film, and bands at
1889, 1723, 1644, 1483, 1403 cm-1 in the irradiated PBS
film were observed. Bands found at 1645 and 1489 cm-1,
can be ascribed to stretching vibration of the substituted
benzene rings; it means that the aromatic rings lose their
symmetry through the photo-oxidation processes, and are
almost in the same position as observed in polystyrene
spectrum [13]. The other observation in the IR-spectrum
is concerned with the large increase in the relative ab-
sorption intensity in the region (1610-1028 cm-1), with
the bands1412, 1092, and 1073 cm-1 compared to that of
pure PCS and PBS films. This indicates that there is an
increase in the number of (C=C) that resulted from hy-
drogen abstraction during chains-scission process. The
presence of the absorption band at 830 cm-1, as can be
seen in Figure 7 and Figure 8, may suggest that the
formation of conjugated double bond sequences in the
main polymer chain. The same band was observed by
Grassie and Weir [21] on photo-oxidation of polystyrene.
4. Conclusions
Based on the obtained values of absorption spectra, fluo-
rescence quenching, and FT-IR spectra for the irradiated
plasticized and Pure (PCS and PBS) solid films, the con-
clusions can be drawn:
1) Irradiation of PCS and PBS films in the presence of
air led to significant modification to UV absorption
spectra of the exposed sample. Photo-oxidation
processes of polymeric chains provoked a marked
increase in the absorption and a change in the shape
of absorption spectra.
2) It was found that irradiation of blended PCS and
PBS films at 265 nm resulted in a decrease in the in-
tensity of excimer fluorescence, changes in the
shape of the fluorescence spectra and the formation
of new fluorescence bands at longer wavelength.
This indicates that there is a possibility of photo-
degradation in the polymeric chains.
3) In the UV-irradiated of pure and blended PCS and
PBS films (in the presence of atmospheric air), the
observed increases in the carbonyl and hydroxyl re-
gions of the FT-IR spectra, provide evidence for the
photodegradation as well as the photo-oxidation of
polymeric chains. The increase in the analyzed
ranges can be attributed to the formation of aromatic
and aliphatic ketones. It has been reported that
photo-irradiation of polystyrene films with 254 nm
resulted in the formation of carboxylic acids, esters,
anhydrides, cyclic structures and other photopro-
ducts [36,39]. Moreover, the photo-oxidative degra-
dation can lead to significant formation of low mo-
lecular weight photoproducts that can migrate out of
the polymer sample. The formation of low molecular
weight compounds, such as benzoic acid, acetophe-

Plasticization Effect on the Photodegradation of Poly (4-Chlorostyrene) and Poly (4-Bromostyrene) Films 367
none, benzaldehyde, formic acid, acetic acid, styrene
monomer, and benzene were identified in UV-
irradiated polystyrene. Thus infrared analysis of the
oxidative evolution of the irradiated solid sample
does not permit recording the formation of all the
photoproducts.
5. Acknowledgements
We gratefully acknowledge the financial support of Ab-
dul Hammed Showman Foundation. Thanks are also due
to Manal al buzor, Muna Hawi, May Anabtawi, and Suha
Khanfar for their help in this research work, and to Pro-
fessor Mikdad Al Arif for useful discussions.
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