Vol.2, No.4, 307-319 (2010) Natural Science
http://dx.doi.org/10.4236/ns.2010.24039
The thermoanalytical, infrared and pyrolysis-gas
chromatography-mass spectrometric sifting of poly
(methyl methacrylate) in the presence of phosphorus
tribromide
Muhammad Arshad1*, Khalid Masud2, Muhammad Arif3, Saeed-ur-Rehman4,
Jamshed H. Zaidi1, Muhammad Arif1, Aamer Saeed5, Tariq Yasin6
1Chemistry Division, Directorate of Science, PINSTECH, Islamabad, Pakistan;
2New Laboratories Pinstech, Islamabad, Pakistan
3Department of Chemistry, Bahauddin Zakariya University, Multan, Pakistan
4Institute of Chemical Sciences, University of Peshawar, Peshawar, Pakistan
5Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
6DCME, Pakistan Institute of Engineering & Applied Sciences, Islamabad, Pakistan
Received 23 December 2009; revised 25 January 2010; accepted 29 January 2010.
ABSTRACT
The behaviour of poly(methyl methacrylate) was
examined in the presence of phosphorus tri-
bromide (PBr3) with varying concentrations.
Films were cast from common solvent and
subjected to TG, DTA, DTG, IR and Py-GC-MS for
evaluating the degradation routes. Despite early
decomposition of the blends, certain tempera-
ture zones were identified for stabilization of the
system. New products were found and mecha-
nisms of their formation were proposed. Pyro-
lysis of the blends was also carried out at dif-
ferent temperatures to ascertain the nature of
interaction between the constituents of the
system.
Keywords: PMMA; PBr3; Thermoanalytical Study;
IR Spectroscopy; GC-MS Investigation
1. INTRODUCTION
The thermal degradation and flammability characteris-
tics of poly (methyl methacrylate) chemically modified
with silicon-containing groups, functionalized by phos-
phorus-containing groups and also neat poly(methyl
methacrylate) with a number of additives have been re-
ported by several researchers [1-12].
Poly (methyl methacrylate) is widely used and studied
poly alkyl methacrylate thermoplastic polymer, but it is
highly flammable owing to the ease with which it de-
grades thermally (depolymerise), releasing large quanti-
ties of highly flammable volatile, monomeric and oli-
gomeric frangments. Thermal decomposition character-
istics of PMMA are well-understood [2,9,10,13,14] and
a lot of research work is underway to improve its flam-
mability as well as other features by additive-route tech-
nique.
Our interest in the thermal behaviour of polymeric/
copolymeric systems and these systems in combination
with additives (organometallics) has resulted in a num-
ber of publications [15-21]. It was observed with over-
whelming evidence that polymers/ copolymers showed
markedly different thermal behaviour when heated even
in the presence of minor amounts of additives. The in-
teraction between the constituents was chemical as well
as physical. The products of degradation were identified
as either completely different (new ones) or if same,
exhibited variation in amounts when this feature of the
neat and blended systems was compared. Physical nature
of interaction was noticed due to the sublimation of ad-
ditives in addition to the heat- sinking property of stable
residues from the degradation of additives. The shifting
of Ti (temperature corresponding to the first weight-loss),
T50 (temperature which designates the 50% weight-loss
of the system) and Tmax (temperature which gives the
maximum weight-loss) clearly indicates the effects of
additives on the degradation of polymers/copolymers.
Recently, our research activities have seen a shift in the
nature of additives, i.e., from organometallics, we have
started introducing purely inorganic compounds in
polymers/copolymers of commercial importance [22,23].
This change in approach is based on the fact that the
degradation of organometallics also results in the pro-
duction of those species which are themselves flamma-
ble, whereas our aim is to modify the degradation
mechanism in such a way as not only to increase the

M. Arshad et al. / Natural Science 2 (2010) 307-319
308
temperature of degradation but also to seek the forma-
tion of non-flammable or less flammable degradation
products.
This paper is concerned with the influence of phos-
phorus tribromidea non-metal halideon the PMMA
for the course of degradation with the aim to establish
possible chemical interaction between the components
by using different ratios of polymer and additive. Em-
phasis is laid on the mechanism of the observed effects,
in particular, on the formation and identification of deg-
radation products.
2. EXPERIMENTAL
2.1. Chemicals
All the reagents and solvents obtained from standard
source suppliers (E. Merck) were of analytical grade.
The monomer, methyl methacrylate, was freed from in-
hibitor (hydroquinone) by washing with aqueous 5%
sodium hydroxide followed by de-ionised water until
neutral and then it was dried over anhydrous calcium
chloride for 24 hours [24]. It was distilled under reduced
pressure prior to use, only middle portion was chosen for
polymerization. 2, 2’-azobisisobutyronitrile (AIBN) was
selected as radical initiator for polymerization and was
purified by re-crystallizing from absolute ethanol. The
crystals obtained were dried under vacuum and kept in
refrigerator (black paper wrapped around bottle). Phos-
phorus tribromide was prepared by the standard proce-
dure [25]. All solvents were distilled by standard litera-
ture procedures before use.
2.2. Preparation of Poly (Methyl Methacrylate)
The homopolymer was synthesized by free radical po-
lymerization by the reported procedure [26]. The puri-
fied monomer was de-aerated and vacuum-distilled into
the calibrated dilatometer containing sufficient amount
of 2, 2’-azobisisobutyronitrile initiator to give 0.7% w/v
in the solution. The dilatometer was sealed under vac-
uum and polymerization was carried to 10% conversion
at 60oC in hot water bath. The mixture was then added to
100 mL of toluene and the polymer was precipitated
from 1 liter of methanol. The polymer was collected by
filtration, vacuum dried, purified by reprecipitation
(thrice) and finally dried in a vacuum oven at 50oC for
24 hours.
2.3. Formulation of Blend for Analysis
The blends with varying compositions of PMMA and
phosphorus tribromide in the form of thin films were
prepared by employing common solvent, i.e., acetone.
The known amounts of polymer and additive were
mixed separately in a sufficient quantity of acetone and
were left overnight in closed Pyrex tubes to dissolve
completely at ambient temperature. Both the solutions
were mixed, shaken thoroughly, placed for 24 hours in
dark place to mix completely and then poured into a
well-cleaned transparent Pyrex dish. Complete evapora-
tion of the solvent was effected at STP. The resultant
film was transparent in the dish confirming the compati-
bility of the components of the pair studied.
2.4. Procedure to Prepare Strip for
Flammability Test
For neat PMMA sample, the polymer was added to ace-
tone and kept overnight to dissolve completely. The so-
lution thus obtained, was poured into an aluminum mold
with the dimensions, 1 mm  7 mm  150 mm, the in-
side cavity of which was covered with high density
polythene sheet. The mold was left for 48 hrs in dark for
complete dryness. For the blends, both polymer and ad-
ditive in definite ratios were dissolved in acetone sepa-
rately and set aside for 24 hrs. Individual solutions were
then intermingled and placed in dark place for complete
miscibility. This solution was then poured in the mold
and allowed to dry for 48 hrs in a thoroughly-cleaned
dark place. The dry sample was removed and kept in
desiccator for the required test.
2.5. Physiochemical Methods
Thermoanalytical (TG-DTA-DTG) curves were obtained
using Netzsch Simultaneous Thermal Analyzer STA 429.
All the measurements were carried out with samples
having 30-60 mg initial mass. These were heated over
the temperature range from ambient to 800oC in an inert
atmosphere (nitrogen), using kaolin as reference material.
The heating rate was 10oC min-1.
Infrared (IR) spectra of polymer, additive and those of
residues produced after heating the blends at various
temperatures were recorded with Nicolet 6700 FT-IR
spectrometer in the range 4000-400cm-1.
The liquid chromatograph, Hitachi 655-A-11 with
GPC software and integrator (D-2200 GPC) along with
column GLA-100m (Gelko), was employed for molecu-
lar weight determination of polymer at room temperature.
The detector system consisted of Hitachi 655-A UV
variable wavelength monitor (= 254 nm) and SE-51
(Shodex) refractive index detector. Polystyrene standards
were used for calibration curves and HPLC grade tetra-
hydrofuran (Aldrich) was used as solvent. The molecular
weight was found 120000.
The samples were subjected to an Agilent 6890N type
GC-MS coupled with 5973 inert MSD, by Agilent Ana-
lytical Instruments, Agilent Technologies, USA. Analy-
sis of the products in acetone was performed with a
DB-5MS column. The injection volume was 1 µL. The
temperature program entailed an initial increase of tem-
perature from 120-150oC at 10oC min-1 and from
150-280oC at 15oC min-1. The mass spectrometer was
operated in the electron-impact (EI) mode at 70 eV.

M. Arshad et al. / Natural Science 2 (2010) 307-319
309
Horowitz and Metzger method [27] was used to cal-
culate activation energy (Eo) and order of reaction (n) of
polymer and its blends. A plot of ln ln Wo/Wt (where Wo
= initial weight of material and Wt = weight of material
at temperature T) against θ (θ = T – Ts) resulted in a
straight line. The activation energy was determined from
its slope which was equal to Eo/RTs2 (where R = gas
constant and Ts = temperature (from DTG peak) at
which maximum weight-loss occurs). Order of reaction
was calculated by using the relation between reaction
order and concentration at maximum slope.
The horizontal burning test (HBT) of homopolymer
and its blend was conducted in accordance with the
ASTM standards [28,29]. The blend compositions given
in Table 1 were prepared by mixing the polymer with
additive in an aluminum mold with the specified dimen-
sions.The specimen was held horizontally and a flame
fuelled by natural gas was supplied to light one end of it.
The time for the flame to reach from the first reference
mark (25 mm from the end) to the second reference
mark at 100 mm from the end, was measured. The re-
sults are reproduced in Figure 12.
3. RESULTS AND DISCUSSION
3.1. Thermogravimetry, Derivative
Thermogravimetry and Differential
Thermal Analysis
The thermal traces of additive (X), neat polymer (A) and
blends, B1-B5, are shown in Figures 1-4, while ther-
moanalytical data are given in Table 1. The TG curve of
neat phosphorus tribromide gives a single step weight-
loss. This additive begins to lose weight around 60oC
and the whole process completes around 178oC (Figure
1). The first fifty per cent of the original weight requires
heating of 105oC to disappear whereas the remaining
Figure 1. Thermal (TG-DTA-DTG) traces (dynamic nitrogen,
heating rate 10oC/min) for phosphorus tribromide additive (X)
in nitrogen atmosphere.
Figure 2. Thermogravimetry curves (dynamic nitrogen, heat-
ing rate 10oC/min) for PMMA-PBr3 blends: (I) A, (II) B1, (III)
B2, (IV) B3, (V) B4 and (VI) B5.
fifty per cent leaves the crucible within a temperature
range of just 15oC. A DTG peak is found at 178oC while
DTA peak is noted at 176oC. When PBr3 approaches its
boiling point (175oC), the weight-loss (evaporation) be-
comes brisk. This is also evident from the preceding
observation. At the termination of weight- loss step, no
residue is encountered.
This blend (PMMA 97.5%: PBr3 2.5%hereafter des-
ignated as B1) begins to degrade around 81oC and the
first stage comes to an end at 169oC (Figure 2(II)). Nine
per cent weight-loss is observed. The products evolved
at this stage clearly indicate the interaction between the
two components of the system (GC-MS results). The
neat polymer exhibits T0 (temperature corresponding to
the detection of first weight-loss) at 250oC (Figure 2(I)),
whereas additive starts losing weight around 60oC when
heated alone. This is another clue for interaction. From
169oC to 279oC the system remains intact thereby
showing the stability of the intermediate. This interme-
diate is not pure PMMA as neat polymer commences to
decompose around 250oC. So it is believed that bonds
between PBr3 and PMMA are formed which result in the
stabilization of intermediate (169-279oC). The second
stage which terminates at 430oC accounts for 91%
weight-loss. No residue is noticeable at the completion
of degradation process. One DTG peak (Figure 3(II)) at
393oC and one DTA peak (Figure 4(II)) at 408oC are
noted for the final (second) stage. The sharp fall in TG
traces for the second stage manifests the rupture of all
types of bonds as the rising energy content cannot be
resisted.
The second blend of this series B2 (PMMA 95%: PBr3
5%) starts losing weight around 80oC and by the end of
the first stage (165oC), accounts for 12% weight-loss
(Figure 2(III)). It is clear now that by increasing the

M. Arshad et al. / Natural Science 2 (2010) 307-319
310
Table 1. Comparative thermoanalytical data for PMMA(A), PBr3(X) and blends, B1-B5.
Endo = Endothermic, Exo = Exothermic.
Figure 3. Derivative thermogravimetry curves (dynamic ni-
trogen, heating rate 10oC/min) for PMMA-PBr3 blends: (I) A,
(II) B1, (III) B2, (IV) B3, (V) B4 and (VI) B5.
concentration of additive (PBr3), the T0 does not show
any change, however, the per cent weight-loss has in-
creased. Same type of interaction is believed to have
occurred for this blend as was observed for B1. The
range of temperature for stable residue (165-262oC) in
this case exhibits a reduction when compared with the
same range for the first member of this series (B1). It may
be due to less number of bonds/links formed between
Figure 4. Differential thermal analysis curves (dynamic nitro-
gen, heating rate 10oC/min) for PMMA-PBr3 blends: (I) A, (II)
B1, (III) B2, (IV) B3, (V) B4 and (VI) B5.
the constituents of the system despite the presence of
relatively higher concentration of additive. The last stage
(262-440oC) gives a weight-loss of 88 %. From 262oC to
360oC, the weight-loss is only 7% which is attributed to
the strength of bonds/interactions developed in the ear-
lier part of the degradation between the components of
the system resulting in the stable intermediate. For first
stage, one DTG peak (111oC) and one DTA peak (120oC)
TG, oC DTG,
oC
Blend composi-
tion (%)
PMMA-PBr3
Temperature
range, oC Stage Weight loss, %
T0 T
25 T 50 T 100 I II
DTA, oC,
Thermal Effect
A (100-00) 250-440 I 100 250 378 390 440 396 -- 319 (Endo), 412 (Exo)
B1 (97.5-2.5) 81-169
279-430
I
II
9
91 81 378 392 430 110 393
130 (Exo), 350 (Endo),
408 (Exo)
B2 (95-5) 80-165
262-440
I
II
12
88 80 380 390 440 111 396
120 (Exo), 363 (Endo),
407 (Exo)
B3 (92.5-7.5) 70-175
280-445
I
II
14
86 70 370 390 445 115 397
118 (Exo), 350 (Endo),
404 (Exo)
B4 (90-10) 70-190
260-441
I
II
16
84 70 365 390 441 110 393
124 (Exo), 365 (Endo),
406 (Exo)
B5 (87.5-12.5) 62-192
243-448
I
II
11
89 62 370 394 448 123 397
136 (Exo), 365 (Endo),
415 (Exo)
X (00-100) 60-178 I 100 60 155 168 178 178 -- 176 (Exo)

M. Arshad et al. / Natural Science 2 (2010) 307-319
311
appear. For second step, one DTG (Figure 3(III)) and
two DTA (Figure 4(III)) peaks are noticed at 396oC,
363oC and 407oC, respectively. No residue is found at
the termination of the degradation process.
B3 (PMMA 92.5%: PBr3 7.5%) begins to degrade
around 70oC and loses 14 % of original weight in the
first stage which terminates at 175oC (Figure 2(IV)).
The intermediate formed at this stage is stable up to
280oC after which the pyrolysis again starts and the sec-
ond step shows a weight-loss of 86 % with no residue at
the completion of the decomposition (445oC). From
280oC to 338oC, only 6% weight-loss is observed which
is indicative of the toughness of bonds that developed
during the early part of pyrolysis. One DTG (Figure
3(IV)) and one DTA (Figure 4(IV)) peak appear for first
stage (115 and 118oC, respectively), however, for second
stage one DTG and two DTA peaks at 397oC , 350oC and
404oC, respectively, arise.
B4 (PMMA 90%: PBr3 10%) shows a weight-loss of
16 % for first stage. It commences to decompose around
70oC and stops losing weight around 190oC (Figure
2(V)). Single DTG (Figure 3(V)) and DTA (Figure 4(V))
peaks are found at 110oC and 124oC, respectively. The
intermediate withstands a temperature of 70oC (190-
260oC) before the inception of second stage of degrada-
tion. The second step comes to an end at 441oC marking
a weight-loss of 84%. The first 6% weight-loss of sec-
ond stage requires heating of 96oC which is due to the
strong bonds/links produced in the early part of the deg-
radation. One DTG and two DTA peaks are observed at
393, 365 and 406oC, respectively. No residue is notice-
able at the completion of degradation process.
B5 (PMMA 87.5%: PBr3 12.5%) commences its weight-
loss around 62oC for first stage which comes to an end at
192oC (Figure 2(VI)). One DTG and one DTA peak
appear for this step at 123oC and 136oC, respectively.
Eleven per cent weight-loss is evident from TG traces
(Figure 2(VI)). The intermediate that is stable up to
243oC, starts decomposing as the temperature increases.
The second stage terminates at 448oC. One DTG (Figure
3(VI)) and two DTA (Figure 4(VI)) peaks are found at
397oC, 365oC and 415oC, respectively. The first 8%
weight-loss for the second step (out of 89%) requires
heating of 109oC (from 243 to 352oC) whereas the re-
maining larger portion (81 %) leaves the scene for a
heating of 96oC (352-448oC). This is basis of the types
of bonds present in the intermediate. There was no resi-
due at the end of pyrolysis of this blend.
The interaction is clear between the components of the
system throughout the series, i.e., B1-B5. The nature of
interaction seems to be same for all members of the se-
ries with effectiveness decreasing down the series. The
percentage of degradation for first stage is higher than
the total percentage of additive in the blends B1-B4. The
molecular level mixing of the constituents favours the
development of links between them which, in turn, in-
fluences the degradation of both parts from the begin-
ning. The evolution of new products (GC-MS results) in
the early part of pyrolysis confirms the chemical interac-
tion and mutual effect of the ingredients on each other’s
decomposition.
3.2. Blend’s Composition Effect on Thermal
Behaviour
Figure 5 shows the graph between temperature and
weight % of additive. The results reveal a very clear
trend of destabilization when T0 is considered. It is ob-
served that as the percentage of additive in the blends is
increased, a slight stabilization of 20oC is noted which
may be attributed to the number of links which are de-
veloped between phosphorus and pendent oxygens of
polymer per unit volume of additive. For T25 (tempera-
ture at which 25% weight-loss occurs), the trend in de-
stabilization is not so different for blends when weight
percentage of additive goes from 2.5 to 12.5. This seems
to be due to the less number of interactions, i.e., cumula-
tive impact to lowers. At T50 (temperature at which 50%
weight-loss is observed), a very inappreciable stabiliza-
tion is observed as energy content is too great to be re-
sisted by the different types of interactions or bonds be-
tween additive and polymer irrespective of the weight
percentage of additive. T100 (temperature for 100 weight-
loss) does not show much difference for polymer and
blends which may be due to very high temperature re-
gion signifying the completion of decomposition process.
In this zone, almost all kinds of bonds are prone to
breakage.
3.3. Activation Energy (Eo) and Order of
Reaction (n) Determination
Table 2 presents the activation energy and order of reac-
tion of thermal decomposition of polymer, additive and
polymer-additive systems. A decreasing trend of activa-
tion energy is noticed with the increasing percentage of
Figure 5. Effect of blend composition on T0, T25, T50 and T100
values of A and B1-B5 blends.

M. Arshad et al. / Natural Science 2 (2010) 307-319
312
Table 2. Activation energies and order of reaction for A, X and
PMMA-additive blends.
Blend composition (%)
PMMA-PBr3
Eo*
(KCal/mol)
Order of reaction
(n)
A 138.9 3/2
B1 43.68 1/2
B2 42.17 1/2
B3 40.29 1
B4 37.65 1
B5 38.03 3/2
X 93.32 0
* = overall activation energy.
Figure 6. UV-spectra of X (I) and B4 (II) blend in acetone.
additive (2.5-12.5%) in the blends. These results were
computed from TG curves. It is believed that decrease in
the activation energy is due to the destabilization of the
blended system observed in the earlier part of pyrolysis
keeping T0 in view. The interaction at the outset of deg-
radation between the components of blends triggers an
early loss of weight which is attributed to the decreasing
trend this parameter exhibits down the series (B1B5).
The shifting of T0 to lower temperatures from B1 to B5
is quite evident in the current thermal investigation.
3.4. UV Findings
It is well-known fact that PMMA does not absorb in UV
region. On the contrary, PBr3 gives a distinct peak at
325 nm (in acetone) whereas its blend with PMMA also
absorbs in UV range (Figure 6). The shift in wavelength
for PMMA-PBr3 (330 nm) clearly indicates interaction
between the components of the system. This shift is at-
tributed to the establishment of links between phospho-
rus of additive and carbonyl oxygen of polymer and
bromines of additive and carbons of polymer backbone
(main chain).
3.5. IR Spectra
Poly(methyl methacrylate) is a widely-studied polymer
and its IR spectrum (Figure 7(I)) gives the characteristic
peaks for the presence of ester linkages (1730-1735
cm-1). The absence of peaks in the region of 1630-1640
cm-1 confirms the formation of polymer. The stretchings
attributed to C-H bonds can be observed around 3000
cm-1.
The IR of PBr3 (Figure 7(II)) shows a broad band at
3362 cm-1 which is due to water absorption (all our en-
deavors to save PBr3 from taking moisture from sur-
roundings failed as the humidity was high at the time of
IR run). The remaining peaks (485, 476, 458, 442, 418,
407 cm-1) are assigned to P-Br bond [30]. The IR peaks
for blend (B4PMMA 90%:PBr3 10%selected arbi-
trarily to represent the whole series) exhibit some inter-
esting features (Figure 7(III)). “Free” PBr3 is either
completely absent or if present, is only at trace levels.
The absence of peaks around 3362 cm-1 (O-H stretch-
ing for water) overrules the presence of free PBr3. The
shift observed for ester linkages of PMMA (IR peak at
1718 cm-1) and appearance of some sharp peaks at 1434,
1386, 1141 cm-1 suggest formation of a ‘complex-type’
arrangement involving carbonyl oxygen of PMMA pen-
dent groups (either of the same chain or two different
chains) and phosphorus of PBr3. The following struc-
tures are proposed.
Few more peaks at 1238, 667, 599, 564 cm-1 indicate
that Br of P-Br bond ‘experiences’ a pull from nearby
carbons (backbone as well as ester carbons) [30-33]. For
true C-Br and CH3-Br bonds, the stretchings are found at
515-680 and ~1230 cm-1, respectively. This may result in
the weakening of this bond (P-Br) as Br ‘moves’ closer
to the more electropositive carbon atoms. The results of
GC-MS point towards these types of developments.
Figure 7. (I) Infrared spectra of PMMA; (II) Additive, PBr3;
(III) Blend, B4, PMMA (90%) + PBr3 (10%).

M. Arshad et al. / Natural Science 2 (2010) 307-319
313
CH
2
CCH
2
CH
3
C
CH
3
C
H
3
CO OOH
3
CO C
P
Br Br
Br
CH
3
C
CH
3
CO H
3
CO
P
Br
Br
Br
OCOCH
3
CCH
2
CH
3
and
H
2
CC
CH
3
CH
2
C
C=O
O
H
3
C
C=O
OCH
3
P
Br
Br
Br
CH
3
and
H
2
CCCH
2
C
CH
3
CH
3
C=O C=O
OOCH
3
H
3
CBr
P
Br Br
OCH
3
C
O=
C
CH
2
CH
3
and
C
CH
3
H
2
CC
C=O
O
C=O
O
CH
3
CH
3
P
Br
Br
Br
CH
3
CH
2
3.6. Pyrolysis-Gas Chromatography-Mass
Spectrometry Behaviour
The blend B4 (PMMA:PBr3, 90%:10%) was heated to
250oC for a minute and after bringing the residue to
room temperature, GC-MS was taken in acetone to
check the nature of degrading blend around this tem-
perature. B4 was selected arbitrarily to represent the
present series. Since the blends show stability at or
around 250oC (TG traces, Figure 2), the identification of
products is expected to shed light on the interactions
developed by the constituents of blends at this stage.
GC-MS of this blend (Figure 8) shows a number of
peaks. The products identified clearly indicate the inter-
action between the components of the system from an
early stage of degradation. The absence of PBr3 in the
degradation products (it could not be found in a trap at
-196oC) after heating B4 up to 250oC suggests its in-
volvement with the pendent groups of the neat polymer
or even with the backbone of the PMMA. However, the
early weight-loss is attributed to the decomposition of
some ‘free’ PBr3 which initiates the degradation of
polymer. The formation of Br. (free radicals) may result
in the products of peaks at 1, 3, and 4. Peak number 7,
gives the bromine radicals replacing the methyls at-
tached to the backbone carbons. The other peaks hint at
either the contacts developed by one constituent (P) of
the additive (PBr3) or both. The product at peak 8 pro-
vides the convincing clue for the stability of the system
in the region unfolded by TG curves (Figure 2). The

M. Arshad et al. / Natural Science 2 (2010) 307-319
314
Figure 8. GC-MS results of blend, B4 (PMMA (90%) + PBr3
(10%)), heated at 250oC.
Figure 9. GC-MS results of blend, B4 (PMMA (90%) + PBr3
(10%)), heated at 300oC.
interactions proposed as per IR studies (Figure 7) may
be taken as proof now supported by GC-MS studies. The
‘binding’ of pendent groups of PMMA by phosphorus of
additive may stop the degradation of polymer in certain
temperature ranges furnishing stability to the system.
The strength of the overall system lies in the ‘engage-
ment’ of various chains by undegraded or partially de-
graded additive. The mechanism of the production of
these compounds is presented in Schemes I-IV. Peak no.
9 provides a clue (which may also be regarded as the
reason of stability of the system around this temperature,
i.e., 250 oC) whereby phosphorus is found as part of the
backbone. It is worth-noting that phosphorus present in
backbone of polymer is attached to carbon and hydrogen
whereas bromine replaces either the –OCH3 of pendent
group or CH3 attached to backbone carbons. The for-
mation of –PH2 and –PH- from PBr3 appears to have
taken place along the degrading polymer. This also ex-
plains the “blockades” experienced by the degrading
polymer [15,20,21].
The GC-MS taken after heating the blend (B4) up to
300oC is to get insight into the nature of products arisen,
after the decomposition of stable intermediate (Figure 9).
Figure 10. GC-MS results of blend B4, (PMMA (90%) + PBr3
(10%)), heated at 400oC.
Figure 11. GC-MS results of blend B4 (PMMA (90%) + PBr3
(10%)), heated to boiling, cooled and mixed with acetone.
The product identified at peak number 5 does provide
enough information about the stable intermediate. Phos-
phorus seems to be linked to two separate chains
(Scheme V). Another product (peak no. 6) suggests as if
Br. (free radicals) blocks the depolymerisation of the
chains (Scheme VI).
The products identified (Table 3) after heating the
blend (B4) to 400oC also furnish evidence of the mecha-
nism of degradation close to the completion of decom-
position process (GC-MS, Figure 10). Despite inclusion
of phosphorus in the chain (peak 3), replacement of
some of the part of pendent group by phosphorus (peak 6)
and presence of bromine (peak 6) at the end of few
modified MMA units, the breaking of bonds takes place
owing to the energy content of this temperature zone (at
or around 400oC). Unzipping of the chains cannot be
hindered by phosphorus or bromine. Oligomers of neat
MMA are absent which is another indication of interac-
tion between the components of the system.
Another GC-MS (Figure 11) of this blend was re-
corded after heating to boiling for two minutes, cooling
and then dissolving it in acetone. This was performed to
check the overall behaviour of the blend subjecting it to

M. Arshad et al. / Natural Science 2 (2010) 307-319
315
H
2
CC CH
2
CCH
2
C
C=O C=O C=O
OCH
3
OCH
3
OCH
3
P
CH
3
CH
3
CH
3
Br
Br
Br
H
2
C C CH
2
CCH
2
C
C=O C=O C=O
CH
3
CH
3
CH
3
OCH
3
H abstraction
H
2
CC CH
2
CCH
2
C
C=O C=O C=O
CH
3
CH
3
CH
3
OCH
3
+
OCH
3 OCH
3
P
Br
Br
Br
Methanol
HH
MMA +
H
3
C CCH
2
CH
C=O C=O
CH
3
CH
3
HH
H
3
C C CH
2
CH
C=O C= O
CH
3
Br
HH
Replacement of
CH
3
with Br
Scheme I
H
2
CC CH
2
CH
2
C
C=O C=O
CH
3 CH
3
OCH
3
C
C=O
CH
3
OCH
3
PH
2
H
3
C
Br
P
Br
Br
C
CH
3
CH
3
H
3
C
Br
C=O
OCH
3
Br C=O
OCH
3
Br
OCH
3
Scheme II

M. Arshad et al. / Natural Science 2 (2010) 307-319
316
H
2
C CCH
2
CCH
2
C=O O=C
CH
3
CH
3
CH
3
O
CH
3
OCH
3
P
Br
Br
Br
P
Br
Br
Br
H
3
CCCH
2
CCH
3
C=O C=O
HH+
+
OH
Br
(Traces)
H
3
C CCH
2
CCH
3
C=O C=O
HBr
HH
HBr
abstraction
CH
3
Scheme III
H
2
C C CH
2
CCH
2
C=O C=O
CH
3
CH
3
OCH
3
OCH
3
P
Br Br
Br
CCH
2
C=O
CH
3
OCH
3
P
Br Br
Br
P
Br Br
Br
H
3
C CCH
2
C=O
C
C=O
H and Br
H
3
CCH CH
2
C=O
CH
C=O
Br H
Decomposing
PBr
3
H
3
CCH CH
2
C=O
CH
C=O
Br H
P
H
HC CH
3
C=O
H
H
3
CCH CH
2
C=O
CH
C=O
Br H
P
H
CH CH
3
C=O
H
OCH
3
Remaining part of pendent group
Scheme IV

M. Arshad et al. / Natural Science 2 (2010) 307-319
317
H
2
C C CH
2
C
C=O C=O
CH
3
CH
3
OO
H
3
CCH
3
P
Br
Br
Br
CCH
2
C=O
CH
3
O
CH
3
H CCH
2
CH
O=C C=O
CH
3
CH
3
OO
P
CH CH
3
C=O
O
CH
3
+
Br which may terminate few
depolymerizing modified and
unmodified MMA units
Scheme V
H
2
C C CH
2
C
C=O C=O
CH
3
CH
3
OOCH
3
CH
3
Br
effected by the presence
of PBr
3
H
3
CC CH
2
C
C=O C=O
CH
3
CH
3
OOCH
3
CH
3
Br
Scheme VI
Table 3. GC-MS results of blend, B4 after heating at 250oC, 300oC and 400oC.
Blend heated at
250oC
Blend heated at
300oC
Blend heated at
400oC
Peak
no. Product identified Peak no. Product identified Peak no. Product identified
1 C2H3O2Br, C3H6O,
CH4O 1 C2H3OBr 1 C5H9Br
2 C5H11O2P 2 C2H4OPBr 2 C2H4PBr or CH2OPBr
3 C3H8PBr 3 CH3OBr 3 C7H14O3P2, C8H13O4P
4 C4H9Br 4 C6H12PBr 4 C7H11O2Br
5 Unidentified 5 C11H17O6P 5 C8H11O2PBr
6 Unidentified 6 C10H17O4Br 6 C12H21O3P2Br
7 C4H5O2Br -- -- -- --
8 C4H7Br2 -- -- -- --
9 C9H14O3PBr -- -- -- --
high temperature for short time. Modified MMA units
were found confirming the products identified in differ-
ent temperature zones earlier. Traces of MMA units were
also detected which is in accordance with earlier find-
ings. It is further concluded (peak 5) that parts of the
pendent groups of MMA units are equally liable to re-
placement by bromine and phosphorus.
The interaction between additive and polymer is es-
tablished. The GC-MS studies help in understanding the
mechanism of degradation of the blended system. This
interaction imparts stability to the system in certain re-
gions (TG curves). The orientation of PBr3 in the system
appears to have profound impact on the formation of the
products identified during degradation at different tem-
peratures. The cross-linking of adjacent chains by the
presence of phosphorus gives stability to the system. In
addition to this, phosphorus and bromine when terminate
the degrading polymer also play role in the formation of
these products which ‘block’ further degradation in the
regions of stability.
3.7. Flammability Behaviour of Neat Polymer
and its Blends
Horizontal burning rate (HBR) and time to burn neat

M. Arshad et al. / Natural Science 2 (2010) 307-319
318
Figure 12. Horizontal burning rate of polymer and its blends.
Table 4. Horizontal burning rate (HBR) for polymer (A) and
blends, B1-B4.
Polymer/Blend
code number A B1 B2 B3 B4 B5
Time to burn
(sec) 11 39 43 49 58 65
Length of strip
(mm) 75 75 75 75 75 75
HBR (mm/sec) 6.8 1.9 1.7 1.5 1.291.15
mm = millimeter, sec = second.
polymer and its blends are tabulated in Table 4. The
trend is clearly a linear one (Figure 12). Higher the con-
centration of additive in the blend, lower is the rate of
burning obtained. It has been observed that burning rate
of blend (B5) decreases to 6 times compared to neat
polymer (A). Reduction in burning rate is much more
pronounced even with the lowest proportion of additive
(B1) and this is easily explained by the retardency
caused by the additive towards polymer’s flammability.
The uniform distribution of all concentrations of additive
throughout polymer is also confirmed.
4. CONCLUSIONS
1) The blends (PMMA-PBr3) lose weight at lower tem-
peratures than neat polymer.
2) Despite early destabilization, the blends exhibit sta-
bilization temperature zones.
3) The interaction between the components appears to
be purely chemical.
4) The earlier decomposition is attributed to the split-
ting of PBr3 releasing bromine free radicals (Br.).
5) The formation of products involving phosphorus as
part of degrading polymer imparts stability to the blends.
6) The “engaging” of separate polymer chains by
phosphorus is another reason of stabilization of the bi-
nary system.
7) It seems that free radicals (Br.) not only start the
early depolymerization of the polymer but also inhibits
this process, thus, providing one more point for stabili-
zation.
8) The pendent groups of polymer or a part of them
are equally liable to replacement by phosphorus and
bromine.
9) The production of monomer has decreased signifi-
cantly furnishing ample evidence for chemical interac-
tion between the constituents of the system.
5. ACKNOWLEDGEMENTS
The authors would like to express their gratitude to PINSTECH, Is-
lamabad, Pakistan for providing the opportunity to undertake this
research work. Messrs Nehad Ali (Senior Tech. IAD, PINSTECH),
Nadeem Ahmad and Muhammad Adeel Khattak are acknowledged for
drawing of figures and technical help.
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