albr3 impact on the thermal degradation of p(s-co-mma): a study performed by contemporary techniques

ORIGINAL PAPER

AlBr3 impact on the thermal degradation of P(S-co-MMA):a study performed by contemporary techniques

Muhammad Arshad • Khalid Masud •

Aamer Saeed

Received: 17 August 2011 / Accepted: 26 December 2011 / Published online: 22 February 2012

� Iran Polymer and Petrochemical Institute 2012

Abstract Pyrolysis of copolymer, [P(S-co-MMA)], in the

presence of AlBr3 was inspected in an inert atmosphere.

Five different proportions (copolymer/additive) were cho-

sen. Films were cast from common solvent. It was noticed

that copolymer showed more stability on the basis of T0,

however, regions of stability were also observed for the

blends. Copolymer showed T0 at 260 �C, whereas blends

started degrading around 70 �C. Tmax was the same for the

copolymer and the blends. Low-temperature decomposi-

tions of blends were attributed to the generation of free

radicals (Br•) and the zones of stabilizations were assigned

to the formation of a ‘‘complex type’’ structure between Al

and the carbonyl oxygens of MMA units. Degradation

products were collected and identified employing Py-GC–

MS technique. Intermediates (solid) at different tempera-

tures (300, 350 and 400 �C) were examined through FTIR

spectroscopy. In the light of gathered data, a degradation

mechanism was proposed. New products were encoun-

tered, viz., bromobenzene, ‘brominated’ anhydride ring,

etc., which established the chemical interactions between

the constituents of the blends, i.e., copolymer and additive.

Anhydride rings were absent when poly (methyl methac-

rylate) was pyrolyzed in the presence of AlBr3. Oligomers

of styrene were not found hinting at the involvement of

additive in ‘‘targeting’’ the degrading styrene units. The

blends indicate 2–7% residue of original mass; the additive

exhibits 9% while the copolymer does not leave residue at

the completion of the TG run. The presence of char in the

residues of blends suggests that the additive imparts sta-

bility to the copolymer. Horizontal burning rate was lowest

(6 times less than that of neat copolymer) for [P(S-co-

MMA):AlBr3, 87.5:12.5%], thereby revealing the effi-

ciency of the additive as thermal stabilizer. The highest

activation energy was calculated for the copolymer

(169.46 kJ/mol) and the range of this parameter for the

blends was found from 52.72 to 27.14 kJ/mol.

Keywords P(S-co-MMA) copolymer � AlBr3 �TG–DTG–DTA sifting � IR analysis � GC–MS scrutiny �Activation energy

Introduction

Polymers/copolymers are the backbone of modern indus-

tries. These find use in almost every conceivable field.

Their cost-effectiveness and desirable properties make

them indispensable stuff for present day requirements for

assorted applications. However, flammability and toxicity

of products arising from flammability have attracted the

attention of a large number of researchers [1–5] to render

the use of these important materials safe.

Many compounds, organic as well as inorganic [6–9],

have been tried, either at the molecular level or as mixtures

to enhance the stability and to change the mode of degra-

dation of polymers/copolymers during fire (high tempera-

tures). Polymer mixtures have also been studied [1, 10].

One of the studies [10] maintains that the mixture [poly(-

methyl methacrylate) (PMMA) and polystyrene (PS) in the

M. Arshad (&)

Chemistry Division, Directorate of Science, PINSTECH, Nilore,

Islamabad, Pakistan

e-mail: [email protected]

K. Masud

New Labs PINSTECH, Nilore, Islamabad, Pakistan

A. Saeed

Department of Chemistry, Quaid-i-Azam University,

Islamabad, Pakistan

Iran Polymer andPetrochemical Institute

123

Iran Polym J (2012) 21:143–155

DOI 10.1007/s13726-012-0017-2

form of thin film] may not exhibit any detectable interac-

tion between the polymers, while the presence of styrene

exerts disproportionate stabilizing effect on the methyl

methacrylate polymer chain keeping in view the behavior

of the copolymer as being between that of the individual

homopolymers. The introduction of different functional

groups in polymers is another mode, which proved valu-

able [11]. It revealed through limiting oxygen indices that

phosphorated polymers have potential fire retardant prop-

erties. The search for other avenues in this direction has

been flourishing for many years.

Our interest on this aspect has produced several publica-

tions ranging from thermal degradation of polymers and

copolymer, to the pyrolysis of mixtures of polymers/

copolymers with organometallic substances and blends

(molecular-level mixing film cast from common solvent) of

polymer with purely inorganic salt. The blending of phenyl

methacrylate/styrene (PMA/ST) with aluminum isopropox-

ide [12] imparted stabilization (up to 50 �C) to the system as

the pyrolysis progressed. For copolymers, it was noticed that

even the presence of 10 mol% of styrene in the system, PMA/

ST pushed the T0 (temperature corresponding to the start of

degradation) to 285 �C when compared with the T0 of PPMA,

which was recorded as 190 �C [13]. The destabilizing effect

of 10 mol% methyl methacrylate (MMA) in allyl methac-

rylate/methyl methacrylate (AMA/MMA) is apparent as T0

goes down from 210 �C [poly(allyl methacrylate) (PAMA)]

to 200 �C for the copolymer [14]. AMA/MMA (blended with

aluminum ethoxide-physical mixing of powder) started to

degrade at lower temperature than either of the monomers;

however, stabilization was also observed in different zones of

degradation [15]. Additive appeared stabilized in the initial

stage of thermal decomposition. A similar thermal behavior

was noted when the PMA/ST system was heated in the

presence of aluminum ethoxide [16]. The stabilization went

up to 60 �C at different points during pyrolysis. When the

copolymers, i.e., AMA/MMA, was mixed with aluminum

isopropoxide [17], stabilization up to 45 �C was noticeable at

different stages of thermogravimetric analysis after initial

destabilization. New products were encountered and chemi-

cal interaction was proposed. When PMMA was blended

with AlBr3, PBr3 and SnCl4 [19–21]—films were cast from

common solvent—interesting results were obtained. PBr3

and SnCl4 showed stabilization in the presence of the poly-

mer, whereas AlBr3 seemed destabilized. In all these cases,

halogen-free radicals were generated in the early part of

thermal degradation, which initiated the decomposition of the

polymer. Their interaction produced those compounds which

were absent when PMMA was degraded alone. Both parts of

the additive, viz., metallic and non-metallic such as Al and Br,

played important roles in imparting stability to the system.

The present communication pertains to the thermal

degradative examination of copolymer [P(S-co-MMA)]

mixed with AlBr3 (in selected proportions) as a continua-

tion of our previous studies. This system has not been

studied so far by any worker. The aim was to check the

nature of disintegration products comprehensively, i.e., at

different temperatures and to propose a mechanism based

on these evaluations. TG–DTG–DTA, FTIR and Py-GC–

MS were employed to ascertain the interactions exhibited

by the constituents of the current system. Activation

energies and order of reaction (overall) were calculated

using Horowitz–Metzger method [22].

Experimental

Reagents

All reagents and solvents obtained from standard source

suppliers (E. Merck) were of analytical grade. The mono-

mer, methyl methacrylate, was processed for copolymeri-

zation as reported earlier [23]. Styrene (Aldrich) was

treated as had already been described [24]. 2,20-Azobisi-

sobutyronitrile (AIBN) was selected as free radical initiator

and purified by the known procedure [25]. All solvents

were distilled before use.

Preparation of poly (styrene-co-methyl methacrylate)

Styrene (Aldrich) and methyl methacrylate (E. Merck) were

purified by the standard methods. The compositions of

monomer mixtures necessary to produce copolymers of

given proportions were calculated from copolymer com-

position equation using literature values of the reactivity

ratios for this polymer pair (r1 = 0.52, r2 = 0.46;

M1 = styrene, M2 = methyl methacrylate) [26–29]. After

addition of initiator, 2,20-azobisisobutyronitrile, the appro-

priate amounts of the two monomers were distilled into

dilatometer under vacuum with mild warming. After dis-

tilling and freezing the contents of the dilatometer to liquid

nitrogen temperature, the dilatometer was sealed under high

vacuum. Upon sealing, polymerization was carried out in a

water bath at 60 �C to a maximum conversion of 5% (2 h).

The copolymer was precipitated and reprecipitated from

chloroform solution by methanol and dried under vacuum at

room temperature for several days and kept in a desiccator.

The molecular weight was found to be 120,000.

Formulation of blend for analysis and preparation

of strip for flammability test

The same steps were followed for the preparation of blends

with varying compositions of P(S-co-MMA) and AlBr3 as

were employed for PMMA–AlBr3 blendings [19]. Pyrex

glassware was employed for dissolving copolymer,

144 Iran Polym J (2012) 21:143–155


123

additive and copolymer/additive blends. The additive was

handled with extreme care. The mode outlined for the

preparation of PMMA–AlBr3 strips for flammability test

was maintained for the present system.

Physiochemical methods

Thermoanalytical (TG–DTA–DTG) curves were obtained

using Netzsch Simultaneous Thermal Analyzer STA 429.

All the measurements were carried out with samples hav-

ing 30–60 mg initial mass. These were heated over the

temperature range from ambient to 800 �C in an inert

atmosphere (nitrogen), using kaolin as reference material.

The heating rate was 10 �C.min-1. Activation energy (Eo)

and order of reaction (n) of copolymer and its blends were

computed by a known method [22]. A plot of ln Wo/Wt

(where Wo = initial mass of material and Wt = mass of

material at temperature T) against h (h = 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 mass loss occurs). The order of reaction was

calculated by using the relation between reaction order and

concentration at maximum slope.

Infrared (IR) spectra of copolymer, additive and those of

residues, produced after heating the blends at various

temperatures, were recorded with Nicolet 6700 FTIR

spectrometer in the range of 4,000–400 cm-1 by directly

placing a little quantity on the slit.

The liquid chromatograph, Hitachi 655-A-11 with GPC

software and integrator (D-2200 GPC) along with column

GLA-100 m (Gelko), was employed for molecular weight

determination of copolymer 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 tetrahydrofuran

(Aldrich) was used as solvent.

The samples were subjected to an Agilent 6890N type

GC–MS coupled with 5,973 inert MSD, by Agilent Ana-

lytical Instruments, Agilent Technologies, USA. Analysis

of the products in acetone was performed with a DB-5MS

column. The injection volume was 1 lL. The temperature

program entailed an initial increase of temperature from

120 to 150 �C at 10 �C.min-1 and from 150 to 280 �C at

15 �C.min-1. The mass spectrometer was operated in the

electron-impact (EI) mode at 70 eV. The horizontal burn-

ing test (HBT) of copolymer and its blends was conducted

in accordance with the ASTM standards [30, 31]. The

blends’ compositions given in Table 1 were prepared by

mixing the copolymer with additive in an aluminum mold

with the specified dimensions. The specimen was held

Table 1 Comparative thermoanalytical results for copolymer (D) and its blends, D1–D5

Blends’ composition (%)

P(S-co-MMA)–AlBr3

Temperature

range (oC)

Stage Mass

loss

(%)

TG (oC) DTA (oC)

T0 T25 T50 Tmax I II Thermal effect

100–00 (D) 260–440 I 100 260 380 396 440a 355 406 356 (Endo), 418 (Exo)

97.5–2.5 (D1) 70–170 I 4 70 370 390 440 150 394 141 (Endo), 240 (Exo), 287 (Exo), 329

(Endo), 401 (Exo)170–440 II 94

[440 Resi. 2

95–5 (D2) 70–170 I 5 70 380 394 440 170 394 139 (Endo), 231 (Endo), 280 (Exo), 317

(Endo), 409 (Exo)290–440 II 92

[440 Resi. 3

92.5–7.5 (D3) 70–190 I 5 70 375 390 440 170 396 125 (Exo), 165 (Endo), 207 (Exo), 236

(Endo), 280 (Exo), 310 (Exo), 396 (Exo)250–440 II 90

[440 Resi. 5

90–10 (D4) 70–190 I 8 70 380 395 440 170 408 123 (Endo), 165 (Endo), 210 (Exo), 238


[440 Resi. 5

87.5–12.5 (D5) 70–180 I 8 70 375 394 440 170 396 125 (Endo), 165 (Endo), 209 (Exo), 236


[440 Resi. 7

00–100 70–223 I 82 70 174 200 800 215 – 95 (Exo), 375 (Endo), 588 (Endo)

223–800 II 9

[800 Resi. 9

Max maximum mass loss, Endo endothermic, Exo exothermic, Resi residuea = 100% mass loss

Iran Polym J (2012) 21:143–155 145


123

horizontally and a flame fueled by natural gas was supplied

to light its one end. The time for the flame to reach from

the first reference mark (25 mm from the end) to the sec-

ond reference mark at 100 mm from the end was measured.

Results and discussion

TG–DTG–DTA investigations

The thermal decomposition of neat copolymer (D) (Fig. 1,

curve I) in nitrogen atmosphere shows a single-step mass

loss starting to degrade around 260 �C and ceasing to

disintegrate at 440 �C (Table 1). Two DTG depressions at

355 and 406 �C (Fig. 2, curve I) and two DTA peaks at 356

and 418 �C (Fig. 3, curve I) corresponding to the single-

step TG curve are noticeable. The copolymer furnishes

mostly monomers styrene and methyl methacrylate, which

is in agreement with the findings of other contributors [32–

36]. There is no residue at the termination of single stage

thermal decomposition process.

The thermal curves of blends, D1–D5, are presented in

Figs. 1, 2 and 3 and thermoanalytical data are entered in

Table 1. The blend (D1) begins to degrade around 70 �C

and the first stage comes to an end at 170 �C (Fig. 1, curve

II). A 4% mass loss is observed. One DTG peak at 150 �C

(Fig. 2, curve II) and one DTA peak at 141 �C (Fig. 3,

curve II) are noted for the first stage. The products evolved

at this stage clearly indicate the interaction between the

two components of the system (FTIR and GC–MS results).

The neat copolymer (D) exhibits T0 (temperature corre-

sponding to detection of first mass loss) at 260 �C, whereas

the additive starts degrading around 70 �C when heated

alone in nitrogen atmosphere. This is another clue for

interaction. At the end of the first stage (170 �C), the

intermediate is not stable and starts degrading. The second

stage which terminates at 440 �C accounts for 94% mass

loss. Two per cent residue is noticeable at the completion

of the degradation process. One DTG peak at 394 �C and

four DTA peaks at 240, 287, 329 and 401 �C are indicated

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.

Fig. 1 TG curves (dynamic nitrogen, heating rate: 10 �C/min) for

P(S-co-MMA)–AlBr3 blends: D(I), D1(II), D2(III), D3(IV),

D4(V) and D5(VI)

Fig. 2 DTG Curves (dynamic nitrogen, heating rate: 10 �C/min) for


D4(V) and D5(VI)

Fig. 3 DTA curves (dynamic nitrogen, heating rate: 10 �C/min) for


D4(V) and D5(VI)

146 Iran Polym J (2012) 21:143–155


123

The second blend of this series, D2, starts losing mass

around 70 �C and, by the end of the first stage (170 �C),

accounts for 5% mass loss (Fig. 1, curve III). It can be

observed that by increasing the concentration of additive

(AlBr3), the T0 remains unchanged (moving from D1 to

D2); however, the percent mass loss registers an increase.

The same type of interaction is believed to have occurred

for this blend as observed for D1. The intermediate formed

at the completion of the first stage is very stable and

withstands an additional temperature of 120 �C (after

170 �C) before initiation of the next stage. The last stage

(290–440 �C) shows a mass loss of 92%. From 290 to

360 �C, the mass loss is only 7% which is regarded as

resistance offered by the bonds/interactions developed in

the earlier part of the degradation between the components

of the system. For the first stage, one DTG peak (170 �C)

and three DTA peaks (139, 231 and 280 �C) appear (Fig. 2,

curve III and Fig. 3, curve III, respectively). For the second

step, one DTG and two DTA peaks are noticed at 394, 317

and 409 �C, respectively. Three per cent residue is found at

the termination of the degradation process.

The blend, D3, begins to degrade around 70 �C and

loses 5% of original mass for the first stage which termi-

nates at 190 �C. The intermediate formed at this stage is

stable in the temperature range, 190–250 �C, after which

the pyrolysis again starts and the second step shows a mass

loss of 90% with 5% residue at the completion of the

decomposition process (440 �C) (Fig. 1, curve IV). The

range of temperature for stable intermediate (190–250 �C),

in this case, exhibits a reduction when compared with the

same range for the second member of this series (D2). It

may be due to the less number of bonds/links formed

between the constituents of the system despite the presence

of relatively higher concentration of additive. From 250 to

360 �C, only 9% mass loss is observed, which requires

heating to 110 �C. This is clearly indicative of the strength

of bonds developed during the early part of pyrolysis and

retained by the intermediate. One DTG (Fig. 2, curve IV)

and four DTA peaks (Fig. 3, curve IV) emerge for the first

stage (170, 125, 165, 207 and 236 �C, respectively);

however, for the second stage, one DTG and three DTA

peaks at 396, 280, 310 and 396 �C, respectively, arise.

The blend (D4) experiences a mass loss of 8% for the

first stage (Fig. 1, curve V). It starts decomposing around

70 �C and stops losing mass around 190 �C. One DTG

(Fig. 2, curve V) and four DTA peaks (Fig. 3, curve V) are

found at 170, 123, 165, 210 and 238 �C, respectively. The

intermediate resists 50 �C extra heating (190–240 �C)

before the inception of the second stage of degradation.

The second step comes to an end at 440 �C marking a mass

loss of 87%. The first 6% mass loss of the second stage

(240–440 �C) requires 130 �C heating temperature, which

is attributed to the resistance offered by strong bonds/links

produced during the early part of the pyrolysis. One DTG

and three DTA peaks are observed at 408, 280, 320 and

408 �C, respectively. TG analysis shows that the residue is

5% of the original mass of the blend after 440 �C.

The blend, D5, commences its mass loss around 70 �C

for the first stage which comes to an end at 180 �C (Fig. 1,

curve VI). One DTG and two DTA peaks appear for this

step at 170, 125 and 165 �C, respectively (Fig. 2, curve VI

and Fig. 3, curve VI); 8% mass loss is evident from TG

traces. The intermediate that is stable up to 220 �C (stable

in the temperature range, 180–220 �C) starts decomposing

subsequently as the energy content increases. The second

stage terminates at 440 �C. One DTG and five DTA peaks

are found at 396, 209, 236, 285, 320 and 400 �C, respec-

tively. The first 8% mass loss for the second step (out of

85%) requires heating temperature of 140 �C (from 220 to

360 �C), whereas the remaining larger portion (77%)

leaves the crucible on heating to 80 �C (360–440 �C). This

is attributed to the strength of the bonds present in the

intermediate. The residue formed after the completion of

the decomposition process is 7% of the blend’s original

mass.

The interaction is clear between the components of the

system throughout the series, i.e., D1–D5. The nature of

interaction is same for all members. The percentage of

degradation for the first stage is higher than the total per-

centage of additive in the blends D1–D4. The molecular-

level mixing of the constituents allows complete homoge-

nization which, in turn, gives way to early degradation of

both parts. The evolution of new products in the early part

of pyrolysis (Py-GC–MS studies) confirms the chemical

interaction and mutual influence of the ingredients on each

other’s decomposition.

Effect of blends’ composition on thermal degradation

Figure 4 gives the plots of T0, T25, T50 and Tmax of

copolymer and its blends. Considering T0, a very clear

trend of destabilization is seen. As the percentage of

additive in the blends is increased, no stabilization is noted

and almost similar trend of destabilization is observed,

which may be attributed to the decomposition of the

additive [generation of free radicals (Br•)]. However, for

T25 (temperature at which 25% mass loss results), the trend

of destabilization is almost the same when mass percentage

of additive changes from 2.5 to 12.5. This seems to be due

to the production of free radicals (Br•) by the degradation

of the additive, which causes accelerated degradation of the

copolymer. At T50 (temperature corresponding to 50%

mass loss), a very inappreciable stabilization is observed as

energy content is too great to be resisted by the different

types of interactions or bonds between additive and

copolymer irrespective of the mass percentage of additive.

Iran Polym J (2012) 21:143–155 147


123

Tmax (the temperature at which maximum mass loss occurs)

is same for copolymer and blends, which is attributed to the

production of those bonds which are liable to break at this

temperature and are not alike for the two systems (FTIR

and Py-GC–MS studies). This plot, however, does not

furnish the information as to how much residue is left at the

end of the disintegration process.

Infrared spectroscopy

The IR spectrum of the copolymer (Fig. 5, curve I) gives

typical stretching of MMA ester groups around 1,725 cm-1.

The slight displacement is assigned to the presence of styrene

units. C–H stretchings are noticeable for saturated and aro-

matic segments around 3,000–2,940 cm-1 and 3,040–

3,010 cm-1, respectively. Characteristic overtones are

observed in the region 2,000–1,660 cm-1. For aromatic un-

saturation (C = C), bands are observed at 1,606, 1,495 and

1,460 cm-1. No peaks are found around 1,640–1,630 cm-1

which means that polymerization is complete [37–40].

The IR of AlBr3 has already been discussed [18].

Briefly, moisture was found and a broad band to this effect

was noticed in the region 3,600–3,000 cm-1. The peaks at

1,603, 1,089, 676, 580 and 478 cm-1 were linked with Al–

Br bond (Fig. 5, curve II).

The blend (Fig. 5, curve III) shows a broad band around

3,600–3,200 cm-1, which may be attributed to water. This

also points toward the presence of some ‘free’ AlBr3. It

may be interesting to note that when blended with pure

PMMA, the homogenization of AlBr3 (‘‘complex forma-

tion’’) and polymer occurs in such a way that absorbance of

moisture by this additive virtually becomes impossible

[18]. This is an indication of less number of ester linkages

present per unit volume of the copolymer and per unit

chain length, and hence more chances of AlBr3 to remain

‘free’. The C–H stretching, both aliphatic and aromatic, are

found in the region as have already been described for the

IR spectrum of pure copolymer. The C = O stretching has

shifted to lower frequency, i.e., 1,716 cm-1, thereby

showing a sort of ‘‘co-ordination’’ between the metal (Al)

of additive and carbonyl group (it is not like the real co-

ordination observed for transition elements). Al–Br bonds

also exhibit some shifting as these appear now at 699, 550

and 470 cm-1. This may be attributed to the surroundings

of this additive, i.e., styrene and MMA units. It is clear that

all MMA units will not be available for ‘co-ordination’.

The other bands (related to benzene ring) are found at their

normal positions with slight displacements (this seems to

be due to AlBr3, as it also affects the phenyl part of the

styrene units, particularly Br).

IR spectra of blend at different temperatures

The blend was heated at three different temperatures (300,

350 and 400 �C for a minute, cooled to room temperature

and then IR of residues was run to check the changes

occurring during the course of degradation). These tem-

peratures were selected for the regions showing some sta-

bility, middle of the total decomposition process and close

to the completion of pyrolysis of the system, respectively.

When heated to 300 �C, the IR (Fig. 6, curve I) shows

some developments which are different from the IR of the

undegraded blend (Fig. 5, curve III). Moisture is com-

pletely absent (no peaks in the region 3,600–3,200 cm-1),

which may be attributed to the absence of ‘free’ AlBr3. A

slight displacement for C = O stretching (1,719 cm-1) is

observed and it clearly reveals that ‘coordination’ Al has

developed with the carbonyls of MMA units. Peaks around

680–515 cm-1 indicate the formation of C–Br bonds. A

band at 1,191 cm-1 may be assigned to Al–C bond, though

no such bond could be detected in GC–MS studies. A slight

Fig. 4 Effect of blends’ composition on T0, T25, T50 and Tmax values

of D (copolymer) and D1–D5 blends

Fig. 5 IR Spectra of neat copolymer, D(I), additive, X(II) and blend,

D4(III)

148 Iran Polym J (2012) 21:143–155


123

indication for the presence of anhydride rings (1,800, 1,760

and 1,030 cm-1) can be noticed. As the styrene units form

the overall structure along with MMA, the framework for

the production of anhydride rings may not be an obvious

choice. Some Al–Br bonds still exist as peaks at 698, while

571 and 484 cm-1 appear with diminished intensities. C–H

stretchings are present as such, i.e., 3,040–2,940 (aliphatic

and aromatic).

On heating the blend to 350 �C, the IR (Fig. 6, curve II)

of the residue assumes drastically different appearance

from the IR obtained at 300 �C. The intensities of almost

all stretching bands are reduced showing the evaporation of

many products at this stage. There are no signs (peaks) of

anhydride rings (no bands at 1,800, 1,760 and 1,030 cm-1).

Some peaks around 1,200–900 cm-1 give indication of C–

O–Al bonds along with shifting of peak around 1,715 cm-1

(reduced intensity) and appearance of a new peak at

1,698 cm-1. The number of Al–Br bonds also appears to

have decreased owing to the intensity of relevant peaks

(695, 573 and 479 cm-1) and the participation of Br in the

formation of other compounds. C = C unsaturation (aro-

matic) is, however, present at its normal position.

The IR of the remnant recorded after heating the blend

to 400 �C (Fig. 6, curve III), produces those peaks, which

may be expected close to the completion of degradation

process as bonds are breaking quickly and the products are

leaving the scene. Only those compounds which can resist

such a high temperature are found at this stage. A few

peaks for C–H vibrations (much reduced in size) are

observable at 3,000–2,940 cm-1. Some undegraded por-

tion of copolymer with limited chain lengths gives indi-

cations at 1,465, 1,380 and 720 cm-1. The peaks for the

‘co-ordination’ have decreased in size, which is clear evi-

dence of the change this arrangement undergoes. This is

attributed to the fact that a number of MMA units have

been consumed for the formation of different products. The

remaining units (carbonyl oxygens) are in the process of

forming true bonds with Al. Peaks at 1,080, 1,100 and

1,142 cm-1 may be taken as a clue to the presence of

preceding structure.

IR of residue after pyrolysis

After complete pyrolysis, the residue was subjected to IR.

This IR (Fig. 7, curve II) is very simple and is very similar

to the IR of residue recorded for PMMA–AlBr3 blends.

The peaks at 2,945, 2,987 and around 3,000 cm-1 arise due

to C–H stretching (aliphatic). The bands in the region

1,200–900 cm-1 [18] indicate the presence of Al–O–C

linkages, whereas for C–C bonds the stretchings are found

around 900–400 cm-1. It may be concluded that the resi-

due consisted of char, aluminum attached to some carbo-

naceous material through oxygen (Scheme 1) and

aluminum metal.

IR of liquid portion after heating the blend to high

temperature

For further information and attaining conclusive proof

about the products of degradation of the blend [P(S-co-

MMA) ? AlBr3], one of the blends was heated at high

temperature for 1 min and then cooled to ambient tem-

perature. IR of this portion (Fig. 7, curve I) was taken and

studied. Water is present as a broad peak visible at

3,394 cm-1. C–H stretchings (aliphatic and aromatic) are

observed at 3,000–2,940 cm-1 and 3,040–3,010 cm-1,

respectively. The peaks for anhydride rings are present,

though diminished in intensity, around 1,800, 1,759 and

1,027 cm-1. The frequency at 1,745 cm-1 is attributed to

C = O of carboxylic acid with its related C–O stretchings

located at 1,190–1,075 cm-1. The carbonyl (C = O)

vibration for ester is found at 1,732 cm-1, whereas the

accompanied C–O stretching bands are observed at

Fig. 6 IR Spectra of blend, D4, after heating at 300 �C (a), 350 �C

(b) and 400 �C (c)

Fig. 7 IR Spectra of blend, D4, after pyrolysis at high temperature–

liquid (I) and residue (II)

Iran Polym J (2012) 21:143–155 149


123

1,210–1,160 cm-1. Benzene ring C = C vibrations arise at

1,606, 1,498 and 1,455 cm-1. Monosubstituted benzene

present as bands are observed at 727 and 693 cm-1. The

peaks around 1,640–1,630 cm-1 suggest the presence of

unsaturation and vinyl-type unsaturation is also clear from

the bands appearing at 1,415 and 1,420 cm-1. C–Br

vibrations appear in their normal range, i.e., 680–515 cm-1.

Pyrolysis–gas chromatography-mass spectrometry

The detailed GC–MS studies of P(S-co-MMA) by Grassie

et al. [41, 42] and McNeill [43] revealed that although the

behavior of the copolymer is intermediate between that of

the individual homopolymers, the presence of styrene is

found to have a disproportionate stabilizing effect on the

methyl methacrylate polymer chain owing to: (1) the

presence of fewer unstable chain ends in copolymers than

PMMA, because of a favored cross-termination step in the

copolymerization; and (2) the operative cage effect

(advanced by McNeill) results in the production of a pair of

polystyryl radicals after an initial scission between a pair of

MMA units in the copolymer chain, thus preventing further

unzipping. On the basis of preceding observations, the

thermograms for S/MMA are not simply an ‘average’ of the

thermograms for the corresponding homopolymers.

During the present study, the copolymer of S/MMA was

heated in the presence of AlBr3 at high temperature for

2 min and then cooled to room temperature. The liquid, thus

obtained, was subjected to GC–MS. This resulted in a

number of peaks and the products identified are tabulated in

Table 2. The GC is given in Fig. 8. The nature of products

clearly shows that AlBr3 has not only interacted with MMA,

but also made compounds with styrene units. A number of

new products are formed which were never found in the

studies conducted earlier with neat S/MMA thermal

decompositions. Oligomers of styrene (tetramers, trimers,

dimers) were absent when compared with the results of

Grassie et al. [41]. Monomeric amounts decreased

Scheme 1 Residue consisting

of char, aluminum attached to

some carbonaceous material

through oxygen

150 Iran Polym J (2012) 21:143–155


123

significantly as styrene and MMA were modified in the

presence of AlBr3. The presence of bromobenzene, a-

methyl styrene and phenyl methacrylate suggests the

answer to the reduced amounts of monomers produced. The

mechanisms of the formation of preceding compounds are

proposed in Schemes 2 and 3. These products also indicate

the effect of styrene and MMA units on each other’s deg-

radation. It is argued that AlBr3 binds the pendant groups of

MMA units in such a way as to facilitate the effect of

monomeric units on each other (styrene units flanked by

MMA units, which are further ‘pulled’ by Al of AlBr3

‘trapping’ styrene monomers in ‘cyclic’ type structure). The

production of a-methyl styrene and phenyl methacrylate

may be taken as proof. The anhydride rings appear ‘bro-

minated’ as one of the methyls is believed to have been

replaced by bromine (Scheme 4). The anhydride rings were,

however, absent when PMMA was degraded in the presence

of AlBr3 [19]. Toluene is also found among the products

identified (Scheme 4). Moreover, ethyl benzene and ben-

zene are observed (Scheme 5), which may arise due to the

presence of additive.

Activation energy and order of reaction

Activation energy may be construed as the measure of

thermal stability of a system. It is, however, not an absolute

criterion. Other factors such as amount of residue, nature of

products formed, type of interaction, duration of pyrolysis,

atmosphere, etc., invariably affect the overall stability of

the material being degraded thermally. The values of

activation energy for virgin copolymer and blends indicate

that the copolymer is more stable than the blends. TG

curves furnish this experimental verification.

The activation energies and order of reactions of neat

polymer (D) and its blends (D1 to D5) were determined

from TG curves [22]. It is pertinent to state at this stage that

activation energies of degradation calculated from TG

curves are based on mass loss and not on the formation of

individual products during degradation. Activation ener-

gies and order of reaction for the pyrolysis of this

copolymer and its blends are presented in Table 3. It is

inferred that P(S-co-MMA) is more stable than the blends

of all compositions under investigation. The copolymer is

also much more stable than neat PMMA. With the increase

of the additive’s (AlBr3) percentage in the blend, a

decrease in activation energies is observed, although the

trend is not a linear one. The results not only show the early

destabilization of the system, but also indicate the inter-

action associated with the additive’s degradation, which is

concentration based. The data also unfold the promotion of

the blends’ disintegration at lower temperatures when

compared with that of the neat copolymer.

Flammability of copolymer and blends

Horizontal burning rate and time to burn neat copolymer

and its blends, D1 to D5, are tabulated in Table 4. A linear

trend is obtained (Fig. 9) depicting that higher the con-

centration of additive in the blend, lower is the rate of

burning. It is observed that the burning rate of blend (D5)

decreases to six times when compared with that of neat

copolymer (D). It is also noticed that reduction in burning

Table 2 GC–MS results of

blend, D4, after heating it to

high temperature, cooling the

fractions and dissolving in

acetone

Peak no. Time

(min)

MS (m/e) Products identified (name/formula)

1 2.514 91, 92, 39, 65 Toluene (C7H8)

2 2.952 78, 52, 51, 50, 39, 77 Benzene (C6H6)

3 4.519 77,156, 158, 51, 50, 74, 78 Bromobenzene (C6H5Br)

4 6.031 41, 69, 100, 39, 99 Methyl methacrylate (CH2 = C(CH3)CO2CH3)

5 6.908 104, 78, 103, 51, 77 Styrene (CH2 = CHC6H5)

6 7.292 118, 117, 103, 78 a-Methyl styrene (CH2 = C(CH3)C6H5)

7 9.694 91, 106, 92, 77, 51 Ethyl benzene (C8H10)

8 14.107 69, 41, 39, 94, 65, 162 Phenyl methacrylate

(CH2 = C(C6H5)CO2CH3)

9 16.149 150, 152, 220, 222, 70, 86, 134, 136 ‘Brominated’ anhydride ring (C7H9O3Br)

Fig. 8 GC–MS results of blend, D4, heated to boiling, cooled and

dissolved in acetone

Iran Polym J (2012) 21:143–155 151


123

rate is much more pronounced even with the lowest pro-

portion of additive (D1) and this is easily explained by the

entangling of the constituents (positioning) and interaction

of ‘complexation’ type, which are believed to hinder the

burning of copolymer. The uniform distribution of all

concentrations of additive throughout the copolymer is also

established.

Conclusions

The copolymer is more stable than its blends when their T0

(temperature at which first mass loss is detected) are

compared. The low-temperature pyrolysis of blends is

attributed to decomposition of the additive, which gener-

ates free radicals (Br•). These radicals then initiate the

early decomposition of copolymer or block the degradation

at some later stage. In the later part of the degradation

process, these radicals also attack the disintegration prod-

ucts of constituting monomers along with the monomers

themselves. Increasing concentration of additive from 2.5

to 12.5% does not affect T0 and Tmax (temperature corre-

sponding to that mass loss after which no further change in

mass is noticeable) of the blends. Thermal stability at the

completion of the first stage of degradation is evident for

D2–D5. It is believed that the interactions/bindings develop

Scheme 2 Route for the

formation of a few compounds

due to the effect of AlBr3 on

P(S-co-MMA)

152 Iran Polym J (2012) 21:143–155


123

in the very initial stages of pyrolysis between the compo-

nents of the blends, thus, hindering the continuous mass

loss. These interactions are, however, more pronounced

and dominant for D2 indicating the effectiveness of this

percentage, i.e., five of the additive. The amount of residue

at the completion of pyrolytic process has shown increase

while moving from D1 to D5. It is yet another clue of

stability. As the nature of products collected during and at

the end of degradation reveals a clear change, it can easily

be deduced that the interaction is chemical. Oligomers of

styrene are absent (they are present when the copolymer is

heated alone) and the presence of new compounds suggests

Scheme 3 Mechanisms for the formation of a-methyl styrene and

other minor products

Scheme 4 ‘Brominated’

anhydride ring and toluene

formation

Scheme 5 Ethylbenzene and benzene observed among degradation

products

Iran Polym J (2012) 21:143–155 153


123

the alteration in the way the two comonomers (styrene and

MMA) affect each other’s disintegration.

Acknowledgments The authors would like to express their grati-

tude to PINSTECH, Islamabad, Pakistan for providing the instru-

mentation facilities. Messrs Nadeem Ahmad, Muhammad Saleem

(Draftsman) and Muhammad Adeel Khattak (SA-II, CD) are

acknowledged for their technical assistance.

References

1. Chen H, Hu X, Cebe P (2008) Thermal properties and phase

transitions in blends of Nylon-6 with silk fibroin. J Therm Anal

Calorim 93:201–206

2. Sobhi H, Matthews ME, Grandy B, Masnovi J, Riga AT (2008)

Selecting polymers for medical devices based on thermal ana-

lytical methods. J Therm Anal Calorim 93:535–539

3. Varesano A, Tonin C, Ferrero F, Stringhetta M (2008) Thermal

stability and flame resistance of polypyrrole-coated PET fibres.

J Therm Anal Calorim 94:559–565

4. Gao M, Wu W, Yan Y (2009) Thermal degradation and flame

retardancy of epoxy resins containing intumescent flame retar-

dant. J Therm Anal Calorim 95:605–608

5. Polli H, Pontes LAM, Araujo AS, Barros JMF, Fernandes VJ

(2009) Degradation behavior and kinetic study of ABS polymer.


6. Ahmed J, Zhang JX, Song Z, Varshney SK (2009) Thermal

properties of polylactides; effect of molecular mass and nature of

lactide isomer. J Therm Anal Calorim 95:957–964

7. Worzakowska M (2009) The influence of chemical modification

of unsaturated polyesters on viscoelastic properties and thermal

behavior of styrene copolymers. J Therm Anal Calorim

96:235–241

8. Aboulkas A, Harfi KE, Bouadili AE, Nadifiyine M, Benchanaa M

(2009) Study on the pyrolysis of Moroccan oil shale with poly

(ethylene terephthalate). J Therm Anal Calorim 96:883–890

9. Szocik H, Jantas R (2004) Multimonomer and cross-linked

polymers formed by its copolymerization-thermal studies.


10. Grassie N, McNeill IC, Cooke I (1968) Thermal degradation of

polymer mixtures. I. Degradation of polystyrene-poly(methyl

methacrylate) mixtures and a comparison with the degradation of

styrene-methyl methacrylate copolymers. J Appl Polym Sci

12:831–837

11. Gentilhomme A, Cochez M, Ferriol M, Oget N, Mieloazynski JL

(2003) Thermal degradation of methyl methacrylate polymers

functionalized by phosphorus-containing molecules. II: Initial

flame retardance and mechanistic studies. Polym Degrad Stab

82:347–355

12. Zulfiqar S, Masud K, Ameer Q (2003) Thermal degradation

behavior of blends of phenyl methacrylate–styrene copolymers

with aluminum isopropoxide. J Therm Anal Calorim 73:877–886

13. Zulfiqar S, Masud K, Siddique B, Piracha A (1996) Thermal

degradation of phenyl methacrylate–styrene copolymers. Polym

Degrad Stab 52:293–299

14. Zulfiqar S, Masud K, Piracha A, McNeill IC (1997) Thermal

degradation of allyl methacrylate–methyl methacrylate copoly-

mers. Polym Degrad Stab 55:257–263

15. Zulfiqar S, Masud K (2000) Thermal degradation of blends of

allyl methacrylate–methyl methacrylate copolymers with alumi-

num ethoxide. Polym Degrad Stab 70:229–236

Table 3 Activation energies

and order of reactions for

copolymer (D) and copolymer–

additive blends, D1–D5

Blends’ code

P(S-co-MMA)–AlBr3

Eo (kJ/mol) Order of

reaction (n)

D 169.46 1

D1 52.72 1/2

D2 37.65 1/2

D3 52.72 1

D4 27.14 1

D5 45.18 1

Table 4 Horizontal burning rate for neat copolymer and P(S-co-MMA)–AlBr3 blends

Copolymer/blend code number D D1 D2 D3 D4 D5

Time to burn (s) 22 68 78 93 109 134

Length of strip (mm) 75 75 75 75 75 75

HBR (mm/s) 3.4 1.10 0.98 0.80 0.68 0.56

Fig. 9 Horizontal burning rate of copolymer (D) and its blends, D1–

D5

154 Iran Polym J (2012) 21:143–155


123

16. Zulfiqar S, Masud K, Ameer Q (2002) Thermal degradation of

blends of phenyl methacrylate–styrene copolymers with alumi-

num ethoxide. Polym Degrad Stab 77:457–464

17. Zulfiqar S, Masud K (2002) Thermal degradation of blends of

allyl methacrylate–methyl methacrylate copolymers with alumi-

num isopropoxide. Polym Degrad Stab 78:305–313

18. Arshad M, Masud K, Arif M, Rehman S, Chohan ZH, Arif M,

Qureshi AH, Saeed A, Salma U, Awan MS (2008) A comparative

study of roles played by aluminum tribromide and aluminum

acetylacetonate on the thermal degradation of PMMA by simul-

taneous thermoanalytical techniques. The Nucleus 45:63–72

19. Arshad M, Masud K, Arif M, Rehman S, Arif M, Zaidi JH,

Chohan ZH, Saeed A, Qureshi AH (2009) The effect of AlBr3

additive on the thermal degradation of PMMA: a study using TG–

DTA–DTG, IR and Py-GC–MS techniques. J Therm Anal Cal-

orim 96:873–881

20. Arshad M, Masud K, Arif M, Rehman S, Zaidi JH, Arif M, Saeed

A, Yasin T (2010) The thermoanalytical, infrared and pyrolysis-

gas chromatography–mass spectrometric sifting of poly (methyl

methacrylate) in the presence of phosphorus tribromide. Nat Sci

2:307–319

21. Arshad M, Masud K, Arif M, Rehman S, Saeed A, Zaidi JH

(2011) Characterization of poly(methyl methacrylate)–tin (IV)

chloride blend by TG–DTG–DTA, IR and pyrolysis-GC–MS

techniques. Bull Korean Chem Soc 32:3295–3305

22. Horowitz HH, Metzger G (1963) A new analysis of thermo-

gravimetric traces. Anal Chem 35:1464–1468

23. Riddick JA, Bunger WB, Sakano TK (1986) Organic solvents-

physical properties and methods of purification. Wiley, New

York

24. Priddy DB, Pirc M (1990) Purification of styrene for anionic

polymerization. J Appl Polym Sci 40:41–45

25. Seymour RB, Carraher CM Jr (1988) Polymer chemistry, an

introduction, 2nd edn. Marcel & Dekker, New York

26. Meyer VE (1967) Reactivity ratios of styrene and methyl meth-

acrylate at 90 �C. J Polym Sci Part A1. Polym Chem

5:1289–1296

27. Cabaness WR, Lin TYC, Parkanyi C (1971) Effect of pH on the

reactivity ratios in the copolymerization of acrylic acid and

acrylamide. J Polym Sci, Part A-1. Polym Chem 9:2155–2170

28. Lewis FM, Walling C, Cummings W, Briggs ER, Mayo FR

(1948) Copolymerization. IV. Effects of temperature and solvents

on monomer reactivity ratios. J Am Chem Soc 70:1519–1523

29. Nozaki N (1946) Reactivity of monomers in copolymerization.

J Polym Sci 1:455–465

30. Flammability Test, UL94, ASTM D 635.

31. Sain M, Park SH, Suhara F, Law S (2004) Flame retardant and

mechanical properties of natural fibre-PP composites containing

magnesium hydroxide. Polym Degrad Stab 83:363–367

32. Hurduc N, Cascaval CN, Schneider IA, Reiss O (1975) Etude de

la degradation thermique de copolymers: comparaison de ne-

langes de polymers, decopolymers sequences, statistiques et al-

ternes a bas de styrene et al. de methacrylate de methyl. Eur

Polym J 11:429–435

33. Gronowski A, Wojtezak Z (2003) Thermal stabilities of copoly-

mers of styrene with lithium, sodium and potassium acrylates and

methacrylates. Acta Polymerica 40:265–268

34. Cascaval CN, Schneider IA, Poinescu IGC, Butnaru M (1979)

Pyrolysis-gas chromatography of some copolymers of styrene.

Eur Polym J 15:661–666

35. Beldie C, Onu A, Bourceanu G, Poinescu IGC (1985) Glass

transition temperatures of some copolymers of styrene with

methyl methacrylate using DTA and chromatographic data. Eur

Polym J 2:321–323

36. Hamoudi A, McNeill IC (1978) Preparation and degradation of

copolymers of methyl methacrylate with alkali metal methacry-

lates-III, Quantitative studies of products of degradation to

500 �C. Eur Polym J 14:779–784

37. Smith AL (1979) Applied infrared spectroscopy fundamentals,

techniques and analytical problem-solving, John Wiley and Sons,

A Wiley-Interscience Publication, New York, pp 297–308

38. The Sadtler Standard Spectra, Sadtler Research Laboratories

(1974), Philadelphia, PA 5

39. Robinson JW (ed) (1974) CRC handbook of spectroscopy, vol II.

CRC Press, Inc, USA

40. Szymanski HA, Erikson RE (eds) (1970) Infrared Band Hand-

book, vol., 1 and 2, 2nd edn. IFI/Plenum, New York

41. Grassie N, Farish E (1967) The thermal degradation of copoly-

mers of styrene and methyl methacrylate. Eur Polym J 3:305–315

42. Grassie N, Grant EM (1966) The thermal degradation of

copolymer of a-chloroacrylonitrile with styrene and methyl

methacrylate. Eur Polym J 2:255–268

43. McNeill IC (1968) A study of the degradation of methyl meth-

acrylate polymers and copolymers by thermal volatilization

analysis. Eur Polym J 4:21–30

Iran Polym J (2012) 21:143–155 155


123

albr3 impact on the thermal degradation of p(s-co-mma): a study performed by contemporary techniques

Documents