GC/MS Identification of Pyrolysis Products from Fire-retardant Brominated Epoxy Resin


Balabanovich, A. I.

Journal of Fire Sciences 23(3): 227-245

2005


Brominated epoxy resins cured with diaminodiphenyl sulfone are thermally less stable than nonbrominated analogs. This thermal instability is likely to be caused by the formation of hydrogen bromide which destabilizes the epoxy network. As a result of the reaction of HBr with the epoxy resin, brominecontaining aromatics (brominated phenols, alkenyl aryl ether, hydroxyalkyl aryl ethers), as well as nonbromine-containing compounds form high-boiling decomposition products. The mass spectra of the brominated products collected from pyrolysis at 300 C in the open system under helium are presented and discussed.

GC/NIS
Identification
of
Pyrolysis
Products
from
Fire-retardant
Brominated
Epoxy
Resin
Al.
BALABANOVICH,
1
'
3
'*
M.P.
LUDA
1
AND
L.
()PERT?
1
Dipartimento
di
Chimica
IFM
dell'Universita
Via
P.
Giuria
7
10125
Torino,
Italy
3Dipartimento
di
Chimica
Generale
ed
Organica
Applicata
dell'Universia
C.so
Massimo
d'Azeglio
48
10125
Torino,
Italy
3
Guest
researcher
from
Research
Institute
for
Physical
Chemical
Problems
of
the
Belarusian
State
University,
ul.
Leningradskaya
14
220050
Minsk,
Belarus
(Received
March
10,
2004)
ABSTRACT:
Brominated
epoxy
resins
cured
with
diaminodiphenyl
sulfone
are
thermally
less
stable
than
nonbrominated
analogs.
This
thermal
instability
is
likely
to
be
caused
by
the
formation
of
hydrogen
bromide
which
destabilizes
the
epoxy
network.
As
a
result
of
the
reaction
of
HBr
with
the
epoxy
resin,
bromine-
containing
aromatics
(brominated
phenols,
alkenyl
aryl
ether,
hydroxyalkyl
aryl
ethers),
as
well
as
nonbromine-containing
compounds
form
high-boiling
decomposition
products.
The
mass
spectra
of
the
brominated
products
collected
from
pyrolysis
at
300°C
in
the
open
system
under
helium
are
presented
and
discussed.
KEY
WORDS:
pyrolysis,
electronic
scrap,
fire-retardant,
halogen,
GC/MS,
epoxy
resins,
tetrabromobisphenol
A,
brominated
phenols,
alkenyl
aryl
ethers,
hydroxyalkyl
aryl
ethers.
*Author
to
whom correspondence
should
be
addressed.
E-mail:
JOURNAL
OF
FIRE
SCIENCES,
VOL.
23
-
MAY
2005
227
0734-9041/05/03
0227-19
$10.00/0
DOI:
10.1177/0734904105047006
©
2005
Sage
Publications
228
A.I.
BALABANOVICH
ET
AL.
INTRODUCTION
A
DIGLYCIDYL
ETHER
of
bisphenol
A
(DGEBA)-based
epoxy
resin
is
widely
used
as
a
material
for
advanced
technologies,
in
particular,
in
the
manufacturing
of
printed
circuit
boards.
The
fire
risk
of
the
epoxy
resins
cured
with
a
traditional
curing
agent
4,4'-diaminodiphenyl
sulfone
(DDS)
is
a
major
drawback
of
these
materials.
Thus,
halo-
genated
fire-retardants
structures
are
copolymerized
to
decrease
the
flammability
of
epoxy
resins.
A
diglycidyl
ether
of
2,2-bis(3,5-dibromo-4-
hydroxyphenyl)propane
(DGEBTBA,
I)
is
the
most
commonly
used
comonomer
of
DGEBA
to
obtain
fire-retardant
materials.
Nowadays,
ever
increasing
quantities
of
polymeric
wastes
from
elec-
tronic
equipment
are
collected,
of
which
brominated
epoxy
resins
form
a
relevant
part.
The
thermal
treatment
of
these
wastes
is
a
promising
approach
of
recycling,
which
allows
recovery
of
energy
and
material,
in
particular
gold
and
precious
metals
from
printed
circuit
boards,
which
compensate
for
the
cost
of
the
whole
recycling
operation.
Despite
their
excellent
fire-retardant
qualities,
bromine-containing
structures
could
produce
corrosive
and
obscuring
smoke
and
might
give
supertoxic
halogenated
dibenzodioxins
and
dibenzofurans
when
burned.
Concern
exists
regarding
the
possibility
of
environmental
contamination
by
toxic
halogenated
dibenzofurans
and
dibenzodioxins
[1,2].
Analysis
of
human
adipose
tissues
showed
the
presence
of
halogenated
diphenyl
ethers,
suggesting
widespread
dispersion
of
these
materials
into
the
environment
[3].
In
this
respect,
environmentally
friendly
fire-retardant
systems
are
currently
being
developed
to
substitute
halogen-based
systems
in
recycling-designed
material
for
electronics.
However,
the
huge
amount
of
electronic
components
thrown
to
waste
still
contains
halogenated
fire-retardants.
From
the
environmental
point
of
view,
a
detailed
knowledge
of
the
mechanism
of
thermal
degradation
of
these
polymeric
materials
is
of
relevance
in
performing
the
appropriate
control
of
recycling
operation
[4].
Reportedly
[5-7]
DGEBTBA
and
brominated
epoxy
resin
(BER)
are
less
stable
at
high
temperatures
than
the
nonbrominated
epoxies.
By
means
of
the
FTIR
analysis
of
evolved
gases
and
GC/MS
it
was
shown
that
in
air
between
300
and
340°C
CO
2
,
H
2
O,
HBr,
methyl
acet-
aldehyde
and
other
aldehydes,
methanol
and
other
alcohols,
methyl
formate
and
esters,
and
several
brominated
and
unbrominated
phenols
were
released.
Amine,
silicone
[7],
and
copper
oxides
[8]
were
found
to
significantly
accelerate
the
thermal
decomposition
of
BER.
Creasy
[9]
applied
pyrolysis
Fourier
transform
mass
spectrometry
to
identify
BER
decomposition
products.
In
a
previous
work
[10]
the
authors
have
GC/MS
Identification
of
Pyrolysis
Products
229
shown
that
the
thermolysis
of
BER
occurs
in
three
steps:
decomposition
of
the
brominated
part
of
BER,
decomposition
of
the
nonbrominated
part
of
BER,
and
the
char
formation.
Brominated
aliphatics,
mono-
and
dibrominated
phenols
are
released
in
the
first
stage.
Nonbrominated
part
of
BER
decomposes
with
the
evolution
of
nonsubstituted
and
alkylsubstituted
phenols,
bisphenol
A,
and
alkoxyaromatics.
However,
analytical
problems
still
exist
in
identifying
the
pyrolytic
products
despite
the
huge
amount
of
work
being
carried
out
in
this
field
[11-18];
electronic
libraries
of
mass
spectra,
for
instance,
are
not
spe-
cially
devoted
to
these
compounds
in
spite
of
their
strong
biological
activity,
which
depends
on
the
substitution
grade
and
pattern.
In
an
effort
to
contribute
to
fill
this
gap,
we
present
the
results
obtained
from
a
systematic
research
on
pyrolysis
of
known
fire-
retardant
structures
[10,19-21],
which
enabled
us
to
collect
a
large
amount
of
MS
spectra
of
brominated
compounds.
Thus,
structures
of
degradation
products
can
be
deduced
from
pyrolytic
behavior
also
apart
from
GC-MS
data.
In
addition,
this
paper
contributes
to
the
discussion
of
the
degradation
mechanism
of
fire-retardant
brominated
epoxy
resin.
EXPERIMENTAL
Materials
Commercial
DGEBA
(Epikote
828EL,
Shell
Chemie,
Nederland)
and
DGEBTBA
(Shell
Chemie,
Nederland)
were
used
as
received
as
epoxy
monomers.
0
.
H
2
C—
HC—
H
2
C—
0
CH
3
C
CH
3
,0
\
0 -
CH2
-
CH
CH2
0
O
(DGEBTBA)
The
mixture
DGEBA—DGEBTBA
was
cured
with
85%
of
stoichio-
metric
amount
of
DDS,
(HT
976,
Ciba
Geigy,
Switzerland)
under
air
in
an
oven
heated
at
160°C
for
1
h
and
then
at
180°C
for
1
h.
The
obtained
epoxy
resin
(BER)
contained
20%
bromine.
Owing
to
the
deficient
230
A.I.
BALABANOVICH
ET
AL.
stoichiometry,
mainly
tertiary
amine
groups
were
present
in
the
final
network:
OH
I
...H
2
C-HC-H
2
C-
CH
3
0
i
CH
OH
O-CH
2
-CH
-CH
2
N,....
0=S:=0
0
Y
OH
I
-H
2
C-HC-H
2
C-O
Y
CH
3
'
C
I
CH
,
Y
14
-
CH2
-
CH
-
CH2
-
0v"
1
I
O
-
CH2
-
CH
-
CH
2
OH
I
OH
(BER)
Techniques
The
thermal
decomposition
pattern
was
mainly
studied
by
thermo-
gravimetry,
where
solid
residues
collected
at
different
steps
of
thermal
decomposition
were
analyzed
by
FTIR
[10].
Alternatively,
microscale
pyrolysis
was
carried
out
with
samples
of
500
mg.
The
thermal
degradation
procedure
has
been
described
in
detail
earlier
[22].
In
short,
the
high-boiling
degradation
products
(HBPs)
were
collected
under
helium
in
a
vertical
degradation
tube,
the
bottom
part
of
which
was
heated
at
10°C/min
up
to
300°C
and
held
at
this
temperature
for
15
min.
The
epoxy
resin
was
noticed
to
undergo
decomposition
at
the
pyrolysis
temperature
(300°C)
in
a
short
period
of
time,
followed
by
the
formation
of
a
charred
residue.
Because
of
this,
a
prolonged
heating
for
15
min
did
not
change
the
composition
of
HBPs
significantly.
As
soon
as
the
degradation
starts,
the
most
volatile
products
evolve
at
10-20
s
and
quickly
reach
the
cooled
walls
of
the
degradation
apparatus,
indicating
that
mostly
primary
degradation
products
were
trapped.
The
HBPs
condensed
in
the
upper
part
of
the
test
tube,
cooled
by
running
water,
were
washed
out
by
acetone.
The
acetone
solution
was
analyzed
by
GC/MS
(GC/MS
model
HP
5890/5970)
using
a
HP-5
30
m
IV
c
tor
resp
onse
Ill
2
II
3
0
GC/MS
Identification
of
Pyrolysis
Products
231
column
(outer
diameter
0.25
mm,
phase
thickness
0.25
µ)
with
the
following
heating
program:
2
min
at
70°C,
temperature
increases
to
280°C
at
a
rate
of
10°C/min
and
for
10-20
min
at
280°C.
In
addition,
gaseous
degradation
products
were
trapped
at
liquid
nitrogen
temperature
and
successively
analyzed
by
GC/MS
(GC/MS
model
HP
5890/5970).
The
mass
spectra
were
obtained
by
electron
ionization
at
70
eV
keeping
the
source
at
about
180°C.
Infrared
spectroscopy
investigations
were
carried
out
with
the
aid
of
a
Perkin
Elmer
FT-IR
spectrometer
(type
Spectrum
2000)
using
KBr
pellets.
RESULTS
Figure
1
shows
a
gas
chromatogram
of
HBPs
from
the
pyrolysis
of
BER.
The
pyrolysis
of
BER
resulted
in
the
formation
of
a
mixture
of
nonbrominated
and
brominated
compounds.
A
list
of
the
peaks
of
the
HBPs
are
presented
in
Table
1.
To
identify
the
compounds,
the
library
facility
of
the
GC/MS
system
was
utilized;
the
structures
identified
by
the
Wiley
and
NBS
libraries
are
indicated
with
an
asterisk
in
the
table
and
their
mass
spectra
are
not
further
discussed.
The
mass
spectra
of
2,4-
and
2,6-dibromophenols
(Compounds
5
and
6
in
Table
1)
were
published
in
[17],
whereas
that
of
2-bromo-4-isopropylphenol
(4),
2-bromo-4-isopropenylphenol
(7),
bromobisphenol
A
(15),
dibromo-
bisphenol
A,
and
tribromobisphenol
A
(18)
were
presented
in
[16].
However,
the
identity
of
most
of
the
structures,
including
the
two
isomers
of
dibromobisphenol
A
had
to
be
deduced
manually
using
fragmentation
pattern.
Their
mass
spectra
are
reported
in
Figures
2-12.
No
nitrogen-containing
thermally
produced
compounds
were
identified
in
the
HBPs.
VI
15
16
12
113
17
18
1
.
2
16
Retention
time
/
min
Figure
1.
The
total
ion
gas
chromatogram
of
the
acetone-soluble
HBPs
of
BER
collected
in
the
degradation
tube
in
an
inert
atmosphere.
Peak
assignment
in
Table
1.
V
I
6
VI
10
5
7
11
14
\AA.
20
24
232
A.I.
BALABANOVICH
ET
AL.
Table
1.
HBPs
emitted
during
pyrolysis
of
BER
in
helium.
Peak
No.
Compound
Mol.
Mass
(m/z)
1.
1,3-dibromo-2-propanol*
216
2.
2-bromophenol*
172
3.
2-bromo-4-ethylphenol
200
4.
2-bromo-4-isopropylphenol
214
5.
2,4-dibromophenor
250
6.
2,6-dibromophenor
250
7.
2-bromo-4-isopropenylphenol
212
8.
3-bromoprop-1-enyl
phenyl
ether
212
9.
3-bromo-2-hydroxypropyl
phenyl
ether
230
10.
2,6-dibromo-4-isopropylphenol
292
11.
2,6-dibromo-4-isopropenylphenol
290
12.
3-bromo-2-hydroxypropyl
4-isopropylphenyl
ether
272
13.
bromo-p-hydroxybiphenyl
248
14.
1,2-dibromopropyl
4-isopropylphenyl
ether
334
15.
2-(3-bromo-4-hydroxyphenyl)-2-(4-hydroxyphenyl)propane
306
16.
2,2-bis(3-bromo-4-hydroxyphenyl)propane
384
17.
2-(3,5-dibromo-4-hydroxyphenyl)-2-(4-hydroxyphenyl)propane
384
18.
2-(3,5-di
bromo-4-hyd
roxyp
henyI)-2-(3-bromo-4-hydroxyp
henyl)
propane
462
I
phenol*
94
II
3-methyl
benzofu
ran*
132
III
ethyl
p
henol*
122
IV
4-isopropylphenol*
136
V
3,4-d
ihydro-2H-1-benzopyran-3-ol*
150
VI
p-hyd
roxybi
phenyl*
170
VII
bisphenol
A*
228
*
Identification
by
Wiley
or
NBS
libraries.
Roman
Numbering:
nonbrominated
compounds.
Arabic
Numbering:
bromine
containing
structures.
Br
Cg1iaCIBr2
HO
0
198
119
1
134
40
8C..
120
160
200
24C
286
rn/z
Figure
2.
The
mass
spectrum
of
2,
6-dibromo-4-isopropylphenol
(peak
10
in
Figure
1).
ter
63
_
B9
I
7f
„,111..,4
277
292
Br
0 0
119
77
91
I
125
165
GC/MS
Identification
of
Pyrolysis
Products
233
HO
132
290
I
i
h
111
.
A I li
(
Ili
1
1
11..
kim..
.
,....._..
_.....,
198
ilt
1
03
250
1
2751
40
BO
120
160
rniz
200
240
2K
Figure
3.
The
mass
spectrum
of
2,6-dibromo-4-isopropenylphenol
(peak
11
in
Figure
1).
77
a
191
C
0
:
8•
212
40
80
1
20
160
2+0
240 260
ni!z
Figure
4.
The
mass
spectrum
of
2-(3-bromo-4-hydroxyphenyl)-2-(4-hydroxyphenyl)-
propane
(peak
15
in
Figure
1).
r
Br
C
1
5H1402B
r2
HO
0 0
OH
369
386
y.
40
105
134
152
I
118
I
165
-
80
120
160
197
213
275
290
I
1
1
I
A.•
it
Li
.
28
200
frI/Z
240
0
320 360
Figure
5.
The
mass
spectrum
of
2,2-bis(3-bromo-4-hydroxyphenyl)propane
(peak
16
in
Figure
1).
In
Figure
2,
the
mass
spectrum
of
the
first
unknown
is
shown.
The
peaks
at
m/z
=
51,
53,
63,
and
77
indicate
the
presence
of
a
benzene
ring.
The
isotopic
cluster
at
m/z
292/294/296
(ratio
1
:
2
:
1), which
are
molecular
ions
indicates
the
presence
of
two
bromine
atoms
and
the
234
A.I.
BALABANOVICH
ET
AL.
C
15E11402B
r2
0 0
OH
369
HO
40
80
120
160
277
..di
yi..1..1.11111d1.401.161,11
•4
i
d
1
ll
il
e
A
.1,016
.40..
id
.
Al
r
.
l
e
.
..111
1
II.
...id.
,
.
I
I.
,
m/z
200
240
280
320
360
105
119
135
211
386
Figure
6.
The
mass
spectrum
of
2-(3,5-dibromo-4-hydroxyphenyl)-2-(4-hydroxyphe-
nyl)propane
(peak
17
in
Figure
1).
Br Br
Ci5F11302Br3
HO
0 0
OH
197
118
134
181
291
370
210
105
,
277
,
1
1
152
I I
1
/
213
I I
I
50
100
150
200 250
t11/Z
300
350
400
Figure
7.
The
mass
spectrum
of
2-(3,5-dibromo-4-hydroxypheny0-2-(3-bromo-4-
hydroxypheny0propane
(peak
18
in
Figure
1).
119
C91
-
190Br
O
OCH=CHCH
2
Br
464
447
450
105
133
212
51
77
9
I,
L.,
11,11
.LEI
40
80
120
rniz
160
200
Figure
8.
The
mass
spectrum
of
3-bromoprop-1-enyl
phenyl
ether
(peak
8
in
Figure
1).
elemental
composition
is
C
9
H
10
OBr
2
.
The
molecular
ion
shows
an
easy
loss
of
a
methyl
group.
These
data
are
fitted
by
2,6-dibromo-4-
isopropylphenol
(10);
the
substituent's
position
in
the
ring
corresponds
to
that
of
tetrabromobisphenol
A
(TBBPA),
which
is
the
starting
Br
CH3CHCH-0
Br
O
136
161
GC/MS
Identification
of
Pyrolysis
Products
235
EirChPiCHCH9-0
C
13
1-1
11
0
2
13r
OH
77
107
94
80
,
119
133
137
.
.
J
,
.
1
2n.
1
rniZ
186
200
51
57
40
Figure
9.
The
mass
spectrum
of
3-bromo-2-hydroxypropyl
phenyl
ether
(peak
9
in
Figure
1).
121
BrCH
2
CHCH
2
-0
OH
O
Cl2H1702Br
179
mlz
260
2;10
Figure
10.
The
mass
spectrum
of
3-bromo-2-hydroxypropyl
4-isopropylphenyl
ether
(peak
12
in
Figure
1).
91
77
136
107
51
57
6
I
149
,
5
.1
„ii,
Ili
40
80
120 160
257
272
176
I
,
Ai
J
ii
..111,
..
.1
1,
ii
,
..
I
I
, I .
I
J'
40
80
120
160
m/z
200
240
280
320
Figure
11.
The
mass
spectrum
of
1,2-dibromopropyl
4-isopropylphenyl
ether
(peak
14
in
Figure
1).
pyrolysis
material
for
(10).
The
molecular
ion
shows
four
competing
decomposition
pathways
due
to
(1)
loss
of
a
CH
3
Br
moiety
(m/z
292/294/296
—>
198/200),
(2)
loss
of
a
methyl
radical
(m/z
292/294/296—*
277/279/281),
121
91
65
I
107
C121
-
11606
r2
334
239
319
236
A.I.
BALABANOVICH
ET
AL.
0 0
OH
Ci2H9BrO
248
Br
139
40
80
120
M/Z
160
200
r
240
Figure
12.
The
mass
spectrum
of
bromo-p-hydroxybiphenyl
(peak
13
in
Figure
1).
(3)
loss
of
a
bromine
radical
(m/z
292/294/296
—>
213/215),
(4)
loss
of
COH
(m/z
292/294/296
—>
263/265/267).
The
main
degradation
pathways
of
2-bromo-4-isopropylphenol
(4)
[16]
are
as
in
the
previous
case.
However,
the
effect
of
the
second
bromine
on
the
fragmentation
pattern
of
the
molecular
ion
is
evident:
Path
1
in
the
spectrum
of
(4)
is
preserved
but
the
fragment
stability
(m/z
198/
200)
is
lowered;
the
spectrum
is
dominated
by
the
loss
of
a
methyl
radical
(path
2).
The
other
competing
decompositions
due
to
the
loss
of
bromine
and
COH
radicals
are
not
influenced
as
the
intensity
of
the
corresponding
ions
is
comparable
(Figures
2
and
3
in
[16]).
The
ions
at
m/z
=
290/292/294,
275/277/279,
and
250/252/254
(Figure
3)
contain
two
bromine
atoms,
and
the
250/252/254
is
that
of
dibromophenol,
most
probably
2,6-bromophenol
because
of
the
initial
structure
of
BER.
The
transitions
m/z
290/292/294
—>
275/277/
279
and
290/292/294
—>
250/252/254
appear
to
be
due
to
the
loss
of
methyl
radical
and
CHC—CH
3
and
would
support
the
structure
of
2,6-dibromo-4-isopropenylphenol
(11),
showing
similarities
to
those
of
2-bromo-4-isopropenylphenol
(Figure
3
in
[16]).
The
next
four
mass
spectra
(Figures
4-7)
show
similarities,
because
they
are
derived
from
TBBPA
by
the
loss
of
3,
2,
2,
and
1
bromine
atoms.
The
main
degradation
pattern
they
all
share
is
(1)
loss
of
CH
3
Br
(Figure
4:
m/z
306/308
—>
212;
Figures
5
and
6:
m/z
384/386/388
—>
290/292;
Figure
7
—>
m/z
462/464/466/468
—>
368/370/
372).
(2)
loss
of
a
methyl
radical
followed
by
a
more
or
less
intense
loss
of
CH
3
Br
(Figure
5:
m/z
306/308
—>
291/293
—>
197;
Figures
6
and
7:
m/
z
384/386/388
—>
369/371/373
—>
275/277;
Figure
8:
m/z
462/464/466/
468
—>
447/449/451/453
—>
353/355/357).
115
[1,1
J
„II,
.
11111
II
I
,
II
168
GC/MS
Identification
of
Pyrolysis
Products
237
A
further
common
degradation
pattern
is
proposed
in
Scheme
1.
Br
;-
r
HO
OH
OH
+
HO
\
/
Y
(A)
Y
3„7„....
Y
=
H:
m/z
=
135
CH4
Y
=
Br
m/z
=
213/215
Y
=
Br
OH
-
Br.
Y
=
Br
m/z
=
134
-N.
m/z
=
118
Y
-
Br.
Y=
H:
m/z
=
119
Y
=
Br
m/z
=
197/199
Scheme
1
The
mass
at
m/z
=135
in
the
mass
spectrum
of
2-(3-bromo-4-
hydroxyphenyl)-2-(4-hydroxyphenyl)propane
(Figure
4)
can
be
attrib-
uted
to
4-isopropylphenol
ion
(A,
Y
=
H),
formed
in
accordance
with
Scheme
1.
The
origin
of
the
other
most
important
ions
is
presented
in
Scheme
1.
The
importance
of
the
fragmentation
presented
here
is
that
it
allows
to
distinguish
between
the
mass
spectra
of
two isomers
2,2-bis(3-
bromo-4-hydroxyphenyl)propane
(16,
Figure
5)
and
2-(3,5-dibromo-4-
hydroxyphenyl)-2-(4-hydroxyphenyl)propane
(17,
Figure
6).
The
mass
spectrum
of
(16)
shows
peaks
at
m/z
=
211/213,
197/199,
and
118,
whereas
that
of
(17)
displays
a
peak
at
m/z
=
135,
whose
origin
is
explained
in
Scheme
1.
The
mass
spectrum
of
2-(3,5-dibromo-4-hydroxypheny1)-2-(3-bromo-4-
hydroxyphenyl)propane
(18,
Figure
7)
is
also
supported
by
ions
pre-
sented
in
Scheme
1
at
m/z
213/215
and
134.
However,
the
successive
losses
of
bromine
and
COH
radicals
from
the
ions
at
m/z
=
368/370/372
are
evident
as
depicted
in
Scheme
2.
m/z
462/464/466/468
-A-
368/370/372
-)"-
289
/
291
-CH
3
Br
--
Br
1
--
Br
152
-4-
181E-
210
-
COH
-
COH
Scheme
2
In
Figure
8,
ions
at
m/z
=
51,
77,
91,
105,
119
indicate
the
presence
of
an
aromatic
ring.
The
fragmentations
from
m/z
133
to
m/z
105
and
from
\ /
238
A.I.
BALABANOVICH
ET
AL.
m/z
119
to
m/z
91
are
most
probably
due
to
the
loss
of
CO,
suggesting
an
oxygen
atom
in
the
unknown
substance.
The
molecular
formula
C
9
H
9
OBr
corresponds
to
the
molecular
ion
at
m/z
=
212/214
and
is
an
isomer
of
(7).
The
unknown
substance
is
regarded
as
3-bromoprop-1-
enyl
phenyl
ether
(8).
The
molecular
ion
of
(8)
shows
a
rather
facile
loss
of
CH
2
Br
(212/214
—>
119)
than
bromine
radicals;
that
is
indicative
of
an
aliphatic
bromide
[23].
The
largest
peak
in
the
mass
spectrum
illustrated
in
Figure
9
is
at
m/z
=
94
which
is
usual
for
alkyl
aryl
ethers
[24].
The
ions
at
m/z
=
230/232
point
to
the
presence
of
one
bromine
and
two
oxygen
apart
from
the
phenyl
ring
and
aliphatic
chain.
Taking
into
account
the
initial
structure
of
BER,
3-bromo-2-hydroxypropyl
ether
(9)
can
account
for
the
mass
spectrum
(Figure
9).
This
is
supported
by
the
degradation
pattern
of
the
molecular
ion
being
the
loss
of
bromine
(m/z
=
230/
232
—>
151),
methylene
bromide
(m/z
230/232
—>
137),
and
2-bromo-
1-
hydroxyethyl
radicals
(m/z
230/232
—>
107).
Ions
at
m/z
=
151
and
137
show
successive
loss
of
water.
A
rearrangement
[24]
is
likely
to
be
responsible
for
the
origin
of
m/z
=
94,
as
presented
in
Scheme
3
(R
=
H)
representing
a
typical
McLafferty
transposition.
/
CH,
C
OH
CH
2
Br
0
H
2
R
=
H:
m/z
=
230/232
R
=
C
3
H
7
:
m/z
=
272/274
C
H2Br
Hi
0
CH
2
R
=
H:
m/z
=
94
R
=
C
3
H
7
:
m/z
=
136
Scheme
3
The
m/z
=
57
ion
appears
to
be
CH
3
COCH
2
+
,
which
can
be
formed
in
accordance
with
Scheme
4.
CH2
H
/
I
OH
C
H2
m/z
=
151
H
+
0
0
CH2
CH
2
C~
OH
C
CH2
CH
3
m/z
=
57
Scheme
4
The
next
mass
spectrum
(Figure
10)
shows
similarity
with
the
pre-
vious
one.
In
view
of
the
presence
of
the
peaks
at
masses
at
m/z
=
136,
GC/MS
Identification
of
Pyrolysis
Products
239
121,
107,
91,
77,
65,
51
it
can
be
inferred
that
the
compound
is
a
derivative
of
isopropylphenol.
The
molecular
ion
at
m/z
=
272/274
is
consistent
with
3-bromo-2-hydroxypropyl
p-isopropylphenyl
ether
(12)
referring
to
the
initial
structure
of
BER.
Like
the
previous
compound,
it
shows
masses
due
to
the
loss
of
methylene
bromide
(m/z
=
272/274
—>
179)
and
2-bromo-l-hydroxyethyl
radicals
(m/z
=
272/274
—>
149).
The
origin
of
the
mass
at
m/z
=
136
is
depicted
in
Scheme
3
(R
=
C
3
H
7
).
The
molecular
ion
at
m/z
=
334/336/338
(Figure
11)
is
postulated
to
be
C12H16OBr2
and
the
presence
of
p-isopropylphenol
in
the
structure
is
evident
due
to
masses
at
m/z
=
136,
121,
107,
91,
65.
Loss
of
CH
3
or
Br
2
gives
rise
to
ions
at
m/z
=
319/321/323
and
176,
which
eliminates
Br
2
or
CH
3
to
give
m/z
=
161
species.
The
last
fact
could
be
due
to
the
vicinal
position
of
bromine
in
the
molecule.
No
(M
CH
2
Br)
±
ions,
char-
acteristic
of
the
terminal
CH
2
Br
group
[23],
are
present
in
the
spectrum.
Therefore,
the
structure
is
supposed
to
be
1,2-dibromopropyl
p-iso-
propylphenyl
ether
(14).
The
origin
of
some
important
ions
is
suggested
in
Scheme
5.
p-Isopropylphenol
could
be
formed
in
the
rearrangement
identical
to
that
presented
in
Scheme
3.
m/z
=
334/336/338
Br
2
m/z
=
176
-.D.
-• CH3
--)p.
-• CH3
Scheme
5
m/z
=
334/336/338
Br
2
m/z
=
161
The
doublet
molecular
ion
at
m/z
=
248/250
(Figure
12)
corresponds
to
C
12
H
9
0Br.
The
transition
248/250
—>
168
point
out
to
the
loss
of
HBr
and
that
at
139
to
the
loss
of
COH
2
Br
moiety.
The
structure
of
bromo-p-
hydroxybyphenyl
(13)
is
designed
for
correspondence
with
its
homo-
logue,
the
nonbrominated
p-hydroxybiphenyl
(VI).
DISCUSSION
Amino-cured
epoxy
resins,
either
fire-retarded
with
reactive
TBBPA
units
or
non
fire-retarded,
exhibit
under
dynamic
heating
in
nitrogen
a
sudden
loss
of
about
40-60%
of
initial
weight
at
290-400°C,
followed
by
a
smoother
degradation
[10,25].
Usually
20-30%
of
residue
is
left
at
240
A.I.
BALABANOVICH
ET
AL.
600°C
[10,25,26].
Simple
TBBPA
[21]
and
a
brominated
epoxy-polymer
(BEP)
show
similar
behavior
[25].
0—CH2-C
I
H—CH2
OH
n
(BEP)
The
temperature
at
which
the
first
abrupt
degradation
occurs
however
is
very
much
dependent
on
the
structure
of
the
resins
and
on
the
presence
of
TBBPA
units
in
particular.
Dynamic
thermogravimetric
analysis
shows
that
the
fire-retardant
brominated
epoxy
resins
are
less
thermally
stable
than
the
nonbrominated
ones
[25]
with
the
abrupt
weight
loss
occurring
about
50°C
earlier
in
the
bromine
containing
structures.
The
HBPs
and
gaseous
products
(bromomethane,
acetone,
bromoethane,
2-bromopropane,
2-
and
3-bromopropenes,
HBr)
evolve
during
this
step
of
decomposition.
Thus
apparently
the
effect
of
bromine
in
the
resins
is
its
advance
thermal
degradation.
At
the
very
beginning
of
the
degradation,
only
a
small
amount
of
HBr
is
evolved
from
bromine
containing
structure,
major
volatilization
of
light
fragments
occur
instead
[27].
Moreover,
brominated
DGEBA/methylenedianiline
epoxy
resins
are
less
thermally
stable
than
BEP
[25],
indicating
a
coeffect
of
the
nitrogen-containing
structure
on
the
stability
of
the
epoxy
network.
Destabilization
of
the
epoxy
network
can
be
imputed
to
the
effect
of
HBr
which
is
able
to
form
an
unstable
tert-amine
hydrobromides
(VIII),
as
shown
in
Scheme
6.
The
salt
(VIII)
gives
rise
to
broad
absorption
bands
between
2700
and
2500
cm
-1
in
the
IR
spectrum
for
the
solid
residue
of
BER
obtained
on
heating
at
300°C
in
a
closed
system
under
nitrogen
(Figure
13).
Figure
13
shows
the
IR
spectrum
of
the
initial
BER
also
for
comparison.
Above
200°C
the
amine
salt
decomposes,
and
one
of
the
decomposition
products
is
the
alkyl
bromide
(IX).
This
reaction
is
known
in
organic
chemistry
as
a
halo-deamination
process,
a
side
reaction
of
the
Hofmann-Martius
reaction
[28].
The
compound
(IX)
gives
rise
to
products
9
and
12.
In
addition,
HBr
causes
the
decomposition
of
aliphatic-aromatic
ethers;
a
reaction
known
from
literature
as
halo-
dealkoxylation
[28].
In
this
particular
case,
the
reaction
yields
product
(1)
from
(IX)
(Scheme
6)
and
a
phenol
derivative
which
can
give
rise
to
products
I
and
IV
(Table
1).
r r
o
o
r r
GC/MS
Identification
of
Pyrolysis
Products
241
O
(VIII)
Br9
®
H
0-CH
2
-CH-CH
2
-N-CH
2
«.
OH
1
-
•""wC6H4NHCH2m
,
O
b
a
o
(IX)
O
0-CH2-
?
H-CH2-Br
a
\
OH
l/
product
12
O
-CH2-
?
H-CH2-Br
OH
\F
t
HBr
O
OH
+
OH
BrCH
2
CHCH
2
Br
product
1
O
0-CH2-
?
H-CH2-Br
OH
product
9
Scheme
6
Appearance
of
a
brominated
phenol
derivative
(X)
is
likely
to
proceed
either
through
the
reaction
of
BER
with
HBr
(halo-dealkoxylation)
or
splitting
of
the
glycidyl
backbone
[10].
Like
TBBPA
[21],
the
derivative
(X)
is
expected
to
be
unstable
above
280°C
and
is
able
to
eliminate
the
bromine
radical.
A
possible
mechanism
shown
in
Scheme
7
is
related
to
the
formation
of
thermally
less
stable
cyclohexadienone
structure
(XI)
due
to
keto-enol
tautomerism.
The
intermediate
(XI)
generates
bromine
and
phenoxyl
radicals
due
to
scission
of
the
C(allylic)—Br
bond,
which
is
to
a
marked
degree
lower
in
energy
than
3418
2965
93
1
465
1361
1
1182
1000
I
1035
827
737
568
1
04
2929
13
686
912
87_
A
BER
3202
150
-7
49
1452
122
754
822
558
1299
2664
2546
residue
300
°C
3000
2000
1500 1000
400,0
em
-t
Figure
13.
The
infrared
spectra
of
the
BER
and
its
solid
residue
obtained
on
heating
at
300°C
in
a
closed
system
under
nitrogen.
4000,0
H
(XI)
r
\-•
Br
Br
Br
a
0
+
RH
-4
-
R
0
242
A.I.
BALABANOVICH
ET
AL.
the
C(arom)-Br
bond.
In
its
turn,
the
phenoxyl
radical
abstracts
proton
from
hydrogen
donors,
thereby
completing
the
debromination.
Formation
of
the
volatile
products
2,4,
as
well
as
15-18
(refer
Table
1)
would
occur
in
this
way.
Br
Br
0
Br
(30
r
0
product
2
Br
0
product
4
Scheme
7
Thermal
lability
of
ortho/para-bromophenols
containing
structures
is
widely
recognized
[4,17,18,29].
Through
this
reaction,
a
relatively
large
amount
of
very
mobile
Br
radicals
are
injected
into
the
system
at
a
relatively
low
temperature,
which
likely
propagates
H
abstraction
and
0-scission
processes
leading
to
HBr
and
volatile
fragments
formation.
Neither
hydroxybiphenyl
(VI)
nor
bromophenylphenol
(14)
was
found
in
the
thermal
degradation
of
tetrabromobisphenol
A
[17,21]
whereas
they
are
relatively
abundant
in
the
thermal
degradation
of
BER.
Thus
it
is
likely
that
these
are
formed
involving
condensation
of
the
glycidyl
structure
and
successive
dehydrogenation.
Besides
the
degradation
reactions
presented
herein,
crosslinking
occurs.
For
instance,
products
containing
dioxin-like
rings
have
been
found
from
2,4
dibromophenol
thermal
degradation
[4],
a
similar
reaction
occurring
on
a
bifunctional
bisphenol
A-based
structure
will
lead
to
dioxin-like
rings
blocked
in
the
residue.
Moreover,
macroradicals
formed
by
H
abstraction
could
contribute
to
the
cross-linking
of
the
residue
by
the
coupling
or
polymerization
of
double
bonds.
CONCLUSIONS
The
major
thermal
(290-310°C)
instability
of
amino-cured
bromi-
nated
epoxy
resins
is
likely
to
be
caused
by
the
formation
of
hydrogen
GC/MS
Identification
of
Pyrolysis
Products
243
bromide,
which
destabilizes
the
epoxy
network.
As
a
result
of
the
reaction
with
HBr,
bromine-containing
aromatics
are
evolved
amongst
HBPs
(at
300°C
about
30%
of
the
polymer
is
decomposed,
and
the
HBPs
quickly
condense
on
the
cooled
walls
of
the
reactor).
However,
no
halogenated
dibenzofurans
and
dibenzodioxins
have
been
found
amongst
the
major
degradation
products
of
such
resins
in
the
present
pyrolytic
conditions
(oxygen
and
a
higher
temperature
may
however
have
a
dramatic
effect
on
the
pyrolysis
products
distribution).
This
makes
the
low-temperature
pyrolysis
of
TBBPA-based
epoxy
resins
relatively
free
from
the
risk
of
persistent
organic
pollutant
production.
Nevertheless,
the
high
boiling
fraction
containing
brominated
com-
pounds
is
unsuitable
for
further
processes
(i.e.,
of
energy
recovery)
and
the
cross-linked
residue
should
be
treated
as
well,
as
it
still
contains
bromine.
Thus
a
further
effort
is
expected
in
order
to
redirect
the
pyrolytic
process
toward
a
controlled
elimination
of
bromine
for
instance
by
using
scavengers
or
appropriate
additives.
In
this
respect,
the
knowledge
of
mass
spectra
of
a
large
selection
of
brominated
compounds
is
of
relevance
in
determining
the
change
of
the
degradation
mechanism
under
the
modified
pyrolysis
conditions.
ACKNOWLEDGMENT
MPL
is
grateful
to
the
European
Community
for
funding
this
work
in
the
frame
of
competitive
and
sustainable
growth
(Growth)
programme
GIRD-CT-2002-03014.
The
authors
are
thankful
to
one
of
the
referees
for
the
careful
reading
of
the
manuscript.
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