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Polymer International 39 (1996) 289-293
Preparation and Properties of
Bismaleimide Resins of Aromatic
Sulfone Ether Diamine
Lianlai Zhang,* Qitai Jiang, Luxia Jiang & Xingxian Cai
Department of Polymer Science and Materials, Sichuan Union University, Chengdu 610065, People's Republic of China
(Received 15 September 1995; accepted 14 October 1995)
Abstract: Aromatic sulfone ether diamine, bis[4-(4-aminophenoxy)phenyl]sulfone (SED), was prepared by the nucleophilic aromatic substitution of 44'dichlorodiphenylsulphone by p-aminophenolate. The reaction was conducted in
the presence of excess potassium carbonate as a weak base, toluene as the dehydrating agent and N-methylpyrrolidone as the dipolar aprotic solvent. SED
showed good solubility in common organic solvents, such as dioxan, tetrahydrofuran, butanone and acetone. SED was reacted with maleic anhydride to
obtain aromatic sulfone ether bismaleimide, bis[4-(4-maleimidophenoxy)phenyl]sulfone (SEM). The compounds were characterized by FTIR and 'H NMR
analysis. Furthermore, copolymer resins of SED with 4,4'-bismaleimidodiphenyl
methane (BMI) and SEM were prepared. After curing, crosslinked resins with
better thermal stability resulted. The temperature at maximum rate of weight
loss (T,,J and the heat-resistant temperature index (TJ in air were found to be
426"C, 208°C and 579"C, 221°C for BMI/SED and SEM/SED resins, respectively. Compared with the corresponding 4,4'-diaminodiphenyl methane (DDM)
system, BMI/SED and SEM/SED showed a slight decrease in T,,, and q. SEDmodified BMI/amine resin based glass cloth laminates for printed circuit boards
showed higher mechanical properties than those of the corresponding unmodified system. With SED instead of the original amine component in 3-5% weight
fraction, the tensile strength, flexural strength and impact strength of the laminates increased markedly. Meanwhile, the stripping strength and weld resistance
were also improved by the addition of SED.
K e y words: aromatic sulfone ether diamine, copolymer resins, thermal stability,
glass cloth laminates, mechanical properties, modifier.
INTRO DUCTlON
However, the brittle nature of these resins remains a
weakness. Moreover, the low basicity of the amine due
to the electron withdrawing sulfone group, and its low
activity limits its use for thermoplastics. For example,
when DDS was reacted with dianhydride to prepare
polyimides, only low molecular weight product was
obtained because of the hydrolysis of the polyamic acid
intermediate.'
Aromatic sulfone ether diamine (SED), bis[4-(4aminophenoxy)phenyl]sulfone, is another sulfonecontaining aromatic diamine, whose activity is comparable with that of diaminodiphenylether. SED has
found application in the modification of epoxy resins.2
The aromatic ether bond offers advantages in improving fracture toughness and hot-wet properties of the
Aromatic diamines are very important as monomers for
the synthesis of various thermoplastic polymers, such
as polyamides, polyimides and polyureas. They are also
widely used in thermosets as the curing agent for
epoxies, or chain extender for bismaleimides. In order
to improve the mechanical and thermal properties of
these resins, aromatic diamines bearing rigid groups,
such as sulfone, e.g. diaminodiphenylsulfone (DDS), are
often used to modify epoxy and bismaleimide resins.
* To whom correspondence should be addressed at: Chengdu
Institute of Organic Chemistry, Academia Sinica, Chengdu
610041, People's Republic of China.
289
Polymer International 0959-8103/96/$09.00 01996 SCI. Printed in Great Britain
290
resulting cured resins. SED can also be used in the synthesis of polyamides, polyimides, and poly(amideimide)s and in the modification of bismaleimides. The
last named has received less attention.
In this paper, we describe the synthesis of SED by a
new, convenient procedure. The SED was then introduced into bismaleimide resin systems, and the properties of the modified resins were investigated.
EX PER IM ENTAL
Materials
p-Aminophenol was recrystallized from anhydrous ethyl
alcohol under nitrogen, then vacuum dried. 4,4'Dichlorodiphenylsulphone (DCDPS) was recrystallized
from toluene, and dried under vacuum. N-Methylpyrrolidone (NMP) was treated with calcium hydride
for 24 h and vacuum distilled.
Anhydrous potassium carbonate, maleic anhydride
(MA), 4,4'-bismaleimidodiphenyl methane (BMI), 4,4diaminodiphenyl methane (DDM), toluene, N,N'-dimethylacetamide (DMAC) and other reagents were used
as received.
Synthesis of SED
SED was synthesized by nucleophilic aromatic substitution of DCDPS by the phenolate of p-aminophenol.
The reaction was conducted in the presence of excess
potassium carbonate as a weak base, toluene as the
dehydrating agent and N M P as the dipolar aprotic
solvent.
Thus, to a 500 ml four-necked round-bottom flask,
fitted with a condenser, Dean-Stark trap, nitrogen inlet,
a thermometer and a mechanical stirrer, DCDPS
(44.5 g, 0.155 mol), p-aminophenol (38.73 g, 0.355 mol,
14% excess to DCDPS) and NMP (250 ml) were added.
Then, anhydrous potassium carbonate (27.0 g,
0.195mol) and toluene (120ml) were charged to the
flask. The reaction mixture was stirred under purge of
nitrogen and first heated to reflux (about 140"C), and
maintained at this temperature for 3 h. Then the toluene
was removed and the temperature was raised to 175°C
for another 4h. After cooling to 100°C, the reaction
mixture was coagulated in 2 litre water, and neutralized
with dilute HCl. The precipitate was filtered, washed
with water, finally washed with methanol and dried.
The crude product was dissolved in DMAC, reprecipitated to remove unreacted p-aminophenol and any
trapped salts, filtered and dried in a vacuum oven at
100°C. The yield was above 85%, with m.p. of 192°C.
L-L. Zhang et al.
mixture was stirred for 15min, then cooled with ice to
O"C, and MA (3-2g, 0.0326mol) was added. The reaction was maintained at 15-20°C for l h to form the
amic acid intermediate.
Then by adding acetic anhydride and triethylamine,
the cyclization of the amic acid was carried out immediately. The temperature of the reaction was maintained
at 20°C for 4 h, and then raised to 60°C for another 2 h.
After cooling, the solution was poured into 250 ml cold
water. The precipitate was collected by filtration,
repeatedly washed with methanol and dried at 50°C in
a vacuum oven. The product was a light grey powder,
the yield about 87.8%.
Preparation of modified B MI resins
SED (4.3 g, 0.00995 mol) and DMAC (25ml) were
added to a 100ml three-necked flask equipped with a
condenser, a thermometer, and a mechanical stirrer.
The mixture was heated to 90-95"C7 and BMI (13.3g,
0.0364mol in 50ml DMAC solution) was added
through a funnel over 15min. After another 30min, the
solution was cooled with ice to below 30"C, and poured
into water. A dark red precipitate resulted, which was
filtered off.
Using a similar procedure, other copolymer resins
were prepared. They were cured at 180°C for 2 h, 200°C
for 4 h, and postcured at 250°C for 40 min. The SEDmodified BMI/amine resins were prepolymerized in
acetone, then glass cloths were immersed in the solution, dried, and processed to printed circuit board,
which was covered with copper foil on one side. The
laminates were about 1.5 mm thick.
Instrumentation
Melting point was measured with a CDR-1 differential
thermoanalyser in air at a heating rate of lO"C/min.
FTIR spectra were recorded on a Nicolet 20 SXB-IR
spectrophotometer, using KBr disc samples. 'H NMR
was performed on a Varian FT-80 NMR instrument
using CD,COCD, as solvent, and TMS as internal
standard. Thermal stability of the cured resins was
studied using a Perkin-Elmer TG-7 thermogravimetric
analyser at a heating rate of 10"C/min in air, or nitrogen. Mechanical properties were measured using a
laboratory mechanical tester.
RESULTS AND DISCUSSION
Synthesis of SED
Reaction of SED with MA
SED (6.0g, 0.0139mol) and DMAC (50ml) were
charged to a 100ml three-necked flask, equipped with a
condenser, a thermometer, and mechanical stirrer. The
The synthesis of SED was previously studied by Kawakarni,,q4 and this was followed by several Japanese
patents.'-' In summary, these reactions were carried
out in dimethylsulfoxide (DMSO)/strong base (NaOH,
POLYMER INTERNATIONAL VOL. 39, NO. 4, 1996
291
Bismaleimide resins of aromatic surfone ether diamine
aqueous or solid) using usually a two-step procedure to
prevent hydrolysis of DCDPS. Firstly, a dehydration
reaction was carried out to remove a large amount of
water and form the metal salt of p-aminophenol. Secondly, DCDPS was added to the system, and the
nucleophilic aromatic substitution reaction was carried
out. Use of N-methylpyrrolidone (NMP)/anhydrous
potassium carbonate is an alternative method. This convenient procedure has been used to synthesize amineterminated poly(ary1ene ether sulfone) oligomers.'
Using solid potassium carbonate as a weak base instead
of aqueous alkali solution or alkali solid essentially prevents the hydrolysis side reaction of the halide
monomer. The reaction scheme can be simplified to a
one-step procedure as shown in Scheme 1.
The structure of SED was confirmed by FTIR and
'H NMR spectra. The FTIR spectrum of SED is shown
in Fig. 1. The absorption at 3455cm-' was assigned to
the stretching of the N-H band in the NH, group. The
two resonance peaks at 1500cm-' and 1486cm- ' were
due to the resonances of terminal amino-bearing
benzene rings and sulfone-bearing benzene rings. The
resonance peaks at 1290 cm- ' and 1145cm-' were
attributed to asymmetric and symmetric vibrations of
SO, groups. Figure 2 presents the 'H NMR spectrum
of SED. The resonances at 7.85 ppm and 7-75ppm were
assigned to protons in SO,-bearing benzene rings, while
the resonances at 6.75 ppm and 6.70 ppm were assigned
to protons in terminal amino-bearing benzene rings.
8
I
6
5
4
6 (ppm)
3
Fig. 2. 'H NMR spectrum of SED.
Reaction of SED with MA and BMI
SED-modified bismaleimide resins may be obtained by
synthesis of bismaleimides of SED, or by reaction of
BMI with SED. Aromatic sulfone ether bismaleimide
(SEM), bis[4-(4-maleimidophenoxy)phenyl]sulfone was
synthesized from SED and MA. The reaction route is
shown in Scheme 2.
The reaction was confirmed by FTIR and 'H NMR
spectra. The FTIR spectrum of SEM is shown in Fig. 3
(lower). The presence of absorptions at 1775 cm- and
1710cm-' due to the formation of imide rings, and the
absence of N--H absorptions at 3455 cm-' can be seen.
The 'H NMR spectrum of SEM also presents similar
results.
SED and SEM showed good solubility in common
organic solvents, such as tetrahydrofuran (THF), butanone, dioxan, and acetone, as shown in Table 1.
BMI/SED copolymer resin was obtained by the
Michael addition reaction of BMI and SED. Figure 3
(upper) gives the FTIR spectrum of uncured BMI/SED
and
copolymer. The absorptions at 3455 cm3367 cm- for SED decreased significantly.
Copolymer resins of BMI/SED and SEM/SED and
the corresponding DDM systems, BMI/DDM and
SEM/DDM, were prepared. After curing, crosslinked
resins were obtained.
'
'
I
4000
I
3600
3200 2800
2400
2000
Wavenumber
1600
1200
800
400
Properties of modified bismaleimide resins
(cm-')
Fig. 1. FTIR spectrum of aromatic sulfone ether diamine
(SED).
SED is a good modifier for bismaleimide resins. Table 2
shows the results of thermogravimetric analysis for
3.
Solvent/Base
Scheme 1. Synthesis of aromatic sulfone ether diamine (SED).
POLYMER INTERNATIONAL VOL. 39, NO. 4, 1996
292
L-L. Zhang et al.
TABLE 1. Solubility of SED and SEM
SED
SEM
THF
Butanone
Dioxan
Acetone
Chloroform
Butanol
Toluene
0
0
0
0
0
0
0
@
@
@
@
0
8
0
0 Easily soluble, @ soluble, 8 partly soluble, 0 insoluble.
cured copolymer resins in air. The sulfone ether based
bismaleimide (SEM)/diamine copolymer showed initial
weight loss in the range 340-370"C, and a temperature
at maximum rate of weight loss (T,,,) of about 580°C.
For the BMI systems, initial weight loss was in the
range 27O-29O0C, and T,,, 426-465°C.
Compared with the data for the corresponding BMI
copolymers, BMI/DDM and BMI/SED, SEM copolymers, SEM/DDM and SEM/SED, showed a higher
heat-resistant temperature index (T),220-230°C. A relatively lower thermal stability and T of the SED systems
BMI/SED and SEM/SED than the corresponding
DDM systems BMI/DDM and SEM/DDM were
found.
Thermogravimetric curves of SEM/SED copolymer
resins are shown in Fig. 4. Below 540°C (36% weight
loss), the two curves in air and N2 are almost identical,
indicating the resins to have a high level of thermooxidative stability.
TABLE 2. Results of TG for cured copolymers (in
air)
4000
2533
950
1633
400
Wavenumber (cm-')
Fig. 3. FTIR spectra of aromatic sulfone ether bismaleimide
(SEM) (lower) and uncured SEM/SED copolymer (upper).
0
Copolymer'
T6' ("C)
T30C ("C)
SED/B M I
DDM/BMI
SED/SEM
DDM/SEM
291
273
340
363
514
540
527
531
("C)
426
46 5
579
584
T,' ("C)
208
21 2
221
227
BMI, 4,4'-bismaleimidodiphenyl methane; DDM, 4,4diaminodiphenyl methane.
5% weight loss temperature.
30% weight loss temperature.
dTemperature at maximum rate of weight loss.
' Heat-resistant temperature index, T, = 0.49[T5 + 0.6(T3,
-Tdl.
0
0
0
T,,:
0
0
Scheme 2. Synthesis of aromatic sulfone ether bismaleimide (SEM).
POLYMER INTERNATIONAL VOL. 39, NO. 4, 1996
Bismaleimide resins of aromatic sulfone ether diamine
293
4.5
strength and weld resistance were also improved when
the content of SED was 5%.
CONCLUSION
t
.
100
200
300
500
400
600
700
Ternpersture('C )
Fig. 4. Thermogravimetric curves for cured SEM/SED
copolymer in air (-)
and in N, (-----).
SED-modified BMI resin based glass cloth laminates
for printed circuit boards, covered with copper foil on
one side, showed higher mechanical properties than
those of the corresponding unmodified system, as
shown in Table 3. With SED instead of the original
amine component in 3-5% weight fraction, the tensile
strength, flexural strength and impact strength of the
laminates increased markedly. Meanwhile, the stripping
TABLE 3. Properties of glass cloth laminates of
SED-modified B MI/amine system
SED content (%)
Properties
Tensile strength, MPa
Flexural strength, MPa
Impact strength, J/cmZ
Stripping strength, kgfcm
Weld resistance (300"C), s
0
3
5
184.4
388.1
7.55
1.75
5
232.6
449.2
9.75
1.60
10
231.6
398.1
8.01
1.90
47
POLYMER INTERNATIONAL VOL. 39, NO. 4, 1996
Aromatic sulfone ether diamine (SED) has been prepared by a new convenient procedure. The synthesis
reaction was conducted in a N-methylpyrrolidone
(NMP)/anhydrous potassium carbonate system. The
structure of SED was confirmed by FTIR and 'H NMR
spectrometry. SED was reacted with maleic anhydride
and bismaleimide to obtain aromatic sulfone ether bismaleimide and copolymer resins, respectively. Curing
resulted in crosslinked resins with better thermal stability. Compared with the corresponding 4,4'diaminodiphenyl methane (DDM) systems, copolymers
of bismaleimide and SED showed a slight decrease in
the heat-resistant temperature index. SED-modified
BMI/amine resin based glass cloth laminates for printed
circuit boards showed higher mechanical properties
than the corresponding unmodified system.
REFERENCES
1 Adrova, N. A,, Bessonov, M. J., Larus, L. A. & Rudakov, A. P.,
Polyirnide, A New Class of Thermally Stable Polymers. Technomic
Publishing Co., Stamford, Conn., 1970.
2 Delvigs, P., Polym. Comp., 7 (1986) 101.
3 Kawakami, J. H., Kwiatkowski, G. T., Brode, G. L. et al., J . Polym.
Sci., Polym. Chem. Ed., 12 (1974) 565.
4 Brode, G. L. & Kawakami, J. H., US Pat. 3 988 374 (1976).
5 Toray Industries Inc., Jap. Pat. 8221 364 (1982).
6 Toray Industries Inc., Jap. Pat. 8221 365 (1982).
7 Konishi Kagoku Kogyo Co. Ltd, Jap. Pat. 85 04 162 (1985).
8 Jurek, M. J. & McGrath, J. E., Polymer, 30 (1989) 1552.
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