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Bismaleimide (BMI) Resin Modified by PEEK Bearing Pendant Reactive
Propenyl Groups
Fuchuan Ding1,2, a, Qingsong Chen1,2,b, Shoulian Lai1,2,c , Xiaoyan L1,2,d 1College of Chemistry and Materials Sciences, Fujian Normal University, Fuzhou 350007, P. R.
China
2Key Laboratory for Polymer Materials, Fujian Province, Fuzhou, 350007, P. R. China
Keywords: Bismaleimide; DABPA; Reactive PEEK; Toughness
Abstract. A reactive poly (ether ether ketone) PEEK with pendant propenyl groups was prepared by
nucleophilic aromatic substitution of 4, 4’-Difluorobenzophenone (DFBP), diallylbisphenol A
(DABPA) and bisphenyl A (BPA) as monomer. The prepared reactive PEEK with varying proportion
was introduced to toughen bismaleimide (BMI) resin composing of 4,4'-bismaleimidodiphenyl
methane (BMDM) and DABPA by melt technique without any solvent. The properties of the BMI
resin as a function of the reactive PEEK concentration were evaluated. The presence of PEEK
heightened the temperature of “ene” reaction for BMI and DABPA and slightly lowered the glass
transition temperature (Tg) of the blends. The impact strength and fracture toughness were highest
elevated from 9.0 KJ/m2 and 186 J/m2 to 15.2 KJ/m2 and 239 J/m2 by 10 phr PEEK, respectively. At
the same time, the thermal stability was improved by increasing the proportion of the PEEK. Scanning
electron microscopy (SEM) of fracture surface revealed that the blends have good interfacial
adhesion.
Introduction
Due to the excellent bonding, physics-chemical, thermal, mechanical, dielectric, and aging
characteristics, bismaleimide (BMI) resins are known to have high temperature performance and
excellent processability.[1,2] They are one of the most important high performance thermosetting
engineering plastics that have found wide applications in both microelectronics and aerospace, such
as in multilayer printed circuit boards, advanced composite for aerospace industries, and structural
adhesives.[3,4] But like any other thermoset polymers, BMI resins undergo dramatic and irreversible
physical changes during the cure process. As a result, the high crosslink density arised from
polymerization (cure) reaction lead to BMI resins with inherent brittleness, thus limiting their use in
some more demanding applications.[5,6] So modification for BMI resins to overcome brittleness is a
very crucial and widely studied. Many works are done to reduce crosslink density or to increase the
distance between crosslinks by the addition of reactive or inert component such as aromatic
diamines,[ 7 ]
diallyl bisphenol A, certain epoxies and carboxyl-terminate butadiene/acrylonitrile
(CTBN) elastomers.[8,9] A two-component bismaleimide system (XU292), composed of BMDM and
DABPA, has been developed by the Ciba Geigy Corporation to improve mechanical properties and
processability.[ 10 ]
During curing, DABPA copolymerizes with BMDM via an ene-type linear
chain-extension reaction followed by the Diels-Alder reaction. The brittleness of the cured resin is
improved, compared with the conventional bismaleimide resins. The toughness of these
thermosetting resins has been increased by blending with functionalized thermoplastics.[11] But most
modification might reduce the glass transition temperatures and the thermal stability of the cured BMI
resins.
Engineering thermoplastics are interesting materials as modifers for BMI resins from the
viewpoint of the maintenance of mechanical and thermal properties for the matrix resins.[12,13]
High
performance thermoplastics with high glass transition temperatures and toughness, such as poly(ether
imide),[14,15]
poly(ether sulfone) (PES) ,[16]
and PEEK , [17]
have been extensively used to toughen
Advanced Materials Research Vols. 197-198 (2011) pp 1299-1305Online available since 2011/Feb/21 at www.scientific.net© (2011) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.197-198.1299
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 134.148.29.34, University of Newcastle, Callaghan, Australia-17/03/14,04:57:45)
brittle BMI resins. But most these BMI resins have poor phase adhesion for their poor compatibility.
Therefore, many functionalized PEEK with groups that may react with BMI had been prepared to
modified BMI resins. An interesting finding was got that the functionalized PEEK would impressive
improve the fracture toughness but with no appreciable drop in grass transition temperature. [18]
In this work, a PEEK bearing reactive pendant propenyl groups statistically distributed along the
backbone is introduced to use as modifiers for bismaleimide resin. The phase adhesion can be
improved by the reaction of the propenyl groups with bismaleimide. The influence of the PEEK
amount on the toughness, glass temperature transition and morphology for PEEK/BIM matrix will be
studied.
Experimental
Materials. DFBP (99.8%) was bought from Changzhou Huashan Chemical Co. (Jiangsu China).
DABPA (99.2%) was purchased from Laiyu Chemical Co. (Laizhou Shandong China). Highly pure
BMDM was kindly provided by the Northwest Research Institute of Chemical Industry (Shanxi
China). Reagent-grade methanol, N,N’-dimethylacetamide (DAMc), bisphenol A (BPA), toluene,
methanol, chloroform and anhydrous potassium carbonate were obtained from commercial sources
and used without further purification.
Preparation of PEEK with pendant propenyl groups. The propenyl groups functionalized
PEEK was prepared by nucleophilic aromatic substitution of DFBP with the mixture of DABPA and
BPA in DMAc at about 25% solid content (w/w) and 25% excess of powdered potassium carbonate as
initiator (Scheme 1). The molar ratio of the DABPA and BPA was 1/1. The mixture was refluxed for
3 h at 140 to azoetrope off the formed water by toluene. After distilling off the excess toluene, the
temperature was slowly raised to 160 and maintained at this temperature for 6 h. Before cooling
down the reaction, additional DMAc was added to dilute the reaction solution. The result viscous
polymer solution was poured into the mixture of methanol/water (l:1 v/v) to precipitate out the
polymer. The precipitate was filtered off and washed with water. The recovered polymer was dried at
80 under vacuum. The yield was 96% and the inherent viscosity was 0.56g/dL.
C FF
O
C
CH3
CH3
OHHO
C
CH3
CH3
OO C
O
C
CH3
CH3
OO C
O
+ +
DMAc, Toluene, K 2CO31407 , 3h
C
CH3
CH3
OHHOn n 2n
n n
1607 , 6h
Scheme 1. Synthesis of the reactive PEEK.
Preparation of BMI/PPEK Blends. The blends containing 0 to 10 phr PEEK (Table1) were
prepared as follows: PEEK was dissolved in DABPA solvent at 160 . The clear yellow solution
was cooled down to 130 and the BMI powder was added. The mixture was stirred continuously
until a homogenous solution was got. The weight proportion of the DABPA and BMI was fixed at
100:75. The resulting clear blends were degassed under vacuum at 130 and poured into a
preheated mold. When the proportion of the PEEK exceed 10 phr, the viscosity of the mixture would
turn to too high to blend the composites uniformly. The curing cycle was 160 /2 h +190 /2 h +
1300 New and Advanced Materials
230 /4 h. After curing the oven was switched off and the plaques were allowed to cool slowly to
room temperature to avoid cracking.
Table1. Formulations of modified BMI blends.
Sample
BMDM/DABPA
(wight ration) PAEK (wt %)
S1 100/75 0
S2 100/75 2.5
S3 100/75 5
S4 100/75 7.5
S5 100/75 10
Characterizations
The thermal curing behavior and the glass transition temperatures (Tg’s) of the blends were
determined on a NETZSCH 200 PC DSC instrument at a heating rate of 10 /min under nitrogen
protection.
Thermal stability was analyzed using a Seiko TG analyzer (TGA/dynamic thermal analysis, model
SSC-5200) under a nitrogen atmosphere (200 ml/min) at temperature range of 70-600 . The
heating rate was 10 /min.
Inherent viscosity was determined for a solution of 0.5 g/dL in DMAc at 30 with a calibrated
Ubbelonhde viscometer.
The unnotched Izod impact strength of the samples was evaluated as per ASTM D-256-88 by
SANS (Shenzhen, China) impact strength measurement set (ZBC1400-2). As many as five test pieces
were used to generate the data points for the mechanical tests.
The fracture surfaces of the failed specimens from impact measurement were analyzed with a
JSM-7500F SEM. All specimens were sputter coated with a layer of gold before they were examined
by microscope.
Results and discussion
Synthesis of PEEK. The reactive functionalized PEEK with pendant propenyl groups was prepared
by nucleophilic aromatic substitution of DFBP with 1/1 molar ratio mixture of DABPA and BPA as
monomer . The 1H NMR spectrum of PEEK was shown in Figure 1. It could be found from the
1H
NMR data that the ally groups of DABPA were rearranged into propenyl groups by the potassium
carbonate as the base-catalyze in the reaction mixture [19]
. The typical propnyl group signals for the E
isomer appear at 1.71 ppm (methyl protons), 6.21 ppm and 6.50 ppm. The two smaller resonances at
5.75 ppm and 6.38 ppm belong to the double-bond protons of the Z stereoisomer of the propenyl
group. The peak intensity of the E and Z isomer indicates that the propenyl groups mostly state in the
stable Z situation. The double bond containing PEEK with 0.56g/dL inherent viscosity readily
obtained. The polymer is soluble in chlorinated solvents such as chloroform and dipolar solvents such
as NMP. Therefore, they could cast from solution to form flexible and transparent membranes. It
should be noted that some cross-linking reaction occurred during the polymerization when the
reaction temperature exceed 165
, resulting insoluble product. So the reaction temperature was
accurately controlled under 165 . There is a thermally cross-linking exothermic peak from
235~270 at the DSC trance of the polymer in Figure 2. This means that the prepared polymer
could be easily cured by thermal.
Advanced Materials Research Vols. 197-198 1301
Figure 1. 1H NMR spectrum of the prepared PEEK.
150 200 250 300 350
Temprerature,oC
Exo
Endo
Figure 2. The DSC trance of the thermal cross-linking reaction for the prepared polymer.
Preparation of BMI/PEEK Blends. The prepared PEEK with propenyl groups is easily soluble in
the DABPA at high temperature about 170 without any solvent by melt process. Because the
cross-linking reaction for the propenyl groups of the PEEK and the ally groups of the DABPA would
not occur under this temperature, so this technique is optional, environmental and saving. The BMI
would cured with the propenyl groups of the PEEK and the ally groups of the DABPA at high
temperature, so it was added to the DABPA and PEEK solution below the 130 .
Curing behavior of Blends. The curing behavior is important to comprehend the cure reaction.
Hence, dynamic DSC measurements were carried out to track the curing behavior for the BMI blends
containing 0 and 10 phr PEEK at 10 K/min, respectively. The DSC curves of the blends were shown
in Figure 3. Obviously, there were two exothermic peaks on the DSC curves in the range of 100–300
. The first exothermic peak in the range of 100-190 was attributed to the “ene” reaction of the
BMI and DABPA monomers to form “ene” adduct. And the principal cure reactions occur in the
range of 200–300 via the –C=C– double bonds, such as Wagner-Jauregg reaction, Diels-Alder
reaction, thermal rearrangement, and thermal cross-linking, to form a three-dimension networks.
Comparing the curve S1 and S5, it was found that the top exothermic peak of the first peak for the
1302 New and Advanced Materials
curve S5 (165 ) was 10 higher than that of curve S1 (155 ). It indicated that the presence of
PEEK heightened the temperature of “ene” reaction for BMI and DABPA. The DSC curves of the
cured BMI blends were showed in Figure 4. The added PEEK decreased the cross-linking density, so
the Tgs of the blends decreased from 272 to 245 with increasing reactive PEEK from 0 phr to
10 phr. The thermal stability of the cured blends was also characterized by TGA. Figure 5 shows the
TGA profiles of cured blends containing the modifier PEEK from 0 phr to 10 phr labeled as S1, S2, S3,
S4 and S5. It could be seen that all samples show similar decomposition trend, but the difference was
that the decomposition rate decreased with the PEEK content increasing. This means that the PEEK
has good contribution to the thermal stability of the blends.
100 150 200 250 300 350
Temperature, oC
S1
S5Exo
Endo
Figure 3. The DSC trances of the thermal curing behavior for the BMI blends.
100 150 200 250 300 350
Temperature, oC
Exo
Endo
S1
S2
S3
S4
S5
Figure 4. The Tgs of the BMI blends.
Advanced Materials Research Vols. 197-198 1303
100 200 300 400 500 60020
30
40
50
60
70
80
90
100
Weight remaining,oC
Temperature, oC
S1
S2
S3
S4
S5
Figure 5. The TGA curves of the BMI blends.
Morphology and Toughening Mechanism. The final phase structures and toughness mechanism
can be obtained from the fracture morphology. Therefore, the impact fracture surfaces without further
treatment were directly investigated by SEM. Mechanical properties are important properties of a
matrix for advanced composites, especially those used as structural materials. The impact strength
and fracture toughness (GIC) of the BMI blends were listed in Table2. The impact strength and
fracture were significantly improved by the reactive PEEK. The toughening mechanism could be
reflected from the morphology of the failure surface. It can be seen that the fracture surface of S1
sample is smooth and crack propagation uninterrupted (Figure 6a), suggesting a brittle fracture. There
are microcracks and ridge patterns on the fracture surface of S5 sample (Figure 6b). The crack
deflection and bifurcation at the crack tip region absorbed more energy for propagation of the crack.
In this case, the crack was split into some branches and initiated more ductile microcracks, resulting in
increased surface area of the cracks, thereby increasing the toughness. There are very little PEEK
particles separated out from the BMI phase with curing reaction developing, but no obvious separated
phase structure could be found. This is due to the adequate interfacial adhesion between the PEEK
and BMI resin resulted from cross-linking reaction of pendant propenyl groups with BMI.
Table2. Impact strength of the blends
Property S1 S2 S3 S4 S5
Impact strength (KJ/m2) 9.0 12.3 13.5 14.6 15.2
GIC (J/m2) 186 207 221 231 239
Figure 6. SEM micrographs of fracture surface for cured BMI blends.
1304 New and Advanced Materials
Conclusions
In this study, a reactive PEEK with pendant propenyl groups was prepared by nucleophilic aromatic
substitution of DFBP, DABPA and BPA as monomer. The prepared reactive PEEK was introduced to
toughen BMI resin with varying proportion. When the PEEK reached 10 phr, the impact strength and
fracture toughness were elevated from 9.0 KJ/m2
and 186 J/m2 to 15.2 KJ/m
2 and 239 J/m
2,
respectively. The PEEK improved the thermal stability of the blends. Due to the adequate interfacial
adhesion between the PEEK and BMI resin, there is no obvious separated phase structure could be
found on the failure surface.
Acknowledgements
The authors acknowledge the support of natural science foundation of Fujian province of China (No.
2009J05024).
References
[1] P. Mison, B. Sillion: Adv. Polym. Sci. Vol. 140 (1999), p137
[2] Y. L. Liu, Y. H. Wang: J. Polym. Sci: Part A: Poly. Chem. Vol. 42 (2004), p3178
[3] S. Fan, F. Y. C. Boey, M. J. M. Abadie: Eur. Polym. J. Vol. 44 (2008), p2123
[4] C. P. R. Nair, D. Mathew, K. N. Ninan: Adv. Polym. Sci. Vol. 155 (2001), p1
[5] H. H.wang, C. Li, C. Wang: Polym. Int. Vol. 55 (2006), p1341
[6] I. Takao, S. Hidehiko, F. Wakicki, E. Masao: J. Appl. Polym. Sci.Vol.65 (1997), p1349
[7] A. V. Tungare, G. C. Martin: J. Appl. Polym. Sci. Vol. 46 (1992), p1125
[8] D. C. Liao, K. H. Hsieh, S. C. Kao: J. Polym. Sci. Part A: Polym. Chem.Vol. 33 (1995), p481
[9] M. Abbate, E. Martuscelli, P. Musto, G. Ragosta: J. Appl. Polym. Sci. Vol. 65 (1997), p979
[10] H. D. Stenzenberger: Br. Polym: J. Vol. 20 (1988), p383
[11] I. Hamerton, P. Klewpatinond: Polym. Int. Vol. 50 (2001), p1309
[12] X. Y. Liu, G. Z. Zhan, Z. W. Han, et al: J. Appl. Polym. Sci, Vol. 106 (2007), p77
[13] Y. J. Han, G. X. Liao, Y. J. Xu, G. P. Yu, X. G. Jian: Polym. Engin. Sci. Vol. 49 (2009), p2301
[14] H. H. Qin, P.T. Mather, J. B. Baek, L. S. Tan: Polymer. Vol. 47 (2006), p2813
[15] J. Jin, X. Tang, Y. Ding, J. Wang, S. Li: Macromol.Chem. Phys.Vol. 200 (1999), p1956
[16] S. P. Wilkinson, T.C. Ward, and J.E. McGrath: Polymer. Vol. 34 (1993), p870
[17] B. Zhang, P. Li, X. Chen: J. Mater. Sci.Vol. 33 (1998), p5683
[18] H. D. Stenzenberger, P. Konig, High Perform. Polym. Vol. 5(1993), p123
[19] J. V. Crivello, K. D. Jo: J. Polym. Sci. Part A: Polym. Chem. ED. Vol. 31(1993), p1473
Advanced Materials Research Vols. 197-198 1305
New and Advanced Materials 10.4028/www.scientific.net/AMR.197-198 Bismaleimide (BMI) Resin Modified by PEEK Bearing Pendant Reactive Propenyl Groups 10.4028/www.scientific.net/AMR.197-198.1299
DOI References
[3] S. Fan, F. Y. C. Boey, M. J. M. Abadie: Eur. Polym. J. Vol. 44 (2008), p2123
doi:10.1016/j.eurpolymj.2008.04.024 [4] C. P. R. Nair, D. Mathew, K. N. Ninan: Adv. Polym. Sci. Vol. 155 (2001), p1
doi:10.1007/3-540-44473-4_1 [7] A. V. Tungare, G. C. Martin: J. Appl. Polym. Sci. Vol. 46 (1992), p1125
doi:10.1002/app.1992.070460701 [9] M. Abbate, E. Martuscelli, P. Musto, G. Ragosta: J. Appl. Polym. Sci. Vol. 65 (1997), p979
doi:10.1002/(SICI)1097-4628(19970801)65:5<979::AID-APP16>3.0.CO;2-N [10] H. D. Stenzenberger: Br. Polym: J. Vol. 20 (1988), p383
doi:10.1002/pi.4980200503 [11] I. Hamerton, P. Klewpatinond: Polym. Int. Vol. 50 (2001), p1309
doi:10.1002/pi.776 [14] H. H. Qin, P.T. Mather, J. B. Baek, L. S. Tan: Polymer. Vol. 47 (2006), p2813
doi:10.1016/j.polymer.2006.02.062 [15] J. Jin, X. Tang, Y. Ding, J. Wang, S. Li: Macromol.Chem. Phys.Vol. 200 (1999), p1956
doi:10.1002/(SICI)1521-3935(19990801)200:8<1956::AID-MACP1956>3.3.CO;2-J [16] S. P. Wilkinson, T.C. Ward, and J.E. McGrath: Polymer. Vol. 34 (1993), p870
doi:10.1016/0032-3861(93)90346-C
