Highly cross-linked thermosetting resin of maleimidobenzoxazine functionalized with benzocyclobutene

Article abstract of DOI:10.1016/j.polymer.2012.11.008

Maleimidobenzoxazine monomer functionalized with benzocyclobutene (BCB) and its cured resin has been successfully prepared. BCB-modified maleimidobenzoxazine monomer (HMI-AB) was synthesized by the reaction of 4-aminobenzocyclobutene (AMBCB), p-hydroxyphe

Full text of DOI:10.1016/j.polymer.2012.11.008

Polymer 54 (2013) 143e147
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Polymer
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Highly cross-linked thermosetting resin of maleimidobenzoxazine functionalized
with benzocyclobutene
*
Yuanrong Cheng, Tianke Qi, Yunxia Jin, Dunying Deng, Fei Xiao
Department of Materials Science, Fudan University, 220 Handan Road, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Maleimidobenzoxazine monomer functionalized with benzocyclobutene (BCB) and its cured resin has
been successfully prepared. BCB-modified maleimidobenzoxazine monomer (HMIeAB) was synthesized
by the reaction of 4-aminobenzocyclobutene (AMBCB), p-hydroxyphenylmaleimide (HMI) and para-
formaldehyde in dioxane under reflux. Fourier transform infrared spectroscopy (FTIR), 1H and 13C nuclear
magnetic resonance spectroscopy (NMR) were used to characterize the structure of the monomer. The
monomer HMIeAB possesses three kinds of polymerizable functional groups of BCB, maleimide and
benzoxazine. The polymerization behavior of the monomer is studied by differential scanning calo-
rimetry (DSC) and FTIR. DMA study demonstrates that the cured resin show high storage modulus and
high Tg at ca. 350 ꢀC. TGA study shows that the cured resin possess good thermal stability.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 3 August 2012
Received in revised form
23 October 2012
Accepted 2 November 2012
Available online 7 November 2012
Keywords:
Maleimide
Benzoxazine
Benzocyclobutene
1. Introduction
maleimide enhances the thermal stability and Tg. Besides, poly-
merizable groups such as allyl [20], propargyl [20] and nitrile [27]
The preparation and study of benzoxazine (BOZ) resins has
attracted much attention for the high flexibility in molecular design
and excellent performance compared to traditional phenol resins
[1e3]. In order to improve the performance for applications in
rigorous environments, many approaches have been applied for the
development of high-performance polybenzoxazine-based mate-
rials. The first strategy is to enhance the toughness or reinforce
polybenzoxazines with other polymers [4e8] or inorganic additives
[9e16]. The second strategy is to enhancing the thermal properties
of polybenzoxazines through the introduction of other polymer-
izable functionalities into the BOZ structure via molecular engi-
neering and tailoring of BOZ monomer. There has been
considerable interest in functionalized polybenzoxazine to improve
the thermal stability and thermomechanical performance to
expand their end-use applications in harsh environments. Many
polymerizable functionalities such as allyl [17], methacryloyl [18],
maleimide [19e21], norbornane [21], acetylene [22,23], propargyl
[24], epoxy [25], and nitrile group [26] have been introduced into
BOZ monomers.
have been introduced into maleimidobenzoxazine. The corre-
sponding polymers with high crosslinking show improved thermal
stability and higher Tg. The maleimidobenzoxazine monomer with
nitrile functionality can be cross-linked by cyclotrimerization of
nitrile catalyzed by Lewis acid.
Polymers functionalized with benzocyclobutene (BCB) have
drawn much attention for their excellent thermal stability and
dielectric performance [28e30]. BCB based polymers have been
especially applied in integrated circuit packaging, MEMS packaging,
etc. BCB ring can be converted to conjugated diene structure at
proper temperature and undergoes radical polymerization or
DielseAlder reaction. In this paper, BCB ring as a polymerizable
group was introduced in the maleimidobenzoxazine monomer to
enhance the performance of BOZ resins. We originally synthesized
monomer with multifunctional groups containing maleimide, BCB
and BOZ. So the monomers can be cured at proper temperature to
prepare highly cross-linked resins. These resins demonstrate
improved heat resistance, thermal properties, and thermo-
mechanical properties compared with the BOZ resins reported.
Maleimide-modified BOZ N-(3-phenyl-3,4-dihydro-2H-benzo
[e] [1,3]oxazin-6-yl)-maleimide (HMIeAN) [19e21] has been
prepared by using p-hydroxyphenylmaleimide (HMI) as a reactive
phenol with aniline. It was demonstrated that the introduction of
2. Experimental section
2.1. Materials
4-Bromobenzocyclobutene (BrBCB, 97%) was purchased from
Chemtarget Technologies Co., Ltd. p-Hydroxyphenylmaleimide
* Corresponding author. Tel.: þ86 21 65642110; fax: þ86 21 65103056.
E-mail address: feixiao@fudan.edu.cn (F. Xiao).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.11.008

144
Y. Cheng et al. / Polymer 54 (2013) 143e147
(HMI), dioxane, dichloromethane, paraformaldehyde, anhydrous
sodium sulfate and sodium carbonate were used as received.
Aniline (AN) was purified by vacuum distillation. 4-Amin-
obenzocyclobutene (AMBCB) was prepared by aminating of BrBCB
with ammoniaewater according to the literature else [31]. HMIe
AN was prepared according to the literature [21].
2.4. Preparation of the thermosetting resin
The prepared monomers existed as powders at room temperature
were placed into glasseplate molds (40 mm ꢂ 20 mm ꢂ 2 mm). After
degassing inavacuum oven at130ꢀC foranhourwith anapproximate
pressure at 0.01 MPa, the molds were then heated at 150 ꢀC for 2 h,
then at 180, 200, 220, 240 and 260 ꢀC for 1 h, respectively. After cooled
to room temperature, the thermosetting resins were polished as
rectangular bars with a size of 30 mm ꢂ 13 mm ꢂ 2 mm for DMA test.
2.2. Characterization
1H NMR and 13C NMR spectra were recorded with a Bruker
DMXe500 Spectrometer using CDCl3 as solvent. Fourier transform
infrared (FTIR) spectra were recorded on a Nicolet MagnaeIR 550 II
FTIR spectrophotometer operating at a resolution of 4 cmꢁ1. The
samples for FTIR test were prepared by KBr pellet method. Thermal
gravimetric analysis (TGA) was performed on a Shimadzu DTGe
60H simultaneous DTAeTG apparatus with a heating rate of
10 ꢀC minꢁ1 in nitrogen atmosphere. Differential scanning calo-
rimetry (DSC) was measured on a TA Q200 calorimeter. Dynamic
mechanical analysis (DMA) was carried out on a TA Q800 instrꢁu1-
ment by the 3-point bending method at a heating rate of 3 ꢀC min
with the test frequency at 1 Hz.
3. Results and discussion
3.1. Preparation and characterization of BCBefunctionalized BOZ
The novel hybrid monomer HMIeAB was prepared by the
reaction of HMI and paraformaldehyde with AMBCB as shown in
Scheme 1. HMIeAN as control sample was prepared by HMI and
paraformaldehyde with aniline for comparison. Both monomers are
soluble in many common organic solvents such as acetone, chlo-
roform, ethyl acetate, dioxane, tetrahydrofuran.
Fig. 1 shows the 1H NMR spectra of HMIeAB and HMIeAN. As to
HMIeAN, the characteristic protons of the oxazine ring appeared as
two singlets at 4.66 and 5.37 ppm assigned to AreCH2eNe and e
OeCH2eNe, respectively. The singlet at 6.82 ppm was assigned to
the protons of eCHaCHe in the maleimide structure. The
multiplets at 6.84e7.37 ppm were assigned to protons of the
aromatic ring. As to HMIeAB, the characteristic protons of the
oxazine ring appeared as two singlets at 4.61 and 5.33 ppm. The
characteristic protons of maleimide structure appeared at
6.82 ppm, and the multiplets at 6.84e7.27 ppm were assigned to
protons of the aromatic rings. The singlet at 3.07 ppm was attrib-
uted to the methylene protons of the fouremembered ring of BCB.
The 1H NMR spectra established the structures of HMIeAN and
HMIeAB. The structure of monomer HMIeAB was confirmed by 13C
NMR (shown in Fig. 2). The peak at 29.17 ppm was assigned to the
methylene of the four-membered ring of BCB. The characteristic
carbon resonances of the oxazine ring appeared at 51.22 ppm for
AreC*H2eNe and at 80.84 ppm for NeC*H2eOe, respectively. The
strong resonance at 134.14 ppm corresponded to the olefinic
carbons of maleimide, and 169.78 ppm was attributed to the
carbonyl carbons of maleimide.
2.3. Preparation of monomer
N-(3-(Benzocyclobutene-4-yl)-3,4-dihydro-2H-benzo[e] [1,3]oxa-
zin-6-yl)-maleimide (HMIeAB). AMBCB (1.19 g, 10 mmol), para-
formaldehyde (0.60 g, equal to 20 mmol formaldehyde), HMI
(1.89 g 10 mmol) and dioxane (30 mL) was added in a 50 mL single
necked round-bottomed flask equipped with
a PTFE-coated
magnetic stir bar and a reflux condenser. The solution was stirred
and heated to reflux for 12 h, and the turbid solution became
transparent with light yellow. After cooling down to room
temperate, the solution was condensed on a rotary evaporator and
the crude product was obtained. The crude product was then dis-
solved in 50 mL dichloromethane and washed with 20% Na2CO3
solution for 3 times and then with deionized water until neutral.
The dichloromethane solution was separated and dried over
anhydrous sodium sulfate for 12 h, and then filtered, concentrated
and dried under vacuum to give 2.52 g HMIeAB in 76% yield. 1H
NMR (500 MHz, CDCl3): 3.07 (s, 4H), 4.61(s, 2H), 5.33(s, 2H), 6.82(s,
2H), 6.84e7.27 (m, 6H).
Scheme 1. Preparation of the maleimidobenzoxazine monomers from different aromatic amines.

Y. Cheng et al. / Polymer 54 (2013) 143e147
145
Fig. 3. FTIR of the monomers HMIeAB and HMIeAN.
Fig. 1. 1H NMR of the monomer HMIeAB compared with HMIeAN.
The cure behavior of the monomers was studied by DSC at
a ramping rate of 10 ꢀC minꢁ1, and the DSC curves are list in Fig. 4.
For HMIeAN, An exothermal peak at 190 ꢀC with a shoulderꢁa1t
Fig. 3 shows the FTIR spectra of the monomers of HMIeAN and
HMIeAB. Both two FTIR spectra showed the typical symmetric and
asymmetric stretching absorption of C]O in the cyclic maleimide
ring at about 1710 and 1774 cmꢁ1, respectively [20]. The band at
1146 cmꢁ1 was assigned to the CeNeC bending mode of the mal-
eimide ring. Another characteristic absorption for the maleimide
structure was observed at 690 cmꢁ1. The absorption peak at
827 cmꢁ1 was assigned to the bending mode HeC]CeH of
aromatic rings and maleimide ring. The characteristic absorptions
of the benzoxazine structure appeared at 1500 cmꢁ1 (trisubstituted
benzene ring), 1236 cmꢁ1 (asymmetric stretching of CeOeC), at
1031 cmꢁ1 (symmetric stretching of CeOeC), and at 935 cmꢁ1
(trisubstituted benzene ring). As to HMIeAN, the absorption peak
at 3398 cmꢁ1 was assigned to the residual phenolic OH on account
of the difficulty to purify the crude product [20]. As to HMIeAB, the
characteristic peak for BCB at 1475 cmꢁ1 was observed with
partially overlapped by trisubstituted benzene ring of BOZ. Another
peak at 2828 cmꢁ1 was assigned to the vibration of eCH2e in BCB.
233 ꢀC was observed with total polymerization heat of 333 J g
.
This exothermic transition corresponds to the homopolymerization
of maleimide and the ring-opening polymerization of benzoxazine
[19]. For HMIeAB, the DSC curve showed two exothermic peaks,a
moderate peak at 193 ꢀC and a maximum at 247 ꢀC, and the total
heat of polymerization is 392.2 J gꢁ1. The exothermal peak at 193 ꢀC
was mainly ascribed to homopolymerization of maleimide. The
maximum exothermal peak at 247 ꢀC was assigned to the poly-
merization of BOZ and BCB. Compared to HMIeAN, the second peak
shift from 233 ꢀC to 247 ꢀC. We believe that the polymerization of
BCB needs higher temperature than that of BOZ.
The cure behavior of HMIeAB was further studied by FTIR. The
spectra were recorded after the sample was treated 1 h at 120, 150,
180, 210 and 240 ꢀC, respectively and shown in Fig. 5. After treat-
ment at 150 ꢀC, the absorption at 690 cmꢁ1 for C]CeH diminished
obviously, indicating the homopolymerization of maleimide. The
band at 1146 cmꢁ1 assigned to the CeNeC bending mode of the
Fig. 2. 13C NMR of the monomer HMIeAB.
Fig. 4. DSC curves of the monomers HMIeAN and HMIeAB.

146
Y. Cheng et al. / Polymer 54 (2013) 143e147
Fig. 6. DMA curves of the thermosetting resins of HMIeAN and HMIeAB.
polymerization mechanism is illustrated in Scheme 2. The homo-
polymerization of maleimide groups occurred in the first stage,
following with the ring-opening polymerization of benzoxazine
and then the ring-opening polymerization of BCB.
Fig. 5. FTIR of the monomer HMIeAB at different curing stage.
maleimide ring shifted to 1182 cmꢁ1 corresponds to the CeNeC
bending mode of the succinimide ring, which also proved the
polymerization of maleimide group [27]. While the characteristic
absorption bands of benzoxazine structure at 935 cmꢁ1 decreased
slower than that of maleimide at 690 cmꢁ1. We can conclude that
the polymerization of maleimide occurred earlier than the ring-
opening of benzoxazine. The intensity of the absorption at
827 cmꢁ1 due to ]CeH of maleimide decreased after treatment at
150 ꢀC for an hour. After curing at 210 ꢀC for an hour, the absorption
band at 690 cmꢁ1 for maleimide and the absorption bands for
benzoxazine at 1236 cmꢁ1, 1031 cmꢁ1 and 935 cmꢁ1 disappeared,
while the absorption peak at 2828 cmꢁ1 for BCB still existed.ꢁA1fter
cured at 240 ꢀC for an hour, the absorption peak at 2828 cm for
BCB finally disappeared. The peak at 827 cmꢁ1 still existed and it
was ascribed to the out-of-plane bending absorption of other ]Ce
H of aromatic rings. Based on the DSC and FTIR study, the
3.2. Property of cured BCBemaleimide BOZ resin
The DMA curves of cured HMIeAN and HMIeAB were shown in
Fig. 6. The initial storage modulus of the cured HMIeAN and HMIe
AB is as high as 5.9 GPa and 5.0 GPa at 30 ꢀC, respectively. For the
cured HMIeAN, the high initial storage modulus of the resin was
caused by the high crosslinking of the monomer by dual poly-
merization including homopolymerization of maleimide and ring-
opening polymerization of benzoxazine. The cured HMIeAN
maintains the high storage modulus below 210 ꢀC and shows the
glass transition temperature at 255 ꢀC. Compared to HMIeAN, the
cured HMIeAB resin maintains high storage modulus in a wide
temperature range up to 300 ꢀC and shows the glass transformation
Scheme 2. Schematic illustration of thermal polymerization mechanism of HMIeAB.

Y. Cheng et al. / Polymer 54 (2013) 143e147
147
behavior of the monomer is studied by DSC and FTIR. DMA study
demonstratesthatthecuredHMIeABshowhighstoragemodulusand
high Tg atca. 350 ꢀC. TGA studyshows that thecured HMIeAB exhibits
improved thermal stability compared with HMIeAN without BCB
group.
Acknowledgments
This research was supported by National Science and Technology
Major Project of China (Nos. 2009ZX02038 and 2011ZX02602) and
China Postdoctoral Science Foundation.
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4. Conclusion
The hybrid monomer, BCB-modified maleimidobenzoxazine
(HMIeAB), has been successfully prepared by the reaction of AMBCB,
HMI and paraformaldehyde in dioxane under reflux, while HMIeAN
was prepared as control sample. The structure of the monomer
HMIeAB was characterized by FTIR, 1H and 13C NMR. The monomer
possesses three kinds of polymerizable functional groups of mal-
eimide, BOZ and BCB. The monomer can be cured at proper temper-
ature to prepared highly cross-linked resins. The polymerization
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