epoxy resin containing octamaleimidophenyl polyhedral oligomeric silsesquioxane
TRANSCRIPT
Epoxy Resin Containing Octamaleimidophenyl
Polyhedral Oligomeric Silsesquioxane
Yong Ni, Sixun Zheng*
Department of Polymer Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240,P. R. ChinaFax: (þ86) 21 54741297; E-mail: [email protected]
Received: June 24, 2005; Revised: August 12, 2005; Accepted: August 15, 2005; DOI: 10.1002/macp.200500267
Keywords: epoxy; nanocomposites; polyhedral oligomeric silsesquioxane
Introduction
Organic-inorganic nanocomposites have received consid-
erable attention since they can combine the advantages of
inorganic materials (e.g., rigidity, stability) and organic
polymers (i.e., flexibility, ductility, and processibility).[1–4]
During the past decades, polymeric-inorganic nanocompo-
sites have been prepared via the sol-gel process,[2,5–8]
intercalation, and exfoliation of layered silicates by organic
polymers.[9–13] Polyhedral oligomeric silsesquioxane
(POSS) macromer and POSS-containing polymers have
been emerging as a new technology for the preparation
of organic-inorganic nanocomposites; POSS-containing
nanocomposites are becoming the focus of many studies
due to the excellent comprehensive properties of this class
of hybrid materials and the simplicity in processing.[14–16]
Polyhedral oligomeric silsesquioxanes are a class of
important nanosized cage-like compounds (Scheme 1),
derived from hydrolysis and condensation of trifunctional
organosilanes and possess a formula of [RSiO3/2]n, n¼ 6–
12, where R can be various types of organic groups, one (or
more) of which is reactive or polymerizable. The copoly-
merization of POSS macromers with organic monomers
has been proved to be an efficient approach to afford the
nanocomposites due to the formation of covalent bonds
between POSS cages and polymer matrices.
Epoxy resins are a class of important thermosets, which
have been widely used as matrices of composite materials,
adhesives, and electronic encapsulating materials due to
their high mechanical strength, excellent chemical resist-
ance, and simplicity in processing. The extensive applica-
tion motivates to prepare the organic-inorganic hybrid
composites of epoxy resins with improved properties. The
modification of epoxy resin via POSS could endow the
materials with some superior properties such as impro-
ved thermomechanical properties, thermal and oxidative
Summary: Octamaleimidophenyl polyhedral oligomericsilsesquioxane (OmipPOSS) was synthesized via the imid-ization reaction between octaaminophenyl polyhedral oligo-meric silsesquioxane (OapPOSS) and maleic anhydride, andit was characterized by means of Fourier transform infrared(FTIR) and NMR spectroscopies. OmipPOSS was furtheremployed to prepare epoxy hybrids. The thermosettinghybrids containing OmipPOSS up to 10 wt.-% were obtainedvia in situ polymerization of diglycidyl ether of bisphenolA (DGEBA) and 4,40-diaminodiphenylmethane (DDM) inthe presence of OmipPOSS. High-resolution transmissionelectronic microscopy (TEM) indicates that the nanometer-scaled dispersion of POSS molecules was obtained, suggest-ing that the nanocomposites were successfully prepared. Theresults of DSC showed that the glass transition temperatures(Tg’s) of the POSS-containing nanocomposites are dependenton the content of POSS in the nanocomposites. When thecontents of POSS are less than 5 wt.-%, the nanocompositesdisplayed the enhanced glass transition temperatures (Tg’s) in
comparison with control epoxy. Thermogravimetric analysis(TGA) showed that all the nanocomposites containing POSSdisplayed improved char yield, suggesting the flame retar-dance of the materials is improved.
Macromol. Chem. Phys. 2005, 206, 2075–2083 DOI: 10.1002/macp.200500267 � 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Full Paper 2075
stability, and dielectric properties.[17–32] Lee et al.[21]
reported that the molecular level reinforcement of POSS
cages could significantly retard the physical aging process
of epoxy resin in the glassy state. Using a series of
octasilsesquioxanes with various R groups such as amino-
phenyl, dimethylsiloxypropyl glycidyl ether groups, Laine
et al.[18,19,28–31] investigated the dynamic mechanical
properties, fracture toughness, and thermal stability of the
epoxy nanocomposites and concluded that the modifica-
tions of epoxy resins via POSS were quite dependent on the
types of R groups, tether structures between epoxymatrices
and POSS cages, and the defects in silsesquioxane cages,
etc. Williams et al.[24] reported that a primary liquid-liquid
phase separation occurred at the time of adding the cuing
agent to epoxy due to the incompatibility between epoxy
and isobutyl POSS glycidyl. Matejka et al.[25,26] inves-
tigated the effects of POSS-POSS interactions on the
thermal properties of the nanocomposites. More recently,
Zheng et al.[20,27] studied the correlations between
morphology and thermomechanical properties of POSS-
containing epoxy hybrid composites.
In this work, we reported the synthesis of a novel octa-
functional POSS, octamaleimidophenyl POSS (Omip-
POSS) (Scheme 2), which was subsequently incorporated
into epoxy system. From the structural point of view,
OmipPOSS can be taken as a POSS-modified maleimide
and thus can offer high temperature performance of
polyimides and maintain the epoxy-like processing. It is
expected that theMichael addition between aromatic amine
and maleimide can be involved with the crosslinking
reaction among epoxy, aromatic amine, and OmipPOSS,
which will facilitate the fine dispersion of POSS macromer
in the composite system. The goal of this work is to
report the synthesis of OmipPOSS and to investigate the
morphology structure and thermal properties of the POSS-
containing nanocomposites by means of transmission
electronic microscopy (TEM), differential scanning calo-
rimetry (DSC), and thermogravimetric analysis (TGA),
respectively.
Experimental Part
Materials
Epoxy monomer, diglycidyl ether of bisphenol A (DGEBA)with epoxide equivalent weight 185–210 was purchased fromShanghai Resin Co., China. Phenyltrichlorosilane (PhSiCl398%) was purchased from Changzhou Chemical Factory,Jiangsu, China. Maleic anhydride, 4,40-diaminodiphenyl-methane (DDM), acetic anhydride, and sodium acetatetetrahydrate were of analytical grade, obtained from ShanghaiReagent Co., Shanghai, China. The bismaleimide (BMI) basedon DDM and maleic anhydride was prepared in this labaccording to the literature methods.[33] The solvents such asacetone, chloroform, triethylamine, methanol, N,N0-dimethyl-formamide (DMF), and tetrahydrofuran (THF)were purchased
Si O Si
O O
SiSi O
O O
O O
Si Si
Si
O
O
O O
Si
R
R
R
R
R
R
R
R
Scheme 1. Structure of octameric framework POSS molecule.
H2N
NH2
Si O Si
O
SiOSi
O
Si O Si
OOO O
O OSiOSi
NH2
NH2
NH2
NH2H2N
H2N
Si O Si
O
SiOSi
O
Si O Si
OOO O
O OSiOSi
N
OC
CO
N
OC
CO
N
OC
CO
N
OC
CO
N
OC
CO
N
OC
CO
N
OC
CO
N
OC
CO
(1) Maleic anhydride
(2) Sodium acetate tetrahydrate + acetic anhydride
Scheme 2. Synthesis of OmipPOSS from OapPOSS.
2076 Y. Ni, S. Zheng
Macromol. Chem. Phys. 2005, 206, 2075–2083 www.mcp-journal.de � 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
from commercial sources and they were further purified ingeneral ways prior to use.
Synthesis of Octamaleimidophenyl POSS
A multi-step approach was employed to synthesize Omip-POSS, which was based on the syntheses of octaphenyl POSS[(C6H5)8Si8O12], octanitrophenyl POSS [(O2NC6H4)8Si8O12],and octaaminophenyl POSS (OapPOSS) [(H2NC6H4)8Si8O12].The preparations of the later three POSS have been detailedpreviously;[20,34–36] therefore, only the general scheme isgiven here. The octaphenyl POSS was synthesized viahydrolysis and condensation of phenyltrichlorosilane andsubsequent rearrangement reaction catalyzed by benzyltri-methylammonium hydroxide, which was described by Brownet al. in 1964.[36] The nitrification of octaphenyl POSS wasemployed to prepare octanitrophenyl POSS, which was furtherreduced to afford OapPOSS.[20,34,35]
Octamaleimidophenyl POSS was synthesized via theimidization reaction betweenOapPOSS andmaleic anhydride.The synthetic method used in the present work is slightlydifferent from that reported by Krishnan et al.[37] In this work,sodium acetate (NaAc) was used as the catalyst to facilitate theimidization.[38–41] Typically, in a 250 ml three-necked flaskequippedwith amagnetic stirrer and a reflux condenser,maleicanhydride (1.359 g, 13.872 mmol) dissolved in 100mlanhydrous DMF was charged at 80 8C with vigorous stirringand then OapPOSS [(H2NC6H4)8Si8O12] (2.0 g, 1.734 mmol)that was pre-dissolved in 50 ml anhydrous DMF was droppedto the system within 30 min in nitrogen atmosphere. Thereactionwas allowed to be carried out at 80 8C for 24 h and thenboth sodium acetate tetrahydrate (NaAc � 4H2O) (0.1180 g,0.867 mmol) and acetic anhydride (2.124 g, 20.808 mmol)were added. The reactive mixture was held at 60 8C withstirring for additional 48 h. After the system was cooled toroom temperature, the majority of solvents were removed viarotation evaporation and the concentrated solution was precipi-tatedwith1 000mlofdeionizedwater.Thepowderyproductwasre-dissolved in the mixture of THF and ethyl acetate, and wasprecipitated into 1 000 ml of hexane. The product was collectedby filtration and dried in vacuo at room temperature to give2.341 g of slightly brown powdery solids (yield: 75.2%).
FTIR (KBr powder): 1 145 (Si–O–Si), 1 381 (C–N),1 603 (C C), 1 716 (C O in phase), 1 775 cm�1 (C O outof phase).
1H NMR (DMSO-d6): 8.0–6.6 (m), 6.1 (s).13C NMR (DMSO-d6): 172.1, 169.7, 167.2, 162.3, 135.3,
134.5, 131.3, 128.4.29Si NMR: �78.2, �81.4.
Preparation of Nanocomposites
To prepare the nanocomposites containing POSS, the desiredamount of OmipPOSSwas dissolved with the smallest amountofDMF, and the solutionwas charged to pre-weightedDGEBAwith vigorous stirring to afford homogenous solution. Afterthat, the curing agent, DDM was added with respect to theamount of DGEBA. The mixtures were poured into Teflonmould and the majority of solvent was evaporated at 60 8C
overnight. To remove the residual solvent, all the samples weredried in vacuo at 60 8C for at least 24 h. The contents ofOmipPOSS in the nanocomposites were controlled to be 2.5, 5,7.5, and 10 wt.-%, respectively. The systems were cured at80 8C for 2 h, 160 8C for 2 h, and 200 8C for 2 h to access acomplete curing reaction.
Reaction Between DDM and OmipPOSS
To investigate the reaction between DDM and OmipPOSS,OmipPOSS (2.24 g, 1.25mmol) andDDM (0.99 g, 5.00mmol)were dissolved with a small amount of DMF and the solutionwas poured into a Teflon mould. The major solvent wasevaporated at 60 8C overnight, and the films were further driedinvacuo at 60 8C for at least 24 h to remove the residual solvent.The mixture was cured at 80 8C for 2 h, 160 8C for 2 h, and200 8C for 5 h to attain a complete curing reaction. The curedsample was subject to FTIR measurement.
Measurement and Techniques
Fourier Transform Infrared Spectroscopy (FTIR)
The FTIR measurements were conducted on a Perkin-ElmerParagon 1000 Fourier transform spectrometer at roomtemperature (25 8C). The samples were mixed with the powderof KBr and then pressed into small flakes. The specimens weresufficiently thin to be within a range where the Beer-Lambertlaw is obeyed. In all cases, 64 scans at a resolution of 2 cm�1
were used to record the spectra.
NMR Spectroscopy
The 1H and 13C NMR measurements were carried out on aVarian Mercury Plus 400 MHz NMR spectrometer at 25 8C.The samples were dissolved with deuterated dimethylsulfoxide (DMSO-d6) and the solutions were measured withtetramethylsilane (TMS) as the internal reference. The high-resolution 29Si NMR spectra were obtained using the cross-polarization (CP)/magic angle spinning (MAS) together withthe high-power dipolar decoupling (DD) technique. The908-pulse width of 4.1 ms was employed with free inductiondecay (FID) signal accumulation, and the CP Hartmann-Hahncontact time was set at 3.5 ms for all experiments. The rate ofMAS was 4.0 KHz for measuring the spectra. The Hartmann-Hahn CP matching and DD field was 57 KHz. The chemicalshifts of all 29Si spectra were determined by taking the siliconof solid Q8M8 relative to TMS as an external referencestandard.
Differential Scanning Calorimetry (DSC)
The DSC measurement was performed on a Perkin ElmerPyris-1 thermal analysis apparatus in a dry nitrogen atmo-sphere. The instrument was calibrated with standard indium.All samples (about 10 mg in weight) were heated from�20 to250 8Cand the thermogramswere recorded using a heating rateof 20 8C �min�1. The glass transition temperatures were takenas the midpoint of the capacity change.
Epoxy Resin Containing Octamaleimidophenyl Polyhedral Oligomeric Silsesquioxane 2077
Macromol. Chem. Phys. 2005, 206, 2075–2083 www.mcp-journal.de � 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Transmission Electronic Microscopy (TEM)
The TEM was performed on a JEM 2010 high-resolutiontransmission electronmicroscope at the accelerating voltage of200 kV. The samples were trimmed using an ultramicrotomeand the specimen sections (ca. 70 nm in thickness) were placedin 200 mesh copper grids for observation.
Thermogravimetric Analysis (TGA)
APerkin-Elmer TGA-7 thermal gravimetric analyzer was usedto investigate the thermal stability of the nanocomposites. Allthe thermal analysis was conducted in nitrogen atmospherefrom ambient temperature to 800 8C at the heating rate of20 8C �min�1. The thermal degradation temperature was takenas the onset temperature at which 5 wt.-% of weight lossoccurs.
Results and Discussion
Syntheses of OmipPOSS
The imidization reaction between OapPOSS and maleic
anhydride was utilized to synthesize OmipPOSS, which is
described as Scheme 2. Shown in Figure 1 are the FTIR
spectra of OmipPOSS andOapPOSS. In the FTIR spectrum
of OmipPOSS, the five major bands characteristic of
Si–O–Si stretching vibration, C–N–C, double bond (C C),
and carbonyl (C O in phase and out of phase) were seen at
1 138, 1 378, 1 603, 1 716, and 1 775 cm�1, respective-
ly.[42,43] In the FTIR spectrum of OapPOSS, the character-
istic bands at 3 365 and 1 138 cm�1 are assigned to the
stretching vibration of N–H and Si–O–Si, respectively.
Both disappearance of the OapPOSS bands and appearance
of the characteristic bands of OmipPOSS indicate a
complete conversion of amine groups into maleimide
groups.
The 1H NMR spectra in the range of 4.0–10.0 ppm for
OmipPOSS and OapPOSS were presented in Figure 2. In
the 1H NMR spectrum of OmipPOSS, the single and sharp
resonance at 6.1 ppm is ascribed to the protons in carbon
double bonds (C C) of maleimide groups. It is seen that
upon imidization, the resonance of the protons in aromatic
rings was seen to shift low field possibly due to deshielding
effect of maleimide groups. At the same time, the broad
resonance at 5.3–3.5 ppm, which is assigned to the protons
of amino groups of OapPOSS disappeared, suggesting that
all the amino groups of OapPOSS were virtually converted
into maleimide groups. In the 29Si NMR spectrum, the
appearance of two peaks at�78.2 and�69.2 ppm indicates
that the OmipPOSS is the combined isomers containing
meta- and para-position substitutions, which is just like the
case ofOapPOSS (see Figure 3). The 29SiNMR result is in a
good agreement with that reported by Tamaki et al.[35]
Morphology and Thermal Properties ofNanocomposites
Morphology
To prepare the epoxy nanocomposites containing Omip-
POSS, the miscibility (or solubility) of OmipPOSS with
epoxy monomers (viz. DGEBA and DDM) is critical. All
the ternary mixtures composed of DGEBA, DDM, and
OmipPOSS were homogenous and transparent, suggesting
that all the components are miscible in the concentration
ranges investigated. The ternary mixtures were subject to
the curing reaction at elevated temperature to prepare
the POSS-containing composites. The organic-inorganic
epoxy composites containing 2.5, 5, 7.5, and 10 wt.-% of
OmipPOSS were prepared.
4000 3600 3200 2800 2400 2000 1600 1200 800 400
B
A
Wavenumber (cm-1)
Abs
orba
nce
3358 cm-1
3219 cm-1
1138 cm-1
1775 cm-1
1716 cm-1
1378cm-1
1603 cm-1
Figure 1. The FTIR spectra: (A) OmipPOSS; (B) OapPOSS.
10 9 8 7 6 5 4
Chemical shift (ppm)
OmipPOSS
OapPOSS
Figure 2. The 1H NMR spectra of OmipPOSS and OapPOSS.
2078 Y. Ni, S. Zheng
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It is observed that all the cured composites were
transparent, suggesting that the composites are homoge-
neous, i.e., no phase separation occurs on the scale at least
more than the wavelength of visible light. In the present
work, TEMwas employed to examine the degree of disper-
sion of POSS cages in the composite system. Figure 4 repre-
sentatively presents the TEM micrographs of the sectioned
composites containing 10 wt.-% of OmipPOSS. To contrast
with the background, the TEM image was taken at the edge
of the sectioned sample. It is seen that the dark area (the
portion of the hybrid composite) was virtually homogenous
and no localized domains were detected at this scale,
implying that the POSS component was homogenously
dispersed in the continuous epoxy matrix at the nanoscale.
The result of TEM indicates that the nanocomposites were
obtained. It is proposed that it is crucial for the nano-
composites that the chemical bonds are formed between the
crosslinked networks and OmipPOSS since the polymer-
ization-induced phase separation of OmipPOSS could be
suppressed from the in situ polymerization system.[20,27]
Curing Reactions
In the ternary reactive systems composed of DGEBA,
DDM, and OmipPOSS, two major reactions are involved
with the formation of thermosetting composites including
the polymerization betweenDGEBA andDDM that affords
the tightly crosslinked networks (Reaction 1) and the
Michael addition between aromatic amine (viz. DDM) and
the maleimide groups of OmipPOSS (Reaction 2) as shown
in Scheme 3. TheMichael addition under the present curing
conditions was evidenced by the curing reaction between
OmipPOSS and DDM. With the Michael addition,
OmipPOSS is incorporated into the crosslinked networks
of epoxy via the formation of covalent bonds. FTIR was
used to examine the degree of curing reaction after the
POSS cages were introduced to the systems. Shown in
Figure 5 are the FTIR spectra of DGEBA, the control epoxy
and the nanocomposites containing 2.5, 5, 7.5, and 10wt.-%
of POSS. The pure DGEBA is characterized by the
stretching vibration band of epoxide groups at 915 cm�1
(see curve F). Under the present condition the curing
reaction of the control epoxy was quite complete, which
was evidenced by the disappearance of the epoxide band
(see curve A). It is noted that all the epoxide bands were
virtually vanished for the POSS-containing nanocompo-
sites under the identical curing conditions, indicating that
the curing reactions in the nanocomposites were carried out
to completion. In order to confirm the occurrence of the
Michael addition between OmipPOSS and DDM, the
stoichiometric mixture of the two compounds were cured
using the identical condition with the preparation of epoxy
composites. The solubility test of the cured sample in some
common solvents such as DMF indicates that the cross-
linked products were obtained. The DDM-cured Omip-
POSS was subject to the FTIR analysis, and the FTIR
spectrum of DDM-cured OmipPOSS is presented in
Figure 6, and the FTIR spectra of OmipPOSS and DDM
were also incorporated into this figure (curves A and B) for
comparison. It is seen that the intensity of the stretching
vibration band at 1 716 cm�1, attributable to carbonyl in
unreacted maleimide moieties of OmipPOSS, was sig-
nificantly decreased. In the maleimide moiety of Omip-
POSS, the C C double bond and the carbonyl of imide
could constitute a conjugated system. The conjugated
system could be interrupted with the occurrence ofMichael
addition between N–H bonds in amino groups of DDM
and the C C double bonds. Therefore, the characteristic
carbonyl band of maleimide at 1 716 cm�1 was drastically
reduced. It should be pointed out that in the range of 4 000–
3 000 cm�1, the stretching vibration bands of amino groups
100 50 0 -50 -100
Chemical shift (ppm)
OapPOSS
OmipPOSS
Figure 3. The 29Si NMR spectra of OmipPOSS and OapPOSS.
Figure 4. The TEMmicrograph of the nancomposite containing10 wt.-% of OmipPOSS.
Epoxy Resin Containing Octamaleimidophenyl Polyhedral Oligomeric Silsesquioxane 2079
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O CH2 HC CH2
O
NH2
DGEBA
+ O CH2 HC CH2
OH
N
DDM
NH2+N
C
C
HC
CH2
N
+
OmipPOSS DDM
(2)
(1)
NC
C
O
O
O
O
Scheme 3. Preparation of the POSS-containing nanocomposites.
4000 3600 3200 2800 2400 2000 1600 1200 800 400
Wavenumber (cm-1)
915 cm-1
Abs
orba
nce
A
B
C
D
E
F
Figure 5. The FTIR spectra of the nanocomposites containing:(A) 0, (B) 2.5, (C) 5.0, (D) 7.5, and (E) 10 wt.-% of OmipPOSS;(F) DGEBA.
4000 3600 3200 2800 2400 2000 1600 1200 800 400
Wavenumber (cm-1)
Tra
nsm
ittan
ce
A
B
C
1132
33663203
1716
Figure 6. The FTIR spectra of: (A) OmipPOSS, (B) DDM, and(C) DDM-cured OmipPOSS.
2080 Y. Ni, S. Zheng
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(N–H) at 3 366 and 3 203 cm�1 are still discernible,
suggesting that not all of amino groups (N–H) participated
in the Michael addition under the present curing condition.
Nonetheless, the FTIR results imply that under the identical
curing reaction the Michael addition can occur between
DDM and OmipPOSS.
Glass Transition Behavior
All the nanocomposites were subject to thermal analysis.
The DSC curves of control epoxy resin, POSS-containing
nanocomposites are presented in Figure 7. All the DSC
thermograms displayed single glass transition temperatures
(Tg’s) in the experimental temperature range (�20–
250 8C). It is noted that the composites containing 2.5 and
5 wt.-% of OmipPOSS displayed the enhanced Tg’s (178
and 174 8C) in comparison with the control epoxy resin
(172 8C), while the hybrids containing 7.5 and 10 wt.-% of
OmipPOSS have the lower Tg’s than the control epoxy. The
enhancement in glass transition temperatures could be
ascribed to the nanoreinforcement effect of POSS on the
polymer matrix. It is proposed that in POSS-modified
polymers there could be the two competitive factors to
determine the glass transition temperatures of resulting
materials. On the one hand, POSS cages on the segmental
level could restrict the motion of macromolecular chains,
and thus the glass transition temperatures are enhanced. On
the other hand, the presence of the bulky POSS cages could
act as the internal plasticizer, which gives rise to decreased
Tg’s. In the present system, the Michael addition between
DDMandOmipPOSS could be an additional factor to lower
the glass transition temperatures of nanocomposites. In the
present work, the curing agent, DDM was stoichiome-
trically added with respect to the amount of DGEBA.
Therefore, it is proposed that the tightly crosslinked
networks would not be formed in the POSS-containing
nanocomposites as in the control epoxy since a part of
curing agent (viz. DDM) could be consumed by OmipOSS
through the Michael addition reaction.[44–46] This effect is
quite pronounced for the nanocomposites containing the
higher amount of OmipPOSS.
Thermal Stability
Thermogravimetric analysis was applied to evaluate the
thermal stability of the POSS-containing epoxy nano-
composites. Shown in Figure 8 are the TGA curves of the
control epoxy, OmipPOSS, DDM-cured OmipPOSS, and
the POSS-containing nanocomposites, recorded at 20 8C �min�1 in nitrogen atmosphere. Within the experimental
temperature range, all the TGA curves displayed similar
degradation profiles. This observation indicates that the
existence of POSS did not significantly alter the degrada-
tion mechanism of the matrix polymers. The temperatures
of degradation (Td) were taken as the onset temperatures at
which 5wt.-% ofmass loss occurred. For the control epoxy,
the initial decomposition occurred at 413 8C, and no
residual of decomposition was detected when the degrada-
tion was carried out at 740 8C as expected. For OmipPOSS,
the residue of decomposition was 53.7%, which is much
higher than theoretical ceramic yield of 23.6%, suggesting
that a great amount of char exists in the residues of decom-
position of silsesquioxane-containing compound. This
observation was further confirmed by the degradation of
0 50 100 150 200 250
163oC
170oC
174oC
178 oC
172oC
10
7.5
5
2.5
0
OmipPOSS wt%
End
o
Temperature ( oC)
Figure 7. The DSC curves of the control epoxy resin and of thePOSS-containing nanocomposites.
200 400 600 8000
20
40
60
80
100
OmipPOSS wt%
10.07.55.02.5
0
Wei
ght (
%)
Temperature ( oC)
OmipPOSS
DDM-cured POSS
Figure 8. The TGA curves of the control epoxy, DDM-curedBMI, and POSS-containing nanocomposites.
Epoxy Resin Containing Octamaleimidophenyl Polyhedral Oligomeric Silsesquioxane 2081
Macromol. Chem. Phys. 2005, 206, 2075–2083 www.mcp-journal.de � 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
DDM-cured OmipPOSS, in which the theoretical ceramic
yield is even lower than OmipPOSS. From Figure 8, it is
seen that both OmipPOSS and DDM-cured OmipPOSS
have the lower Td’s than the control epoxy. The Td’s of the
nanocomposites are intermediate between those of the
control epoxy and DDM-cured OmipPOSS. More impor-
tantly, the incorporation of OmipPOSS into epoxy resin
networks results in retarded weight loss rates and enhanced
char yield of the materials at high temperatures. This effect
was increasingly pronounced with increasing the concen-
tration of OmipPOSS. In this system, the cubic POSS cages
and the maleimidophenyl groups were connected onto the
crosslinking networks via the formation of covalent bonds,
which thus hamper the continuous decomposition of the
epoxy matrix. The nanocomposites exhibited very high
char yields, implying that there are fewer volatiles that were
released from the nanocomposites during heating and thus
the flame retardance is improved.
Conclusion
In this work, OmipPOSS was synthesized via the imidiza-
tion reaction between OapPOSS and maleic anhydride.
The octafunctional POSS was characterized by means of
FTIR and NMR spectroscopies. OmipPOSS was employed
to prepare the nanocomposites with epoxy resin. The
thermosetting nanocomposites containing OmipPOSS up
to 10 wt.-% were obtained via in situ polymerization of
DGEBA and DDM in the presence of OmipPOSS. High-
resolution TEM indicates that the nanometer-scaled dis-
persion of POSS molecules was obtained, suggesting that
the nanocompositeswere successfully prepared. The results
of DSC showed that the glass transition temperatures (Tg’s)
of the POSS-containing nanocomposites are dependent on
the content of POSS in the nanocomposites. When the
contents of POSS are less than 5wt.-%, the nanocomposites
displayed the enhanced glass transition temperatures (Tg’s)
in comparison with control epoxy. TGA showed that the
nanocomposites displayed improved flame retardance in
terms of char yield in the materials.
Acknowledgements: The financial support from ShanghaiScience and Technology Commission, China was acknowledgedunder a key project (No. 02DJ14048). We thank the NaturalScience Foundation of China (GrantNo. 50390090 and 20474038)for the partial support.
[1] G. M. Whitesides, T. P. Mathias, C. T. Seto, Science 1991,254, 1312.
[2] T. Lan, P. D. Kaviratan, T. J. Pinnavaia, Chem. Mater. 1995,7, 2144.
[3] E. P. Giannelis, JOM 1992, 44, 28.[4] B.K. G. Theng, ‘‘Formation and Properties of Clay-Polymer
Complexes’’, Elsevier, Amsterdam 1979.[5] M.P.Andrews, S. I. Najafi,Crit. Rev.Opt. Sci. Technol.1997,
CR68, 253.[6] J. Wenzel, J. Non-Cryst. Solids 1985, 73, 69.[7] U. Schubert, N. Huesing, A. Lorenz, Chem. Mater. 1995, 7,
2010.[8] J. V. Crivello, K.Y. Song, R.Ghosha,Chem.Mater. 2001, 13,
1932.[9] T. Lan, P. D. Kaviratna, T. J. Pinnavaia, Chem. Mater. 1995,
7, 2144.[10] E. P. Giannelis, R. Krishnamoorti, E. Manias, Adv. Polym.
Sci. 1999, 138, 107.[11] A. Okada, A. Usuki, T. Kurauchi, O. Kamigaito, ACS Symp.
Ser. 1995, 585, 55.[12] K. Yano, A. E. P. Usuki, A. Okada, T. Kurauchi,
O. Kamigaito, J. Polym. Sci., Part A: Polym. Chem. 1993,31, 2493.
[13] E. P. Giannelis, R. Krishnamoorti, E. Manias, Adv. Polym.Sci. 1999, 138, 107.
[14] M. G. Voronkov, V. I. Lavrent’yev, Top. Curr. Chem. 1982,102.
[15] R. H. Baney, M. Itoh, A. Sakakibara, T. Suzuki, Chem. Rev.1995, 95, 149.
[16] H. Burgy, G. Calzaferri, D. Herren, A. Zhdanov, Chimia1991, 45, 3.
[17] J. D. Lichtenhan, N. Q. Vu, J. A. Carter, J. W. Gilman, F. J.Feher,Macromolecules 1993, 26, 2141.
[18] J. Choi, J. Harcup, A. F. Yee, Q. Zhu, R. M. Laine, J. Am.Chem. Soc. 2001, 123, 11420.
[19] J. Choi, S. G. Kim, R. M. Laine,Macromolecules 2004, 37,99.
[20] Y. Ni, S. Zheng, K. Nie, Polymer 2004, 45, 5557.[21] A. Lee, J. D. Lichtenhan, Macromolecules 1998, 31,
4970.[22] B.X. Fu, B. S. Hsiao, H.White,M. Rafailovich, P. T.Mather,
H. G. Jeon, S. Phillips, J. Lichtenhan, J. Schwab, Polym. Int.2000, 49, 437.
[23] G. Z. Li, L. Wang, H. Toghiani, T. L. Daulton, K. Koyama,C. U. Pittman, Macromolecules 2001, 34, 8686.
[24] M. J. Abad, L. Barral, D. F. Fasce, R. J. J. Williams,Macromolecules 2003, 36, 3128.
[25] L. Matejka, A. Strachota, J. Plestil, P. Whelan, M. Steinhart,M. Slaof,Macromolecules 2004, 37, 9449.
[26] A. Strachota, I. Kroutilova, J. Kovarova, L. Matejka,Macromolecules 2004, 37, 9457.
[27] H. Liu, S. Zheng, K. Nie, Macromolecules 2005, 38,5088.
[28] R. M. Laine, J. Choi, I. Lee, Adv. Mater. 2001, 13, 800.[29] J. Choi, A. F. Yee, R. M. Laine, Macromolecules 2003, 36,
5666.[30] J. Choi, R. Tamaki, S. G. Kim, R. M. Laine, Chem. Mater.
2003, 15, 3365.[31] J. Choi, A. F. Yee, R. M. Laine, Macromolecules 2004, 37,
3267.[32] B. X. Fu, M. Namani, A. Lee, Polymer 2003, 44, 7739.[33] K.-F. Lin, J.-S. Lin, C.-H. Cheng, Polymer 1996, 37, 4297.[34] Y. Ni, S. Zheng, Chem. Mater. 2004, 16, 5141.[35] R. Tamaki, Y. Tanaka, M. Z. Asuncion, J. Choi, R. M. Laine,
J. Am. Chem. Soc. 2001, 123, 12416.[36] J. F. Brown,L.H.Vogt, P. I. Prescott, J. Am.Chem. Soc.1964,
86, 1120.[37] P. S. G.Krishnan, C. He, J. Polym. Sci., Part A: Polym. Chem.
2005, 43, 2483.
2082 Y. Ni, S. Zheng
Macromol. Chem. Phys. 2005, 206, 2075–2083 www.mcp-journal.de � 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
[38] K.-F. Lin, J.-S. Lin, J. Appl. Polym. Sci. 1993, 50, 1601.[39] D. O. Hummel, L.-U. Heinen, H. Stenzenberger, H. Siesler,
J. Appl. Polym. Sci. 1974, 18, 2015.[40] K. N. Ninan, K. Krishnan, J. Mathew, J. Appl. Polym. Sci.
1986, 32, 6033.[41] S. Takeda, H. Akiyama, H. Kakiuchi, J. Appl. Polym. Sci.
1988, 35, 1341.
[42] D. Kumar, G. M. Fohlen, J. A. Parker, J. Polym. Sci., Part A:Polym. Chem. 1983, 21, 245.
[43] C. D. Giulio, M. Gautier, B. Jasse, J. Appl. Polym. Sci. 1984,29, 1771.
[44] M. Chaudhari, T. Galvin, J. King, SAMPE J. 1985, 21, 17.[45] H. D. Stenzenberger, Br. Polym. J. 1988, 20, 383.[46] J. F. Voit, J. C. Seferis, J. Appl. Polym. Sci. 1988, 35, 1352.
Epoxy Resin Containing Octamaleimidophenyl Polyhedral Oligomeric Silsesquioxane 2083
Macromol. Chem. Phys. 2005, 206, 2075–2083 www.mcp-journal.de � 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim