octa(aminophenyl) polyhedral oligomeric silsesquioxane/boron-containing phenol–formaldehyde resin...
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Octa(aminophenyl) Polyhedral OligomericSilsesquioxane/Boron-Containing Phenol–FormaldehydeResin Nanocomposites: Synthesis, Cured,and Thermal Properties
Jungang Gao, Xing Li, Weihong Wu, Haojie LinCollege of Chemistry and Environment Science, Hebei University, Baoding 071002, China
Octa(aminophenyl) polyhedral oligomeric silsesquiox-ane (OAP-POSS) and boron-containing phenol-formal-dehyde resin (BPFR) were synthesized, respectively.The BPFR nanocomposites with different OAP-POSScontent (wt%) were prepared, and their propertieswere characterized. The results show that the thermaldegradation process of this nanocomposites can be di-vided into three stages, and they are all following thefirst order mechanism. The residual ratio and thermaldegradation activation energy Ea of 9 wt% OAP-POSS/BPFR nanocomposites are both better than others andthe Ea increase gradually in three stages, which is 93.3,134.0, and 181.9 kJ mol21, respectively. Its residual ra-tio at 9008C is 36.48%. The mechanical loss peak tem-perature Tp is 2288C for 12 wt% OAP-POSSS/BPFRnanocomposites, which is higher 488C than pureBPFR. POLYM. COMPOS., 32:829–836, 2011. ª 2011 Societyof Plastics Engineers
INTRODUCTION
Phenolic-formaldehyde resin (PFR) is an excellent
thermosetting resin, which has good mechanical properties
and heat resistance, and it has been used in preparing
fiberglass-reinforced laminate, molding compounds, ther-
mal insulation materials, coating, and adhesive. However,
in order to further improve on the heat resistance and me-
chanical properties of PFR, especially high-temperature
ablation and residual ratio, the boron-containing phenol–
formaldehyde resin (BPFR) is synthesized by introducing
element boron into the molecular chain of resolve and
novolac phenolic resin [1–5]. In the phenolic resin, the
boron can form covalent bond with oxygen, and its B��O
bond energy is 773.3 kJ mol21, which is much higher
than that of C��C bond energy (334.7 kJ mol21). The
thermal decomposition temperature Td of BPFR can be
increased about 100–1408C than conventional phenolic
resin. The borate can be used as the flame-retardants in
various materials because it can form non-penetrable glass
coating. Moreover the glass coatings can exclude oxygen
and prevent further propagation combustion. In addition
to the above, the BPFR also has the higher mechanical
properties, dielectric properties and shielding of neutron
radiation. So BPFR is widely used in the high-tech fields,
such as spaceflight, rocketry, and so on. However, the
modification by introducing boron into the main chain of
phenol resin will increase the brittleness and water sensi-
tivity of materials, thus, all of these factors will restrict
the wide application of BPFR. To improve the hydrolytic
stability and physical properties of BPFR, the researchers
have done a lot of works, such as modified by B��N or
B��O coordination, layered-silicate nanoparticles, etc [3,
4, 6, 7].
Organic-inorganic hybrid polymeric materials with an
in situ created inorganic phase are typical nanocompo-
sites, and they have been received significant interest in
the recent years because of their outstanding characteris-
tics [8, 9]. The mechanical properties of nanostructured
hybrid organic–inorganic composites are superior to the
present materials. Polyhedral oligomeric silsesquioxanes
(POSS) is a new organic-inorganic hybrid molecule,
which has great potentials in the synthesis of organic–
inorganic hybrid materials. POSS nanoparticles have been
demonstrated as an efficient way to design the nanostruc-
ture of hybrid materials and preparation of organic-inor-
ganic hybridized materials. POSS contains a Si��O nano-
structured inorganic framework as the core, and its outer
layer is covered by reactive or non-reactive functional
groups. The reactive functional groups in POSS not only
can further homopolymerization, but also can react or co-
polymerize with other reactants or monomer. The non-re-
active groups of POSS make it compatible with polymers,
organic monomers and biological systems. In contrast to
conventional inorganic fillers, POSS has the advantages
Correspondence to: Jungang Gao; e-mail: [email protected]
Contract grant sponsor: Nature Science Foundation; contract grant num-
ber: E2010000287.
DOI 10.1002/pc.21105
Published online in Wiley Online Library (wileyonlinelibrary.com).
VVC 2011 Society of Plastics Engineers
POLYMER COMPOSITES—-2011
of monodispersed size, low density, high thermal stability,
and good compatibility with polymer. Polymer of contain-
ing POSS can show a series of novel properties and is
found widespread application in high performance and
fire-resistance materials, so the POSS has been used as
polymer modifiers and to prepare the polymer/POSS
hybrid materials [10–12].
Some researchers have reported that the phenol resins
were modified by clay and POSS. Tasan has reported that
the mechanical performance of resol type phenolic resin
could be increased by layered silicate nanocomposites
[13]. Lee and Kuo have reported some studies on the mis-
cibility, specific interactions, and self-assembly behavior
of phenolic resin and POSS [14]. Lin and Kuo have
reported the thermal and surface properties of phenolic
nanocomposites containing POSS [15]. Zhang et al. have
reported the phenol resin modified by octa(aminophenyl)
polyhedral oligomeric silsesquioxane [16]. We have
reported the non-isothermal co-curing behavior and
kinetics of bisphenol A epoxy resin/3-glycidyloxypropyl-
POSS with MeTHPA [17].
To the best of our knowledge, there is no precedent
report on the modification of BPFR by POSS. In this
work, the BPFR was synthesized by formaldehyde solu-
tion method according foregoing work [2], the OAP-
POSS/BPFR nanocomposites were prepared, and its
structure and thermal properties were characterized. The
results show that the residual ratio of OAP-POSS/BPFR
nanocomposite at 9008C is 36.48%. The mechanical
loss peak temperature Tp increases with increasing
OAP-POSS contents, which is 2288C when OAP-POSS
content is 12 wt% and higher 488C than that of pure
BPFR.
EXPERIMENTAL
Materials and Instrumentation
Phenyl-trimethoxysilane is chemically pure grade and
supplied by Xiantao Greenchem Industries, China; Formic
acid, tetramethyl ammonium hydroxide (TMAH), isopro-
pyl alcohol, xylene, fuming nitric acid, tetrahydrofuran
(THF), triethylamine, ethyl acetate, anhydrous MgSO4,
hexane, phenol, formaldehyde, NaOH, boric acid and ace-
tone, etc. were all analytically pure grades and supplied
by Tianjin Chemical Reagent, China. A 10 wt% Pd/C cat-
alyst was supplied by ShengDa Chem, Dalian, China.
Fourier transform infrared spectrometer (FTIR, FTS-
40, BIO-RAD, USA) and liquid chromatography-mass
spectrometer (LC/MSD, Agilent 1100, USA) were used to
determine the structure of POSS. Thermal gravimetric
analysis (TGA, Pyris-6, Perkin-Elmer, USA) was operated
under static air, about 15 mg of powder cured was intro-
duced into the thermobalance, and then heated from 25 to
9008C at the heating rate of 158C min21. Thermalgravim-
eter–Mass spectrometer (TG/MS, STA-449C-type, QMS-
403C-type, NETZSCH, Germany) was used to determine
the pyrolysates of samples. About 8 mg sample was
placed into cell, and heated from 25 to 9008C under Ar-
gon flow of 20 mL min21 at the heating rate of 108Cmin21. A torsional braid analyzer (TBA, GDP-4, Jilin
University, China) was used to determine the maximal
mechanical loss temperature (Tp) at the heating rate of
28C min21 from 25 to 2508C.
Synthesis of Octa(aminophenyl)silsesquioxane(OAP-POSS)
Octaphenylsilsesquioxane (OP-POSS) was synthesized
according literature [18, 19]. The mixed solution of
TMAH (0.81 g), water (7.3 g), and isopropanol (130 mL)
was added into a four-necked flask, equipped with a stir-
rer, thermometer and condenser and stirred at 08C. Thenthe mixture of 40.1 g phenyltrimethoxysiloxane and 45
mL isopropanol was dropped into the foregoing system,
and the mixture was stirred for 6 h at the room tempera-
ture. The isopropanol and water were removed by vacuum
distillation from the system. Then the hydrolytic product
was dissolved with 110 mL xylene and heated at 1088Cfor 4 h. After that, the solution was heated to 1268C, andrefluxed for another 4h, during which the Si��O��Si
bonds were formed through the cyclization reaction of
Si��OH groups. At last, the xylene was removed by vac-
uum distillation, and the white product was obtained.
FTIR (KBr powder): 1132 cm21 (Si��O��Si), 1590
cm21 (Phenyl C¼¼C), 3050 cm21 (Phenyl C��H).
The FTIR spectrum showed the absorption peak of
hydroxyl group at 3500 cm21 almost disappeared, and the
condensation reaction of silicon alcohol had completed.
The structure of product was tested by the Liquid-MS
chromatography, and the result showed that the OP-POSS
was obtained.
Octa(nitrophenyl)-POSS (ONP-POSS) was synthesized
in accordance with literature [19]. A 10 g of OP-POSS (9.7
mmol) was added to 50 mL fuming nitric acid and was
stirred at 08C for 1.5 h, and then continue stirred for
another 20 h at room temperature. After filtration through
Celite fonnel, the solution was put into 50 g ice. The flaxen
solid was collected by filtration and washed with water and
ethanol. The powder of Octa(nitrophenyl)-POSS (ONP-
POSS) was obtained and was dried under vacuum at 508C.ONP-POSS (5.0 g) and 10 wt% Pd/C (0.61 g) were
put into a flask equipped with a stirrer, thermometer and
a condenser under N2. About 40 mL of anhydrous THF
and 40 mL triethylamine were then added to this flask.
The mixture was heated to 608C, and 4.4 mL 98% formic
acid was added dropwise into the mixture at this tempera-
ture. After 5 h, the THF layer was separated, and another
15 mL THF was added to this solution, and then the THF
layer was separated again. The two THF extractions were
combined and filtered by Celite fonnel. Then 20 mL ethyl
acetate was added into the filtrate and washed three times
with pure water. The organic layer was dried by anhy-
830 POLYMER COMPOSITES—-2011 DOI 10.1002/pc
drous MgSO4 and precipitated into 500 mL hexane. A
white precipitate was collected by filtration. The product
was further purified by re-dissolved in mixture of 15:25
THF/ethyl acetate solvent and precipitated into 300 mL
hexane. Liquid chromatography-mass spectrometer was
used for determination the components of OAP-POSS and
the detailed structure, the Octa(aminophenyl)silsesquiox-
ane was obtained.
FTIR (KBr powder method): 1,132 cm21 (Si��O��Si),
3,050 cm21 (Phenyl C��H), 3312 cm21 (��NH2).
Synthesis of Boron-Containing Phenol–FormaldehydeResin
Boron-containing phenol formaldehyde resin (BPFR)
was prepared in accordance with formaldehyde solution
method [1, 2]. First, the 73.0 g formaldehyde, 70.5 g phe-
nol, and 0.3 g NaOH were all added into a flask, and
heated at 708C for 1 h, after the water was removed by
vacuum distillation and the saligenol was obtained. Sec-
ond, 12.5 g boric acid was added into the saligenol, and
reaction 1 h at 1058C, then removed the water again by
vacuum until the temperature rises to 1208C, the yellow
BPFR was obtained, the molecular structure as Scheme 1.
Preparation of BPFR/OAP-POSS Hybrid Nanocomposites
BPFR and OAP-POSS were both dissolved to a certain
amount of acetone in specific ratio: 5/0, 4.85/0.15, 4.7/
0.3, 4.55/0.45, and 4.4/0.6, respectively. A homogeneous,
stable and transparent solution was be obtained, and
marked as No. 1–5, respectively. After the solvent was
evaporated in vacuum oven, the sample was cured at 120,
150, 180, and 2208C for 30 min, respectively. Then the
OAP-POSS/BFPR nanocomposites which contained 0, 3,
6, 9, and 12 wt% OAP-POSS were obtained, respectively.
Characterization
The No.1 and No.5 sample was coated onto the KBr
tablets, respectively, and cured at 120, 150, 180, and
2208C for 30 min, separately. After that, two cured sam-
ples were characterized by FTIR. All five samples were
cured 2 h at 2008C, then grinded into powder. The ther-
mogravimetroc analysis (TGA) was performed at 108Cmin21 heating rate from 258C to heat to 9008C. The No.
1, 3, and 5 samples were dissolved into acetone, then the
TBA specimens were prepared via dipping the heat-
cleaned glass fiber braid into it, respectively. After the
solvent was evaporated, these TBA specimens were cured
at 2008C for 2 h. The dynamic mechanical loss peak the-
merature Tp was determine with a torsional braid analyzer
(TBA, GDP-4, Jilin University, China) at the heating rate
of 28C min21 from 25 to 2608C.
RESULTS AND DISCUSSION
Infrared Spectroscopic Analysis
The No. 1 sample (pure BPFR) was coated on KBr
tablets, and cured at 120, 150, 180, and 2208C for 0.5 h,
respectively. Then FTIR spectra of uncured sample and
cured samples were obtained and showed in Fig. 1.
In FTIR spectrum of BPFR, seven major characteristic
bands of ��C6H5, B��O, ��CH2��, C��O of ��C6H4OH,
C��O of C��O��C, C��O of ��CH2OH, and C¼¼O
stretching vibration are observed at 1,600 cm21 or 750
cm21, 1,350 cm21, 1,450 cm21, 1,250 cm21, 1,100 cm21,
1,020 cm21, 3,300–3,500 cm21, and 1,650 cm21, respec-
tively.
As seen from Fig. 1, the B��O characteristic peak in-
tensity at 1,350 cm21 gradually increased when the cured
temperature rise, however, the ��OH characteristic peak
at 3300–3500 cm21 become weaker. It indicates, during
the curing process, the more B��O bond has been formed
through the reactions between ��OH of ��C6H4��CH2OH
SCHEME 1. Schematic structure of BPFR.
FIG. 1. FTIR spectrums of the No. 1 cured at different temperatures
for 0.5 h (1-uncured; 2, 3, 4, 5-cured at 120, 150, 180, and 2208C for
0.5 h, respectively).
DOI 10.1002/pc POLYMER COMPOSITES—-2011 831
or ��C6H4OH and unreacted ��OH group in boric acid.
When the cured temperature is over 1808C, the decrease
of B��O characteristic peak intensity at 1,350 cm21
should be attributed to the coordinate structure of B/O
have been formed [2]. We have reported that the reactiv-
ity of methylol group with boric acid is higher than that
of phenol hydroxyl group, so the reaction of unreacted
��OH groups in boric acid with methylol groups is prior
to phenol hydroxyl group [2, 20]. Then the coordinated
oxygen atom should be offered by phenol hydroxyl group.
According to the literature [2, 21], when the hexatomic
ring containing B/O coordination bond is formed in the
cured resin, the IR absorption band of B��O borate at
1,350 cm21 would disappear, so B��O characteristic peak
of BPFR at 1,350 cm21 become weaker over 1808C. Theabsorption band of carbonyl group at 1,650 cm21 is
attributed to the oxidation of ether bund ��CH2OCH2��,
CH2 and methylol group in the synthesis and cured pro-
cess of BPFR [2, 20, 22].
The No. 5 sample (12%OAP-POSS/BPFR) was treated
in the same way as No. 1, and the FTIR spectra showed
in Fig. 2. As seen from Fig. 2, it has a broad absorption
peak at 1,132 cm21, which is assigned to Si��O��Si
band. But to distinguish between ��OH and ��NH2 is dif-
ficult because their characteristic bands both appeared at
3,300–3,500 cm21. During the cured process, the charac-
teristic absorption peak of B��O increased while ��OH
absorption peak decreased. At the same time, the ��NH2
absorption peak also decreased, it indicates that the
��NH2 of OAP-POSS have reacted with ��OH of meth-
ylol in the BPFR or boric acid, and the ��CH2��NH�� or
B��N bond is formed [2, 6]. But the B��O characteristic
peak at 1,350 cm21 decreases similarly, and it also means
that the coordinate linkages of B/N and B/O have
been formed at higher temperature as shown as Scheme
2b, and the OAP-POSS/BPFR hybrid nanocomposites
have been formed as shown in Scheme 3. The coordinate
structures of B/N and B/O will reduce the sensitivity
of resins on water or moisture which is caused by the un-
FIG. 2. FTIR spectrums of the No. 5 cured at different temperatures
for 0.5 h (1-uncured; 2, 3, 4, 5-cured at 120, 150, 180, and 2208C for
0.5 h, respectively).
SCHEME 2. The coordinate structure of B��O and B��N in cured
BPFR.
SCHEME 3. Schematic representation of OAP-POSS/BPFR nanocomposites.
832 POLYMER COMPOSITES—-2011 DOI 10.1002/pc
saturated nature of boron atoms [6, 7, 23]. Figure 3 is the
distribution of Si in the nanocomposites for 12 wt%
OAP-POSS content. As seen from Fig. 3, the OAP-POSS
can homogeneous distribute in BPFR and form nanocom-
posites. Because of the OAP-POSS is a molecule of poly-
reactive functional groups, it can reactive with BPFR
molecule to form crosslink structure.
Thermogravimetric Analysis of Cured Products (TGA)
The No. 1–5 were cured at 1808C for 2 h, and TGA
curves were obtained and showed in Fig. 4.
As seen from Fig. 4, the thermal loss weight of BPFR is
only 68% at 9008C. It shows that the BFFR has a better
thermal stability. After added OAP-POSS, the thermal sta-
bility of OAP-POSS/BPFR nanocomposites get better and
better as the increasing the OAP-POSS content. However,
when the OAP-POSS content is 12% or over 12%, the ther-
mal stability of the nanocomposites will deteriorate. It may
be due to adding a lot of OAP-POSS, so excess ��NH2
will be introduced matrix polymer, because the ��NH2
group has lower thermal stability than other group, so that
it will reduces the high-temperature residual ratio of sam-
ples. The thermal residual ratio of the nanocomposites at
different temperature is shown in the Table 1.
Figure 5 is the releasing curve of CO2 for pure BPFR
obtained by TG/MS spectrometer. As seen from Fig. 5,
the thermal decomposition process of BPFR can be di-
vided into three stages according to loss weight or releas-
ing CO2 rate, which is 340–808C, 480–7208C, and 720–
9008C. The BPFR has a most decomposition rate between
480 and 7208C. It is generally considered that the weight
loss in the first stage is mainly attributed to decomposi-
tion and oxidation of ether bund ��CH2OCH2��, CH2
and carbonyl group C¼¼O [2, 20]. In the second stage, the
weight loss is mainly attributed to the oxidation and
decomposition of methylene group and phenol groups. In
the third stage, it is a carbonization process of benzene
and borate bond, during this period, it also may be gener-
ate some compounds which contain B��N bond [6], and a
large number of CO and CO2 are released.
As can be seen from Fig. 4 and Table 1, a certain
amount of OAP-POSS can enhance the heat resistance and
high temperature residual ratio of BPFR. However, these
properties will be changed by adding different dosage of
OAP-POSS. When the adding amount of OAP-POSS is less
than 12%, these properties along with the addition of OAP-
FIG. 3. Distribution of Si for 12 wt% OAP-POSS/BPFR nanocompo-
sites. [Color figure can be viewed in the online issue, which is available
at wileyonlinelibrary.com.]
FIG. 4. TGA and DTG curves of the cured samples.
TABLE 1. The residual ratio of samples with different OAP-POSS
contentat.
Temperature (8C) 0% 3% 6% 9% 12%
500 85.15 85.77 87.63 88.55 86.70
600 69.43 71.19 73.86 75.16 72.21
700 53.67 56.78 58.23 61.71 56.10
800 43.84 46.13 47.22 49.97 42.25
900 31.98 35.84 36.48 36.48 29.09
FIG. 5. The release spectrum of CO2 for BPFR at different temperature.
DOI 10.1002/pc POLYMER COMPOSITES—-2011 833
POSS get better and better first, but when OAP-POSS con-
tent is 12% or more, they will get bad. This is due to the
appropriate amounts of OAP-POSS can react with the
BPFR as crosslinker, the ��NH2 group on OAP-POSS can
react with hydroxyl groups of BPFR and H3BO3 to form
C��N, B��N covalent bond, or B/N coordination bond
and hydrogen bonds [6, 7]. On the other hand, the nano-
cage-type Si��O��Si inorganic framework of OAP-POSS
will enhance the heat-resistance of BPFR. But much more
��NH2 groups will not fully participate in reactions, and
such these ��NH2 groups will reduce the thermal stability
of nanocomposites.
Thermal Degradation Kinetics
Thermal degradation kinetic parameters of BPFR can
be calculated from TGA data. To determine the degrada-
tion kinetic parameters from the thermo-gravimetric data,
the first step is to evaluate the conversion of reaction. In
dynamic TGA experiments, the weight change of sample
is regarded as a function of temperature and the conver-
sion a can be expressed as flows:
a ¼ W0 �WT
W0 �W1ð1Þ
where Wo is the initial sample weight in i stage, WT is the
residual weight of the sample at temperature T, W1 is the
final weight at that stage. Therefore, according TGA
curves and Eq. 1, the conversion is calculated for differ-
ent degradation stages.
In the solid-state reaction process, the kinetics of ther-
mal degradation is described as follows:
dadT
¼ kðTÞf ðaÞ ð2Þ
kðTÞ ¼ A exp � Ea
RT
� �ð3Þ
where da/dt is the rate of reaction, f(a) is a dependent ki-
netic model function, k(T) is a temperature-dependent
reaction rate constant, A is the pre-exponential factor, R is
the gas constant (8.314 J mol21 K21), T is thermody-
namic temperature, Ea is the apparent activation energy.
Equation 3 is the Arrhenius equation.
The reaction rate can be treated as a function of tem-
perature if the sample was heated at a constant heating
rate (b), and the temperature is decided by the heating
time. Therefore, the reaction rate can be written as the
following:
dadt
¼ dadT
� dTdt
¼ bdadT
ð4Þ
From the Eqs. 2–4, we have:
dadT
¼ A
bexp � Ea
RT
� �� f ðaÞ ð5Þ
By applying the temperature integral term to Eq. 5, wecan obtain Eq. 6 as follow:
GðaÞ ¼Za
0
daf ðaÞ ¼
A
b
Za
0
exp � Ea
RT
� �dT ð6Þ
where G(a) is the integrals form of the conversion de-
pendence function. The correct form of G(a) depends on
the proper mechanism of degradation reaction. Differen-
tial expression of G(a) for some solid-state reaction mech-
anism can be described as following: for first order (n ¼1), G(a) is 2ln(1 2 a); for second order (n ¼ 2), G(a) is1/(1 2 a); for third order (n ¼ 3), G(a) is 1/(1 2 a)2.
For thermal degradation process of multistage, the
Madhusdanan-Krishnan-Ninan method can be applied
[24]. In this work, the TGA data are analyzed on the base
of the Madhusdanan-Krishnan-Ninan method, which can
be expressed by the following Eq. 7:
lnGðaÞT1:92
¼ lnAEa
bRþ 3:77� 1:92 lnEa � Ea
RTð7Þ
The form of G(a) is different as reaction order changing.
Therefore, three different mechanisms are used to treat
the degradation process, and the Ea and frequency factor
A will be obtained by the slope and intercept of ln [G(a)/T1.92] vs. 1/T curve. The exactly data of No. 4 (9 wt%
OAP-POSS/BPFR) showed in Table 2.
As seen from Table 2, the calculated data on the same
thermal degradation stage with three mechanisms are dif-
ferent. According to the most appropriate reaction mecha-
nism would has the best linear correlation coefficients and
lower standard deviation, the three of thermal degradation
stages are all following the first order, and the activation
energy Ea of degradation reaction is 93.3, 134.0 and
181.9 kJ mol21, respectively. The other thermal degrada-
tion parameters of samples showed in Table 3.
As seen from Table 3, in the three stages, the Ea
increase with increasing temperature for all samples,
moreover, it also increase with increasing OAP-POSS
content (except No. 5). As same as thermal gravimetric
analysis data, the Ea has a highest value when the content
of OAP-POSS is 9 wt%, and then decrease when the
TABLE 2. The kinetic parameters of the No. 4 at 108C min21 heating
rate.
Reaction
order
Correlation
coefficient
Ea
(kJ mol21)
ln
A(S21)
Standard
deviation
First stage 1 0.9738 112.0 19.8 0.3796
2 0.6652 34.3 8.1 0.5936
3 0.7190 80.1 17.1 1.1930
Second stage 1 0.9491 170.5 24.2 0.3885
2 0.8230 112.2 17.9 0.5331
3 0.8234 243.8 36.7 1.1585
Third stage 1 0.9847 198.4 23.7 0.1543
2 0.7876 139.3 18.4 0.5212
3 0.8050 296.0 37.2 1.0436
834 POLYMER COMPOSITES—-2011 DOI 10.1002/pc
OAP-POSS content is more than this amount. It means
that appropriate amount of OAP-POSS can improve the
thermal stability of BPFR.
TBA Analysis
The glass transition temperature (Tg) is a very impor-
tant nature of polymer, and it could be obtained by DSC,
DMA or others. The glass transition temperature can be
used effectively to monitor the molecular motion and cur-
ing reaction. DSC is usually used to determine the Tg of
polymer, but it is not a best method for thermosetting
polymers, especially at higher conversion, because the
shift of DSC curve is very little and unconspicuous at that
time. The TBA method can be used to determine the Tgof the thermosetting system, and it is particularly useful
at high conversion and after vitrification because of the
non-linearity of Tg vs. conversion a [25, 26]. Generally,
there is a one-to-one relationship between Tg and mechan-
ical loss peak temperature Tp. The higher Tp, the higher
Tg is, which depends upon the curing conditions and mo-
lecular structure, such as amount of cross-linked agent,
curing temperature and time. With these change in cured
conditions, the peak temperature Tp and Tg of samples
will also changed, so that, Tg has been used directly as a
parameter in the analysis of reaction kinetics and molecu-
lar structure. OAP-POSS/BPFR nanocomposite is a ther-
mosetting polymer, so their molecular chain movement is
very complicated and difficult. Moreover, small molecules
would release in the cured process. In this work, the TBA
was used to determined Tp and Tg of samples.
No. 1, 3, and 5 samples were dissolved in acetone, and
coated onto the heat-cleaned glass fiber braid, cured at the
2008C for 2 h. After that, the mechanical loss peak tem-
perature Tp of OAP-POSS/BPFR nanocomposites was
determined at 28C min21 heating rate. Figure 6 is plots of
mechanical loss D vs. temperature T. As seen from Fig. 6,
the mechanical loss peak temperature Tp for No. 1, 3, and
5 is about 180, 200, and 2288C, respectively. It shows
that the addition of OAP-POSS can significantly increase
the Tg of BPFR. When OAP-POSS content is 12 wt%, the
Tp will increase about 488C. It may be due to that the
reactions between amino group of OAP-POSS and BPFR
in the curing process can increase the crosslinking degree
of resin, or form hydrogen bond with BPFR molecules.
They will hinder the thermal motion of molecular chains
and increase Tg. In short, OAP-POSS can increase the Tgand the thermal properties of materials, but adding too
much OAP-POSS will decrease the thermal properties of
OAP-POSS/BPFR nanocomposites, because of ��NH2
group has lower the thermal stability than others.
CONCLUSIONS
Octa(aminophenyl) polyhedral oligomeric silsesquiox-
ane (OAP-POSS) can react with boron-containing phenol–
formaldehyde resin (BPFR), and OAP-POSS/BPFR nano-
composites are formed in the curing process. The thermal
degradation process of BPFR can be divided into three
stages: 340–5208C, 520–7208C, and 720–9008C, and all
of the degradation stages are following first order mecha-
nism. Thermal stability of materials is enhanced with
increasing OAP-POSS contents when it is not over 12%,
meanwhile, the 9 wt% OAP-POSS/BPFR nanocomposite
is best, its residual ratio at 9008C is 36.48%, and its deg-
radation activation energy Ea in three stages is 112.0,
170.5, and 198.4 kJ mol21, respectively. The mechanical
loss peak temperature Tp is enhanced with increasing
OAP-POSS content. The Tp of 12 wt% OAP-POSS/BPFR
nanocomposites is highest (2288C), and it is higher about
488C than pure BPFR.
REFERENCES
1. O.M. Abdalla and A. Ludwick, T. Polymer, 44, 7353
(2003).
2. J.G. Gao and L.Y. Xia, Polym. Degrad. Stabil., 83, 71
(2004).
TABLE 3. The kinetic parameters of OAP-POSS/BPFR system for first
order degradation at 108C min21 heating rate.
Resin
no.
Reaction
order
Correlation
coefficient
DEa
(kJ mol21)
ln
A(S21)
Standard
deviation
First stage 1 1 0.9990 96.4 11.5 0.0413
2 1 0.9983 95.1 17.1 0.0687
3 1 0.9780 99.3 17.8 0.3211
4 1 0.9738 112.0 19.8 0.3796
5 1 0.9984 96.4 17.3 0.0722
Second stage 1 1 0.9984 136.3 19.8 0.0395
2 1 0.9911 155.8 22.3 0.1255
3 1 0.9836 161.5 23.1 0.1850
4 1 0.9491 170.5 24.2 0.3885
5 1 0.9962 149.9 21.5 0.0742
Third stage 1 1 0.9994 179.5 21.6 0.0171
2 1 0.9883 184.9 22.3 0.1205
3 1 0.9686 194.8 12.2 0.2335
4 1 0.9847 198.4 23.7 0.1543
5 1 0.9928 175.7 21.3 0.0836
FIG. 6. TBA curves of No. 1, 3, and 5 samples.
DOI 10.1002/pc POLYMER COMPOSITES—-2011 835
3. D.C. Wang, G.W. Chang, and Y. Chen. Polym. Degrad. Sta-bil., 93, 125 (2008).
4. J.G. Gao, C.J. Jiang, and W.T. Ma, Polym. Compos., 29,274 (2008).
5. C. Martin, J.C. Ronda, and V. Cadiz, J. Polym. Sci. Part APolym. Chem., 44, 3503 (2006).
6. H.B. Hoofel, H.J. Kiessling, F. Lampert, and B. Schonrogge,
German Patent, 2,436,360 and 2,436,359 (1975).
7. J.G. Gao, C.J. Jiang, and X.H. Su, Int. J. Polym. Mater., 29,544 (2010).
8. U. Chatterjee, S.K. Jewrajka, S. Guha, Polym. Compos., 30,827 (2009).
9. S.H. Lee, S.Y. Kim, and J.R. Youn, Polym. Compos. 30,1426 (2009).
10. Y. Feng, Y. Jia, S. Guang, and H. Xu, J. Appl. Polym. Sci.115, 2212 (2010).
11. Z.P. Zhang, G. Z. Liang, P.G. Ren, and J.L. Wang, Polym.Compos., 29, 77 (2008).
12. H. Pan and Z. Qiu, Macromolecules, 43, 1499 (2010).
13. C.C. Tasam and C. Kaynak, Polym. Compos., 30, 343
(2009).
14. Y.J. Lee, S.W. Kuo, W.J. Ghuang, H.Y. Lee, and F.C.
Chang, J. Polym. Sci Part B Polym. Phys., 42, 1127 (2004).
15. H.C. Lin, S.W. Kuo, C.F. Huang, and F.C. Chang, Macro-mol. Rapid Commun., 27, 534 (2006).
16. Y.D. Zhang, S.H. Lee, M. Yoonessi, H. Toghiani Jr., and
C.U. Pittman, J. Inorgan. Organometal. Polym. Mater. 17,159 (2007).
17. J.G. Gao, D.J. Kong, and S.R. Li, Polym. Compos. 30, 60 (2010).
18. R. Tamaki, Y. Tanaka, M.Z. Asuncion, J.M. Choi, and R.
Laine, J. Am. Chem. Soc. 123, 12416 (2001).
19. J.C. Huang, C.B. He, Y. Xiao, K.Y. Mya, J. Dai, and Y.P.
Siow, Polymer 44, 4491 (2003).
20. J.G. Gao, Chin. Acta. Chim. Sin., 48, 411 (1990).
21. America Patash Chem Corp. Br Patent, 957,611 (1964).
22. Y.F. Liu, J.G. Gao, and R.Z. Zhang, Polym. Degrad. Stabil.77, 495 (2002).
23. X.L. Hu and G.Z. Liang, Mater. Rev., 16, 58 (2002).
24. P.M. Madhusudanan, K. Krishnan, and K.N. Ninan, Thermo-chim. Acta. 97, 189 (1986).
25. J.K. Gillham, Polym. Int. 44, 262 (1997).
26. R.A. Venditti and J.K. Gillham, J. Appl. Polym. Sci., 64, 3 (1997).
836 POLYMER COMPOSITES—-2011 DOI 10.1002/pc