A novel three-cages POSS molecule: synthesis and thermal behaviour

Article abstract of DOI:10.1007/s10973-018-7206-y

Two novel 4-methyl phenyl (trioxyisobutyl POSS) silane and 4-methyl phenyl (trioxycyclopentyl POSS) silane were synthesized. The nanosystems were characterized by elemental analysis, ¹H NMR and FTIR spectroscopy, in order to verify that the obtained products were those we would prepare. The spectroscopic results were in very good agreement with those expected. The synthesized POSSs were thermally characterized, by the means of thermogravimetric (TGA) and differential scanning calorimetry analyses. TGA was carried out in dynamic heating conditions (25–700 °C), in both flowing nitrogen and static air atmosphere. The temperatures at 5% mass loss (T_5%), determined to evaluate their thermal stability, evidenced a better behaviour in inert environment. The obtained T_5% values were much higher for cyclopentyl POSSs and then for isobutyl ones, suggesting a fundamental role of organic group dimensions at the periphery of the synthesized systems, on the thermal properties. The residue at 700 °C, which were also investigated by FTIR spectroscopy, was a further confirmation of the better thermal stability of these novel nanoparticles.

Full text of DOI:10.1007/s10973-018-7206-y

Journal of Thermal Analysis and Calorimetry
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A novel three-cages POSS molecule: synthesis and thermal behaviour
1
Francesco A. Bottino2 • Paola Bottino3 • Maria A. Chiacchio3
Ignazio Blanco
•
Received: 10 January 2018 / Accepted: 12 March 2018
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2018
Abstract
Two novel 4-methyl phenyl (trioxyisobutyl POSS) silane and 4-methyl phenyl (trioxycyclopentyl POSS) silane were
1
synthesized. The nanosystems were characterized by elemental analysis, H NMR and FTIR spectroscopy, in order to
verify that the obtained products were those we would prepare. The spectroscopic results were in very good agreement with
those expected. The synthesized POSSs were thermally characterized, by the means of thermogravimetric (TGA) and
differential scanning calorimetry analyses. TGA was carried out in dynamic heating conditions (25–700 °C), in both
flowing nitrogen and static air atmosphere. The temperatures at 5% mass loss (T5%), determined to evaluate their thermal
stability, evidenced a better behaviour in inert environment. The obtained T5% values were much higher for cyclopentyl
POSSs and then for isobutyl ones, suggesting a fundamental role of organic group dimensions at the periphery of the
synthesized systems, on the thermal properties. The residue at 700 °C, which were also investigated by FTIR spectroscopy,
was a further confirmation of the better thermal stability of these novel nanoparticles.
Keywords POSS Á Three-cages system Á Thermal stability Á Nanoparticles Á FTIR Á Thermogravimetric analysis
Introduction
The POSSs history, which although the first published
scientific work dates back to 1946 by Scott [2] begins
around the 1980s thanks to the essential contribution of
Lichtenhan and Schawb [3–5], is a story where the thermal
properties have always played a fundamental role. The
inorganic–organic nature of POSSs, which allows to obtain
hybrid materials different from those achievable by a
simple blend at macroscopic level [6, 7], had helped
researchers in the target of obtaining high-performance
materials not only from the thermal point of view. The
inorganic silicate core confers to molecule rigidity, thermal
stability and resistance to oxidation [8], whilst the external
organic corona affects the solubility of POSS in organic
solvents [9] and its compatibility if used as reinforcement
agents for polymers [10, 11]. In the light of this back-
ground, Bolln et al. [12] studied, by the means of ther-
mogravimetric analysis (TGA), alkyl-substituted POSSs at
different chain length of the peripheral organic groups
Among the interesting class of inorganic/organic hybrid
materials of silsesquioxanes (random, ladder, caged or
partially caged) we found the polyhedral oligomeric
silsesquioxanes (POSSs). These nanoparticles consist in a
silicon and oxygen cage, externally completed by organic
R groups covalently bonded with the silicon atoms. POSSs
are well known with the formula (RSiO1.5)n and have 8 as
the most common value of n, thus presenting a very highly
symmetric structure generally indicated in the literature
with the symbol T , with a diameter usually falling in the
8
1
.5–3 nm range [1].
&
Ignazio Blanco
iblanco@unict.it
(
from C to C ). They found that increasing the alkyl
2 10
1
Department of Civil Engineering and Architecture and
INSTM UdR, University of Catania, V.le a. Doria 6,
chain length, the initial mass loss onset temperature shifted
to higher values. Successively, Mantz et al. [13], by the
means of FTIR and mass spectrometry, analysed gases and
chars from pyrolysis of POSSs and evidenced their ten-
dency to sublimation on heating in inert atmosphere. They
9
5125 Catania, Italy
2
3
Department of Chemical Sciences, University of Catania,
V.le a. Doria 6, 95125 Catania, Italy
Department of Pharmaceutical Sciences, University of
Catania, V.le a. Doria 6, 95125 Catania, Italy
2
9
furthermore reported that char analysis, via solid-state Si
123

I. Blanco et al.
1
NMR and X-ray diffraction, indicated a progressive loss of
cage structural order and crystalline structure, with
increasing thermal treatment temperature. A strong input,
to the knowledge of the thermal behaviour of these
nanoparticles, was given by the group of Prof. Camino in
Turin. They firstly evidenced the different degradation
behaviour of octaisobutyl POSSs by passing from inert to
oxidative thermogravimetry analysis, by observing evapo-
ration of POSS leading to an almost complete mass loss
under nitrogen flowing and obtaining an important residue
under oxidative atmosphere [14]. Camino and his collab-
orators then started a deep insight on POSS thermal
properties, in order to be able to tune the final properties of
POSS-containing hybrids and nanocomposites. In particu-
lar, they evidenced a completely different thermal beha-
viour between alkyl T POSSs and phenyl T POSSs, due
Fourier transform IR (FTIR) and H NMR analyses in
order to be sure that they corresponded to what was
designed to achieve with the synthesis.
Experimental
Materials
Tetrahydrofuran (THF) was distilled over a Na–ben-
zophenone mixture. Trisilanol–isobutyl POSS has been
purchased from Hybrid Plastics Co. and used as received.
The cyclopentyl–trisilanol (c C H ) –Si O (OH) were
5 9 7 7 9 3
prepared according to the literature methods [21, 22].
p-Tolyltrichlorosilane has been purchased from Aldrich
Co. and used as received. All the reactions were performed
under an atmosphere of dry nitrogen.
8
8
to the organic groups intrinsic stability, which results in a
higher thermal stability for these latter compounds [15].
With the aim to study the POSSs compatibility with
polymer matrix, and then their capability to undergo
nanometric dispersion, our group started a wide research on
the synthesis and characterization of new thermally
stable POSSs in order to find useful structure–thermal
properties relationships. Initially, we focused our attention
on the periphery of silicon cage by varying, from time to
time, the organic groups bonded to the silicon atoms [8, 16]
or by attempting to combine multiple silicon cages with
aliphatic or aromatic bridges more or less long [17–20]. As
we expected the resistance to the thermal degradation
increased by passing from isobutyl to cyclopentyl and
phenyl-substituted POSSs and by doubling the number of
silicon cages. In this framework, we continue our studies
by reporting in this paper the synthesis and the thermal
characterization of two novel three-cage POSS molecules
Synthesis of POSS nanoparticles
For the synthesis of isobutyl POSS chloride [(C
Si 12]–Cl a solution of 7.9 g (10.00 mmol) of trisilanol–
isobutyl POSS in 100 ml of dry THF at 0–5 °C was added
with 1.7 g (10.00 mmol) of SiCl dissolved in 20 ml of
THF. The solution was stirred, and 3.03 g (30.00 mmol) of
Et N in 50 ml of THF was added. After stirring overnight
at room temperature, the mixture was filtered to remove
Et NHCl and the filtrate was evaporated to dryness. The
H )
4 9 7
O
8
4
3
3
resulting solid was dissolved in THF and dry acetonitrile
was added; the fine white precipitated was collected and
dried to give 6.90 g (81.0% yield).
1
H NMR: 1.87 (m, 7H), 0.95 (m, 42H), 0.62 (m, 14H).
Analysis Calculated for C28
Found: C 39.02, H 7.58.
H63ClO12Si : C 39.47, H 7.45.
8
(
Fig. 1). The purpose was to verify whether this new and,
The same procedure followed for isobutyl POSS chlo-
ride was used for the synthesis of cyclopentyl POSS
to the best of our knowledge, never seen molecular archi-
tecture can lead to a further improvement in thermal
stability.
chloride [(c–C H ) Si O12]–Cl starting from cyclopentyl–
5 9 7 8
trisilanol (8.75 g, 10.00 mmol). Yield 78.6%.
1
H NMR: 1.77 (m, 14H), 1.54 (m, 42H), 1.04 (m, 7H).
The compounds investigated were the following:
Ã
Â
Analysis Calculated for C H ClO Si : C 44.91, H 6.79.
8
3
5
63
12
ðC4H9Þ Si8O12ÀO ÀSiÀArCH3
ð1Þ
ð2Þ
7
3
Found: C 44.37, H 6.88.
For the synthesis of isobutyl POSS mono-ol [(C
Si O ]–OH 5.10 g (6.00 mmol) of isobutyl POSS chloride
Â
Ã
ðC H Þ Si O ÀO ÀSiÀArCH
H )
4 9 7
5
9 7
8
12
3
3
8
12
where Ar = –C H –. We investigated how their resistance
6
4
was suspended in a 50 ml mixture 2:1 of THF/H O and
2
to the thermal degradation, evaluated through both tem-
perature at 5% mass loss (T5%) and the residue at 700 °C,
changed on modifying the aliphatic groups attached to the
silicon cages. In order to compare the founded thermal
parameters with those obtained in the past for similar
compounds but with single or double silicone cages, the
experimental conditions were the same used in the previous
works as well as the parameters investigated. The synthe-
sized samples were spectroscopically characterized by
refluxed for two days. After this time the mixture was
rotoevapored to a white solid that was then dried and
crystallized from toluene/acetonitrile to give 3.95 g (76.4%
yield) of white crystals.
1
H NMR: 1.85 (m, 7H), 0.96 (m, 42H), 0.56 (m, 14H).
Analysis Calculated for C H O Si : C 40.35, H 7.74.
8
2
8
64 13
Found: C 39.96, H 7.68.
Cyclopentyl POSS mono-ol [(c–C H ) Si O ]–OH was
5
9 7
8 12
obtained as described for isobutyl POSS mono-ol starting
1
23

A novel three-cages POSS molecule…
Fig. 1 Molecular structure of
the novel 4-methyl phenyl
X
X
X
(
trioxyisobutyl POSS) silane
and 4-methyl phenyl
trioxycyclopentyl POSS) silane
X
Si
O
O
(
O
O
O
O
O
O
O
O
X
Si
O
O
X
Si
X
X
X
X
X
Si
O
H C
Si
O
3
O
O
O
O
O
O
O
X
O
Ar
O
O
Si
O
O
X
X
O
O
X
O
X
O
O
O
O
X
X
O
O
O
O
O
X
O
X
X
X = (CH ) CH–CH –or
3
2
2
from 5.60 g (6.00 mmol) of cyclopentyl POSS chloride to
obtain 4.30 g (77.0% yield) of white crystals.
the synthesis of 4-methyl phenyl (trioxycyclopentyl POSS)
silane [(C H ) Si O –O] –Si–ArCH starting from 2.75 g
5
9 7
8
12
3
3
1
H NMR: 1.74 (m, 14H), 1.56 (m, 42H), 0.98 (m, 7H).
(3.00 mmol) of cyclopentyl POSS mono-ol to obtain
Analysis Calculated for C H O Si : C 45.84, H 7.03.
3
1.92 g (66.9% yield) of white crystals.
1
H NMR: 7.63 (dd, 2H), 7.12 (dd, 2H), 2.35 (s, 3H),
5
64 13
8
Found: C 44.16, H 7.10.
-Methyl phenyl (trioxyisobutyl POSS) silane [(C4-
H ) Si O –O] –Si–ArCH was synthesized by dissolving,
4
1.73 (m, 42H), 1.54 (m, 126H), 0.99 (m, 21H). Analysis
Calculated for C112H196O Si : C 47.06, H 7.54. Found: C
39 25
9
7
8
12
3
3
under a dry nitrogen atmosphere, 3.00 g (3.60 mmol) of
isobutyl POSS mono-ol in 40 ml of dry THF and then by
adding, under stirring, 0,30 g (1.33 mmol) of p-tolyl-
trichlorosilane in 10 ml of THF. The clear solution was
cooled at 0–5 °C in an ice bath, and 0.41 g (4.00 mmol) of
41.17, H 6.87.
1
Yield, H NMR spectroscopy and elemental
analysis
1
A Varian Unity Inova spectrometer ( H 500 MHz) was
1
used to record H NMR spectra. Measurements were taken
Et N was added. The solution was stirred and the tem-
3
perature was maintained at 0–5 °C for 24 h. After filtration
to remove Et NHCl, the filtrate was evaporated to dryness
by using CDCl as solvent and TMS as internal standard.
3
1
The H NMR data found for the various compounds
3
and the resulting solid was crystallized from THF/MeCN
mixture to give 2.41 g of white crystals (76.9% yield).
investigated are reported afterwards, together with ele-
mental analysis data and the yields.
1
H NMR: 7.60 (dd, 2H), 7.15 (dd, 2H), 2.38 (s, 3H),
1
.81 (m, 21H), 0.94 (m, 126H), 0.59 (m, 42H). Analysis
Calculated for C H O Si : C 41.94, H 7.54. Found: C
91 196 39 25
FTIR analysis
4
4
1.17, H 7.68.
The same procedure just seen for the preparation of
-methyl phenyl (trioxyisobutyl POSS) silane was used for
Fourier transform IR (FTIR) analysis was performed in a
PerkinElmer Spectrum 100 spectrometer, at r.t. from 4000
123

I. Blanco et al.
-
1
-1
to 650 cm with a resolution of 4.0 cm . An universal
ATR sampling accessory was used for measurements,
which were made directly on samples without any pre-
liminary treatment.
properties of three metal samples (Isatherm, Nickel-alloy
and Trafoperm 86) at their Curie points (148, 355 and
-
3
750 °C, respectively). Samples of about 5 3 10 g, put
into open alumina crucibles, were degraded from 25 up to
-
1
7
00 °C, at the heating rate of 10 °C min , in both flowing
-1
DSC analysis
nitrogen (0.06 L 3 min ) and static air atmosphere. To
correct the error in the mass determination due to the
reduction of the buoyancy force on increasing temperature,
a blank TG run with an empty pan was preliminarily per-
formed in the same experimental conditions used for
samples. This blank curve was subtracted from those of
samples, so obtaining corrected degradation TG curves.
These data were later used to plot the percentage of
undegraded sample, (1 - D)%, as a function of tempera-
ture, where D = (W - W)/W , and W and W were the
A Shimadzu DSC-60 apparatus was used for the calori-
metric characterization. The enthalpy and temperature
calibrations of equipment were made according to the
procedure suggested by the manufacturer using as standard
materials: indium (NIST SRM 2232), tin (NIST SRM
2
220) and zinc (NIST SRM 2221a) for temperature; indium
(
NIST SRM 2232) for heat flow. Samples of about
-
.0 9 10 g, held in sealed aluminium crucibles, and a
3
5
o
o
o
-
1
heating rate of 10 °C min were used for measurements.
Differential scanning calorimetry (DSC) scans were carried
out from r.t. to 300 °C under a nitrogen flow of
masses at the starting point and during scanning.
-
1
0
.06 L min
.
Results and discussion
1
Elemental analysis and the H NMR spectroscopy of the
Thermogravimetric analysis
synthesized samples were firstly performed to verify
whether the syntheses had been successful. Results, which
are reported in detail in the experimental, were in very
good agreement with the expected ones, thus indicating
that the obtained products were those we would prepare. In
addition, FTIR analysis was carried out on the prepared
The synthesized POSSs were thermally characterized in a
Mettler Thermogravimetric Analyzer TGA 1 Star System.
Calibration of the furnace was performed according to the
procedure reported in the Mettler User’s manual of
equipment, which is based on the change of magnetic
(1)
isobutyl
(2)
cyclopentyl
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
650
Wavenumber/cm–1
Fig. 2 FTIR spectra of 4-methyl phenyl (trioxyisobutyl POSS) silane (1) and 4-methyl phenyl (trioxycyclopentyl POSS) silane (2)
1
23

A novel three-cages POSS molecule…
(
1)
isobutyl
(
2)
cyclopentyl
4000
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
650
Wavenumber/cm–1
Fig. 3 FTIR spectra of mono-phenyl hepta isobutyl POSS (1) and mono-phenyl hepta cyclopentyl POSS (2)
1
0
8
6
4
2
0
2
4
6
8
Table 1 Temperatures at 5% mass loss (T5%) and residue % at 700 °C
of the synthesized POSSs in flowing nitrogen and in static air
atmosphere
1
2
POSSs
Air static atmosphere
Nitrogen flow
5%/°C
T5%/°C
Residue/%
T
Residue/%
1
2
288.0
357.2
37.3
49.8
293.8
382.0
26.1
49.1
–
–
–
–
groups in the external coronas of the here-synthesized
samples.
Samples 1 and 2 were calorimetric characterized by
carrying out DSC scans from r.t. to 300 °C in flowing
nitrogen. No thermal effect was observed for the com-
pounds before their melting that occurs with decomposition
as shown in Fig. 4. From the same figure and in agreement
1
00
150
200
250
300
5
0
Temperature/°C
-1
Fig. 4 DSC curves, at 10 °C min , under nitrogen flow of samples 1
and 2
(as we will see) with TGA data (Table 1), it is possible to
observe that exothermic decomposition of the isobutyl-
substituted three-cage POSS starts about 80 °C before that
of the cyclopentyl-substituted one.
compounds and compared with those performed in the past
on similar POSSs, always with isobutyl and cyclopentyl
periphery. As shown in Fig. 2, the characteristic and dif-
ferent, for isobutyl and cyclopentyl, respectively, bands in
Our samples were then degraded, in dynamic heating
conditions (r.t.—700 °C), into the TGA equipment in both
inert and oxidative environment. The thermogravimetric
curves of samples 1 and 2, in flowing nitrogen and static air
atmosphere, were reported in Figs. 5 and 6 respectively,
where the percentage of un-degraded POSS (1-D%) as a
-
1
the region around 3000 cm
and those in the region
300–1500 cm are the same of those obtained in the past
for mono-cage POSSs with the same organic periphery
Fig. 3), thus confirming the presence of different organic
-
1
1
(
123

I. Blanco et al.
100
0
.000
8
6
4
2
0
0
0
0
0
–
–
0.002
0.004
1
2
–
0.006
0
100
200
300
400
500
600
700
800
0
100
200
300
400
500
600
700
800
Temperature/°C
Temperature/°C
-
1
Fig. 7 DTG degradation curves, at 10 °C min , under nitrogen flow
of samples 1
-
1
Fig. 5 TG degradation curves, at 10 °C min , under nitrogen flow
of samples 1 and 2
700 °C. The DTG curves of sample 1 in flowing nitrogen is
reported as example in Fig. 7. As shown in Fig. 5 and
reported in Table 1, cyclopentyl-substituted three-cages
POSS present an higher, of about 90 °C, initial decompo-
sition temperature in respect of the isobutyl-substituted
sample, thus confirming the trend observed during the
calorimetric measurements. The degradation behaviour in
static air did not exhibit substantial differences, and also in
this oxidative environment, both samples degraded in two
stages with the formation of a stable residue at 700 °C that
was higher, like in inert atmosphere, for the cyclopentyl
POSS. As regards the temperature at 5% mass loss,
although maintaining the same difference of about 80 °C
recorded in flowing nitrogen, the T5% values of both
compounds are slightly lower in oxidizing environment
than in inert one.
1
00
8
6
4
2
0
0
0
0
0
1
2
0
100
200
300
400
500
600
700
800
Temperature/°C
The thermal behaviour observed for samples 1 and 2 is
in agreement with that observed in the past for similar,
from the organic periphery point of view, POSS systems
but with a single cage or double cages, thus confirming the
hypothesis that when seven more voluminous groups (cy-
clopentyls) are linked to the silicon atoms of a cage, they
form a thermal barrier among various POSSs molecules,
which make difficult the heat transfer and increase the T5%
leading to the formation of a higher amount of solid silica
residue [16].
-
1
Fig. 6 TG degradation curves, at 10 °C min , in static air atmo-
sphere of samples 1 and 2
function of temperature is plotted. In Table 1, we reported
the T5% values and the amounts of residues at 700 °C,
which are the parameters we consider to evaluate the
resistance to thermal degradation. In particular, the tem-
perature at 5% mass loss was preferred to the onset tem-
perature because it is not depending on the kinetics of the
next-degradation stages and furthermore allows us the
comparison with the results obtained in the past for ana-
logues series of POSS molecules. In inert environment,
both 1 and 2 samples degraded in two quite well-defined
stages, and formed a sizable amount of stable residue up to
Finally, the residues at 700 °C were analysed by FTIR
spectroscopy and the obtained spectra (for the sake of
shortness only those of the residues obtained in inert
atmosphere) are reported in Fig. 8, evidencing only bands
attributable to silica in agreement with the literature data
regarding POSSs degradation [8, 15].
1
23

A novel three-cages POSS molecule…
(1)
1
273.60
8
00.68
1
042.90
(2)
1
274.43
7
99.15
800
1
049.43
1000
4
000
3600
3200
2800
2400
2000
1800
1600
1400
1200
650
Wavenumber/cm–1
Fig. 8 FTIR spectra of the residues at 700 °C, under nitrogen flow, of samples 1 and 2
Conclusions
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