Polyurethane composites based on silsesquioxane derivatives of different structures
Journal of Thermal Analysis and Calorimetry
Polyurethane composites based on silsesquioxane derivatives of different structures
Mariusz Szołyga 0 1 2
Michał Dutkiewicz 0 1 2
Bogdan Marciniec 0 1 2
0 Centre for Advanced Technologies, Adam Mickiewicz University in Poznan, Umultowska 89c , 61-614 Poznan , Poland
1 Poznan Science and Technology Park, Adam Mickiewicz University Foundation , Rubiez 46, 61-612 Poznan , Poland
2 & Bogdan Marciniec
A series of siloxane-silsesquioxane resins with Q8 structures, as network nodes containing reactive Si-H groups in the siloxane backbone, connecting silsesquioxane moieties, were prepared in a hydrolytic condensation process and successfully functionalized by hydrosilylation of allyl alcohol. The proposed material being an alternative to the well-defined silsesquioxanes has been characterized and used for preparation of a series of polyurethane (PU)-based composites by simple reaction of 3-hydroxypropyl groups of siloxane-silsesquioxane resin with 1,6-diisocyanatohexane and subsequently with 1,6-hexanediol to get polyurethane composite. A series of composites based on PU and octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane were prepared in the same manner to investigate the influence of the filler amount (1, 3 or 5%) and its structure on thermal properties of the obtained materials.
Polyurethane; Siloxane-silsesquioxane resins; Composite; Silsesquioxane; Hybrid materials; Hydrosilylation
The incorporation of inorganic or organometallic
components into polymers has been recently explored to develop
new materials of enhanced or tailored properties.
Silsesquioxanes are widely used as components for the
preparation of such materials [
]. Commonly reactive,
functionalized polyhedral oligomeric silsesquioxanes of
well-defined, 3D structure, bearing one or more functional
groups were applied for this purpose [
cagelike silsesquioxanes are known as nanoscale, organic–
inorganic hybrids of approximately 1–3 nm diameter.
Faculty of Chemistry, Adam Mickiewicz University in
Poznan, Umultowska 89b, 61-614 Poznan, Poland
Generally, the procedures for the synthesis of this group of
compounds are based on the hydrolysis and condensation
of trialkoxy- or trichlorosilanes, substitution reactions with
retention of the siloxane cage, corner-capping reactions,
and the functionalization of the obtained compounds with
many catalytic or stoichiometric methods [
Despite all the benefits arising from their use, their price
often makes a barrier, which prevents their use on a large
scale. An alternative and solution to this problem could be
the use of cheaper, silsesquioxane resins which would
retain the capability of functionalization and would have
well-defined, 3D moieties in their structure. However, most
of the cross-linked structures based on silsesquioxane cores
do not have functional groups capable of producing
chemical bonds to polymer, in contrast to the cage-like
silsesquioxane derivatives [
]. The covalent
incorporation of reactive silsesquioxane monomers into polymers
is the greatest advantage of the proposed fillers. The
formation of covalent bonds between the polymer matrix and
the filler permits obtaining inseparable hybrid material
based on organic, functional polymers (e.g., epoxides,
polyamides, methacrylates, or polyurethanes) [
Polyurethanes (PUs) make a class of materials well
known for several decades. They can be obtained by
polyaddition reaction in solution or mass polyaddition
process of diols (HO–R–OH) and diisocyanates (OCN–R–
NCO). Polyurethanes may exist as liquid, soft solids, rubbery
materials as well as rigid thermoplastic and thermoset
materials. PUs have found extensive use in numerous
commercial applications such as coatings, foams, adhesives,
sealants, synthetic leathers, membranes, elastomers, as well
as in many biomedical applications. They are one of the most
useful commercial classes of polymers that have been widely
exploited in the industry and in everyday life. More than 70%
of the literature that deals with PUs are devoted to their
thermal stability or flame retardancy [
]. In order to
increase above-mentioned parameters of polyurethanes,
different strategies can be applied. Thermal stability and
flame retardancy of PU composites can be improved by
incorporation of specific comonomers into the polymer
backbone or by blending with fillers of different nature
(silsesquioxanes, borax, graphite, carbon fillers, silicates,
metals, graphene, phosphates, and many others) [
In this contribution, we present a new type of functional
filler susceptible to modification and capable to form a
covalent bonding with the polymer matrix as well as its
exemplary application as a component for
polyurethanebased hybrid material. To demonstrate the influence of the
filler amount (1, 3 or 5%) and its structure on thermal
properties of the obtained materials, the results are
compared with those for the materials prepared with the use of
well-defined silsesquioxane derivative bearing functional
groups of the same type.
Tetraethyl orthosilicate (98%), tetramethylammonium
hydroxide (solution 25% in methanol) acquired from
Sigma-Aldrich, Poland, methanol (99.8%) purchased from
POCH, Poland, and redistilled water were used for
octaanion solution according to the procedure described
]. Obtained octaanion solution,
chlorodimethylsilane (98%), dichloromethylsilane (97%)
from Sigma-Aldrich, Poland, and hexane (99%) methylene
chloride (99.5%), and methanol (99.8%) purchased from
POCH, Poland, were used for the synthesis of
octakis(hydridodimethylsiloxy)octasilsesquioxane and a series of
siloxane–silsesquioxane resins (SiHQ-2, SiHQ-4, and
SiHQ-8). Allyl alcohol (99%), Karstedt complex (2% in
xylenes) purchased from Sigma-Aldrich, Poland, and
toluene (99.5%) from POCH, Poland, were used for
siloxane–silsesquioxane resins functionalization.
Hexamethylene diisocyanate (HDI, 98%) and 1,6-hexanediol
(HDO, 97%) purchased from Sigma-Aldrich, Poland, were
used for polyurethane composites preparation containing
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane and functionalized
siloxane–silsesquioxane resins (R2, R4, and R8). All chemicals were used
without any further purification. Water used in the
experiments was redistilled immediately prior to use.
Preparation of organosilicon fillers
Synthesis of octakis[(3hydroxypropyl)dimethylsiloxy]octasilsesquioxane (SF)
Synthesized according to the procedure described by
Filho et al. [
octakis(hydridodimethylsiloxy)octasilsesquioxane (20 g, 19.6 mmol) together with 5% excess
of allyl alcohol (11.2 mL, 165 mmol) and 200 mL of toluene
as solvent was placed in a three-necked round-bottom flask
equipped with a thermometer, a condenser, and a magnetic
bar. Then Karstedt catalyst (100 mg, 1.02 9 10-6 mol Pt)
was added at room temperature, and the solution was heated
to 110 C and kept at this temperature for 8 h. After the
reaction mixture cooled down, the solvent and the excess of
olefin were evaporated under vacuum, and the residue was
filtered off to give a product as a wax (28.5 g, 98% of
theoretical yield). The results of spectroscopic analysis of the
product confirmed its structure.
1H NMR (CDCl3, 298 K, 300 MHz) d [ppm] = 0.10
(OSiCH3); 0.58 (SiCH2); 1.60 (CH2); 3.55 (CH2OH); 3.64
(OH). 13C NMR (CDCl3, 298 K, 75.5 MHz) d
[ppm] = - 0.54 (SiCH3); 10.76 (SiCH2); 24.45 (CH2); 51.1
(CH2OH). 29Si NMR (CDCl3, 298 K, 59.6 MHz) d
[ppm] = 13.27 (OSi(CH3)2); - 108.85 (SiOSi).
Synthesis of siloxane–silsesquioxane resins (SiHQ-2, SiHQ-4,
Three types of silicone resins have been synthesized with
differing in amount of SiH groups (and the length of
polysiloxane chains connecting network nodes). In all
cases, the reactions were carried out according to an
identical procedure, changing only the amount of
To the solution of hexane (as solvent) and
dichloromethylsilane placed in three-necked flask equipped
with magnetic stirrer, reflux condenser, thermometer, and
dropping funnel, and cooled down to 3 C, a water–
methanolic solution of octaanion (received in accordance
with the procedure described by Filho et al. [
introduced dropwise through the addition funnel. Resulting
suspension was vigorously stirred for 2 h. After separation of
the layers, the upper hexane layer was collected, and the
solvent was evaporated under reduced pressure. Obtained a
crude product was washed several times with a mixture of
methanol and methylene chloride to remove possible
byproducts and unreacted substrates. Purified product as a
white powder was dried under vacuum, and substrates
quantities and obtained products yields are given in Table 1.
Functionalization of siloxane–silsesquioxane resins (R2, R4, R8)
The obtained siloxane–silsesquioxane resins with different
amount of SiH bonds were functionalized with allyl
alcohol in the hydrosilylation process carried in the presence of
Karstedt complex as a catalyst.
Siloxane–silsesquioxane resin (SiHQ-2, SiHQ-4 or
SiHQ-8) 5.0 g, together with 50 mL of toluene (as a
solvent to improve mixing of the suspension) and 50 mL of
allyl alcohol, was placed in a three-necked flask equipped
with magnetic stirrer, heating bowl, condenser, and
thermometer. The system was heated to 110 C, and the
Karstedt complex solution in xylene 150 lL was added.
The reaction was carried out for 24 h. After reaction
mixture cooled down, solvent and excess of olefin were
evaporated under vacuum. Obtained functionalized resins
R2, R4, and R8 (6.6, 7.2, and 7.5 g, respectively) as white
powders were used for the preparation of PU composites.
Preparation of PU composites
Polyurethane composites containing silsesquioxane
derivatives of different structures were synthesized
according to the known procedure given by Janowski et al.
with minor modifications [
diisocyanate (HDI) 4.0 g was charged into a 50-mL
threenecked round-bottomed flask equipped with a magnetic
stirrer and nitrogen inlet and heated to 80 C. Next
organosilicon fillers in the desired amount was added in
one portion to react 1, 3, or 5% of isocyanate groups
present in HDI (substrates quantities are given in Table 2).
The reaction was carried out under a nitrogen atmosphere
at 80 C for 2 h to form a polyurethane prepolymer. The
NCO group content was determined titrimetrically, and the
prepolymer was mixed with a suitable amount of
1,4hexanediol (HDO). The resulting mixture was poured out
into a glass vial and cured at 110 C for a further 2 h and
post-cured at 80 C for the next 16 h.
1H NMR (300 MHz), 13C NMR (75 MHz), and 29Si NMR
(59 MHz) spectra were recorded on a Varian XL 300
spectrometer at room temperature using CDCl3 as solvent.
X-ray diffraction analysis (XRD)
The X-ray diffraction patterns were measured by an
XCALIBUR S2, Agilent, with a molybdenum lamp. The
O O Si
sample was placed in a soda-lime glass capillary (inner
diameter 0.7 mm). The angular range for the measurement
was 2h (6–40 ).
Scanning electron microscope, energy-dispersive X-ray spectroscopy (SEM, EDS)
The morphology of the fillers and PU composites was
investigated by scanning electron microscopy (SEM)
images using an FEI Quanta 250 FEG field emission
scanning electron microscope equipped with EDAX EDS
detector. Samples were prepared by gluing the polymer
SiHQ and R type resins
R = H for SiHQ-2, SiHQ-4 and SiHQ-8 resins before functionalization
or R =
OH for R2, R4 and R8 functionalizd resins
n = ∼ 1, ∼ 3 or ∼ 7 for SiHQ-2, and R2, SiHQ-4 and R4, SiHQ-8 and R8 resins respectively
powder on the standard SEM carbon adhesive tape and
were not covered by any layer. The microscope was
operated at low- or high-vacuum mode. At low-vacuum
mode (pressure of 50–100 Pa in the chamber) and 10 kV
accelerating voltage, the signal was collected by an LFD
detector type, while at high-vacuum mode (pressure of
about 2.5 9 10-4 Pa in the chamber) accelerating voltage
was 5 kV, and the signal was collected by an ETD
Low-temperature nitrogen sorption for unmodified siloxane
resins was determined using an ASAP 2010 sorptometer
(Micromeritics) at liquid nitrogen temperature
(- 195.6 C) under relative vacuum conditions in the
range of 0.01–1. Masses of 0.2–0.3 g were degassed before
testing at 300 C for 3 h. The specific surface area was
determined using the BET method. The area of the
mesopores, the size distribution of the mesopores, and their
volume were determined from the nitrogen adsorption–
desorption isotherms, using the BJH method.
Thermogravimetric analysis (TGA)
Thermal stabilities of the samples prepared were measured
on a Q50-TGA thermogravimetric analyzer (TA
Instruments, Inc.) under an air flow of 60 mL min-1. Samples
(10–15 mg) loaded in a platinum pan were heated from RT
to 700 C at a rate of 10 C min-1.
Differential scanning calorimetry (DSC)
DSC measurements of prepared PU composites samples
placed in a 40-lL aluminum pans with a pierced lid were
carried out in N2 atmosphere at a flow rate of 25 mL min-1
in a temperature range from 25 to 230 C at a
heating/cooling rate of 10 C min-1 using a Mettler Toledo
DSC-1 differential scanning calorimeter performed for the
determination of their melting and crystallization
Results and discussion
Prepared polyurethane composites containing various
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane or functionalized siloxane–silsesquioxane
resins of different structures (Fig. 1) as fillers were
subjected to the spectroscopic, morphological, and thermal
FTIR analysis of the obtained resins clearly showed that
they differed depending on the reagents stoichiometry
applied. The most significant differences can be observed
in the intensities of bands at 2170 and 950–650 cm-1,
characteristic of Si–H bond (Fig. 2). A significant increase
in the intensity of these bands correlates with the rising
amount of –OSi(CH3)H– units present in siloxane chains
connecting Q8 silsesquioxane nodes. A similar tendency
can be observed for 2970 and 1262 cm-1 bands
characteristic for C–H and Si–C bonds, respectively.
FTIR analysis of the functionalized resins confirmed
total conversion of the reactive Si–H by the disappearance
of characteristic bands at 2170 and 950–650 cm-1. Also
the appearance of new bands at 2934 and 2877 cm-1,
characteristic for C–H bonds present in the introduced
alkyl chain and a broad band at 3331 cm-1 characteristic
for the terminal OH, confirm the complete resins
functionalization (Fig. 3). Moreover, similarly as in the
spectra of the starting resins, also in the spectrum of
functionalized resins, a good correlation between the
intensity of bands characteristic for hydroxypropyl groups
(2934, 2877 and 3331 cm-1) and the reagents
stoichiometry applied for the synthesis of the starting materials can
be clearly observed. The intensity of the mentioned bands
increases with the growing number of –OSi(CH3)H– units
present in siloxane chains connecting Q8 silsesquioxane
The solid-state 29Si single-pulse/magic-angle spinning
(SP/MAS) NMR spectra of obtained for raw siloxane–
silsesquioxane and allyl alcohol functionalized siloxane–
silsesquioxane resins (Fig. 4) also confirmed their
structures and successful functionalization. The NMR spectra of
all resins appear very similar in terms of a number of
signals and their chemical shifts, but they differ remarkably
in their relative intensities. For all resins, three signals at
- 34.9, - 65.2, and - 110.2 ppm can be observed. They
can be attributed to the presence of D (SiO2), T (SiO3), and
Q (SiO4) units in the obtained resins structure, respectively.
The presence of T units can be explained by the occurrence
of a possible side reaction of one of the Cl atoms from
dichloromethylsilane with methanol and subsequent
condensation of methoxy group formed with Si–H bond with a
formation of T structure. It can be observed that the
intensity of D units signal at - 34.9 ppm increases relative
to the intensity of Q units (- 110.2 ppm) which remains in
good correlation with the reagents stoichiometry applied
for the synthesis of investigated samples. For all the
functionalized resins, the signals attributed to D units are
shifted from - 34.9 to - 21.9 ppm which is related to the
addition of hydroxypropyl group to the –OSi(CH3)H–
segments (Fig. 4). Simultaneously, the shift of the signal at
- 65 (T units) to - 55 ppm is observed explained by the
change in the nature of adjacent groups. The Q unit signals
at - 110.0 ppm are unchanged, which confirms the
retention of the silsesquioxane moieties structures in the
The reaction stoichiometry applied for the synthesis of
siloxane–silsesquioxane resins strongly affected their
structure as described above and in consequence influenced
their morphological properties.
The crystalline structures of the siloxane–silsesquioxane
resins verified by XRD analysis, shown in Fig. 5, were
quite different depending on the lengths of siloxane chains
incorporated into their structures. For the SiHQ-2 resin,
three major characteristic diffraction peaks at c.a. 24 , 28 ,
and 41 were observed, indicating a relatively high
proportion of crystalline phase in its structure. For SiHQ-4
resin, the above-mentioned signals are much less
pronounced, while for SiHQ-8 resin, they are not observed at
all, which indicates the amorphous nature of this material.
The morphological effect of different lengths of siloxane
chains linking the Q8 cores can be also observed on the
scanning electron microscopy images of siloxane–
silsesquioxane resins, especially for SiHQ-8 one (Fig. 6).
For SiHQ-2 and SiHQ-4 resins, no major changes resulting
from the number of siloxane units in the chains are
observed, and their structure is built mainly with small
particles growing on one another. In SiHQ-4 also terrace
structures can be observed. SiHQ-8 resin differs
significantly in morphology from SiHQ-2 and SiHQ-4 ones. The
sample is characterized by a monolithic structure with no
crystallite phase present.
Scanning electron microscopy (SEM) was also used to
investigate changes in the prepared PU composites surface
morphology, related to the type and amount of
organosilicon compounds used. For the samples prepared with the
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane, numerous crystalline domains can be
observed on the composite surface. The number as well as
the size of the domains increased with growing
silsesquioxane content and was the most noticeable for the
sample PU-SF-5% containing 5 mass% of the filler. For the
composite samples containing R2, R4, or R8 functionalized
resins, no similar effect was observed even for the highest
(5 mass%) filler loadings (Fig. 7).
Samples of polyurethane hybrid materials were also
analyzed by the energy-dispersive X-ray spectroscopy
(EDS) to identify the degree of fillers dispersion in the
polymer matrix. The results obtained for polyurethane
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane reveal the homogenous filler
distribution in PU matrix regardless of its content. No
formation of agglomerates is observed. For PU-R2, R4, and
R8 composites, the formation of agglomerates is observed
(Fig. 8). It was also observed that the homogeneity of the
filler dispersion increases with increase in siloxane chain
length and number of reactive hydroxypropyl groups
present in the resin used (from R2 to R8).
The siloxane chain lengths, degree of crystallinity, and
resins morphology influenced also their textural properties
such as the specific surface area, average pore diameter, or
pore volumes determined by the adsorption–desorption
nitrogen isotherms of investigated samples. The obtained
results are summarized in Table 3. The shape of measured
isotherms reflects the mesoporous nature of the tested
materials. Most similar in shape to type IV isotherm
(according to classification IUPAC characteristic of
mesoporous adsorbents) is the isotherm recorded for SiHQ-8
sample. The isotherms recorded for SiHQ-2 and SiHQ-4
can be defined as deformed type IV, because the adsorption
hysteresis pulses are not closed even for the small values of
relative pressure p p0-1. The observation of not closing the
hysteresis is difficult to explain. For no reason, IUPAC can
be referenced in the systems studied (it is the stiffening of
the non-rigid porous structure, irreversible adsorption of
adsorbent particles in pores with a diameter close to the
particle size of the adsorbent molecule, and strong
chemical interaction of adsorbate with adsorbent) [
]. Loops of
adsorption hysteresis of SiHQ-8 sample represent type H2
according to IUPAC classification (or E, according to de
Boer classification [
]). The hysteresis of SiHQ-2 and
SiHQ-4 samples can be specified as Type H3 or B. It
should be noted that there is a difference between the
hysteresis of the last two samples and the shape of the
classical H3 loop, in the fact that the hysteresis does not
close. Clearly, different textural properties of individual
samples are determined by the length of the siloxane chains
linking the silsesquioxane Q8 units.
The surface area and the pore volume are clearly
decreasing with increase in the number of siloxane units in
the chain. The average pore diameter indicates the presence
of mesopores (it is 2–50 nm according to the IUPAC
]. This demonstrates that the
characteristic mesoporous character of silsesquioxane units
has been retained in all resin samples. The largest surface
area and pore volume (293 m2 g-1 and 0.387 cm3 g-1)
were observed for SiHQ-2 resin, in which the lengths of the
siloxane chains connecting the network nodes were
statistically the smallest. The dramatic decrease in the surface
Table 3 Textural parameters of
determined on the basis of
lowtemperature nitrogen adsorption
Fig. 10 DSC curves of the
second heating run
the fillers content were described in the terms of 1, 5, and
10% mass loss temperatures and DT values for each sample
series. All data obtained are presented in Table 4.
It can be observed that the influence of the amount of
filler on the thermal properties of each polyurethane
composite series is slightly different for each filler. The
analysis of TG curves for polyurethane composite series
obtained with the addition of
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane showed that 1 and 5%
filler addition drastically reduced the materials’ thermal
stability. However, 3 mass% content of silsesquioxane
increased its 1, 5 and 10% mass loss temperatures by about
15 C. The analysis of TG curves obtained for R2, R4, and
R8 resins based PU composites showed that the thermal
stability was in all samples improved, regardless of the
amount of the filler used. However, the difference between
the 1, 5, and 10% mass loss temperatures observed for pure
PU and the composites containing siloxane–silsesquioxane
resins R2, R4, and R8 were the highest for 1% of filler
loading and decreased with its increase.
Results of DTG curves analysis presented in Table 5
lead to the conclusion that, in average, the highest
temperatures of maximum mass loss rate Tmax were observed
for R4 resin composite samples. Simultaneously measured
for R4 resin composite samples, maximum mass loss rate
dmax and mass loss d at Tmax values were the lowest at all.
The highest values of dmax and d at Tmax were observed for
composites based on R8 resin.
A comparison of the TG and DTG curves for pure PU
and the composites containing 1% of
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane, R2, R4 and R8
resins is presented in Fig. 9. Based on the results of TG and
DTG curves analysis, it is easy to observe that the
composites of the highest thermal stability were those obtained
with the use of R4 resin and the lowest thermal stability
was observed for R8 resin containing composites. This
stems from the difference in the structure of both resins
which influences not only their morphological and textural
properties but also the polymer–filler interactions and
composite properties. Lower thermal stability of R8
resinbased composites in comparison with R4 ones should be
attributed to the presence of statistically twice as long
siloxane chains linking silsesquioxane Q8 nodes in its
structure and lower network density. Increased siloxane
chain length favor the thermo-oxidative mechanism of their
decomposition and decreases composites thermal stability
D (Tc PUC - Tc PU)/ C
Tm PU and Tc PU are melting or crystallization temperatures of the neat polyurethane
Tm PUC and Tc PUC are melting or crystallization temperatures of corresponding polyurethane composites
The thermogravimetric analysis was followed by the
DSC measurements. Analysis of the DSC curves of second
heating run presented in Fig. 10 lead to an observation that
the addition of 1 and 3% of
octakis(3-hydroxypropyldimethylsiloxy)octasilsesquioxane does not affect
significantly the melting temperatures (Tm) of the PU composites
in comparison to those of the neat polyurethane. Only for
5% silsesquioxane loading, a considerable reduction
(almost 12 C) of the melting point was observed. For all
composites based on R2, R4, or R8
siloxane–silsesquioxane resins, no trends in changes in melting temperatures
were observed regardless of the amount of filler used. The
observed variations in the melting points were not greater
than ± 3 C.
Similarly, as it can be observed in Fig. 11 presenting
DSC curves of second cooling run, no simple correlation
between the amount and type of filler and the
crystallization temperatures was observed except for the PU-R8
composites. For all PU-R8 composites, regardless of the
filler content, the increase in crystallization temperatures
was observed by more than 10 C.
This phenomenon, similarly to the results of XRD,
SEM, and TG analyses, is straightly related to the structure
of the fillers used and the length of siloxane chains linking
the silsesquioxane Q8 units present in their structures. The
siloxane chains linking silsesquioxane nodes in the R8
resin are statistically twice as long as those in R4 and four
times longer from those in R2 resin. The mobility of Si–O–
Si bonds of the siloxane backbone as well as loosening of
the resin network strongly affects the properties of filler
and subsequently composites containing it by enabling
polyurethane chains motion, align for nucleation and
crystal lattice formation which is manifested in the case in
the increase of the crystallization temperatures observed
for PU-R8 composite samples [
]. The results of DSC
analysis are summarized in Table 6.
The synthesis of a novel hybrid polyurethane composite
has been studied. To get the desired composites, a series of
siloxane–silsesquioxane resins bearing reactive Si–H
groups were synthesized (SiHQ-2, -4, -8) and
functionalized with hydroxypropyl groups in the allyl alcohol
hydrosilylation process to get a series of reactive fillers
(R2, R4, R8) capable of formation of covalent bonding to
polyurethane matrix. The prepared reactive fillers and
polyurethane composites were characterized with
spectroscopic techniques, scanning electron microscopy (SEM),
energy-dispersive X-ray spectroscopy (EDS),
thermogravimetric analysis (TGA), and differential scanning
calorimetry (DSC). The results obtained confirmed strong
dependence between the structure of resins, their
morphology, textural and thermal properties. FTIR and NMR
analyses confirmed successful functionalization of starting
SiHQ resins with different amounts of hydroxypropyl
groups. XRD analysis showed that the crystallinity of
synthesized SiHQ resins strongly depends on their
chemical structures. The significant influence of the chemical
structures of the synthesized materials on specific surface
and pore volumes, as well as their morphology, has been
also observed based on sorption and microscopic analyses.
Mentioned above parameters affected also the thermal
properties of prepared PU composites. The most significant
was the impact of R4 resin series on the improvement on
PU composites thermal stability, while R8 resins caused
notable reduction in composites stability, what is related to
the different siloxane chains length present in their
structure. The structure–property dependency was also clearly
observed in case of crystallization temperatures determined
by DSC measurements for PU composites.
It has been proven that the proposed materials can be a
valuable alternative for well-defined silsesquioxane
derivatives and their use permits the synthesis of
polyurethane composites of improved thermal stability even at
low filler contribution.
Acknowledgements The authors gratefully acknowledge the financial
support from the National Centre for Research and Development in
Poland (Grant No. PBS3/A1/16/2015).
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1. Barczewski M , Dobrzyn´ ska-Mizera M , Dutkiewicz M , Szołyga M. Novel polypropylene b-nucleating agent with polyhedral oligomeric silsesquioxane core: synthesis and application . Polym Int . 2016 ; 65 ( 9 ): 1080 - 8 .
2. Dutkiewicz M , Szołyga M , Maciejewski H , Marciniec B . Thiirane functional spherosilicate as epoxy resin modifier . J Therm Anal Calorim . 2014 ; 117 ( 1 ): 259 - 64 .
3. Lee SH , Yu S , Shahzad F , Hong JP , Kim WN , Park C , Hong SM , Koo CM . Crystallization derivation of amine functionalized T12 polyhedral oligomeric silsesquioxane-conjugated poly(ethylene terephthalate) . Compos Sci Technol . 2017 ; 146 : 42 - 8 .
4. Groch P , Dziubek K , Czaja K , Dudziec B , Marciniec B . Copolymers of ethylene with monoalkenyl- and monoalkenyl(siloxy)silsesquioxane (POSS) comonomers-synthesis and characterization . Eur Polym J . 2017 ; 90 : 368 - 82 .
5. Zhang W , Camino G , Yang R . Polymer/polyhedral oligomeric silsesquioxane (POSS) nanocomposites: an overview of fire retardance . Prog Polym Sci . 2017 ; 67 : 77 - 125 .
6. Chen HL , Jiao XN , Zhou JT . The research progress of polyhedral oligomeric silsesquioxane (POSS) applied to electrical energy storage elements . Funct Mater Lett . 2017 ; 10 ( 2 ): 1730001 .
7. Wang Z , Ma H , Chu B , Hsiao BS . Super-hydrophobic polyurethane sponges for oil absorption . Sep Sci Technol (Philadelphia) . 2017 ; 52 ( 2 ): 221 - 7 .
8. Gu P , Yang G , Lee SC , Lee JK . Thermal characterization of epoxy nanocomposites containing polyhedral oligomeric silsesquioxane: glass transition temperature and chemical conversion . Fibers Polym . 2017 ; 18 ( 1 ): 131 - 9 .
9. Dobrzyn´ ska-Mizera M , Dutkiewicz M , Sterzyn´ski T, Di Lorenzo ML. Isotactic polypropylene modified with sorbitol-based derivative and siloxane-silsesquioxane resin . Eur Polym J . 2016 ; 85 : 62 - 71 .
10. Czarnecka-Komorowska D , Sterzynski T , Dutkiewicz M. Polyoxymethylene/polyhedral oligomeric silsesquioxane composites: processing, crystallization, morphology and thermo-mechanical behavior . Int Polym Proc . 2016 ; 31 ( 5 ): 598 - 606 .
11. Raftopoulos KN , Pielichowski K. Segmental dynamics in hybrid polymer/POSS nanomaterials . Prog Polym Sci . 2016 ; 52 : 136 - 87 .
12. Kuo SW , Chang FC . POSS related polymer nanocomposites . Prog Polym Sci . 2011 ; 36 : 1649 .
13. Cordes DB , Lickiss PD , Rataboul F . Recent developments in the chemistry of cubic polyhedral oligosilsesquioxanes . Chem Rev . 2010 ; 110 ( 4 ): 2081 - 173 .
14. Tanaka K , Chujo Y. Advanced functional materials based on polyhedral oligomeric silsesquioxane (POSS) . J Mater Chem . 2012 ; 22 ( 5 ): 1733 - 46 .
15. Kuo SW , Chang FC . POSS related polymer nanocomposites . Progr Polym Sci (Oxford) . 2011 ; 36 ( 12 ): 1649 - 96 .
16. Tanaka K , Chujo Y . Chemicals-inspired biomaterials: developing biomaterials inspired by material science based on POSS . Bull Chem Soc Jpn . 2013 ; 86 ( 11 ): 1231 - 9 .
17. Zhang W , Mu¨ller AHE. Architecture, self-assembly and properties of well-defined hybrid polymers based on polyhedral oligomeric silsequioxane (POSS) . Prog Polym Sci . 2013 ; 38 ( 8 ): 1121 - 62 .
18. Blanco I , Abate L , Bottino FA . Synthesis and thermal characterization of new dumbbell-shaped cyclopentyl-substituted POSSs linked by aliphatic and aromatic bridges . J Therm Anal Calorim . 2015 ; 121 ( 3 ): 1039 - 48 .
19. Zhao M , Feng Y , Li Y , Li G , Wang Y , Han Y , Sun X , Tan X. Preparation and performance of phenyl-vinyl-POSS/addition-type curable silicone rubber hybrid material . J Macromol Sci Part A Pure Appl Chem . 2014 ; 51 ( 8 ): 639 - 45 .
20. Liu N , Li L , Wang L , Zheng S . Organic-inorganic polybenzoxazine copolymers with double decker silsesquioxanes in the main chains: synthesis and thermally activated ring-opening polymerization behavior . Polymer (UK) . 2017 ; 109 : 254 - 65 .
21. Zhang C , Babonneau F , Bonhomme C , Laine RM , Soles CL , Hristov HA , Yee AF . Highly porous polyhedral silsesquioxane polymers. Synthesis and characterization . J Am Chem Soc . 1998 ; 120 ( 33 ): 8380 - 91 .
22. Naga N , Oda E , Toyota A , Furukawa H . Mesh size control of organic-inorganic hybrid gels by means of a hydrosilylation cogelation of siloxane or silsesquioxane and a, x-non-conjugated dienes . Macromol Chem Phys . 2007 ; 208 ( 21 ): 2331 - 8 .
23. Naga N , Nagino H , Furukawa H . Synthesis of organic-inorganic hybrid gels by means of thiol-ene and azide-alkene reactions . J Polym Sci Part A Polym Chem . 2016 ; 54 ( 14 ): 2229 - 38 .
24. Guo S , Okubo T , Kuroda K , Shimojima A . A photoresponsive azobenzene-bridged cubic silsesquioxane network . J Sol-Gel Sci Technol . 2016 ; 79 ( 2 ): 262 - 9 .
25. Zhang A , Gao H , Li W , Bai H , Wu S , Zeng Y , Zhou X , Li L . Hybrid microporous polymers from double-decker-shaped silsesquioxane building blocks via Friedel-Crafts reaction . Polymer (UK) . 2016 ; 101 : 388 - 94 .
26. Liu C , Li Z , Wang Y . Novel fluorescent terphenyl bridged crystalline silsesquioxane through self-directed assembly . J SolGel Sci Technol . 2017 ; 81 ( 2 ): 593 - 9 .
27. Li H , Zhang J , Xu R , Yu D . Direct synthesis and characterization of crosslinked polysiloxanes via anionic ring-opening copolymerization with octaisobutyl-polyhedral ohgomeric silsesquioxane and octamethylcyclotetrasiloxane . J Appl Polym Sci . 2006 ; 102 ( 4 ): 3848 - 56 .
28. Gunji T , Shioda T , Tsuchihira K , Seki H , Kajiwara T , Abe Y. Preparation and properties of polyhedral oligomeric silsesquioxane-polysiloxane copolymers . Appl Organomet Chem . 2010 ; 24 ( 8 ): 545 - 50 .
29. Pawlak T , Kowalewska A , Zgardzin´ska B , Potrzebowski MJ . Structure, dynamics, and host-guest interactions in POSS functionalized cross-linked nanoporous hybrid organic-inorganic polymers . J Phys Chem C . 2015 ; 119 ( 47 ): 26575 - 87 .
30. Zhou Y , Huang F , Du L , Liang G . Synthesis and properties of silicon-containing arylacetylene resins with polyhedral oligomeric silsesquioxane . Polym Eng Sci . 2015 ; 55 ( 2 ): 316 - 21 .
31. Handke M , Kowalewska A. Siloxane and silsesquioxane molecules-precursors for silicate materials . Spectrochim Acta Part A Mol Biomol Spectrosc . 2011 ; 79 ( 4 ): 749 - 57 .
32. Arsalani N , Akbari A , Amini M , Jabbari E , Gautam S , Chae KH . POSS-based covalent networks: supporting and stabilizing Pd for heck reaction in aqueous media . Catal Lett . 2017 ; 147 ( 4 ): 1086 - 94 .
33. Pramudya I , Rico CG , Lee C , Chung H . POSS-containing bioinspired adhesives with enhanced mechanical and optical properties for biomedical applications . Biomacromol . 2016 ; 17 ( 12 ): 3853 - 61 .
34. Barczewski M , Czarnecka-Komorowska D , Andrzejewski J , Sterzyn´ ski T , Dutkiewicz M , Dudziec B . Processing properties of thermoplastic polymers modified by polyhedral oligomeric silsesquioxanes (POSS) . Polimery/Polymers . 2013 ; 58 ( 10 ): 805 - 15 .
35. Heneczkowski M , Oleksy M , Oliwa R , Dutkiewicz M , Maciejewski H , Galina H . Application of silsesquioxanes for modification of epoxy resins . Polimery/Polymers . 2013 ; 58 ( 10 ): 759 - 65 .
36. Prza˛dka D , Je˛czalik J , Andrzejewska E , Marciniec B , Dutkiewicz M , Szłapka M. Novel hybrid polyurethane/POSS materials via bulk polymerization . React Funct Polym . 2013 ; 73 ( 1 ): 114 - 21 .
37. Oprea S. Synthesis and properties of polyurethane elastomers with castor oil as crosslinker . J Am Oil Chem Soc . 2010 ; 87 ( 3 ): 313 - 20 .
38. Kim H , Miura Y , MacOsko CW . Graphene/polyurethane nanocomposites for improved gas barrier and electrical conductivity . Chem Mater . 2010 ; 22 ( 11 ): 3441 - 50 .
39. Chattopadhyay DK , Webster DC . Thermal stability and flame retardancy of polyurethanes . Progr Polym Sci (Oxford) . 2007 ; 32 ( 3 ): 352 - 418 .
40. Chattopadhyay DK , Webster DC . Thermal stability and flame retardancy of polyurethanes . Progr Polym Sci (Oxford) . 2009 ; 34 ( 10 ): 1068 - 133 .
41. Delebecq E , Pascault JP , Boutevin B , Ganachaud F . On the versatility of urethane/urea bonds: reversibility, blocked isocyanate, and non-isocyanate polyurethane . Chem Rev . 2013 ; 113 ( 1 ): 80 - 118 .
42. Kong W , Lei Y , Jiang Y , Lei J . Preparation and thermal performance of polyurethane/PEG as novel form-stable phase change materials for thermal energy storage . J Therm Anal Calorim . 2017 ; 130 ( 2 ): 1011 - 9 .
43. Datta J , Kasprzyk P , Błaz_ek K , Włoch M . Synthesis, structure and properties of poly(ester-urethane)s obtained using bio-based and petrochemical 1,3-propanediol and 1,4-butanediol . J Therm Anal Calorim . 2017 ; 130 ( 1 ): 261 - 76 .
44. Michałowski S , Hebda E , Pielichowski K. Thermal stability and flammability of polyurethane foams chemically reinforced with POSS . J Therm Anal Calorim . 2017 ; 130 ( 1 ): 155 - 63 .
45. Chao C , Gao M , Chen S . Expanded graphite: borax synergism in the flame-retardant flexible polyurethane foams . J Therm Anal Calorim . 2018 ; 131 ( 1 ): 71 - 9 .
46. Ciecierska E , Jurczyk-Kowalska M , Bazarnik P , et al. The influence of carbon fillers on the thermal properties of polyurethane foam . J Therm Anal Calorim . 2016 ; 123 ( 1 ): 283 - 91 .
47. Cheng J-J , Zhou F -B. Flame-retardant properties of sodium silicate/polyisocyanate organic-inorganic hybrid material . J Therm Anal Calorim . 2016 ; 125 ( 2 ): 913 - 8 .
48. Chen X , Ma C , Jiao C. Synergistic effects between iron-graphene and ammonium polyphosphate in flame-retardant thermoplastic polyurethane . J Therm Anal Calorim . 2016 ; 126 ( 2 ): 633 - 42 .
49. Liu L , Zhao X , Ma C , et al. Smoke suppression properties of carbon black on flame retardant thermoplastic polyurethane based on ammonium polyphosphate . J Therm Anal Calorim . 2016 ; 126 ( 3 ): 1821 - 30 .
50. Filho NLD , de Aquino HA , Pires G , Caetano L . Relationship between the dielectric and mechanical properties and the ratio of epoxy resin to hardener of the hybrid thermosetting polymers . J Braz Chem Soc . 2006 ; 17 : 533 - 41 .
51. Szołyga M , Dutkiewicz M , Marciniec B , Maciejewski H . Synthesis of reactive siloxane-silsesquioxane resins [Synteza reaktywnych z_ywic siloksanowo-silseskwioksanowych] . Polimery/ Polymers . 2013 ; 58 ( 10 ): 766 - 71 .
52. Janowski B , Pielichowski K. A kinetic analysis of the thermooxidative degradation of PU/POSS nanohybrid elastomers . Silicon . 2016 ; 8 ( 1 ): 65 - 74 .
53. Sing KSW , Everett DH , Haul RAW , Moscou L , Pierotti RA , Rouque´rol J , Siemieniewska T. Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity . Pure Appl Chem . 1985 ; 57 ( 4 ): 603 - 19 .
54. de Boer JH. The structure and properties of porous materials . Londyn: Butterworth; 1958 .
55. Camino C , Lomakin SM , Lazzari M. Polydimethylsiloxane thermal degradation part 1. Kinetic aspects . Polymer . 2001 ; 42 ( 6 ): 2395 - 402 .
56. Shalaby WS , Bair HE . Block copolymers and polyblends . In: Turi E, editor. Thermal characterization of polymeric materials . London: Academic Press; 1981 . p. 366 - 408 .