Preparation and properties of semi-interpenetrating networks combined by thermoplastic polyurethane and a thermosetting elastomer

Article abstract of DOI:10.1039/c7nj03841k

A thermosetting elastomer has been introduced into hydroxyl-terminated polyether thermoplastic polyurethane systems by semi-interpenetrating technology. The novel energetic macromolecule materials are investigated by Fourier transform infrared spectroscopy (FTIR), uniaxial tensile test, dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA). The results show that this material has good mechanical properties with a stress of 9.7 MPa and strain of 1010.7% when the mass percentage of triazole segments is 20 wt%. It is worth noting that the network structure parameters of semi-interpenetrating materials are quantitatively calculated for the first time based on the relationship between the elastic modulus and the effective crosslinking density. The damping analysis results show that the linear polyurethane domains are tightly embedded into the tridimensional network of triazole domains. In addition, it is confirmed from thermal stability and energy analysis that the samples exhibit good thermal stability and positive heat of formation. Therefore, the novel energetic materials are of potential applied value in the areas of aerospace industry and missile technology.

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Preparation and properties of semi-interpenetrating networks
combined by thermoplastic polyurethane and thermosetting
elastomer
Received 00th January 20xx,
Accepted 00th January 20xx
Yajin Li,a Guoping Lia, Jie Li and Yunjun Luo*a
DOI: 10.1039/x0xx00000x
Thermosetting elastomer has been introduced into hydroxyl-terminated polyether thermoplastic polyurethane systems by
semi-interpenetrating technology. The novel energetic macromolecule materials are investigated by Fourier transform
infrared spectroscopy (FTIR), uniaxial tensile test, dynamic mechanical analysis (DMA) and thermal gravimetric analysis
(TGA), respectively. The results show that this material has good mechanical properties with stress of 9.7 MPa and strain
of 1010.7 % when the mass percentage of triazole segments is 20 wt. %. It is worth noticing that the network structure
parameters of semi-interpenetrating materials are quantitatively calculated for the first time based on the relationship
between elastic modulus and effective crosslinking density. The damping analysis results present that the linear
polyurethane domains are tightly embedded into the tridimensional network of triazole domains. In addition, it is
confirmed from thermal stability and energy analysis that the samples exhibit good thermal stability and positive heat of
formation. Therefore, the novel energetic materials are of potential applied value in the area of aerospace industry and
missile technology.
www.rsc.org/
GAP is considered to be a promising binder for propellant
industry. It outperforms other energetic binders that have
been developed in recent years due to its positive effect on
Introduction
The polymeric binders in propellants are normally cross-linked
polyurethane networks, which function as a matrix to combine
some additives (such as oxidizers and metal fuels).1-3 Hydroxyl-
terminated polyether type thermoplastic elastomers (HTPEs)
as the linear polymer have been widely used as polymeric
binders for the preparation of nitrate ester polyether (or
polyester) (NEPE) propellants due to the excellent low-
temperature mechanical properties since this century.4-6 In
these HTPEs, poly(ethylene oxide-co-tetrahydrofuran) (PET)
polymer is composed of ethylene oxide (EO) and
tetrahydrofuran (THF), in which the THF segments offer a
superior strength and low-temperature property while the EO
segments give rise to a favorable flexibility.7 Although the PET-
based propellants have a wide range of mechanical properties,
PET polymeric binder does not possess rich enthalpy which
greatly limited the energy level of propellants. Therefore, to
develop a high performance polymeric binder is the goal for
researchers, and many attempts have been made to improve
this situation via blending polyether polymer with energetic
binders which have positive heat of formation, for example,
glycidyl azide polymer (GAP) binder.
the burning rate and specific impulse of propellant.8-10
.
Furthermore, the presence of azide groups (-N3) in the GAP
polymer chain allows it to react with end-alkynyl compounds
to form triazole cross-linking networks.11-13 The obtained novel
cross-linked networks could not only enhance the thermal
stability and burn rate in the polymeric binders,14-16 but form
three-dimensional networks without any lateral reactions due
to the moieties insensitive nature. Unfortunately, because of
the rigidity for triazoles as crosslinks and the wasted loops
formed by the intermolecular crosslinking, their mechanical
properties are unsatisfactory. Therefore, researchers have
attempted to make some improvements. For example, Min et
al.14 have prepared a dual curing system by urethane- and
triazole-forming reactions. The dual curing systems could
improve the mechanical properties than the single triazole
network, and the new system based solid propellants
exhibited a higher burn rate and a low pressure exponent.
However, the dual system showed two low glass transition
temperatures due to the incompatibility of their polymeric
chains. This phenomenon limits the mechanical property
improvement.
Usually, the chemical and physical combinations of two or
more structurally dissimilar polymers provide a convenient
route for the modification of properties to meet specific
needs.17 Normal blending or mixing of two polymers result in a
multiphase morphology due to thermodynamic incompatibility
which arise from the relatively small gain in entropy of
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mixing.18 If mixing takes place on a lower molecular weight
level and polymerization is carried out simultaneously with
crosslinking, phase separation may be kinetically controlled as
the entanglements are made permanent by crosslinking.
Interpenetrating polymerization represents a third mechanism
by which different polymers can be physically combined.19, 20
In general case, a network in which one or more polymers are
cross-linked, one or more polymers are linear or branched is
named as semi-interpenetrating elastomer networks (semi-
IENs). Considering the advantages of HTPEs and triazole
network, we construct a novel triazole-polyurethane latex
semi-IENs.
In this study, a series of semi-interpenetrating elastomer
networks of PET-TPEs with triazole polymer have been
obtained by the sequential-IPN process. The prepared semi-
IENs were investigated with Fourier transform infrared
spectroscopy (FTIR), uniaxial tensile test, dynamic mechanical
analysis (DMA) and thermal gravimetric analysis (TGA),
respectively. It is expected to provide a novel binder system
for the area of aerospace industry and missile technology.
Scheme 1 Synthesis route of PET-TPE. The react agent is IPDI,
and the chain extender is BDO.
Experimental
Materials
Poly (Ethylene Oxide-co-Tetrahydrofuran) (PET, analytical
grade, Mn = 4000 g/mol) was obtained from Hubei Aviation
Institute of Chemical Technology and purified by vacuum
drying. Isophorone diisocyanate (IPDI, Bayer (Germany); Mn =
222.29 g/mol) was used as received. 1,4-Butanediol (BDO,
analytical grade, Mn = 90 g/mol) was obtained from Beijing
Chemical Plant and used after it was vacuum-dried for 4h at 85
Scheme 2 Synthesis route of triazole system. GAP polymer
reacted with acetic anhydride as end-capping; it can be sure
that the system have not any lateral reactions.
℃
. The catalyst was prepared by the dissolution of dibutyl tin
dilaurate (Beijing chemical plant) into diethyl phthalate.
Glycidyl azide polymer (GAP, Mn = 3600 g/mol) was obtained
from Liming Research Institute of Chemical Industry and
BDO was added to the previous NCO-terminated PET pre-
polymer at 60
℃
the product was cast in a mould to cure at 60
, and the reaction was kept for 20 min. Then,
for around
purified by vacuum drying for 2h at 80
℃. Acyl-GAP was
℃
synthesized by our teams work in recent report21 (synthesis
route see Scheme2). The aliphatic alkynes (BPS) was
synthesized based on literature procedures22 (synthesis route
in Supplementary materials Scheme 1S).
96h in the nitrogen atmosphere. In the meantime, real-time
monitoring of the product molecular weight was conducted by
GPC testing.
Preparation of semi-IENs
Synthesis of PET-TPEs
The semi-IENs were prepared by in situ polymerization
method. Scheme 2 and Fig. 1 illustrate the forming process
and schematic diagram for the triazole based thermosetting
system and semi-IENs, respectively. After the PET-TPE reaching
a certain molecular weight, predetermined masses of the Acyl-
GAP with BPS were added into the PET-TPE, and the mixture
was quickly stirred around 30 min for homogenization. The
mixture was poured into the Teflon mold to cure at 60 °C for
around 96 h in the nitrogen atmosphere to obtain the sample.
The samples with triazole system were marked as 10%-semi-
IEN (10% Acyl-GAP/BPS), 20%-semi-IEN (20% Acyl-GAP/BPS),
30%-semi-IENs (30% Acyl-GAP/BPS), 40%-semi-IEN (40% Acyl-
GAP/BPS) and 50%-semi-IEN (50% Acyl-GAP/BPS), respectively.
The PET-TPE (linear polymer) was synthesized using chain
extender BDO with hard segment weight percentage ratios
(HS=40 wt. %), the synthesis process was illustrated in Scheme
1. The hard segments consisted of IPDI chain-extended with
BDO, while the soft segment was PET. The hard-segment
content (HS) by weight was determined according to the
industry’s standard (the molar ratio of [NCO]/[OH] was 1.0 for
all PET-TPEs samples):
ꢄꢅꢆꢇꢅ + ꢄꢈꢇꢉ
ꢄꢅꢆꢇꢅ + ꢄꢈꢇꢉ + ꢄꢆꢊꢋ
ꢀꢁ(ꢂꢃ. %) =
Where mi is the mass.
A stoichiometric amount of PET polymer was heated and
stirred at 90
℃, then, the catalyst and IPDI were added. The
reaction mixture was stirred and kept for 2 h at 90
℃.
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Results and discussion
Molecular weight analysis
ꢎꢎꢎꢎ
ꢌꢍ) and polydispersity
The number-average molecular weight (
ꢎꢎꢎꢎꢎ ꢎꢎꢎꢎ
⁄
ꢌꢍ) of PET pre-polymers are listed in Table1.
index (PDI; ꢌꢏ
ꢎꢎꢎꢎ
The ꢌꢍ of samples gradually increases with the extension of
pre-polymerization time. The PDI of the prepared PET pre-
polymers is between 1.41 and 2.09, which shows that the
products have high molecular weight and narrow molecular
weight distribution. The formation of macromolecular polymer
inevitably leads to the increase viscosity and may lead to
partial crosslinking. It could be found that some gelation
appeared at longer polymerization time. In Table 1, the
molecular weight has a downward trend and the PDI increases
when the pre-polymerization time is more than 4.5 h. In the
GPC testing process, the samples (PET-5h, PET-6h) couldn’t be
completely dissolved, which indicates that slightly cross-linked
phenomenon occurs. This phenomenon is adverse for the
preparation of semi-IENs. Therefore, we selected 4.5 h as the
pre-polymerization time of PET-TPEs for better preparation
process in this study.
Fig. 1 Schematic route for the preparation of semi-IENs.
Measurements
Fourier transform infrared spectroscopy (FTIR) measurements
were recorded (Nicolet FTIR-8700, Thermo) in the range of
4000~500 cm-1.
The molecular weights were obtained using GPC (LC-20A,
Shimadzu) at 35 °C using THF as the mobile phase and the flow
rate was 1 ml/min. The raw data were calibrated using a
universal calibration with polystyrene standards.
Structure characterization of semi-IENs
FTIR analysis
The prepared PET-TPE and semi-IENs were characterized to
investigate their chemical structures. The FTIR spectrum of
PET, IPDI, BDO and PET-TPE are shown in Fig. 2. From the FTIR
spectra of pristine PET shown in Fig. 2(a), obvious
characteristic peak at 3433 cm-1 is ascribed to the stretching
vibration of O-H group and the C-O-C symmetric stretching
vibration appears at 1130 cm-1. The clear peaks at 2935 cm-1,
2966 cm-1, 2943 cm-1 are corresponding to the C-H vibration
for the polymers. As seen from Fig. 2(b), the characteristic
absorption peak at 2250 cm-1 belongs to the NCO stretching
vibration of IPDI. In the spectra of the prepared PET-TPE, the
peaks for O-H group and NCO group disappear, and a new
peak of 1705 cm-1 is observed, which belongs to the amide
carbonyl stretching vibration. The FTIR spectra of the prepared
semi-IENs is shown in Fig. 3(d), and the same peak as PET-TPE
(see Fig. 3(c)) still appear while the alkynyl group at 3293 cm-1
disappears, which indicates that the Acyl-GAP reacts with BPS
but doesn’t react with PET-TPE.
The mechanical properties, including the largest tensile
strength (σm) and elongation at break (εb), of all the dumbbell-
shape specimens were measured using a universal testing
machine (Instron-6022, Shimadzu Co., Ltd.) at a constant rate
of 100 mm/min and the results were averaged from five
samples.
Dynamic mechanical analysis (DMA) was performed using
METTLER Instrument DMA/SDTA861e at shear model device
and a frequency of 1Hz. The temperature range was from -100
to 100 °C under a nitrogen atmosphere with a heating rate of 3
°C/min. The dimensions of the test specimens were square
samples with the length 4 mm and thickness 2 mm.
The thermal gravimetric analysis (TGA) was performed on
the METTLER Instrument TGA-STAR system at heating rates of
10 °C/min from 30 to 600 °C. The samples of 5 mg were used,
and the flow rate of nitrogen gas was 40 ml/min.
The samples were fractured with liquid nitrogen and the
microphotographs were taken after gold sputtering. Atomic
force microscopy (AFM) measurement of the surface
morphology of samples was conducted in air under ambient
conditions using Brucker Dimension Edge.
Table 1 The GPC results of PET pre-polymers. (The molar ratio of [NCO]/[OH] was 1.0 for all PET-TPEs samples)
Samples
PET-3h
20426
2.02
PET-3.5h
28941
2.01
PET-4h
35450
1.41
PET-4.5h
38779
1.87
PET-5h
36532
2.09
PET-5.5h
35891
2.12
PET-6h
33387
2.11
ꢎꢎꢎꢎ
ꢌꢍ
(g/mol)
PDIa
a
ꢎꢎꢎꢎꢎ ꢎꢎꢎꢎ
PDI: polydispersity index, calculated from ꢌꢏ/ꢌꢍ, where measured in GPC testing.
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Fig. 2 FTIR spectrum of (a) PET; (b) IPDI; (c) BDO; (d) prepared Fig. 4 Hardness testing of semi-IENs.
PET-TPE.
Variations in the shore hardness-A depending upon the
amount of triazole system are shown in Fig. 4. The hardness
increases as the curing reaction proceeds and reaches a
plateau of constant value, indicating reaction is completed. It
can also be seen from Fig. 4 that the final hardness value rises
with the increase of the amount of rigid crosslink points.
Micro-phase Morphology
To confirm the micro-phase morphology of the prepared semi-
IEN composites, the SEM and AFM was conducted. Fig. 5
shows the SEM and AFM images of fractured surface of semi-
IEN with 50 wt. % triazole system, respectively. The fractured
surfaces of semi-IEN depicts smooth microstructures due to
the rigid triazole crosslinks. There are large flat regions existed
in the fish scale fractures, implying an enhanced mechanical
properties with the formation of texture structures.
AFM provides
a method to confirm the micro-phase
Fig. 3 FTIR spectrum of (a) Acyl-GAP; (b) BPS; (c) PET-TPE; (d)
separated nature of semi-IEN. Fig. 5(b) depicts the aggregation
of rigid domains as bright regions whereas the soft matrix as
the darker features.23 The bright regions scatter around the
darker regions imply a weakened micro-phase separated
feature with the synergistic effect of two segments.
prepared semi-IENs.
Hardness analysis
The hardness of the semi-IENs samples was also measured by
shore A tester according to ASTM D2240. Post curing hardness
of semi-IENs system was investigated by measuring surface
hardness-A till reaching a constant value.
Fig. 5 (a) SEM image for the fractured surfaces of the semi-IEN. (b) AFM phase image for the semi-IEN film.
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PAPER
relationship (Eq. (1)). For an elastomer, the elastic modulus
could be expressed as the effective sum of both chemical and
physical crosslinking effects (Eq. (2)). For the polyether type
PUE, the chemical crosslinking effect could be negligible.26
Thus, the elastic modulus with temperature could be
transformed to Eq. (3).
(
)
ꢔꢕ/ꢖꢗ
ꢐꢑ = ꢒ ∗ ꢓ
Eq. (1)
Eq. (2)
Eq. (3)
ꢔꢘ = ꢐꢓ ∗ ꢖꢗ = ꢙꢐꢚ + ꢐꢑꢛ ∗ ꢖꢗ
ꢔ′ = ꢐꢑ ∗ ꢖꢗ
Where Ea is the activation energy of physical crosslinking, E´
is the elastic modulus, Ve is the effective crosslinking density,
Vc is the chemical crosslinking density, Vp is the physical
crosslinking density, R is the general gas constant, A is a
constant, and T is the absolute temperature.
Fig.
6 Comparison of tensile stress and strain of
polyurethane, triazole system and semi-IENs.
In this work, the activation energy of hydrogen bond
dissociation (Ea) and the hydrogen bond density (Vp) of PET-
TPE were evaluated from the elastic modulus-temperature
relationship. Fig. 8 presents the elastic modulus (E´) as a
function of temperature between 273 and 373 K of the PET-
TPE and triazole system. The values of E´ decrease sharply as
the temperatures increase from 273 to 373 K for PET-TPE
system, and the values of E’ almost remain the same level at
higher temperature. This phenomenon is attributed to the
hydrogen bond dissociation. Fig. 9(a) gives the relationship
between Ve and temperature of PET-TPE, and the results
indicate that the Ve gradually decrease with the increase of
temperature for physical crosslinking density decreased. As
mentioned previously, the relationship of ln(E´/T) versus 1/T is
illustrated in Fig. 10. Table 2 shows the values of Ea, A and Vp
of PET-TPE sample calculated from Fig. 10.
Mechanical properties
The interpenetrated and entangled chains of two polymers
network can increase the phase stabilities and enhance the
mechanical properties of the final products. Considering the
stress and strain, we selected the PET-TPE as supporting
materials in semi-IENs. As the PET-TPE can well support the
mechanical, meanwhile the triazole system can increase the
energy for the semi-IENs.
The tensile stress, strain of samples are illustrated in Fig. 6,
as functions of triazole content. It depicts the comparison of
tensile stress and strain of semi-IENs with polyurethane and
triazole system. The results indicate that the semi-IENs exhibit
excellent improved mechanical properties (especially stress)
compared with unitary polyurethane system. When the mass
percentage of triazole system is 20 wt. %, the prepared semi-
IENs keep the maximal mechanical strength and elongation.
The fact that the prepared semi-IENs show better mechanical
properties could be based on the explanation of morphologies
for fractured surfaces as described earlier.
NH
NH
O
O C
NH
O
C
O
O
C
Network structure analysis
O
For semi-interpenetrating elastomer networks, researchers
still have little knowledge about the network structure. In the
present work, we tried to quantitative the results by the
effective crosslinking density (Ve). The PET-TPE sample is
amorphous material and the physical crosslinking would play a
key role on the mechanical properties if its chemical structure
is similar. Hydrogen bond is the most important physical
crosslinking effect of polyurethane (Hydrogen-bonded diagram
as Fig. 7).24-26
NH
O
NH
O C
NH
O
O
C
O
C
O
HB
Weisfeld et al.26 have proposed that the physical
Fig. 7 Schematic representation of “chain” of hydrogen-
crosslinking density of PU accords with the Arrhenius
bonded.
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The hard segments of molecular are connected with each
NJC
other by intermolecular hydrogen bond and form domains to
act as junctions of physical crosslinking for the soft
segments.25,
27
Fig. 8(b) shows that when temperature
increases, the elastic modulus of triazole system increase due
to the aggravation of thermal vibrations for polymer segments
which attributed entropic contribution of the network.28 For
the triazole crosslinking system, there is no hydrogen bonding
interaction, which means that physical crosslinking density is
mainly from the chain entanglement, so the Ve has a small
variation from 3.68
increase of temperature (Fig. 9(b)).
ꢀ ꢀ
104 to 3.45 104 mol/cm3 with the
To further confirm the effect of triazole polymers on
network structure parameters of semi-IENs chains, the Vc and
Vp are calculated based on the above theory. Using the same
testing method as sample PET-TPE, semi-IENs samples were
also measured by DMA at temperature between 273 and 373
K. This temperature range is above the glass transition
temperature (Tg) of all samples.
Fig. 9 Relationship between Ve and T of polyurethane and
triazole system. (a) Relationship between Ve and T; (b)
Relationship between Ve and T.
Fig. 11 and Fig. 12 (a) give the variation trend of the elastic
modulus and Ve of the samples, 10% to 50% semi-IENs,
respectively. In the semi-IENs system, the decrease of elastic
modulus indicates that the elastic modulus in this study
depends strongly upon temperature.
The decrease of Ve is contributed to the decrease of physical
crosslinking rather than the chemical crosslinking.29 According
to the previous analysis, the decrease of effective crosslinking
density (Ve) between any temperatures points belongs to the
extent of hydrogen bond in physical crosslinking diminishes,
which can be expressed by following Eq. (4).
ꢊꢦ/ꢧꢋꢠ
= ꢙꢜ ꢛ ꢟ ꢙꢜ ꢛ = ꢣ ∗ ꢤꢥꢊ /ꢧꢋ ꢟ ꢥ
ꢨ
ꢦ
ꢞ
(
)
( )
ꢟ ꢜ
ꢝ ꢋꢠ
ꢜ
ꢝ
ꢋꢞ
ꢡ
ꢡ
ꢋ
ꢋꢞ
ꢢ
Eq. (4)
The values of Ea, A and Vp of samples (Acyl-GAP content is
10, 20, 30, 40, and 50 wt. % of semi-IENs) can be calculated
through curve fitting as shown in Fig. 12(b) and Table 2. Fig. 13
shows the Vp and Vc as a function of temperatures, and the
values of Vp have same trend with Ve but the Vc basically
remain the same level.
Fig. 8 Elastic modulus of polyurethane and triazole system as a
function of temperature. (a) Relationship between E´ and T; (b)
Relationship between E´ and T.
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the aliphatic (CH2)n segments. At high temperatures, the onset
of the relaxation starts over the temperature of 0 °C and spans
till 55 °C. This relaxation is associated with the coordinated
movements of soft-hard domain of polymer chains. As seen
from Figure 15(b), triazole system has obvious damping peak
at approximate -19 °C, corresponding to the glass transition of
the copolyether strands. When the tridimensional network is
part of the semi-IENs, the most visible changes in the damping
behavior are the decrease of the tan δ peak at high
temperatures. All these modifications come from
entanglement between the chain and chain, and the linear PU
domains are tightly embedded into the tridimensional
network. The decrease of tan δ value presents that the
elastomers have excellent cryogenic property.
Fig. 10 Relationship between ln (E´/T) and 1/T of polyurethane
system. Lines are the regression results.
Obviously, the quantitative data of Vp decrease with the
content of triazole system increase at 25 °C, while the Vc have
no significant change indicating that more topological
entanglement between molecular chain arise. When
temperature increases, the hydrogen bond effect diminishes
and the Vp of elastomers almost overlap. For semi-IENs
samples, they have similar chemical structures but the
interpenetrating percentages are different. The physical
crosslinking contribution to the elastic modulus decrease with
the temperature increase (see Fig. 14), which indicates that
physical crosslinking plays an indispensable role on the tensile
properties especially at ambient temperature.
Damping properties
Fig. 11 Elastic modulus of semi-IENs (triazole system content is
10, 20, 30, 40, and 50 wt. %) as a function of temperature.
The tan δ responses of semi-IENs samples measured by DMA
are shown in Fig. 15. Fig. 15(a) shows the relaxation properties
of PET-TPE system, and the relaxation is centred around -60 °C
on tan δ peak and may be associated with the movement of
Table 2 Values of network structure parameters for semi-IENs (triazole system content is 10, 20, 30, 40, and 50 wt. %)
Sample
Ea a(KJ/mol)
A b
2.61
10-11
3.482
R c
Vp d(25
℃
)
Ep/E e(25°C)
PET/IPDI/BDO
Acyl-GAP/BPS
10% semi-IEN
20% semi-IEN
30% semi-IEN
40% semi-IEN
50% semi-IEN
47.78
ꢀ
0.9988
0.9956
0.9999
0.9995
0.9992
0.9993
0.9989
64.95
1.568
74.54
29.43
23.0
95%
3.73
40%
46.22
5.96
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
10-7
95%
38.19
6.01
3.85
4.57
1.23
10-6
10-5
10-5
10-5
90%
32.97
88%
32.01
18.54
12.46
87%
34.27
81%
a Calculated from Eq. (1), Eq. (4), Figure 10 and Figure 12 (b).
b A is a pre-exponential factor, its physical significance is the value of physical crosslinking density when the temperature is
infinite.
c R is the correlation coefficient of fitting
d Calculated from Eq. (1) when temperature is 25°C.
e Ep/E is the percentage of the contribution of physical crosslinking in elastic modulus.
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Fig. 13 Relationship between Vp , Vc and temperature of semi-
IENs (triazole system content is 10, 20, 30, 40, and 50 wt. %).
Fig. 12 Relationship between Ve and T, ΔVe and 1/T of semi-
IENs (triazole system content is 10, 20, 30, 40, and 50 wt. %).
Lines are the regression results.
Thermal stability of semi-IENs
The TG analysis was conducted to investigate the thermal
stability of the prepared semi-IENs. Fig. 16 shows the TG and
derivative thermo-gravimetric (DTG) curves of triazole system,
PET-TPE and semi-IENs. As shown from Fig. 16(b), all samples
of semi-IENs exhibit three steps thermal degradation, of which
the temperatures range from 205 °C to 500 °C. The initial 5%
weight loss for total semi-IENs occurs around 240 °C,
suggesting that the samples have good thermal stability
properties. Among them, the first step is about 205~282 °C,
which is attributed to the thermal degradation of azide group
and triazole ring; the second step is about 282~362 °C, which is
attributed to the thermal degradation of polyether chain; the
third step is about 362~500 °C, which is attributed to the
thermal degradation of carbamate and other residual
segment.
The corresponding decomposition temperatures obtained
from TG-DTG curves are listed in Table 3. The results show that
the maximum decomposition temperature of semi-IENs has
increased to a certain extent compared with unitary system.
The improvement of thermal stability is caused by the
introduction of crosslinking network which supplies the shield
effect during the thermal degradation. Normally, the Theat-
resistance index (THRI) is recognized as an effective method to define
the heat resistance of materials to ageing under the high
temperature30, 31. The higher THRI, the better thermal stability
of the materials. The THRI can be expressed as Eq. (5):
Fig. 14 Contribution of physical crosslinking of semi-IENs
(triazole system content is 10, 20, 30, 40, and 50 wt. %) as a
function of temperature.
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ꢫ
(
)ꢯ
ꢩꢪꢧꢅ = 0.49 ∗ ꢩꢬꢭ + 0.6 ꢩꢬꢮ ꢟ ꢩꢬꢭ
Eq. (4)
triazole system. Although, the release of heat accelerate the
decomposition of PET-TPEs, the semi-IENs still showed
relatively high thermal stability.
The calculated THRI is also listed in Table 3. It’s seen that
after adding of triazole system into polyurethane matrix, the
THRI of semi-IENs sample is located between pure PET-TPE and
Based on these results, the prepared semi-IENs are very
triazole system. This reveals that well interpenetrating stable in the temperature range for aerospace industry and
structure have advantages for the heat resistance of the missile technology.32
Fig. 15 Dependences of tan δ on temperature. (a) PET/IPDI/BDO system; (b) Acyl-GAP/BPS and semi-IENs system. (triazole
system content is 10, 20, 30, 40, and 50 wt. %).
Fig. 16 TG and DTG curves of PET/IPDI/BDO, Acyl-GAP/BPS and semi-IENs. (triazole system content is 10, 20, 30, 40, and 50 wt.
%).
Table 3 Thermal decomposition data of PET/IPDI/BDO, Acyl-GAP/BPS and semi-IENs. (triazole system content is 10, 20, 30, 40,
and 50 wt. %)
First stage
Second stage
Third stage
Weight loss temperature/°C
Samples
THRI/°C
a
b
c
d
e
Tmax,1
Tmax,2
Tmax,3
Td1
Td2
PET/IPDI/BDO
Acyl-GAP/BPS
10% semi-IEN
20% semi-IEN
30% semi-IEN
40% semi-IEN
50% semi-IEN
-
318.20
361.79
337.38
335.81
331.86
328.52
321.25
401.71
-
295.3
230.8
287.7
258.5
249.0
245.4
242.8
373.7
303.0
383.6
381.3
371.0
366.3
369.8
167.7
134.3
169.2
162.8
157.9
155.8
156.3
248.9
256.28
254.1
254.48
253.91
249.2
407.2
408.87
407.41
410.48
415.34
a The maximum decomposition temperature of the first decomposition stage.
b The maximum decomposition temperature of the second decomposition stage.
c The maximum decomposition temperature of the third decomposition stage.
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d The sample’s decomposition temperature of 5% weight loss.
e The sample’s decomposition temperature of 40% weight loss.
Energy analysis
effective crosslinking density. The damping analysis results
present that the linear PU domains are tightly embedded into
the tridimensional network. It also can be confirmed from
thermal stability and energy analysis that the sample exhibit
good thermal stability and higher positive heat of formation.
Based on all results, it is concluded that prepared semi-IENs
can be considered as promising adhesives for aerospace
industry and missile technology.
There is a positive correlation relationship between heat of
decomposition and heat of combustion for binder. To further
confirm the effect of triazole system on heat of formation, the
heat of decomposition of samples are experimented and
shown in Fig. 17 and Table 4. Obviously, the decomposition
heat of semi-IENs increase from 256 to 1707 J/g with the
content of triazole system increase. The results indicate that
the semi-IENs have a high positive heat of formation, whose
characteristics meet the requirements of the energetic
binders.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
Financial support for this work through the National Natural
Science Foundation of China (NSFC) (Contract No. U1630142)
is greatly appreciated.
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PAPER
Preparation and properties of semi-interpenetrating networks
combined by thermoplastic polyurethane and thermosetting
elastomer
Received 00th January 20xx,
Accepted 00th January 20xx
Yajin Li,a Guoping Lia, Jie Li and Yunjun Luo*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
Table of Content Entry
A novel energetic macromolecule of semi-interpenetrating materials were prepared via sequential-IPN process, which can be used
in the area of aerospace industry and missile technology.
.
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