Synthesis and shape memory behavior study of hyperbranched poly(urethane-tetrazole)

Article abstract of DOI:10.1007/s11426-011-4316-9

A novel hyperbranched poly(urethane-tetrazole) (HPUTZ) was synthesized via the "A₂+BB₂′ " approach using hexadiisocyanate (HDI) and 3-(bis-(2-hydroxyethyl)) aminopropyltetrazole (HAPTZ). The molecular structure was characterized by FTIR and ¹H NMR spectroscopy. The number average molecular weight was measured to be 1.05×10⁴ g/mol with a polydispersity of 1.27 by GPC analysis. The HPUTZ was further cured by the semi-adduct (PEG-IPDI) from polyethylene glycol (PEG) reacting with isophorone diisocyanate (IPDI) to form the crosslinked HAPTZ-PU film in different ratio of HAPTZ to PEG-IPDI. The glass transition temperature of HAPTZ-PU increased from 44.9 to 56.4 °C as the HPUTZ content increased from 20% to 33% from the DSC analysis. The DMA results indicated that the HPUTZ-PU with 20% HPUTZ possessed the highest storage modulus and loss tangent. However, the storage modulus increased with the increasing of HPUTZ segment at higher temperature. The shape memory study showed that all the films presented the excellent shape memory function. Over 98% shape recovery could be obtained for the HAPTZ-PU with 20%-33% HAPTZ segment content within 60 s in the tension deformation test and within 40 s at 80 °C in the bend deformation test.

Full text of DOI:10.1007/s11426-011-4316-9

SCIENCE CHINA
Chemistry
•
ARTICLES •
September 2011 Vol.54 No.9: 1461–1467
doi: 10.1007/s11426-011-4316-9
Synthesis and shape memory behavior study of hyperbranched
poly(urethane-tetrazole)
1
2
1*
QIAO LiGen , ASIF Anila & SHI WenFang
1
CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and
Technology of China, Hefei 230026, China
Interdisciplinary Research Centre in Biomedical Materials, COMSATS Institute of Information Technology, Defence Road,
Off Raiwind Road, Lahore 54000, Pakistan
2
Received March 20, 2011; accepted April 13, 2011; published online June 11, 2011
2
2
A novel hyperbranched poly(urethane-tetrazole) (HPUTZ) was synthesized via the “A +BB′ ” approach using hexadiisocya-
nate (HDI) and 3-(bis-(2-hydroxyethyl)) aminopropyltetrazole (HAPTZ). The molecular structure was characterized by FTIR
1
4
and H NMR spectroscopy. The number average molecular weight was measured to be 1.05×10 g/mol with a polydispersity of
.27 by GPC analysis. The HPUTZ was further cured by the semi-adduct (PEG-IPDI) from polyethylene glycol (PEG) reacting
1
with isophorone diisocyanate (IPDI) to form the crosslinked HAPTZ-PU film in different ratio of HAPTZ to PEG-IPDI. The
glass transition temperature of HAPTZ-PU increased from 44.9 to 56.4 °C as the HPUTZ content increased from 20% to 33%
from the DSC analysis. The DMA results indicated that the HPUTZ-PU with 20% HPUTZ possessed the highest storage mod-
ulus and loss tangent. However, the storage modulus increased with the increasing of HPUTZ segment at higher temperature.
The shape memory study showed that all the films presented the excellent shape memory function. Over 98% shape recovery
could be obtained for the HAPTZ-PU with 20%–33% HAPTZ segment content within 60 s in the tension deformation test and
within 40 s at 80 °C in the bend deformation test.
synthesis, hyperbranched poly(urethane-tetrazole), shape memory behavior, thermal property
1
Introduction
The shape memory polyurethanes (SMPUs) were widely
studied due to their excellent shape memory behavior. The
micro-phase separated structure of SMPU was generated by
a frozen phase and a reversible phase. The presence of
strong hydrogen bonding in SMPU plays a key role in
forming the stable frozen phase. Whereas, the reversible
phase usually consists of soft segments such as long alkyl
chain, and mainly for providing the shape memory perfor-
mance. Because two phases are connected by chemical
bonds, the phase-separation is limited naturally, and endows
SMPU showing the circular shape memory property [4–9].
Moreover, the shape recovery behavior of SMPU can be
adjusted in a large temperature range by controlling the hard
segment content in the polymer chain. Hence, SMPU mate-
rials are designed to prepare various products with different
storage modulus which affects the shape memory function
such as shape-fixed length and shape recovery rate [10, 11].
The conceptual category of smart materials has been ex-
tended to various application fields, such as sensors, medi-
cal, electronic, and so on [1, 2]. In recent years, the shape
memory polymers (SMPs) have been proposed as a group
of smart materials. Their temporary or permanent defor-
mation can be eliminated at a critical temperature. The
SMPs possess some significant advantages such as light-
weight, larger recoverable deformation, lower manufacturing
cost and lower recovery temperature compared to traditional
shape memory alloys. Therefore, the expected industrial ap-
plications have been made for such as heat-shrinkable mate-
rials, self-healing coatings, and packaging materials [3].
*
Corresponding author (email: wfshi@ustc.edu)
©
Science China Press and Springer-Verlag Berlin Heidelberg 2011
chem.scichina.com www.springerlink.com

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Qiao LG, et al. Sci China Chem September (2011) Vol.54 No.9
However, the SMPU materials were recently developed
received. All other chemicals were supplied by First Rea-
gent Co. of Shanghai, China. Diethanolamine (DEA), acry-
lonitrile (AN), isophorone diissocyanate (IPDI) and hexa-
diisocyanate (HDI) were used after distillation, and the sol-
vents were dried before use.
mainly as linear polymers or block copolymers [12–14].
Little was investigated with hyperbranched polymers used as
shape memory materials. Liu and his coworkers synthesized
a series of polyurethanes upon the hyperbranched polyester,
TM
Boltorn H30 [15]. The poly(butyleneadipate)glycol 2000
terminated with methylenediphenyl diisocyanate was used
to cure with the hyperbranched polyester at high tempera-
ture. They have observed that the cured films possessed the
excellent shape memory properties due to the presence of
abundant hydrogen bonding which affects the micro-phase
separated structure. Sivakumar and his coworkers prepared
a series of hyperbranched polyurethanes with different mo-
2
.2 Measurements
1
The H NMR spectra were recorded with an AVANCE 300
Bruker spectrometer using tetramethylsilane as an internal
reference and CDCl , D O and DMSO-d as solvents.
3 2 6
The FTIR spectra were recorded using a Nicoler
MAGNA-IR 750 spectrometer with a KBr disk.
The molecular weight and its distribution were determined
by a waters gel permeation chromatography (GPC) system
with a refractive index detector using DMF as an eluent and
polystyrene as a standard polymer for calibration.
A Pyris Diamond DMS 6100 instrument (Perkin-Elmer
Co., USA) was used to measure the storage modulus and
Tanδ at an oscillation frequency of 1 Hz with an astatic
force of 10 mN. The running temperature was set in the
range of −40 to 120 °C at a heating rate of 10 °C/min under
nitrogen atmosphere. The crosslinking density of curing
films v
chains per cubic centimeter and calculated by the DMA
results from the following equation v = E′/3RT, where E′ is
the storage modulus, R is the gas constant, T is the kelvin
temperature. E′ can be obtained from the DMA results in
the rubber state. Because different composition ratios were
used, the curing films possessed various crosslinking densi-
ties from their mechanical properties.
The DSC curves were recorded using a Perkin-Elmer
Diamond differential scanning calorimeter (DSC) with a
heating rate of 10 °C/min from 20 to 100 °C, and then
cooled to 20 °C at a cooling rate of 200 °C/min, followed by
a second scan at the same heating rate to 100 °C, and cali-
brated with a base line.
lecular weights via the A
2 3
+ B approach [16].
The tetrazole compounds possessing a five-membered
aromatic heterocycle with four N atoms on the ring have been
widely used in organic chemistry, coordination chemistry,
and especially biomedical science [17, 18]. The tatrezole is
shown as a kind of acid (pKa (tetrazole) = 4.89, while pKa
(acetic acid) = 4.75) [19], but undergoes longer metabolic
degradation than a carboxylic acid, which results in that the
tetrazole is a suitable choice instead of carboxylic acid for
biomedical science. Dozens of linear polymers containing
tetrazole group were synthesized in previous studies [19–21].
The poly-1-vinyl-5-aminotetrazole and poly (glycidyl meth-
acrylate) containing 5-aminotetrazole were prepared for dif-
ferent application purposes [20, 21]. Due to the proton
transport between hydrogen bonds of neighboring heterocy-
clic units through structure diffusion, the stable dispersed
domains that act as physical crosslinkers (frozen phase) via
the strong hydrogen bonding in a polymer containing te-
trazole group are expected to form. However, to the best of
our knowledge, the hyperbranched polymers containing both
urethane and tetrazole segments have never been prepared for
shape memory material applications before.
e
is defined as the mole number of effective elastic
e
In this study, the hyperbranched poly(urethane-tetrazole)
(
HPUTZ) via the “A
segment and the hyperbranched poly(urethane-tetrazole)
HPUTZ) hard segment was prepared. The shape memory
2
2
+BB′” approach based on the PEG soft
The shape memory behavior of HPUTZ-PU was exam-
ined using the tension deformation test. The size of 0.8 mm
(
(
thickness) × 30 mm (width) × 10 mm (length) for all sam-
behavior was examined extensively. The linear polymer with
the similar structure as that of HPUTZ-PU was not synthe-
sized in this work. However, from the chemical structure of
hyperbranched copolymer HPUTZ-PU, it can be found that
compared to linear copolymers, the synthesized copolymers
supply much more extensive hydrogen bond structures,
which directly affect the micro-phase separated structure.
And the content and distributing of hard and soft segments
play a key role in the shape recovery property of films.
ples was used in the tests. The sample was first stretched to
the elongation of 250% at 80 °C, and then cooled quickly at
0
°C and kept for 5 min in order to fix the deformation. The
fixed length of the deformed sample was measured. The
deformation length and shape recovery properties were rec-
orded in a water bath at different temperatures during the
shape recovery course. The shape fixity (F
s
) and shape re-
coverability of a film (R ) are defined as follows [15]:
s
F = (L −L )/(L −L )×100%
(1)
(2)
s
F
o
max
o
R = (L −L )/(L −L )×100%
s
F
t
F
o
2
Experimental
Where L
max is the maximum stretched length (at the elongation of
50%), and L is the length in the course of shape recovery
at time.
o F
is the original length, L is the fixed length at 0 °C,
L
2
2
.1 Materials
t
Sodium azide (NaN
3
) was supplied by Aldrich and used as

Qiao LG, et al. Sci China Chem September (2011) Vol.54 No.9
1463
For recording the shape recovery course, the sample size
of 0.5 mm (thickness) × 30 mm (width) × 10 mm (length)
was used in the bend deformation test. The film was firstly
bent to a circular shape with a diameter of 9.55 mm at 80 °C
by a water bath under an external force, then fixed at 0 °C
for 5 min using an ice bath. Afterwards, the temperature
was raised to 80 °C, and the shape recovery behavior was
recorded as the curvature radius changed at various elapsed
times and temperatures during the shape recovery.
The mixture was then cast into a Teflon mould and main-
tained in an oven under vacuum at 60 °C for 4 h, 80 °C for
48 h to obtain the crosslinked film, named HPUTZ-PU.
Moreover, according to the weight ratios of 1:2, 1:3, and 1:4
for HPUTZ:PEG-IPDI in the formulations, the cured
HPUTZ-PU1-2, HPUTZ-PU1-3, and HPUTZ-PU1-4 were
obtained, respectively.
3
Results and discussion
2
.3 Synthesis
3
.1 Synthesis and characterization
3
-(Bis-(2-hydroxyethyl)) aminopropyltetrazole (HAPTZ)
The synthesis route for HPUTZ is shown in Scheme 1. The
intermediate product BHAN was synthesized by the Mi-
chael addition reaction of double bond with amine group,
then further cyclized with nitrile to form the 5-substituted
tetrazole, HAPTZ, in the presence of a protonic acid (HCl)
in DMF. In order to increase the reactivity HAPTZ further
DEA and AN were mixed in water in a molar ratio of 1:2
and stirred for 48 h at room temperature. After evaporating
water and the unreacted AN, the intermediate product,
3
-(bis-(2-hydroxyethyl)) aminopropanenitrile (BHAN) was
obtained. Then NaN
and ZnCl were added into the DMF
solution of BHAN at 120 °C in a molar ratio of 4:4:1 for
NaN
:ZnCl :BHAN, and stirred for 48 h. After being
3
2
reacted with HDI to form HPUTZ as a BB′ type monomer
2
3
2
through the reaction of isocyanate group with the active
hydrogen atom on the tetrazole ring.
cooled to 30 °C, hydrochloric acid (1 M) was dropped into
the reactant, and stirred at 60 °C for another 12 h. After
DMF was removed by distillation, the resultant salt was
filtrated, recrystallized from methylcyanide/ether, and dried
in a vacuum oven, obtaining 3-(bis-(2-hydroxyethyl)) ami-
nopropyltetrazole, named HAPTZ, as a brown viscous liq-
uid (yield: 79%).
The FTIR spectra of BHAN and HAPTZ are shown in
Figure 1. It can be seen that the peak at 2256 cm− in the
FTIR spectrum of BHAN attributing to the stretching vibra-
tion of nitrile group disappeared completely in the FTIR
spectrum of HAPTZ. However, the peak at 1665 cm− at-
tributed to the bending vibration of tertiary amine is main-
tained, which is also attributed to the N-H flexural vibration
of the tetrazole ring.
1
1
Hyperbranched poly(urethane-tetrazole) (HPUTZ)
The obtained HAPTZ (0.1 mol) was firstly dissolved in an-
hydrous DMF at 30 °C. Then HDI (0.1 mol) was dropped
into the HAPTZ solution using a dropping funnel. After
reacting for 8 h, the dibutyltin dilaurate (DBTDL) (1 mL)
used as a catalyst was added, and stirred for 12 h at 90 °C.
Afterwards, the solution was poured into ether and washed
by water. The final product, hyperbranched poly(urethane-
tetrazole), named HPUTZ, was obtained as a brown solid
1
Figure 2 shows the H NMR spectra of BHAN and
HAPTZ. From the spectrum shown in Figure 2 (a), the
peaks at 2.58 and 2.81 ppm attributed to the protons of ni-
trile propyl group (NC-CH -CH -) formed in the Michael
2 2
addition reaction of DEA with AN are observed. The peak
at 8.08 ppm in the spectrum of HAPTZ, as shown in Figure
2
(b), is attributed to the proton of tetrazole, indicating that
(yield: 72%) after water was removed and dried in a vacu-
the cyclizative condensation of nitrile group has taken place
to form HAPTZ. Moreover, four main peaks from 3.00 to
3.80 ppm attributed to the protons of methylene groups ap-
peared, but the shifts altered due to the resonance vibration
of tetrazole ring compared with that for BHAN.
um oven.
Crosslinking of HPUTZ with PEG-IPDI
The semi-adduct (PEG-IPDI) was obtained from the reac-
tion of polyethylene glycol with isophorone diisocyanate.
PEG 400 (0.1 mol) reacted with IPDI (0.2 mol) in anhy-
drous DMF (100 mL) in the presence of DBTDL (1 mL) at
1
Figure 3 shows the H NMR spectrum of HPUTZ. The
peaks at 7.09 and 5.73 ppm are attributed to the protons in
amide and urethane groups formed from the reactions of
isocyanate group with the active hydrogen on tetrazole ring
and hydroxyl group of DEA, respectively. The peaks around
3
0 °C for 4 h. Then HPUTZ was mixed with PEG-IPDI
according to the weight ratio as listed in Table 1, and stirred
for 2 h at room temperature to form a homogeneous solution.
Table 1 Dynamic mechanical properties of HPUTZ-PUs
a)
b)
a)
b)
c)
Sample
HPUTZ to PEG-IPDI (weight ratio)
T
g
(°C)
E
l
′
(MPa)
E
h
′
(MPa)
El′ / Eh′
V
(mol/L)
HPUTZ-PU1-2
HPUTZ-PU1-3
HPUTZ-PU1-4
1:2
1:3
1:4
58.9
57.7
49.8
1620
1450
2170
51.4
41.9
20.1
31.5
34.6
108.1
5.69
4.66
2.28
a) At the temperature of T
g
g
−30 °C; b) at the temperature of T +30 °C; c) crosslinking density by DMTA.

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Qiao LG, et al. Sci China Chem September (2011) Vol.54 No.9
Scheme 1 Synthesis route for HPUTZ.
1
Figure 2 H NMR spectra of BHAN in CDCl
3
2
(a) and HAPTZ in D O (b).
Figure 1 FTIR spectra of BHAN (a) and HAPTZ (b).
4
.19 and 3.95 ppm are attributed to the protons neighbour-
ing the ester group (–CH –OOC–) and hydroxyl group
–CH –OH), respectively. The double peaks around 1.20 ppm
2
(
2
1
Figure 3 H NMR spectra of HPUTZ in DMSO-d
6
.
are assigned to the hydrogen atoms in middle methylene
groups derived from hexadiisocyanate. The peak caused by
the proton of tetrazole ring appears at 8.01 ppm. It is note-
worthy that the peak can be also observed around 4.72 ppm,
which is attributed to the proton of terminal amide group [22].
In order to determine the number average molecular
weight and its distribution by GPC analysis the HPUTZ was
terminated by acetate anhydride, leading to the formation
of terminal ester and 1,3,4-oxadiazole. The GPC trace of
HPUTZ is shown in Figure 4. The number average molec-
actions in the system. Furthermore, HPUTZ showed a bi-
modal distribution of molecular weight, relating to the elution
volumes of 32.5 and 33.8 mL. The similar behavior has been
reported for hyperbranched poly- mers [23–25].
3
.2 Thermal properties
The DSC curves of HPUTZ-PUs are shown in Figure 5. It
can be found that there was no crystallization area in the
films, only the glass transition occurred, indicating that the
microstructures of films are homogeneous [26]. There was
no crystalline phase observed from the DSC curves. The
ular weight (M
1
n
) was experimentally measured to be 1.05×
0 g/mol. The wide molecular weight distribution of 1.27
4
was not only due to the high steric hindrance resulting from
the dense tetrazole rings, but also the statistics of various re-

Qiao LG, et al. Sci China Chem September (2011) Vol.54 No.9
1465
Figure 5 DSC curves of HPUTZ-PU1-2 (a), HPUTZ-PU1-3 (b) and
HPUTZ-PU1-4 (c).
Figure 4 GPC trace of HPUTZ terminated by acetate anhydride.
reason may be that the hyperbranched structure of HPUTZ
restrains the crystalline course of the PEO segment. More-
over, the extensive hydrogen bond structure limits the PEO
segments in order accumulation in the curing film. The sim-
ilar result can be seen in ref. [26]. The DSC curves also
g
show that T increased from 44.9 to 56.4 °C as the weight
ratio of HPUTZ to PEG-IPDI segment content increased
from 1/4 to 1/2. It can be interpreted that the tetrazole rings
in HPUTZ which act as hard segments aggregate together
via strong hydrogen bonding to form stable dispersed do-
mains (frozen phase) [15]. Consequently, the increase of
HPUTZ segment content resulted in the enhancement of
frozen phase, and thus the increase in T
g
, due to the re-
Figure 6 E′ of HPUTZ-PU1-2 (a), HPUTZ-PU1-3 (b) and HPUTZ-PU1-4
striction of motion of the molecular chain caused by the
dense hydrogen bonding.
(c) measured by DMTA.
The effects of HPUTZ segment content on the storage
modulus (E′) of cured film are shown in Figure 6. It is ob-
served that all the HPUTZ-PU films have high glassy E′
values of over 1400 MPa at −40 °C as well in the glass tran-
sition process. However, the E′ value of HPUTZ-PU de-
creases sharply as the temperature increased due to the mo-
tion of amorphous polymer chain. At the rubber state, the E′
values decrease to the range of 10 to 100 MPa. This demon-
strates that HPUTZ-PUs possess the typical crosslinking
network character, having two glass state platforms with a
higher E′ at low temperature and a lower E′ at high temper-
HPUTZ segment content was limited badly. Thus, the high-
er temperature was required to activate the movement of
PEG-IPDI segment, leading to the higher T of HPUTZ-
g
PU1-2 than that of others [26]. The HPUTZ-PU1-4 sample
with the highest PEG-IPDI segment content shows the most
obvious viscous feature. Moreover, the peak width of tanδ
curve becomes broad with increasing the PEG-IPDI seg-
ment content, indicating the more uniform network structure
was obtained [26]. Therefore, the T measured from the tanδ
g
curve increases with increasing the HPUTZ segment con-
l
h
tent in HPUTZ-PU. The highest T of 58.9 °C for HPUTZ-
g
ature (Figure 6). It has been also reported that the E′ in-
h
PU1-2 with the most HPUTZ segment content among the
HPUTZ-PU films was obtained, as listed in Table 1.
creased with increasing the hard segment content because of
that the E′ increased with increasing the hard segment con-
h
tent because of the enhancement of crosslinking density. As
listed in Table 1, the higher crosslinking density of 5.69
mol/L for HPUTZ-PU1-2 was obtained compared with 2.28
mol/L for HPUTZ-PU1-4.
3
.3 Shape memory behavior
The maximum stretched length (Lmax) (at the elongation of
2
50%), fixed length (L ) at 0 °C, and length (L ) in the
F
t
The tanδ curves of HPUTZ-PUs with different HPUTZ
segment contents are shown in Figure 7. The loss tanδ re-
flects directly the movement of polymer chain. The micro-
structure was frozen at the glass state, showing the tanδ
value almost unchanged [27]. As the temperature reached to
the T , the movement of segment was activated completely,
g
showing the tanδ curve changed sharply. In this study, the
course of shape recovery at time t were measured by the
tension and bend deformation tests. The shape fixity (Fs)
values were calculated according to the formula described
in the experimental paragraph to be 90.8%, 92.7% and
93.6% at 0 °C for HPUTZ-PU1-2, HPUTZ-PU1-3 and
HPUTZ-PU1-4, respectively, decreasing slightly with the
increase of HPUTZ segment content directly due to the en-
hancement of film rigidity [15].
molecular chain movement in HPUTZ-PU1-2 with high

1466
Qiao LG, et al. Sci China Chem September (2011) Vol.54 No.9
tion test [22]. The movement of soft segment chain directly
influenced the shape memory behavior of a film. The higher
hard segment content leads to the improvement in the stor-
age modulus at high temperature. Accordingly, the maxi-
mum shape recovery rate can be obtained with the highest
hard segment content [31]. The shape recovery performance
can be also compared by the curvatures as the function of
heating temperature, as shown in Figure 11. All the results
are in good agreement with that in the tension deformation
tests as discussed above.
Figure 7 Tanδ of HPUTZ-PU1-2 (a), HPUTZ-PU1-3 (b) and HPUTZ-
PU1-4 (c) measured by DMTA.
4 Conclusions
In this work, a novel hyperbranched poly(urethane-tetrazole)
s
The shape recovery (R ) of films obtained with different
(
HPUTZ) was synthesized via the polycondensation of an
type monomer with a BB' type monomer for the first
time. The M of HPUTZ was measured to be 1.05×10
HPUTZ segment contents was calculated and plotted for the
shape recovery course at 80 °C and different times, as
shown in Figure 8. It is noticeable that the shape recovery
rate and the time elapsed for the shape recovery are influ-
enced sharply by the HPUTZ segment content [28–30].
Therefore, the HPUTZ-PU1-2 film with higher hard seg-
ment content shows the maximal shape recovery rate and
the fastest shape recovery behavior. All the films recovered
the original shape completely within 60 s at 80 °C in the
tension deformation tests. The shape recovery rate was re-
lated to the stored deformation energy when the film was
cooled. The enough stored deformation energy can make
the film recover the original shape quickly. The HPUTZ-
PU1-2 film, showing the highest storage modulus at high
temperature in DMA (Table 1), possesses the most rapid
shape recovery rate. Generally speaking, the shape memory
A
2
2
4
n
g/mol with a polydispersity of 1.27 by GPC analysis. The
glass transition temperature of HAPTZ-PU increased from
4
4.9 to 56.4 °C as the HPUTZ content increased from 20%
to 33% from the DSC analysis. The DMA results indicated
that the HPUTZ-PU with 20% HPUTZ possessed the high-
est storage modulus and loss tangent. However, the storage
modulus increased with the increasing of HPUTZ segment
at higher temperature. The shape memory study showed that
polymers are required to have a small ratio of E′
l h
/E′ , which
is beneficial to the fixation of shape at low temperature and
deformation at high temperature [26, 27]. From Table 1, the
ratios of 31.5 for HPUTZ-PU1-2 and 108.1 for HPUTZ-
PU1-4 were obtained. Moreover, the high E′ at high tem-
h
perature could store more deformation energy when the
polymer was cooled after deformation at high temperature,
which is helpful to shape recovery at a critical temperature
Figure 8 Strain recovery of HPUTZ-PU1-2 (a), HPUTZ-PU1-3 (b) and
HPUTZ-PU1-4 (c) in the tension deformation tests.
[12–14]. As shown in Figure 9, all the films with different
HPUTZ segment contents possess the excellent shape
memory function at moderate temperatures, which caused
by the interaction between the HPUTZ and PEG-IPDI seg-
ments. Thus, the shape recoverability can be regulated via
changing the HPUTZ segment content in HPUTZ-PU.
In order to further study the shape memory property, the
bend deformation tests for the circular shape films with dif-
ferent HPUTZ segment contents were also carried out based
on the curvature radius changes at various elapsed times and
temperatures during the shape recovery. The curvatures
described as the reciprocal of radius were calculated and are
shown in Figure 10 as the function of elapsing time. It can be
seen that the shape recovery rate increases with increasing
the HPUTZ segment content in HPUTZ-PU, which is the
similar result with that obtained from the tension deforma-
Figure 9 Strain recovery ratio of HPUTZ-PU1-2 (a), HPUTZ-PU1-3 (b)
and HPUTZ-PU1-4 (c) at different temperatures for 60 s in the tension
deformation tests.

Qiao LG, et al. Sci China Chem September (2011) Vol.54 No.9
1467
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