High thermo-responsive shape memory epoxies based on substituted biphenyl mesogenic with good water resistance

Article abstract of DOI:10.1039/c5ra10957d

In this work, a novel epoxy monomer denoted as 3,5′-di-t-butyl-5,3′-dimethyl biphenyl diglycidyl ether (t-BuMBPDGE) was synthesized and applied into in situ composites with 3,3′,5,5′-tetramethyl-4,4′-biphenyl diglycidyl ether (TMBPDGE), accompanied with curing agent aromatic amines. The liquid crystalline phase structure and the crosslink density of substituted biphenyl epoxies were determined by polarized optical microscopy, wide angle X-ray diffraction measurements and dynamic storage moduli data. The samples showed good mechanical properties and could recover quickly from a second state to their initial states with a shape fixity ratio higher than 98% and shape recovery ratio higher than 99%, owing to the oriented structure and increased crosslink network density caused by the orientation of biphenyl mesogenic. The high glass transition temperatures ranging from 160 to 178 °C and good water resistance could contribute to a stable fixed shape. The water resistance is analyzed by contact angles test. The samples exhibited contact angles of 92-98 degrees, which indicated that the water resistance was apparently better than that of conventional epoxy systems.

Full text of DOI:10.1039/c5ra10957d

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DOI: 10.1039/C5RA10957D
High thermo-responsive shape memory epoxies based on
substituted biphenyl mesogenic with good water resistance
Huilong Guo,a,b Yinwen Li,a,b Jian Zheng,a,b Jianqun Gan,a,b Liyan Liang,a Kun Wu,a
Mangeng Lu,a *
a Key Laboratory of Cellulose and Lignocellulosics Chemistry, Chinese Academy of Sciences;
Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, PR China
b University of Chinese Academy of Sciences, Beijing 100049, PR China
Correspondence to: Mangeng Lu (E-mail: mglu@gic.ac.cn
)
ABSTRACT
In this work, a novel epoxy monomer denoted as 3,5'-Di-t-butyl-5,3'-dimethyl biphenyl diglycidyl ether
(t-BuMBPDGE) was synthesized and applied into situ composites with 3,3’,5,5’-tetramethyl-
4,4’-biphenyl Diglycidyl ether (TMBPDGE), accompanied with curing agent aromatic amines. The
liquid crystalline phase structure and the crosslink density of substituted biphenyl epoxies were
determined by polarized optical microscopy, wide angle X-ray diffraction measurements and
dynamic storage moduli data. The samples showed good mechanical properties and could recover
quickly from a second state to their initial states with shape fixity ratio higher than 98% and shape
recovery ratio higher than 99%, owing to the oriented structure and increased crosslink network
density caused by the orientation of biphenyl mesogenic. The high glass transition temperatures
ranging from 160 to 178℃ and good water resistance could make contribute to a stable fixed shape.
The water resistance is analyzed by contact angles test. The samples exhibited contact angles of
92-98 degrees, which indicated that the water resistance was apparently better than that of
conventional epoxy systems.
KEYWORDS: shape memory; liquid crystalline epoxy; substituted biphenyl mesogenic
1.INTRODUCTION
Shape memory polymers (SMPs)1-13 are stimuli-sensitive polymers that are capable of changing their
shapes from a temporary state to their original or permanent shape after being exposed to the
external stimulus such as heat, light, pH, solvents, electric field or magnetic field. Among various
stimuli responsive SMPs, thermo-responsive SMPs are the most attractive due to their numerous
applications in biomedical field14-18, information carriers19, 20, assembly/disassembly21, 22, actuators23-25
,
and aerospace26, 27
.
Low transition temperature (below 100°C) and elastomeric polymers, thermoplastic polyurethanes
(TPU) for example, have been primarily investigated in the research of thermo-responsive SMPs,
which are suitable for the applications in biomedical field. Martin Bothe et al28 used
4,4′-methylenediphenyl diisocyanate, 1,4-butanediol as a chain extender to develop three physically
cross-linked, phase-segregated poly(ester urethane) with differing hard to soft segment ratios,
1

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gaining control over programmable thermo-responsiveness. Higher moisture resistance and
switching temperatures of SMPs are often required in the application in aerospace or structural
components. Ying Shi et al29 developed high thermo-responsive thermoplastic SMPs based on metal
salts of sulfonated PEEK (M-SPEEK) ionomers with transition temperatures as high as 250 °C, but
not every M-SPEEK exhibited high shape fixity and recovery efficiencies during each cycle.
Thermoset polymer systems are the most studied materials as high thermo-responsive SMPs
exhibiting high shape fixity and recovery efficiencies.30-32
Shape memory epoxies, as the chemically cross-linked shape memory polymers, have so many
desirable characteristics, such as good thermal and mechanical properties, ease of processability,
composite forming properties and very good dimensional stability, which make shape memory epoxy
polymers attractive for application in the processing of many smart engineering systems.33, 34 Gao et
al31 prepared a high thermo-responsive (at 150 °C) thermoset epoxy polymer modified with
poly(ether ether ketone). Fan, Wang Kun et al 35 prepared a type of thermal-induced shape memory
polymer using a new epoxy resin-polybutadiene epoxy (PBEP) and bisphenol A-type cyanate ester
(BACE) in different mass ratios with Tg ranging from 136 to 165℃, owing to varying cross-linking
density affected by a flexible long-carbon chain structure of PBEP. Tao Xie et al36 represented a
facile method to precisely tune the Tg of epoxy SMPs decreasing from 89℃ to room temperature by
either reducing the crosslink density or introducing flexible aliphatic epoxy chains. Agustina B.
Leonardi et al4 reported an epoxy network with chemical and physical cross-links which showed an
excellent behavior as an SMP enabling a combination of relatively high tensile strains and recovery
stresses. Hendrik Lützen et al37 studied novel segmented and covalently cross-linked epoxy/poly(
Ɛ
-caprolactone) (PCL) polymers which showed a shape memory effect; the covalently cross linked
epoxy network acts as hard segment to store the permanent shape for the recovery process, and the
reversible process of crystallization and melting in the PCL segment acts as switch for deformation
and fixation in the segment. However, conventional cross-linked epoxy polymers (or epoxy based
SMPs) were highly water absorbing (about 1–4 wt%) and hydrophilic (water contact angle of 50–52
degrees) owing to the existence of large number of hydroxyl groups in the cross-linked networks.
Kumar, K. S. 8 reported hydrophobic shape memory poly(oxazolidone-triazine) cyclomatrix networks
with water contact angles of 82-86 degrees and transition temperatures between 127 and 180℃.
Liquid crystalline epoxides (LCEs), owning oriented and chemically cross-linked networks which are
formed from curing of low molecular weight, rigid rod epoxy monomers with curing agents of
aromatic amine, are superior to conventional amorphous epoxies in the performance of better
mechanical properties, better dimensional stability, lower coefficients of thermal expansion,
increased fracture toughness and noticeable high temperature properties.38-44 It was reported that
the oriented structure of LCEs could increase packing density of the segments, resulting in increased
crosslink network density.45, 46 And the increasing crosslinking density could significantly improve the
shape memory properties.47 In addition, the free volume of polymer could be decreased through the
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closely packed arrangement of mesogens, leading to dramatically reduced solvent absorptions.41, 48
Therefore, it was attractive that biphenyl mesogenics were induced into cross linked epoxy systems,
to gain high-Tg and good water resistance shape memory epoxy resins. However, there were only
few works that were focused on the shape memory effect of hydrophobic liquid crystalline epoxies.49,
50
In this paper, novel epoxy monomers containing biphenyl mesogenics were synthesized and a series
of high-Tg and good water resistance shape memory epoxy resins based on substituted biphenyl
mesogenic were prepared and characterized. Moreover the relationship between structure and water
resistance and shape memory properties was investigated in our work.
2. EXPERIMENTAL
2.1 Materials
4,4’-Diaminodiphenylmethane (DDM, See Scheme 1) was purchased from Aladdin and was used as
curing agent. 2,6-xylenol and 2-tert-butyl-6-methyl-phenol were supplied by Aladdin. Tetrabutyl
ammonium bromide, periodic acid and sodium hydrosulfite were purchased from laboratory Text ＆
Industrial Measurement Instruments multi-source. All other reagents were of analytical grade and
used as received.
2.2 Epoxy monomer synthesis
2.2.1 Synthesis of 3,3’,5,5’-tetramethyl-4,4’-biphenyl Diglycidyl ether [TMBPDGE, abbreviated as (1)]
Diglycidyl ether of 3,3’,5,5’-tetramethyl-4,4’-biphenyl (See Scheme 1) was synthesized in our
laboratory according to our early reports.51 The chemical structure of the product was evaluated by
1
means of H NMR and FTIR (KBr pellet, cm-1) techniques. IR: 912 (epoxy C-O, st), 1380 (aromatic
CH3, band), 1579 and 1477 (aromatic C=C, st). 1H-NMR (CDCl3, in ppm): 7.15–7.17 (d, 4H, aromatic),
2.32–2.34 (d, 12H, CH3), 4.03–4.06, 3.74–3.78 (dd, 4H, CH2, glycidyl), 3.34–3.38 (m, 2H, CH, epoxy),
2.87-2.87, 2.70–2.72 (tdd, 4H, CH2, epoxy). The epoxy equivalent of the product was determined by
the HCl/acetone titration to be 198 (theoretical, 177). The melting point of (1) measured by DSC was
102℃.
2.2.2 Synthesis of 3,5'-Di-t-butyl-5,3'-dimethyl biphenyl diglycidyl ether [t-BuMBPDGE, abbreviated
as (2)]
(2) was synthesized through refluxing 8 g of (0.0245 mol) 3,5'-Di-t-butyl-5,3'- dimethyl biphenyldiol
with excess epichlorohydrin (32.5 g, 0.275 mol) and 20 ml of isopropanol catalyzed by tetrabutyl
ammonium bromide (0.24 g, 0.744 mmol) under nitrogen atmosphere at 85 ℃ till the solution was
clear. Then a 12 g of 30 wt NaOH aqueous solution was added dropwise into the mixture. The
excess epichlorohydrin, water and isopropanol were evaporated under reduced pressure after 1 h.
Finally, the product was extracted by dichloromethane and washed with water and water/methanol
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(9/1 volume) mixture three times respectively, then dried over MgSO4. A product at a 91% yield was
obtained after filtration and removal of dichloromethane. The chemical structure of the product was
1
evaluated by means of H NMR and FTIR (KBr pellet, cm-1) techniques. IR: 912 (epoxy C-O, st),
1380 (aromatic CH3, band), 1579 and 1477 (aromatic C=C, st).1H-NMR (CDCl3, in ppm)： 7.15–7.25
(d, 4H, aromatic)，2.32–2.34 (s, 6H, CH3)，4.03–4.06, 3.74–3.78 (dd, 4H, CH2, glycidyl)，3.34–3.38 (m,
2H, CH, epoxy)， 2.87–2.87, 2.70–2.72 (tdd, 4H, CH2, epoxy)，1.34-1.41（d, 18H, CH3). The epoxy
equivalent of the product was determined by the HCl/acetone titration to be 263 (theoretical, 219).
The softening point of (2) evaluated by DSC was 10.5℃.
3,5'-Di-t-butyl-5,3'-dimethyl biphenyldiol was prepared using oxidative coupling reaction in which
2-tert-butyl-6-methyl-phenol was oxidated by periodic acid. 2-tert-butyl-6-methyl- phenol (5 g, 30.44
mmol), dissolved by 5 ml of dimethylformamide, was added into a 100 mL round-bottom flask with a
magnetic stirring bar at a temperature of 80℃, then 10.96 g of 40 wt% periodic acid aqueous solution
was added dropwise into the mixture. Stop heating till lots of bubbles occurred, one hour later the
mixture was precipitated by 500 ml of water. And the precipitation was identified as
3,5'-Di-t-butyl-5,3'-dimethyl diphenoquinone after being filtrated, washed with water and dried. Then
4 g (0.012 mol) of 3,5'-Di-t-butyl-5,3'-dimethyl diphenoquinone and excess sodium hydrosulfite (3 g),
dissolved in 20 ml of 80 wt% ethanol aqueous solution, was stirring for 1 h at 80℃ till the solution
turned yellowish clear. Finally precipitation identified as 3,5'-Di-t-butyl-5,3'-dimethyl biphenyldiol was
obtained after adding the solution into 500ml of water, filtration, washing the precipitation with water
and being dried under vacuum.
2.3 Curing of substituted biphenyl epoxies
The stoichiometric amount of epoxy monomer (different weight ratios of (1) and (2)) and DDM were
dissolved in dichloromethane, then dichloromethane was removed under reduced pressure at room
temperature, the samples were cured at low temperature of 105 ℃ which is the isotropic
temperature of (1)/DDM mixtures, for 5 h to ensure the totally reaction of linear chain extension and
post-cured at 160℃ for 4 h, 200℃ for 1 h to guarantee completely branching and crosslinking.
After curing, the cured products were extracted from the mold, to be tested. An absorption peak at
912 cm-1 was observed characteristic of the epoxy stretching in the FTIR spectrum of (1) and (2),
while this absorption peak at 912 cm-1 could not be found in the spectrums of (1)/DDM, (2)/DDM and
(1)/(2)/DDM composites (See Figure 2). These indicated all the samples were completely cured.
2.4 Physical measurements
The 1H NMR was obtained with a DRX-400 spectrometer with CDCl3 as a solvent and
tetramethylsilane (TMS) as an internal standard.
Calorimetric measurements were performed using a Perkin–Elmer Diamond DSC calorimeter, under
nitrogen atmosphere to measure the heat flow under nonisothermal conditions. Samples of about 10
mg were sealed in aluminium pans. A first thermal cycle heating from 40 to 250℃ and a cooling
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scan from (250 to 40 °C) was performed to eliminate thermal history. After that, a new heating scan
from 40 to 250℃ was performed to determine the glass transition temperature (Tg) and the melting
point. All the scans were performed at a heating/cooling rate of 20 ℃/min.
The liquid crystalline phase structure of substituted biphenyl epoxies was examined by a polarized
light optical microscopy (POM) (Orthoglan, LEITZ, Germany) and wide angle X-ray diffraction
measurements (WAXS) which were carried out with a Rigaku Diffractometer (D/MAX-1200), using
monochromatic Cu Karadiation (40 kV, 30 mA) and secondary graphite monochromator, with the
X-ray scatting intensities being detected by a scintillation counter incorporating a pulse-height
analyzer.
The tensile test at room temperature (30℃) was carried out by an Instron mechanical testing
machine (SHT5000, Shenzhen SANS Testing Machine) at a strain rate of 2 mm/min. The Young’s
modulus, break strength, and elongation at break were obtained from the stress–strain curves. The
sample dimensions were 100 mm * 10 mm *0.6 mm.
Infrared spectra, recorded on a WQF-410 Fourier Transform Infrared (FTIR) spectrometer in the
wavenumber range from 4000 to 400 cm-1 at 25℃ were used to investigate the change of epoxy ring
before and after curing. The spectra were collected after 32 scans. The time interval between each
spectrum collected was 60 s.
The response of the samples to small-strain mechanical deformation was measured as a function of
temperature (-120 to 200℃) using a NETZSCH DMA 242 dynamic mechanical analyzer in a tensile
mode. The testing was carried out at a heating rate of 5℃/min in a N2 atmosphere, frequencies of 1
Hz, a dynamic stress of 5 N, and a static stress of 0.5 N. The sample displacement was 30 μm.
Storage moduli (E’), loss moduli (E”), and loss tangent (tan δ) were recorded.
The shape memory properties was tested as following: the sample was cut into 80mm*10mm*0.6mm
Strips; then the strips were put into silicone oil at a temperature 20 ℃ higher than the Tg of the
sample for 30 minutes; later the strips were bended around a tube (Peripheral curvature, 7.24/dm-1),
quenched to room temperature with a constant external force; finally the shape recovery process of
bended strips were observed in silicone oil at a temperature 20 ℃ higher than the Tg of the sample.
The shape recovery process were recorded by a camera (SONY, DSC-RX100 M2), then the video
was divided into 25 pictures per second using Corel VideoStudio Pro X4 software. The shape
recovery curvature of the strips was determined by bidimensional measurement software, through
which the shape fixity ratio and shape recovery ratio were calculated using the following equations.
The shape memory cycles were determined by repeating the above process (shape fixity, shape
recovery) 5 times for each sample. Repeated to test three samples for each test condition and
selected averages.
Rf = (R-R0) / (Rt-R0)
(1)
(2)
Rr = (R-R’) / (R-R0)
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Rf : shape fixity ratio
Rr: shape recovery ratio
R: curvature of the sample after fixed
Rt: curvature of the tube(7.24/dm-1)
R0: curvature of the initial state of the sample
R’: Curvature of the recovered sample
3. RESULTS AND DISCUSSION
3.1. The liquid crystalline phase structure of substituted biphenyl epoxies
The polarized optical microscopic pictures after curing of (1)/DDM and (2)/DDM were shown in
Figure 3. Birefringence was observed from both of the POM pictures of (1)/DDM and (2)/DDM
network. And bright droplet-like domains of the liquid crystalline were dispersed in (2)/DDM network
while (1)/DDM illustrated a “schlieren-like” texture with a higher disclination density.
To further investigate the nematic structure of biphenyl epoxies affected by substituents, wide angle
X-ray diffraction patterns of (1)/DDM, (2)/DDM and (1)/(2)/- DDM composites were analyzed, as
shown in Figure 4. It could be seen that all the samples showed broad peaks around 23° with
broader peak in (2)/DDM than that in (1)/DDM.
C.B. McARDLE52 reported that the X-ray diffraction patterns of nematic polymers showed generally a
typical broad peak in the region of 2θ= 15-30°, owing to the average lateral distance between the
neighboring chains with d-spacing of 3-5 Å. All of the (1)/DDM, (2)/DDM and (1)/(2)/DDM composites
illustrated a typical nematic characteristic with broad peaks around 23° corresponding to d-spacing of
3.9 Å. Curing of liquid crystalline epoxies included linear chain extension at early stage, then
branching, and finally crosslinking, which could have significant effects on orientation of mesogenic
and structure of liquid crystalline epoxy resins. During linear chain extension stage, the mobility and
orientation of mesogen units were hindered by steric hindrance of the methyl substituents or
tert-butyl substituents, so that the smectic LC phase could not be formed in all the samples. While in
the first stage of curing at 105℃ which was much lower than the DSC exothermic temperature of the
reaction of epoxy and DDM, the mesogen units could be oriented with great efforts in their isotropic
state before branching and crosslinking. Although during mesogen units orientation stage, steric
hindrance of the tert-butyl substituents was larger than that of methyl substituents, the reactivity of (2)
and DDM might be lower than that of (1) and DDM. Thus, the (2)/DDM resin could stay in isotropic
state longer than (1)/DDM resin, which was observed during curing process that (1)/DDM resin
changed from isotropic state to solid membrane earlier than (2)/DDM resin. Moreover, the softening
point of (2) was much lower than (1), during heating process, the orientation of (2) started earlier than
that of (1), all of these led to a similar nematic LC phase in all the samples with more slightly oriented
structure in (1)/DDM resin.
Uniaxial oriented nematic structure mode of (1)/DDM network was shown schematically in Figure 5.
From which the orientation of substituted biphenyl mesogenic could be more easily analyzed and
understood.
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3.2. The crosslink density of substituted biphenyl epoxies
For ideal networks, Gaussian network model method can be used to determine the level of
crosslinking.
ER’=3ρRT/Mc
Where Mc is total sample weight that contains one mole of elastically effective network chains, ER’ is
the storage modulus at Tg+50℃, T is the absolute temperature of Tg+50K, ρ is the density of the
samples, and R is the gas constant.
The crosslink density can be defined as the number of moles of elastically effective network chains
per cubic centimeter of sample which was denoted as νe
Mc =ρ/νe
So that the Gaussian network model can be changed into the following equation 53
νe=E’/3RT
The calculated crosslink density νe was shown in Table 1, from which it could be seen that the
crosslink density decreased as the increasing of the content of (2). This could be easily explained
that network segments packing was hampered by larger substituents of tert-butyl in (2)/DDM resin
than methyl substituents in (1)/DDM resin, resulting in the highest νe in (1)/DDM resin.
3.3. The mechanical properties of substituted biphenyl epoxies
Figure 6 showed the relationships between the tensile stresses versus strain at room temperature. It
was observed from Figure 6 that the modulus increased with the decreasing of the content of (1),
while the tensile strength and the elongation at break decreased with the increasing of the content of
(2), as was illustrated in Table 2. And it was shown in Figure 7 that the dynamic storage moduli (E’) of
(2)/DDM at room temperature reached the highest position, over 1000MPa higher than the lowest
one of (1)/DDM resin.
The mechanical properties in the glass state mainly depended on the van der Waals interactions.54
Ortiz et al. indicated that glass deformation at small strains involved bending and small angular
55
rotations of network strands.
With stress increasing, the biphenyl mesogenic could be aligned
along the direction of force, resulting in an enhancement in the packing density of polymer chains, so
that the intermolecular resistance to rotation, shear might be enhanced. Therefore, the mechanical
properties could be improved by the alignment of biphenyl mesogenic along the direction of force. It
could be concluded that All of the (1)/DDM, (2)/DDM and (1)/(2)/DDM composites illustrated a similar
nematic characteristic with d-spacing of 3.9 Å. Thus, the orientation of biphenyl mesogenic along the
direction of stress was more difficult in the (2)/DDM resin than in (1)/DDM resin, owing to larger steric
hindrance of the tert-butyl substituents in (2)/DDM resin with similar d-spacing of about 3.9 Å for all
the samples, which could be confirmed though comparing the XRD data before and after tensile test,
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as were illustrated in Figure 4 and Table 3. After tensile test, the nematic d-spacing changed from 3.9
Å to 2.67 Å in (1)/DDM resin, while in (2)/DDM resin the nematic d-spacing only cut back 0.13 Å,
which indicated that biphenyl mesogenic was more easily oriented along the direction of stress in
(1)/DDM resin. Thus, the tensile strength of (1)/DDM resin was reinforced owing to the orientation of
biphenyl mesogenic in the direction of stress. And the modulus could be enhanced in the oriented
direction with stress increasing, so that the slope of the tensile stresses versus strain curve of
(1)/DDM resin increased with increasing of stress. However, the slope of the tensile stresses versus
strain curve of (1)/DDM resin at first stage was lower than that of (2)/DDM resin, which was because
the orientation of biphenyl mesogenic along the direction of stress was obstructed by the larger steric
hindrance of the tert-butyl substituents in (2)/DDM resin, resulting in higher modulus, higher dynamic
storage moduli (E’) and lower elongation at break of (2)/DDM than that of (1)/DDM resin.
3.4. The glass transition temperature (Tg) of substituted biphenyl epoxies
The glass transition temperature of the samples was determined by DSC, as was shown in Figure 8.
It could be seen that the glass transition temperature of the samples decreased from 178℃ to 158℃
with the content of (2) increasing. The Tg of the samples were also confirmed by DMA and the
results were shown in Figure 7 and Table 1.
As was well known, Tg referred to the temperature at which the network segments began to move.
And the movement of network segments could be influenced by the chemical crosslinking, physical
entanglement and the packing density of the segments. In our work orientation of substituted
biphenyl mesogenics could increase packing density of the segments, resulting in increased
crosslink network density. The interchain interactions can be enhanced owing to the increased
packing density of the segments, making the substituted biphenyl mesogens slip and rotate not
easily. Therefore, higher glass transition temperatures than that of conventional epoxy systems (the
Tg of bisphenol-A/DDM system was 155℃, reported by Bin Li 56) were obtained, which acted an
important role in the stable fixed shape. As discussed above, more slightly oriented structure existed
in (1)/DDM resin and the crosslink density decreased as the increasing of the content of (2),
moreover, larger substituents of tert-butyl in (2)/DDM resin could weaken the interchain interactions
and made the mesogens slip and rotate easily. Thus, glass transition temperature of the samples
increased with the content of (2) decreasing.
3.5. The water resistance properties of substituted biphenyl epoxies
The water resistance properties of substituted biphenyl epoxies were determined by contact angle
test, as was shown in Figure 9. It could be seen that the contact angle of the samples increased from
92 degree to 98 degree with the content of (1) increasing.
Kumar, K. S. 8 reported hydrophobic shape memory poly(oxazolidone-triazine) cyclomatrix networks
with water contact angles of 82-86 degrees, which are higher than that for typical epoxy systems. As
was discussed above, the orientation of substituted biphenyl mesogenics could contribute to an
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increased crosslink network density, resulting in closely packed polymer chains. Thus, the water
resistance property was enhanced with the content of (1) increasing owing to more oriented and
closely packed network in (1)/DDM system.
3.6. The shape memory properties of substituted biphenyl epoxies
The shape recovery process and the shape recovery curvature of the strips were shown in Figure 10
and Figure 11. While the shape fixity ratio, shape recovery ratio and shape recovery time of (1)/DDM,
(2)/DDM and (1)/(2)/DDM composites during different shape memory cycles were illustrated in Table
4. It could be found that the shape recovery process of (1)/DDM resin was the fastest and that
became slower with the increase of the content of (2). All the samples could be almost completely
fixed and recovered with shape recovery ratio higher than 98% and shape recovery ratio higher than
99% in the first shape memory cycle. And it could be seen that all the samples still showed an ideal
shape memory properties with shape fixity ratio higher than 97% and shape recovery ratio higher
than 98%. Which indicated all the samples showed a very good reproducibility and stability of the
shape memory behavior. Figure 12 showed the shape recovery process of (2)/DDM from 30℃ to
176℃ in silicone oil at a heating rate of 10℃/min. It could be observed that the shape recovery
process hardly happened below 160℃. And the sample gradually recovered to its original state from
160℃ to 176℃. Moreover, as shown in Table 5, the samples showed an extremely low uptake of
silicone oil. Therefore, it was the temperature change that triggered the shape changes of the
samples rather than oil uptake.
There was oriented and chemically cross-linked structure in substituted biphenyl epoxies. The
oriented mesogen and chemically crosslink network made substituted biphenyl epoxy resins an
excellent shape memory material, with higher shape fixity ratio (98%) and shape recovery ratio (99%)
and extremely fast shape recovery process within 37 s. This shape memory effect is driven by the
entropic behavior in the substituted biphenyl segments between the crosslinks of the epoxy. Below
Tg, the substituted biphenyl segments between the network points could not change any
conformation and were locked into the orientational order network permanently unless a suitably
large mechanical force was applied (comparing the XRD data before and after tensile test, as were
illustrated in Figure 4 and Table 3). The rotational conformations of substituted biphenyl segments
could be changed at relatively lower stresses when heated above Tg. Above Tg, the substituted
biphenyl segments could aligned in the direction of stresses, increasing the stored energy in the
epoxy as the entropy of the epoxy chains decreased. Upon cooling in the deformed shape, the epoxy
chains could no longer freely rotate. The substituted biphenyl segments then recovered this stored
energy by returning to the initial high entropy configuration when the samples were heated above Tg.
57-59
Larger substituents of tert-butyl in (2)/DDM resin might play a negative role in the alignment of
substituted biphenyl segments in the direction of stresses above Tg, so upon cooling in the deformed
shape, the stored energy and the entropy configuration change of (2)/DDM resin would not be as
obvious as that of (1)/DDM resin. Moreover, during shape recovery process, the shape recovery
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stresses might be directly proportional to the innerstress. According to the ideal elasticity equation,
the stress increased with the elasticity modulus under the condition of a same strain, the storage
moduli at temperature 20℃ higher than Tg of (1)/DDM resin was higher that of (2)/DDM resin, so
that the innerstress is of (1)/DDM resin is higher that of (2)/DDM resin at same strains. Thus, the
shape recovery stress of (1)/DDM resin was expected to be higher than that of (2)/DDM resin,
eventually, the shape recovery process was accelerated with the increase of content of (1).
4. CONCLUSION
Quick Thermo-responsive shape memory epoxy resins based on substituted biphenyl mesogenic
were prepared and characterized in this work. The good mechanical and water resistance properties
and extraordinary shape memory properties with high shape memory transition temperatures, shape
fixity ratio higher than 98% and shape recovery ratio higher than 99%, indicating a new idea to
prepare hydrophobic shape memory materials by introducing the mesogenic units into epoxy resins
in the application of self-deployable antennae
.
More slightly oriented structure could be formed in the (1)/DDM resin, and the crosslink density
decreased as the content of (2) increasing, which was attribute to larger steric hindrance of the
tert-butyl substituents in (2).
The modulus and the dynamic storage moduli increased with the decreasing of the content of (1),
while the tensile strength and the elongation at break decreased with the increasing of the content of
(2). The biphenyl mesogenic was more easily oriented along the direction of stress in (1)/DDM resin,
while the orientation of biphenyl mesogenic was obstructed by the larger steric hindrance of the
tert-butyl substituents in (2)/DDM resin, resulting in higher modulus, higher dynamic storage moduli
(E’) and lower elongation at break of (2)/DDM than that of (1)/DDM resin. Moreover, the tensile
strength of (1)/DDM resin was reinforced owing to the orientation of biphenyl mesogenic in the
direction of stress.
The glass transition temperatures, water resistance properties and the shape recovery speed of the
samples were enhanced with the increase of the content of (1), owing to more oriented structure
and increased crosslink network density caused by the orientation of biphenyl mesogenic in (1)/DDM
resin.
ACKNOWLEDGEMENTS
This research was supported by the intergration of Industry Education and Research of Guangdong
Province project (2011A091000007) and the National Natural Science Foundation of China
(20974121)
REFERENCES
1.
2.
H. Meng and G. Q. Li, Polymer, 2013, 54, 2199-2221.
H. M. Chen, Y. Liu, T. Gong, L. Wang, K. Q. Zhao and S. B. Zhou, Rsc Adv, 2013, 3, 7048-7056.
10

Page 11 of 23
RSC Advances
View Article Online
DOI: 10.1039/C5RA10957D
3.
4.
Q. H. Meng and J. L. Hu, Compos Part a-Appl S, 2009, 40, 1661-1672.
A. B. Leonardi, L. A. Fasce, I. A. Zucchi, C. E. Hoppe, E. R. Soule, C. J. Perez and R. J. J. Williams, Euro Polym J,
2011, 47, 362-369.
5.
Y. Li, H. Guo, Y. Zhang, J. Zheng, J. Gan, X. Guan and M. Lu, Rsc Adv, 2014, 4, 17768-17779.
J. Hu, Y. Zhu, H. Huang and J. Lu, Prog Polym Sci, 2012, 37, 1720-1763.
J. Leng, X. Lan, Y. Liu and S. Du, Prog Mater Sci, 2011, 56, 1077-1135.
K. S. S. Kumar and C. P. R. Nair, Rsc Adv, 2014, 4, 2969-2973.
6.
7.
8.
9.
T. Xie, Polymer, 2011, 52, 4985-5000.
10.
11.
12.
13.
14.
C. Liu, H. Qin and P. T. Mather, J Mater Chem, 2007, 17, 1543-1558.
T. Pretsch, Polymers, 2010, 2, 120-158.
L. Sun, W. M. Huang, Z. Ding, Y. Zhao, C. C. Wang, H. Purnawali and C. Tang, Mater Design, 2012, 33, 577-640.
G. J. Berg, M. K. McBride, C. Wang and C. N. Bowman, Polymer, 2014, 55, 5849-5872.
L. Peponi, I. Navarro-Baena, A. Sonseca, E. Gimenez, A. Marcos-Fernandez and J. M. Kenny, Euro Polym J,
2013, 49, 893-903.
15.
16.
I. Navarro-Baena, J. M. Kenny and L. Peponi, Cellulose, 2014, 21, 4231-4246.
J.-M. Raquez, S. Vanderstappen, F. Meyer, P. Verge, M. Alexandre, J.-M. Thomassin, C. Jerome and P. Dubois,
Chemistry-a European Journal, 2011, 17, 10135-10143.
17.
A. Saralegi, M. Luz Gonzalez, A. Valea, A. Eceiza and M. Angeles Corcuera, Compos Sci Technol, 2014, 92,
27-33.
18.
19.
20.
21.
22.
L. Sun and W. M. Huang, Mater Design, 2010, 31, 2684-2689.
M. Ecker and T. Pretsch, Rsc Adv, 2014, 4, 46680-46688.
N. Fritzsche and T. Pretsch, Macromolecules, 2014, 47, 5952-5959.
L. Sun, W. M. Huang, H. B. Lu, C. C. Wang and J. L. Zhang, Assembly Automation, 2014, 34, 78-93.
D. A. van den Ende, H. J. van de Wiel, W. A. Groen and S. van der Zwaag, Smart Mater Struct, 2012, 21, DOI:
10.1088/0964-1726/21/1/015011.
23.
24.
25.
26.
27.
28.
29.
30.
M. Bothe and T. Pretsch, J Mater Chem A, 2013, 1, 14491-14497.
A. Khaldi, J. A. Elliott and S. K. Smoukov, Journal of Materials Chemistry C, 2014, 2, 8029-8034.
L. Sun, W. M. Huang, C. C. Wang, Z. Ding, Y. Zhao, C. Tang and X. Y. Gao, Liq Cryst, 2014, 41, 277-289.
Y. Li, J. Li, W. Li and H. Du, Smart Mater Struct, 2014, 23, DOI: 10.1088/0964-1726/23/12/123001
A. Y. N. Sofla, S. A. Meguid, K. T. Tan and W. K. Yeo, Mater Design, 2010, 31, 1284-1292.
M. Bothe, F. Emmerling and T. Pretsch, Macromol Chem Physic, 2013, 214, 2683-2693.
Y. Shi, M. Yoonessi and R. A. Weiss, Macromolecules, 2013, 46, 4160-4167.
T. H. Tong, Maleimide based high temperature shape memory polymers. US Pat. Appl. US7276195B1, July 26,
2006..
31.
J. P. Gao, C. Q. Zhang, X. C. He, H. Y. Ma, X. F. An, X. S. Yi, G. D. Dang and C. H. Chen, Adv. Mater. Res. 2010,
152-153, 530-535.
32.
33.
34.
35.
36.
37.
38.
P. Mather and C. Liu, Castable shape memory polymers. US Pat. Appl. US2004/0030062A1, April 29, 2003.
K. S. S. Kumar, R. Biju and C. P. R. Nair, React Funct Polym, 2013, 73, 421-430.
X. L. Wu, S. F. Kang, X. J. Xu, F. Xiao and X. L. Ge, J Appl Polym Sci, 2014, 131.
K. Wang, G. Zhu, L. Niu, Y. Wang and Z. Liu, J Polym Res, 2014, 21, DOI: 10.1007/s10965-014-0385-8.
T. Xie and I. A. Rousseau, Polymer, 2009, 50, 1852-1856.
H. Luetzen, T. M. Gesing, B. K. Kim and A. Hartwig, Polymer, 2012, 53, 6089-6095.
M. Wlodarska, A. Maj, B. Mossety-Leszczak, G. W. Bak, H. Galina, L. Okrasa and M. Izdebski, J Polym Res,
2013, 20, DOI: 10.1007/s10965-013-0227-0.
11

RSC Advances
Page 12 of 23
View Article Online
DOI: 10.1039/C5RA10957D
39.
40.
41.
42.
43.
44.
45.
Y. Li, P. Badrinarayanan and M. R. Kessler, Polymer, 2013, 54, 3017-3025.
A. Mija and C. N. Cascaval, Polimery-W, 2009, 54, 786-789.
C. Farren, M. Akatsuka, Y. Takezawa and Y. Itoh, Polymer, 2001, 42, 1507-1514.
Y. Li and M. R. Kessler, Polymer, 2014, 55, 2021-2027.
C. Carfagna, E. Amendola and M. Giamberini, Compos Struct, 1994, 27, 37-43.
G. G. Barclay and C. K. Ober, Prog Polym Sci, 1993, 18, 899-945.
H. Guo, M. Lu, L. Liang, J. Zheng, Y. Zhang, Y. Li, Z. Li and C. Yang, J Appl Polym Sci, 2014, 131, DOI:
10.1002/app.40363.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
J. Y. Lee and J. Jang, Polym Bull, 2007, 59, 261-267.
K. Wei, G. Zhu, Y. Tang, T. Liu and J. Xie, Journal of Materials Research, 2013, 28, 2903-2910.
J. Feng, K. Berger and E. Douglas, J Mater Sci, 2004, 39, 3413-3423.
T. Shen, F. Wu and C. Sun, J Macromol Sci A, 2013, 50, 1085-1090.
L. Liang, D. Zhou and M. Lu, in Advances in Liquid Crystals, ed. Y. M. Huang, 2010, vol. 428-429, pp. 391-393.
S. Ren, L. Liang, Y. Lan and M. Lu, J Appl Polym Sci, 2007, 106, 2917-2924.
C. McARDLE, Side Chain Liquid Crystal Polymers; Chapman and Hall: New York, NY, 1989; Chapter 6.
L. W. Hill, Prog Org Coat, 1997, 31, 235-243.
E. F. Oleinik, Advances in Polymer Science, 1986, 80, 49-99.
C. Ortiz, R. Kim, E. Rodighiero, C. K. Ober and E. J. Kramer, Macromolecules, 1998, 31, 4074-4088.
G.-R. Xu, M.-J. Xu and B. Li, Polym Degrad Stab, 2014, 109, 240-248.
H. Guo, Y. Li, J. Zheng, J. Gan, L. Liang, K. Wu and M. Lu, J Appl Polym Sci, 2015, DOI: 10.1002/app.42616.
Y. Dong, J. Ding, J. Wang, X. Fu, H. Hu, S. Li, H. Yang, C. Xu, M. Du and Y. Fu, Compos Sci Technol, 2013, 76,
8-13.
59.
M. Di Prima, K. Gall, D. L. McDowell, R. Guldberg, A. Lin, T. Sanderson, D. Campbel and S. C. Arzberger, Mech
Mater, 2010, 42, 304-314.
Figure captions
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Scheme 1 Chemical structures of (1), (2) and DDM
Scheme 2 synthesis of (2)
Fig 1 1H NMR of (1) and (2)
Fig 2 FTIR spectrum of uncured pure (1) and (2), (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM
composites
Fig 3 Polarized optical microscopic pictures of (2)/DDM resin and (1)/DDM resin after curing at room
temperature
Fig 4 Wide angle X-ray diffraction measurements of (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM
composite
Fig 5 Uniaxial oriented nematic structure mode of (1)/DDM resin
Fig 6 Stress versus strain curves for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composites at
room temperature
Fig 7 Dynamic storage moduli (E’) and loss tangent (tan δ) of (2)/DDM resin, (1)/DDM resin and
(1)/(2)/DDM composite
Fig 8 DSC curves for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composite
Fig 9 Contact angles of (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composite
Fig 10 shape recovery process pictures for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM
composites
Fig 11 shape recovery curvature versus time for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM
composites
Fig 12 shape recovery process pictures for (2)/DDM from 30℃ to 176℃ in silicone oil at a heating
rate of 10℃/min.
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Scheme 1 Chemical structures of (1), (2) and DDM
Scheme 2 synthesis of (2)
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Fig 1 1H NMR of (1) and (2)
Fig 2 FTIR spectrum of uncured pure (1) and (2), (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composites
Fig 3 Polarized optical microscopic pictures of (2)/DDM resin and (1)/DDM resin after curing at room temperature
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Fig 4 Wide angle X-ray diffraction measurements of (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composites
Fig 5 Uniaxial oriented nematic structure mode of (1)/DDM resin
Fig 6 Stress versus strain curves for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composites at room temperature
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Fig 7 Dynamic storage moduli (E’) and loss tangent (tan δ) of (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composite
Fig 8 DSC curves for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composite
Fig 9 Contact angles of (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composite
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Fig 10 shape recovery process pictures for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composites
Fig 11 shape recovery curvature versus time for (2)/DDM resin, (1)/DDM resin and (1)/(2)/DDM composites
Fig 12 shape recovery process pictures for (2)/DDM from 30℃ to 176℃ in silicone oil at a heating rate of 10℃/min.
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Table 1 DMA results and crosslink density of (2)/DDM resin, (1)/DDM resin and (1)/(2) /DDM composite
Storage moduli
(E’)(MPa)20℃
(ER’)(MPa)
(Tg+50℃)
Samples
Tg(℃)
νe (mol/cm3)
(1)/DDM
(2)/(1)5:5/DDM
(2)/DDM
2007
3145
3215
38.03
29.87
21.15
178
169
160
3.07*10-3
2.42*10-3
1.75*10-3
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Table 2 Tensile results of (2)/DDM resin, (1)/DDM resin and (1)/(2) /DDM composites at room temperature
sample
E(MPa)
Ƹb (%)
δb (MPa)
(1)/DDM
651
712
6.03
5.17
4.85
4.47
4.12
47.31
44.16
44.19
42.48
41.09
(2)/(1)3:7/DDM
(2)/(1)5:5/DDM
(2)/(1)7:3/DDM
(2)/DDM
1458
1120
1831
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Table 3 Data of XRD before and after tensile test of (2)/DDM resin, (1)/DDM resin and (1)/(2) /DDM composites
2θ/º
d/Å
sample
beforer
After
before
after
tensile test
tensile test
tensile test
tensile test
(1)/DDM
22.5
22.0
21.8
21.6
21.8
7.6/33.5
7.4/29.4
9.4/23.7
9.4/23.6
8.52/22.6
3.95
4.05
4.08
4.12
4.08
11.62/2.67
11.97/3.03
9.36/3.75
9.40/3.77
10.38/3.92
(2)/(1)3:7/DDM
(2)/(1)5:5/DDM
(2)/(1)7:3/DDM
(2)/DDM
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Table 4 Shape fixity ratio, shape recovery ratio and shape recovery time of (1)/DDM, (2)/DDM and (1)/(2)/DDM composites
during 5 shape memory cycles
(1)/DDM
(2)/(1)3:7/DDM
(2)/(1)5:5/DDM
(2)/(1)7:3/DDM
(2)/DDM
N
Rf/%
98.3
98.4
98.2
97.8
97.6
Rr%
99.2
99.1
99.2
98.9
98.5
Tr/s
22
21
24
24
26
Rf/%
Rr%
99.3
99.2
99.2
99.0
98.4
Tr/s
Rf/%
Rr%
99.1
99.3
98.9
98.6
98.3
Tr/s
Rf/%
Rr%
99.4
99.2
99.3
98.9
98.3
Tr/s
Rf/%
98.6
98.5
98.3
97.7
97.6
Rr%
99.1
99.3
99.3
98.6
98.2
Tr/s
37
38
38
39
41
1
2
3
4
5
98.4
98.3
98.1
97.6
97.5
23
25
25
26
25
98.4
98.2
98.1
97.3
97.2
31
32
30
34
35
98.5
98.3
98.2
97.8
97.4
34
35
36
35
39
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Table 5 silicone oil uptake of (2)/DDM resin, (1)/DDM resin and (1)/(2) /DDM composites at 200℃
silicone oil uptake for 10min
/(%)
silicone oil uptake for 30min silicone oil uptake for 60min
Samples
/(%)
/(%)
0.62
(1)/DDM
0.21
0.24
0.27
0.43
0.66
0.71
(2)/(1)5:5/DDM
(2)/DDM
0.47
0.51
23