Influence of interim alkyl chain length on phase transitions and wide-band reflective behaviors of side-chain liquid crystalline elastomers with binaphthalene crosslinkings

Article abstract of DOI:10.1021/ma300618t

A series of side-chain polysiloxane liquid crystalline elastomers, E-Cm (where m is the number of carbon atoms in the interim alkyl groups, and m = 4, 6, 8, 10), with binaphthalene derivatives as crosslinkings, were designed and synthesized. The mesophase

Full text of DOI:10.1021/ma300618t

Article
pubs.acs.org/Macromolecules
Influence of Interim Alkyl Chain Length on Phase Transitions and
Wide-Band Reflective Behaviors of Side-Chain Liquid Crystalline
Elastomers with Binaphthalene Crosslinkings
Xiaojuan Wu,† Hui Cao,† Renwei Guo,† Kexuan Li,† Feifei Wang,† Yanzi Gao,† Wenhuan Yao,†
Lanying Zhang,‡ Xiaofang Chen,§ and Huai Yang*,†,‡
†Department of Materials Physics and Chemistry, School of Materials Science and Engineering, University of Science and Technology
Beijing, Beijing 100083, P. R. China
‡Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, P. R. China
§Department of Polymer Science and Engineering and The Key Laboratory of Polymer Chemistry and Physics of Ministry of
Education, College of Chemistry, Peking University, Beijing 100871, P. R. China
ABSTRACT: A series of side-chain polysiloxane liquid
crystalline elastomers, E-Cm (where m is the number of
carbon atoms in the interim alkyl groups, and m = 4, 6, 8, 10),
with binaphthalene derivatives as crosslinkings, were designed
and synthesized. The mesophase structures of these elastomers
were dependent on the value of m. The elastomers with m ≤ 8
could form cholesteric (Ch) phases, while both smectic A and
Ch phases could be formed for the elastomer with m = 10.
Blue phases can be achieved when m ≥ 8. Besides, the helical
twisting power (HTP) of all the elastomers exhibits a turning
point with changing temperature. Both the turning temper-
ature and HTP have an apparent dependence on the value of
m. By adjusting the interim alkyl chain length in the elastomers, both visible and near-infrared light wide-band reflective films can
be obtained. The broadband reflection mechanism was confirmed by SEM investigations.
and extraordinary (ne) refractive indices of the CLC, P is the
cholesteric pitch corresponding to the length of a 2π molecular
rotation. The reflected bandwidth (Δλ) is given by Δλ = (ne −
no) P = ΔnP, where Δn = ne − no is the birefringence of the
liquid crystal. Because a Δn value for colorless organic material
is generally smaller than 0.3, the bandwidth of a single-pitch
CLC in visible region is less than 100 nm, which is insufficient
for some applications such as brightness enhancement films,
wide-band reflective polarizers, and so on. To broaden the
bandwidth, forming a pitch gradient36,37 or a nonuniform pitch
distribution38,39 in a stable CLC film is usually used.
Chiral binaphthyl derivatives are widely used as high HTP
chiral dopants in host liquid crystals to form CLCs.40−43
Studies on LCEs derived from chiral binaphthyl derivatives are
less reported. Herein, we report the synthesis and character-
ization of a series of side-chain LCEs, E-Cm (where m is the
number of carbon atoms in the interim alkyl groups, and m = 4,
6, 8, 10), with binaphthyl derivatives as crosslinkings and
cholesterol derivatives as mesogenic groups. We examined the
liquid crystallinity and HTP of these elastomers using various
techniques, such as POM, DSC, WAXD, and Cano-wedge, and
INTRODUCTION
■
Liquid crystalline elastomers (LCEs) represent fascinating
materials of soft matter, combining the properties of polymeric
elastomers (entropy elasticity) with liquid crystals (self-
organization). To achieve liquid crystallinity, flexible spacers
are usually introduced in LCEs to decouple the dynamics of the
main chain and the mesogenic side groups.1 If the side groups
(at least partially) are chiral, a helically twisted structure (the
so-called cholesteric structure) can be obtained. Recently, LCEs
have received a lot of interest,2−5 owing to their special
optical,6,7 thermal,8,9 mechanical,10−13 and electrical14−16
properties. Correspondingly, they exhibit potential applications
in actuators,17−20 shape-memory materials,21−25 and pho-
tonics.26−28 LCEs have also been actively investigated as an
alternative for piezoelectrics, hydrogels, conducting polymers,
dielectric elastomers, and many other polymer systems for use
as artificial muscles or actuators.29,30
Cholesteric liquid crystalline elastomers (ChLCEs) and
polymers hold inherent characteristics of cholesteric liquid
crystal (CLC) and present promising applications in wide-band
reflective devices.31−34 Because of the unique helical supra-
molecular structure, CLC can selectively reflect circularly
polarized incident light with the same handedness as its helical
axis.35 At normal incidence, the mean reflection wavelength, λ =
nP, where n = (no + ne)/2 is the average of the ordinary (no)
Received: March 27, 2012
Revised: May 8, 2012
Published: June 29, 2012
© 2012 American Chemical Society
5556
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
Figure 1. Chemical structures of the materials used.
Scanning electron microscopy (SEM) was used to observe the
morphology of the fractured surface of the wide-band reflective films
on a Zeiss EVO18 instrument.
Synthesis of Monomers. The synthetic routes of the cross-
linkings, 1,1′-binaphthyl-2,2′-diyl bis(4-(alkenyl-oxy)benzoate (L-Cm),
and the liquid crystalline monomers, cholesteryl-4-alkenyl-oxybenzoate
(M-Cm, where m is the number of carbon atoms in the alkenyl groups,
and m = 4, 6, 8, 10), are shown in Scheme 1. The experimental details
of monomer synthesis and characterization are described below using
L-C10 and M-C10 as an example.
found that both the liquid crystal (LC) phase structures and
helical twisting behaviors were affected by the interim alkyl
chain length. Furthermore, visible and near-infrared light wide-
band reflective films with nonuniform pitch distributions were
obtained by using elasotmers with short and long interim alkyl
chain length, respectively. The microstructures of the films were
investigated by SEM observations.
EXPERIMENTAL SECTION
■
Synthesis of 4-(Dec-9-enyloxy)benzoic Acid, Acid-C10. 10-
Bromodec-1-ene (55.0 mmol, 12.05 g) was added dropwise to a
mixture of ethyl 4-hydroxybenzoate (50.0 mmol, 8.30 g), 100 mL of
butanone, NaOH (55.0 mmol, 2.20 g), and KI (1.00 g) at room
temperature and heated to 85 °C under magnetic stirred for 16 h.
After filtration and removal of solvent, the residue was dissolved in 500
mL of 10% NaOH and extracted twice by ether. After removal of
ether, 4-(dec-9-enyloxy)phenyl propionate ethyl (1d) was obtained.
Then, a solution of 300 mL og water and 20.00 g KOH were added to
an ethanol (50 mL) solution of 1d at room temperature. The mixture
was heated to 110 °C, refluxed for 10 h, and acidified to PH 3.0 with
hydrochloric acid. After filtration, the residue was recrystallized from
ethanol to give Acid-C10 as a white crystal. Yield: 12.70 g (92%). FT-
IR (KBr, cm−1): 2934−2852 (−CH2−, CH2 and CH), 2663−
2558 (−OH in −COOH), 1688 (CO), 1607, 1514 (Ar−), 1258
Materials. Polymethylhydrosiloxane (PMHS, Mn = 390, Sigma-
Aldrich) and H2Pt6Cl (Sinopharm Chemical Reagent Co. Ltd.) were
used as received. Toluene was distilled from Na/benzophenone under
N2 for at least 8 h until the solution turned blue. 1,1′-Binaphthyl-2,2′-
diol, ethyl 4-hydrozy benzoate, 4-bromobut-1-ene, 6-bromohex-1-ene,
8-bromooct-1-ene, 10-bromodec-1-ene, cholesterol, and other reagents
and solvents were used as received from commercial sources. Besides,
a room temperature nematic LC, SLC-1717 (no = 1.519, ne = 1.720,
Slichem Liquid Crystal Material Co. Ltd.), a photopolymerizable LC
monomer, 1,4-di-[4-(6-acryloyloxy) hexyloxy benzoyloxy]-2-methyl
benzene (C6M), a photoinitiator, 2,2-dimethopxy-1,2-diphenyl-
ethanone (IRG651, TCI Co. Ltd.), and an inhibitor, 2,6-di-tert-
butyl-4-methylphenol (DMP, TCI Co. Ltd.) were used. C6M was
synthesized according to the method suggested by Broer.44 Figure 1
shows the chemical structures of these materials.
1
(C−O−C). H NMR (300 MHz, CDCl3, TMS, δ, ppm): 8.04−8.02
Characterization and Measurements. 1H NMR (300 MHz)
spectra were recorded on a Bruker DMX-300 spectrometer using
deuterated chloroform (CDCl3) with tetramethylsilane as the internal
standard at room temperature.
Fourier transform infrared spectroscopy (FT-IR) was conducted on
a Perkin-Elmer Spectrum One in solid state by the KBr method with
wavenumber ranging from 400 to 4000 cm−1.
Thermogravimetric analysis (TGA) was performed on a STA 449
F3 instrument at a heating rate of 10 °C/min in a nitrogen
atmosphere.
Differential scanning calorimetry (DSC) examination was carried
out on a Perkin-Elmer Pyris 6 calorimeter with a heating and a cooling
rate of 10 °C/min under a dry nitrogen purge.
Polarized optical microscopy (POM) was carried out to observe the
LC textures of the samples on a Olympus BX51 microscope with a
Linkam THMS-600 hot stage calibrated to an accuracy of 0.1 °C.
One-dimensional (1D) wide-angle X-ray diffraction (WAXD)
experiments were carried out on a Philips X’Pert Pro diffractometer
with a 3 KW ceramic tube as the X-ray source (Cu Kα) and an
X’celerator detector.
(d, 2H, J = 6.3 Hz, Ar-H), 6.92−6.90 (d, 2H, J = 6.3 Hz, Ar-H), 5.83−
5.76 (m, 1H, CH2CH−), 5.00−4.90 (m, 2H, CH2CH−), 4.02−
3.98 (t, 2H, J = 4.8 Hz, CH2−CH2O−), 2.05−2.00 (q, 2H, J = 4.8 Hz,
=CH−CH2−), 1.82−1.75 (m, 2H, CH2−CH2O−), 1.44−1.41 (t, 2H,
J = 5.4 Hz, −CH2−), 1.31 (s, 8H, −CH2−).
Compounds Acid-C4, Acid-C6, and Acid-C8 were similarly
prepared as mentioned for Acid-C10.
4-(But-3-enyloxy)benzoic Acid, Acid-C4. FT-IR (KBr, cm−1
)
3025−2817 (−CH2−, CH2 and CH), 2678−2564 (−OH in
−COOH), 1678 (CO), 1604, 1577, 1511 (Ar−), 1250 (C−O−C).
1H NMR (300 MHz, CDCl3, TMS, δ, ppm): 8.05−8.03 (d, 2H, J = 6.3
Hz, Ar-H), 6.93−6.91(d, 2H, J = 6.3 Hz, Ar-H), 5.94−5.84 (m, 1H,
CH2CH−), 5.19−5.10 (m, 2H, CH2CH−), 4.09−4.05 (t, 2H, J =
5.1 Hz, CH−CH2O−), 2.58−2.53 (q, 2H, J = 5.1 Hz, −CH2−).
4-(Hex-5-enyloxy)benzoic Acid, Acid-C6. FT-IR (KBr, cm−1)
3082−2850 (−CH2−, CH2 and CH), 2672−2547 (−OH in
1
−COOH), 1689 (CO), 1603, 1511 (Ar−), 1255 (C−O−C). H
NMR (300 MHz, CDCl3, TMS, δ, ppm): 8.03 (s, 2H, Ar-H), 6.90 (s,
2H, Ar-H), 5.82−5.78 (t, 1H, J = 5.1 Hz, CH2CH−), 5.04−4.96 (t,
2H, J = 7.2 Hz, CH2CH−), 4.02−4.00 (d, 2H, J = 3.9 Hz, CH2−
5557
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
Scheme 1. (a) Synthetic Routes of the Crosslinkings and the Liquid Crystalline Monomers; (b) Synthetic Route and Schematic
Representation of Elastomers
CH2O−), 2.11 (s, 2H, CH−CH2−), 1.80 (s, 2H, CH2−CH2O−),
1.57 (s, 2H, −CH2−).
solution. The solution was added dropwise to 2d (11.0 mmol, 3.20 g),
heated to 90 °C, and refluxed for 10 h. The mixture was cooled,
filtered, poured in 200 mL of cold water, and extracted twice by
CH2Cl2. After removal of the solvent, the residue was purified by
column chromatography (silica gel, ethyl acetate/petroleum ether = 3/
2) to obtain L-C10. Yield: 2.41 g (60%). FT-IR (KBr, cm−1): 3063,
2928, 2854 (−CH2−, CH2 and CH), 1779, 1733 (CO), 1641
(CHCH2), 1604, 1511 (Ar−), 1251 −(C−O−Ar), 1159 (C−O−
C). 1H NMR (300 MHz, CDCl3, TMS, δ, ppm): 8.08−8.06 (d, 2H, J
= 6.6 Hz, Ar-H), 7.99−7.93 (m, 2H, Ar-H), 7.79−7.24 (m, 10H, Ar-
H), 6.93−6.92 (d, 2H, J = 4.2 Hz, Ar-H), 6.70−6.68 (d, 4H, J = 6.6
Hz, Ar-H), 5.82−5.76 (m, 2H, CH2CH−), 5.00−4.90 (m, 4H,
CH2CH−), 4.02−3.98 (t, 2H, J = 5.1 Hz, CH2−CH2O−), 3.91−
3.87 (t, 2H, J = 4.8 Hz, CH2−CH2O−), 2.03−1.99 (t, 4H, J = 6.0 Hz,
CH−CH2−), 1.78−1.68 (m, 4H, −CH2−), 1.37−1.22 (m, 20H,
−CH2−).
4-(Oct-7-enyloxy)benzoic Acid, Acid-C8. FT-IR (KBr, cm−1):
2924−2851 (−CH2−, CH2 and CH), 2672−2547 (−OH in
1
−COOH), 1690 (CO), 1606, 1513 (Ar−), 1251 (C−O−C). H
NMR (300 MHz, CDCl3, TMS, δ, ppm): 8.04−8.02 (d, 2H, J = 6.3
Hz, Ar-H), 6.92−6.90 (d, 2H, J = 6.6 Hz, Ar-H), 5.81−5.79 (m, 1H,
CH2CH−), 5.01−4.91 (m, 2H, CH2CH−), 4.02−3.99 (t, 2H, J =
4.8 Hz, CH2−CH2O−), 2.07−2.02 (q, 2H, J = 4.8 Hz, CH−CH2−),
1.83−1.76 (m, 2H, CH2-CH2O−), 1.46−1.24 (m, 6H, −CH2−).
Synthesis of 4-(Dec-9-enyloxy)benzoyl Chloride, 2d. Acid-C10
(21.0 mmol, 5.80 g) and thionyl chloride (45.0 mmol, 5.36 g) were
added into a round flask equipped with an absorption instrument of
hydrogen chloride. The mixture was heated to 90 °C and refluxed for 6
h. After removal of the solvent, 2d was obtained and stored
hermetically until further reactions.
Synthesis of 1.1′-Binaphthyl-2,2′-diyl Bis(4-(dec-9-enyloxy)-
benzoate), L-C10. 1,1′-Binaphthyl-2,2′-diol (5.0 mmol, 1.43 g) and
pyridine (1.0 mL) were dissolved in dry THF (50 mL) to form a
Crosslinkings L-C4, L-C6, and L-C8 were synthesized using the
same method as mentioned for L-C10.
5558
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
1.1′-Binaphthyl-2,2′-diyl Bis(4-(but-3-enyloxy)benzoate), L-C4.
FT-IR (KBr, cm−1): 3063, 2948, 2861 (−CH2−, CH2 and 
CH), 1733 (CO), 1643 (CHCH2), 1606, 1514 (Ar−), 1250 (C−
O−Ar), 1167 (C−O−C). 1H NMR (300 MHz, CDCl3, TMS, δ,
ppm): 8.10−8.08 (d, 2H, J = 6.3 Hz, Ar-H), 7.95−7.93 (d, 2H, J = 6.6
Hz, Ar-H), 7.89−7.87 (d, 2H, J = 6.3 Hz, Ar-H), 7.78−7.76 (d, 2H, J =
6.6 Hz, Ar-H), 7.62−7.31 (m, 8H, Ar-H), 6.70−6.68 (d, 4H, J = 6.3
Hz, Ar-H), 5.88−5.78 (m, 2H, CH2CH−), 5.15−5.97 (m, 4H,
CH2CH−), 3.97−3.94 (t, 4H, J = 4.8 Hz, CH2−CH2O−), 2.57−
2.46 (m, 4H, CH−CH2−).
3.6 Hz, −CH2−CHO−), 4.01−3.98 (t, 2H, J = 4.8 Hz, −CH2−),
2.44−2.42 (d, 2H, J = 5.7 Hz, −CHO−CH2−), 2.12−2.10 (d, 2H, J =
5.4 Hz, CH−CH2−), 1.87−0.67 (m, 45H, −CH2−CH2O−,
cholesteryl-H).
Cholesteryl-4-(oct-7-enyloxy)benzoate, M-C8. FT-IR (KBr,
cm−1): 2946, 2850 (−CH3 and −CH2−), 1700 (CO), 1641
(CHCH2), 1605, 1512, 1466 (Ar−), 1254 (C−O−Ar), 1171 (C−
1
O−C). H NMR (300 MHz, CDCl3, TMS, δ, ppm): 7.97−7.95 (d,
2H, J = 5.7 Hz, Ar-H), 6.88−6.86 (d, 2H, J = 6.0 Hz, Ar-H), 5.84−5.74
(m, 1H, CH2CH−), 5.39 (s, 1H, CH− in cholesteryl), 5.00−4.91
(m, 2H, CH2CH−), 4.81 (m, 1H, −CH2−CHO−), 3.99−3.96 (t,
2H, J = 4.5 Hz, −CHO−CH2−), 2.43−2.41 (d, 2H, J = 6.0 Hz,
−CH2−), 2.05−0.90 (m, 42H, −CH2−, cholesteryl-H), 0.85−0.83 (d,
6H, J = 4.8 Hz, −CH−CH3), 0.66 (s, 3H, −CH−CH3).
1.1′-Binaphthyl-2,2′-diyl Bis(4-(hex-5-enyloxy)benzoate), L-C6.
FT-IR (KBr, cm−1): 3063, 2942, 2874 (−CH2−, CH2 and 
CH), 1778, 1732 (CO), 1641 (CHCH2), 1605, 1511 (Ar−),
1251 (C−O−Ar), 1167 (C−O−C). 1H NMR (300 MHz, CDCl3,
TMS, δ, ppm): 8.10−8.08 (d, 2H, J = 6.3 Hz, Ar-H), 8.06 (m, 2H, Ar-
H), 7.98−6.93 (m, 14H, Ar-H), 6.70−6.67 (d, 2H, J = 6.6 Hz, Ar-H),
5.80−5.78 (m, 2H, CH2CH−), 5.03−4.94 (m, 4H, CH2=CH−),
4.05−4.00 (m, 2H, CH2−CH2O−), 3.94−3.89 (m, 2H, CH2−
CH2O−), 2.15−2.06 (m, 4H, CH−CH2−), 1.83−1.73 (m, 4H,
−CH2−), 1.59−1.49 (m, 4H, −CH2−).
Synthesis of Elastomers. All elastomers were synthesized by a
one-step hydrosilylation reaction. As the crosslinkings and the
mesogenic monomers both have chiral centers with the same
handedness in the molecules, the synthesized elastomers are all
chiral.45 The synthetic route and schematic representation of
elastomers are shown in Scheme 1(4). A typical polymerization
procedure was carried out as the following, again, using E-C10 as an
example. About 0.15 g (0.19 mmol) of crosslinking agent L-C10 and
0.73 g (1.14 mmol) of monomer M-C10 were dissolved in 50 mL of
dry, fresh distilled toluene. To the stirred solution, 0.16 g (0.40 mmol)
of PMHS and 2 mL of H2PtCl6/THF (0.50 g of hexachloroplatinic
acid hydrate dissolved in 100 mL of tetrahydrofuran) were added and
heated under nitrogen and anhydrous conditions at 110.0 °C for 36 h.
After removal of the solvent, the residue was dissolved in THF and
precipitated in methanol three times. Finally, the elastomer was dried
under vacuum.
Preparation of the Cells. To obtain homogeneous alignment, a
2.0 wt % polyvinyl alcohol (PVA) aqueous solution was coated onto
the inner surfaces of the substrates of the cells by spin-casting. The
deposited film was dried at 80.0 °C for about 1 h and subsequently
rubbed with a textile cloth under a pressure of 2.0 g cm−2 along one
direction. To induce homeotropic orientation of liquid crystals, the
inner surfaces of the substrates were treated with N,N-dimethyl-N-
octadecyl-3-aminopropyltrimethoxysiyl chloride (DMOAP) solution
(0.1% by volume in water).46 The mechanical effects are very strong in
cholesteric elastomers,47 and the studied sample was filled into the cell
by capillary action in the temperature range of the cholesteric or
isotropic phase.
Preparation of the Mixtures. To investigate the influence of the
flexible carbon chain length on the helical twisting behaviors of
monomers and elastomers, mixtures 1−12 were prepared by doping
them into a nematic LC. As the monomers and elastomers are all
chiral, mixtures 1−12 were cholesteric liquid crystals and exhibited a
cholesteric structure when filling them into a homogenously treated
cell. Mixtures 13 and 14 were prepared to fabricate wide-band
reflective films. All the mixtures were obtained by dissolving different
components in dichloromethane and evaporating the solvent slowly.
The compositions, weight ratios, phase transition temperatures, and
corresponding enthalpy changes of these mixtures are listed in Table 1.
Characterization of Helical Twisting Power of Monomers
and Elastomers. A CLC can be formed when a nematic LC host is
doped with a chiral dopant guest. The pitch of the CLC so obtained, P
= [(HTP)Xc]−1, where HTP and Xc are the helical twisting power and
molar concentration of the chiral dopant, respectively.48 To character-
ize the twisting power of the synthesized monomers and elastomers,
the value P of the CLCs (mixtures 1−12), induced by doping them in
a nematic LC SLC-1717, was used as the weight ratio was fixed in 2 wt
%.
1.1′-Binaphthyl-2,2′-diyl Bis(4-(oct-7-enyloxy)benzoate), L-C8.
FT-IR (KBr, cm−1): 3061, 2933, 2856 (−CH2−, CH2 and 
CH), 1777, 1733 (CO), 1641 (CHCH2), 1604, 1512 (Ar−),
1251 (C−O−Ar), 1166 (C−O−C). 1H NMR (300 MHz, CDCl3,
TMS, δ, ppm): 8.10−8.08 (d, 2H, J = 6.9 Hz, Ar-H), 8.00−7.93 (m,
2H, Ar-H), 7.79−7.76 (t, 2H, J = 2.7 Hz, Ar-H), 7.62−7.60 (d, 2H, J =
6.3 Hz, Ar-H), 7.52−7.50 (d, 2H, J = 6.3 Hz, Ar-H), 7.36−7.22 (m,
4H, Ar-H), 6.95−6.90 (q, 2H, J = 6.6 Hz, Ar-H), 6.70−6.68 (d, 4H, J =
6.3 Hz, Ar-H), 5.82−5.75 (m, 2H, CH2CH−), 5.00−4.91 (m, 4H,
CH2CH−), 4.04−3.98 (q, 2H, J = 5.1 Hz, CH2−CH2O−), 3.91−
3.89 (t, 2H, J = 4.8 Hz, CH2−CH2O−), 2.06−2.01 (m, 4H, CH−
CH2−), 1.72−1.69 (t, 4H, J = 4.8 Hz, −CH2−), 1.40−1.22 (m, 12H,
−CH2−).
Synthesis of Cholesteryl-4-(dec-9-enyloxy)benzoate, M-C10.
Cholesterol (10.0 mmol, 3.86 g) and pyridine (1.0 mL) were
dissolved in dry THF (50 mL) to form a solution. The solution was
added dropwise to 2d (11.0 mmol, 3.20 g), heated to 90 °C, and
refluxed for 10 h. The mixture was cooled, filtered, poured in 200 mL
of cold water, and extracted twice by CH2Cl2. After removal of the
solvent, the residue was purified by column chromatography (silica gel,
ethyl acetate/petroleum ether = 3/2) to obtain M-C10. Yield: 4.19 g
(65%). FT-IR (KBr, cm−1): 2940, 2853 (−CH3 and −CH2−), 1701
(CO), 1641 (CHCH2), 1606, 1512, 1467 (Ar−), 1254 (C−O−
1
Ar), 1168 (C−O−C). H NMR (300 MHz, CDCl3, TMS, δ, ppm):
7.97−7.95 (d, 2H, J = 6.6 Hz, Ar-H), 6.88−6.86 (d, 2H, J = 6.6 Hz, Ar-
H), 5.84−5.74 (m, 1H, CH2CH−), 5.39 (d, 1H, J = 2.4 Hz, CH−
in cholesteryl), 4.99−4.90 (m, 2H, CH2CH−), 4.81 (m, 1H,
−CH2−CHO−), 3.99−3.96 (t, 2H, J = 4.8 Hz, −CHO−CH2−),
2.43−2.41 (d, 2H, J = 6.0 Hz, −CH2−), 2.03−0.85 (m, 46H, −CH2−,
cholesteryl-H), 0.84−0.83 (d, 6H, J = 1.2 Hz, −CH−CH3), 0.66 (s,
3H, −CH−CH3).
Liquid crystalline monomers M-C4, M-C6, and M-C8 were
synthesized using the same method as mentioned for M-C10.
Cholesteryl-4-(but-3-enyloxy)benzoate, M-C4. FT-IR (KBr,
cm−1): 2944, 2867 (−CH3 and −CH2−), 1711 (CO), 1645
(CHCH2), 1608, 1511, 1467 (Ar−), 1252 (C−O−Ar), 1165 (C−
1
O−C). H NMR (300 MHz, CDCl3, TMS, δ, ppm): 7.97−7.95 (d,
2H, J = 6.6 Hz, Ar-H), 6.89−6.87 (d, 2H, J = 6.6 Hz, Ar-H), 6.06−6.03
(m, 1H, CH2CH−), 5.40−5.39 (d, 1H, J = 3.0 Hz, CH− in
cholesteryl), 5.18−5.09 (m, 2H, CH2CH−),4.06−4.03 (t, 3H, J =
4.8 Hz, −CH2−CHO−, −CH2−CH2O−), 2.57−2.52 (q, 2H, J = 5.1
Hz, −CHO−CH2−), 2.44−2.42 (d, 2H, J = 6.0 Hz, CH−CH2−),
2.02−0.67 (m, 41H, cholesteryl-H).
The pitch lengths were measured by the Cano-wedge technique.49
In this measurement, a wedge-shaped cell (KCRK-07, Japan) with a
wedge angle, θ (0.01937 rad), was used and the inner surfaces of its
two glass substrates were treated to provide a homogeneous
orientation of the LC molecules. After the mixture was filled into
the cell, a Grandjean-Cano texture formed with disclination lines
separated by a distance D. The pitch length P is determined from P =
2D tan θ ≈ 2Dθ.
Cholesteryl-4-(hex-5-enyloxy)benzoate, M-C6. FT-IR (KBr,
cm−1): 2944, 2868 (−CH3 and −CH2−), 1711 (CO), 1641
(CHCH2), 1608, 1511, 1466 (Ar−), 1248 (C−O−Ar), 1163 (C−
1
O−C). H NMR (300 MHz, CDCl3, TMS, δ, ppm): 7.97−7.95 (d,
2H, J = 6.6 Hz, Ar-H), 6.88−6.86 (d, 2H, J = 6.6 Hz, Ar-H), 5.82−5.80
(m, 1H, CH2CH−), 5.40−5.39 (d, 1H, J = 3.0 Hz, CH− in
cholesteryl), 5.04−4.95 (m, 2H, CH2CH−), 4.82−4.79 (t, 1H, J =
5559
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
Table 1. The Compositions, Weight Ratios, Phase Transition
Temperatures, and Corresponding Enthalpy Changes of
Mixtures 1−14
mixture
(type)
TCh‑I
ΔH
d
c
wt ratio (wt %)
(°C)
(J g−1
)
a
a
a
a
a
a
a
a
a
a
a
a
1
2.0/−/−/−/−/−/−/−/−/−/−/−/98.0
−/2.0/−/−/−/−/−/−/−/−/−/−/98.0
−/−/2.0/−/−/−/−/−/−/−/−/−/98.0
−/−/−/2.0/−/−/−/−/−/−/−/−/98.0
−/−/−/−/2.0/−/−/−/−/−/−/−/98.0
−/−/−/−/−/2.0/−/−/−/−/−/−/98.0
−/−/−/−/−/−/2.0/−/−/−/−/−/98.0
−/−/−/−/−/−/−/2.0/−/−/−/−/98.0
−/−/−/−/−/−/−/−/2.0/−/−/−/98.0
−/−/−/−/−/−/−/−/−/2.0/−/−/98.0
−/−/−/−/−/−/−/−/−/−/2.0/−/98.0
−/−/−/−/−/−/−/−/−/−/−/2.0/98.0
85.3
85.6
85.6
85.1
91.8
92.8
92.6
91.8
90.4
90.7
90.1
90.5
143.4
142.2
0.39
0.21
0.12
0.28
0.32
0.37
0.28
0.23
0.28
0.40
0.81
0.39
0.43
0.54
2
3
4
5
6
7
8
9
10
11
12
13
14
b
95.98/−/4.0/0.01/0.01
b
−/95.98/4.0/0.01/0.01
a
Weight ratio: L-C4/L-C6/L-C8/L-C10/M-C4/M-C6/M-C8/M-
b
C10/E-C4/E-C6/E-C8/E-C10/SLC-1717. Weight ratio: E-C8/E-
C10/C6M/IRG651/DMP. TCh‑I: clearing temperature from choles-
teric to isotropic phase. ΔH: Delta H from cholesteric to isotropic
phase.
c
d
Preparation of the Wide-Band Reflective Films. Mixture 13 or
14 was filled into homogeneous treated cells with different cell
thickness (10, 20, 40, 60, or 80 μm) at high temperature below their
clearing temperatures. The wide-band reflective cells were prepared by
carrying out the following procedure. The cells of mixtures were
irradiated with UV light (5 mW cm−2, 365 nm) for different times (10,
20, 40, 60, or 80 min) at high temperature (115 °C for mixture 13 and
131 °C for mixture 14), during which polymer network was formed
from the photopolymerization of C6M. Then they were cooled slowly
to low temperature and quenched below their glass transition
temperatures.
The samples for SEM studies were prepared as follows. The wide-
band reflective cells of the mixtures were plunged in liquid nitrogen
and broken in a direction perpendicular to the plates. Then the
fractured surfaces of the cells were sputtered with a thin layer of gold
and observed.
Figure 2. (a) FT-IR spectra of E-C10, PMHS, L-C10, and M-C10; (b)
partial amplification of the spectra in (a) between 1800 and 1500
cm−1.
Phase Transitions of Monomers. The thermal properties
of the acids and monomers were determined by DSC and POM
measurements, which data are summarized in Figure 3. Acid-
C8 and Acid-C10 showed smectic A (SmA) and nematic (N)
phases, but Acid-C4 and Acid-C6 showed only N phase in the
heating process. M-C8 and M-C10 showed SmA and Ch
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Monomers and
Elastomers. As shown in Scheme 1, the monomers were
synthesized in four steps. The structures of the monomers were
1
confirmed by FT-IR and H NMR spectroscopic methods.
Target elastomers were synthesized by the hydrosilylation of
PMHS with the binaphthalene derivates and cholesterol
derivates using H2PtCl6 as the catalyst.
With E-C10 as an example, FT-IR spectra of E-C10, PMHS,
L-C10, and M-C10 are shown in Figure 2. The disappearance
of the sharp vibrational band at 2164 cm−1, which was assigned
as the Si−H stretching, showed that all the Si−H groups were
reacted completely. The appearance of the vibrational bands at
2934−2850, 1710, 1605−1470, and 1121−1020 cm−1, which
were attributed to vibrations from methylene (−CH2−), ester
carbonyl (CO), aromatic (Ar−), and Si−O−Si, respectively,
illustrated the successful preparation of the elastomer. Addi-
tionally, from the partial amplification of the spectra between
1800 and 1500 cm−1 as shown in Figure 2b, it can be found that
the vibrational band at 1641 cm−1 corresponding to olefinic
CC stretching disappeared, indicating totally reaction of the
monomers.
Figure 3. Phase transition temperatures of the acids, liquid crystalline
monomers, and crosslinkings.
5560
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
Table 2. Thermal Properties of Elastomers E-Cm
DSC
POM
a
a
a
b
c
d
elastomers
Tg (°C)
Tm (°C)
Ti (°C)
transition temperature (°C)
G 110.0 Ch 164.0 I
ΔT (°C)
Td (°C)
E-C4
52.3
109.0
162.6
53.6
46.5
42.2
62.3
305
(0.40)
(16.37)
(0.97)
G 99.0 Ch 154.0 I
E-C6
E-C8
E-C10
42.1
116.2
162.7
G 118.0 Ch 165.0 I
G 110.0 Ch 156.0 I
312
270
261
(0.80)
(14.25)
(0.71)
42.4
110.4
152.6
G 114.0 Ch 154.0 I
(1.24)
(13.89)
(0.73)
G 90.0 Ch 127.0 BP 144.1 I
56.1
89.3
151.6
G 90.0 SmA 140.0 Ch 152.0 I
(2.52)
(6.53)
(0.84)
G 65.0 SmA 135.4 Ch 143.8 BP 146.1 I
a
b
Evaluated by DSC at a rate of 10 °C/min. The data in the parentheses are the corresponding enthalpy changes (ΔH in J g−1). Evaluated by POM
measurement during heating (the up row) and cooling (the down row) processes. G, glassy; Ch, cholesteric phase; I, isotropic phase; SmA, smectic
A phase; BP, blue phase. Mesophase temperature ranges from DSC measurement. The temperature at which 5% weight loss of the sample from
c
d
TGA under nitrogen atmosphere at a heating rate of 10 °C/min.
Figure 4. Optical textures of E-C8 and E-C10 when cooled from their isotropic states. No birefringence of glassy at 90 °C (a1), planar texture of Ch
phase at 127 °C (a2), BP texture at 144 °C (a3) and isotropic state at 154 °C (a4) for E-C8 in a homogenously treated cell; fan-shaped texture of
SmA phase at 135 °C (b1), cholesteric phase texture at 143 °C (b2), BP texture at 146 °C (b3) and isotropic state at 152 °C (b4) for E-C10 in a
homogenously treated cell; pseudoisotropic texture of SmA phase at 135 °C (c1), focal-conic texture of Ch phase at 143 °C (c2) and BP texture at
146 °C (c3) for E-C10 in a homeotropically treated cell, respectively. (d) The 1D WAXD pattern of E-C10 at 135 °C during a cooling process. The
inset is partial amplification of the pattern between 3 and 10°.
phases, while M-C4 and M-C6 showed only Ch phase in the
heating process. In other words, increase of the terminal alkenyl
chain length helps to the formation of SmA phase. Crosslinking
agent L-Cm shows no liquid crystalline phases during both
heating and cooling processes because of their nonlinear
structure. Besides, the clearing or melting temperature of acids
5561
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
and monomers decreased with increasing alkenyl chain length
due to the increased flexibility by the alkenyl end chains.
Phase Transitions and Phase Structures of the
Elastomers. The phase behaviors of all the elastomers were
investigated by DSC and POM measurements. The thermal
properties of these elastomers, which are dependent on the
number of carbon atoms in the interim alkyl groups, m, for the
E-Cm series, are listed in Table 2.
As shown in Table 2, the temperatures at 5% weight loss
under N2 (Tds) were all over 260 °C, indicating that all the
elastomers had good thermal stabilities. From DSC measure-
ment, a glass transition temperature (Tg), a melting transition
temperature (Tm), and a clearing temperature (Ti) can be
detected in the curves of all the synthesized elastomers. Ti
decreased with increasing interim alkyl chain length from E-C4
to E-C10 due to the increased plasticization by the alkyl chains.
All the elastomers have wide mesophase temperature ranges as
summarized in Table 2.
To confirm the liquid crystalline phase transitions, all the
elastomers were observed by POM measurement. During Tm
and Ti, E-C4 and E-C6 showed Ch phase textures in both the
heating and cooling processes. E-C8 showed Ch phase in the
heating process but blue phase (BP) and Ch phase in the
cooling process. Worthily, E-C10 showed smectic (Sm) and Ch
phases in a heating process, and BP, Ch, and Sm phases in the
cooling process. Figure 4 shows the POM photographs of E-C8
and E-C10 when cooling from their isotropic states. When the
elastomer was filled into a homogenously treated cell above its
clearing temperature, it showed a black field corresponding to
isotropic state (Figure 4a4,b4). As cooling, E-C8 exhibited
subsequently blue phase texture (Figure 4a3), planar texture for
Ch phase (Figure 4a2), and then turned glassy below 90 °C,
presenting no texture and birefringence as shown in Figure 4a1.
Different from E-C8, E-C10 showed fan-shaped texture
corresponding to Sm phase (Figure 4b1), after its BP texture
(Figure 4b3) and Ch phase texture (Figure 4b2).
To identify the kind of Sm phase for E-C10, it was filled into
a homeotropically treated cell. In a cooling process, it exhibited
a black field for isotropic state, BP texture (Figure 4c3), and
focal conic texture containing orderly fingerprint texture for the
Ch phase (Figure 4c2). Subsequently, it showed a black field
(Figure 4c1) again, which is the characteristic of SmA or SmB
phase. In the 1D WAXD pattern of E-C10 at 135 °C, a sharp
peak at 2θ = 2.26° and equidistant diffractions in the small-
angle region emerge along with a broad and unconspicuous
halo centering at 2θ ≈ 17° in the wide-angle region (Figure
4d). As the appearance of a single sharp diffraction at the wide-
angle region is necessary to indicate the existence of SmB
phase,50 we rule out the possibility of a SmB phase. Combined
with the results of Figure 4b1,c1, the Sm phase of E-C10 could
be determined to be a SmA phase. In conclusion, the increase
of the interim alkyl chain length contributes to the formation of
SmA phase and blue phase for the elastomers.
Helical Twisting Behaviors of Monomers and Elas-
tomers. Figure 5 shows the temperature dependence of the
pitch lengths of mixtures 1−4, 5−8, and 9−12, respectively. It
can be seen that the crosslinkings L-Cm or monomers M-Cm
with different terminal alkenyl chain length exhibit a similar
temperature dependence of HTP. For example, P increases for
mixtures 1−4, decreases for mixtures 5−8 with increasing
temperature as shown in parts a and b of Figure 5. But it should
be noted that L-Cm and M-Cm have opposite temperature
dependence of HTP. Furthermore, the values of P increase first
Figure 5. Temperature dependence of the pitch lengths of mixtures
1−4 (a), mixtures 5−8 (b), and mixtures 9−12 (c).
and then decrease with increasing terminal alkenyl chain length.
Typically, the P values at 20 °C were 2.9 μm for mixture 1, 23.5
μm for mixture 2, 18.5 μm for mixture 3, and 4.8 μm for
mixture 4, respectively. It was found that the twisting power is
weakly dependent on the nature of the aliphatic chiral
center,51,52 the decreasing or increasing HTP values (increasing
or decreasing P values) with increasing terminal alkenyl chain
length from 4 to 10, may result from smaller or greater
anisometry of molecular structure.
The HTP of elastomers grafting both L-Cm and M-Cm
exhibited a turning point with increasing temperature due to
the coordination of the crosslinkings and the liquid crystalline
monomers. For instance, the pitch length of mixture 11
increases from 15.5 to 16.2 μm with increasing temperature
from 20 to 50 °C, while it decreases to 13.9 μm when
increasing temperature continuously to 90 °C as shown in
Figure 5c. The turning point extrapolated from the P values
were 80 °C for E-C4, 45 °C for E-C6, 50 °C for E-C8, and 55
°C for E-C10, respectively. Besides, the HTP decreases first
and then increases with increasing interim alkyl chain length
from 4 to 10 following the same rule as to the monomers.
5562
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
Figure 6. POM micrographs of mixtures 11 and 12 at different temperature in wedge-shaped cells: mixture 11 at 20 °C (a1), 50 °C (a2) and 90 °C
(a3), D11-3 < D11-1 < D11-2; mixture 12 at 20 °C (b1), 55 °C (b2) and 90 °C (b3), D12-3 < D12-1 < D12-2, respectively.
Typically, the HTP of E-C10 is larger than that of E-C8.
Correspondingly, the pitch length of mixture 12 is smaller than
that of mixture 11 as shown in Figure 6. Taking the pitch length
at their turning point as an example, the distance of parallel
disclination lines in Figure 6b2 is L narrower than that in Figure
6a2. In conclusion, the interim alkyl chain length in the
synthesized elastomers has a great influence on their helical
twisting behaviors.
Application of Elastomers in Visible and Near-Infra-
red Wide-Band Reflective Films. Figure 7 shows the
Figure 7. The transmission spectra of E-C8 at different temperature
and the POM photographs corresponding to temperature.
transmission spectra of E-C8 at different temperature. It can
be found that the reflection wavelength becomes shorter with
increasing temperature, and is located in 752, 621, 527, 435,
and 396 nm at 119, 120, 121, 123, and 125 °C, respectively.
This is due to that the HTP of E-C8 increases with increasing
temperature above its turning point 50 °C. Worthily, it
remained good planar texture with the increase of temperature
from 119 to 125 °C as shown in the inset of Figure 7, which
ensured the high reflective intensity.
To fabricate wide-band reflective films, mixture 13 containing
LCEs without SmA phase and mixture 14 containing LCEs
with SmA phase were prepared. Figure 8a shows the
transmission spectra of mixtures 13 and 14 before and after
UV curing for 40 min in the cells with 40 μm thickness. It can
be seen that the bandwidth of the spectra become broadened
Figure 8. (a) The transmission spectra of mixtures 13 and 14 before
and after UV curing for 40 min in the cells with 40 μm thickness; (b)
UV curing time and cell thickness dependence of the reflection
bandwidth for mixture 13 after polymerization.
after UV curing. Mixture 13 reflects the visible light flux range
of 350−850 nm after polymerization at 109 °C (curve 2). The
center reflection wavelength of mixture 14 locates in 2055 nm
at 129 °C before UV curing (curve 3). And the reflection band
broadened to 970 nm in the near-infrared light flux range of
1370−2340 nm after polymerization (curve 4). In other words,
visible and near-infrared wide-band reflective films can be
obtained from E-C8 and E-C10 by blending with a small
quantity of photopolymerizable monomers, respectively.
5563
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
Figure 9. The schematic representation of LCE molecules in the cell containing mixture 13 (a1 and a2) or mixture 14 (b1 and b2) when temperature
changes: before UV curing at high temperature (a1 and b1) and after UV curing at low temperature (a2 and b2).
Then we investigated the influence of the UV curing time
and the cell thickness on the optical properties of the wide-
band reflective films. Figure 8b shows the UV curing time and
cell thickness dependence of the reflection bandwidth for
mixture 13 after polymerization. It can be seen that the
reflection bandwidth increases obviously with increasing UV
curing time from 10 to 40 min, while it tends to be stable after
40 min even when increase in the UV curing time continued. In
addition, it changes little with different cell thickness from 10 to
100 μm as shown in Figure 8b.
A conceivable explanation to above phenomenon is given
considering the change of pitch length in synthesized
elastomers when temperature changes and the anchoring effect
of the polymer network. Figure 9a shows the schematic
representation of the rearrangement of the LCE molecules in
mixture 13 when temperature changes. At high temperature, it
was filled into a homogeneously treated cell and exhibited
uniform short pitch as shown in Figure 9a1. Then this short
pitch was fixed in some local regions surrounded by the
polymer network formed from the photopolymerization of
C6M after UV curing. As the HTP of E-C8 increased with the
increase of temperature above its turning point, its pitch length
had a tendency to decrease as the temperature rose. So when
cooling, the pitch length of mixture 13 became long in some
other regions, where the anchoring effect of the polymer
network was not enough to prevent the LCE molecules from
rearranging, as shown in Figure 9a2. Different from mixture 13,
mixture 14 was filled into the cell at a temperature a little above
its SmA-Ch phase transition temperature and exhibited uniform
pitch larger than that of mixture 13 as shown in Figure 9b1.
When cooling, it tended to change to be SmA phase in the
regions with weak anchoring effect of the polymer network, and
the pitch length became longer correspondingly, as shown in
Figure 9b2. Finally, benefiting from the polymer property hold
by the LCEs, the longer pitch can be frozen after quenching
cells below their glass transition temperatures. As a result, small
and large nonuniform pitch distributions are formed in mixture
13 and mixture 14, as shown in parts a2 and b2 of Figure 9,
respectively.
It is well-known that the polymerization of the photo-
polymerizable monomer proceeds gradually with increasing UV
curing time and stops when the monomer is exhausted. As the
concentration of the monomer C6M in mixtures 13 and 14 is
fixed, the anchoring effect of the polymer network, which
contributes to the fixation of the short pitch, increases first and
then changes little with the increase of UV curing time.
Correspondingly, the reflection bandwidth of the mixtures after
polymerization increases first and then tends to be stable with
increasing UV curing time. Besides, as the nonuniform pitch
distributions are formed under certain UV intensity, the
reflection bandwidth is scarcely influenced by the cell thickness.
To demonstrate the mechanism described above, nonuni-
form pitch distributions of mixtures 13 and 14 after UV curing
for 40 min in the cells with 40 μm thickness were observed with
5564
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
a scanning electron microscopy (SEM). Parts a and b of Figure
10 show SEM images of the fractured surfaces of the irradiated
and SmA phases. In addition, E-C8 and E-C10 can form blue
phases under a cooling process. The results show that the
interim alkyl chain length has a great influence on the helical
twisting behaviors of the elastomers, and visible or near-infrared
light wide-band reflective films can be obtained by utilizing
elastomers with short or long interim alkyl chain length,
respectively. These broadband reflective films have practical
applications in visible brightness enhancement films and IR
shielding films.
AUTHOR INFORMATION
Corresponding Author
*E-mail: yanghuai@mater.ustb.edu.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by National Natural Science Fund for
Distinguished Yong Scholar (grant no. 51025313), National
Natural Science Foundation (grant no. 50973010 and
51173003), Open Research Fund of State Key Laboratory of
Bioelectronics (Southeast University), the Fundamental Re-
search Funds for the Central Universities (grant no. FRF-TP-
12-032A) and National Natural Science Foundation (grant no.
51143001).
REFERENCES
■
(1) Finkelmann, H.; Rehage, G. In Liquid Crystal Polymers; Academic
Press: New York, 1984; pp 99−172.
(2) Urayama, K. Macromolecules 2007, 40, 2277−2288.
(3) Brand, H. R.; Pleiner, H.; Martinoty, P. Soft Matter 2006, 2, 182−
189.
Figure 10. SEM photographs of the fractured surfaces of mixture 13
(a) and mixture 14 (b). The dimension of the bands in the fine
structure on the fractured planes corresponds to a π molecular
rotation, that is, P/2. There is a small nonuniform pitch distribution in
mixture 13, P1 < P2 < P3 < P4; a large nonuniform pitch distribution in
mixture 14, P5 < P6 < P7 < P8.
(4) Sawa, Y.; Ye, F.; Urayama, K.; Takigawa, T.; Gimenez-Pinto, V.;
Selinger, R. L. B. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 6364−6368.
(5) Serra, F.; Matranga, M. A.; Ji, Y.; Terentjev, E. M. Opt. Express
2010, 18, 575−581.
(6) Menzel, A. M.; Pleiner, H.; Brand, H. R. J. Chem. Phys. 2007, 126,
234901.
(7) Beyer, P.; Zentel, R. Macromol. Rapid Commun. 2005, 26, 874−
cells. The dimension of the two bands in the fine structure on
the fractured planes corresponds to a π molecular rotation, that
is, P/2. It can be seen that different pitch lengths distributed
randomly in the fractured plane. For example, pitch lengths
from about 0.15 μm (P1) to 0.36 μm (P4) distributed randomly
in the fractured plane of the irradiated cell containing mixture
13 as shown in Figure 10a, from about 0.54 μm (P5) to 0.93
μm (P8) allocated irregularly in that of the cell containing
mixture 14 as shown in Figure 10b. According to the equation λ
= nP, λ1 should be 350 nm while λ4 should be 850 nm in
theory, which almost covers the visible light region. Similarly, λ5
should be 1370 nm and λ8 should be 2340 nm in theory, which
nearly mantles the near-infrared light region. This demonstrates
that mechanism explained above is reasonable. By adjusting the
interim alkyl chain length in the elastomers, both visible and
near-infrared light wide-band reflective films can be obtained.
879.
(8) Ji, Y.; Huang, Y. Y.; Terentjev, E. M. Langmuir 2011, 27, 13254−
13260.
(9) Sanchez-Ferrer, A.; Finkelmann, H. Solid State Sci. 2010, 12,
1849−1852.
(10) Biggins, J. S.; Warner, M.; Bhattacharya, K. J. Mech. Phys. Solids
2012, 60, 573−590.
(11) Yamazaki, H.; Takeda, M.; Kohno, Y.; Ando, H.; Urayama, K.;
Takigawa, T. Macromolecules 2011, 44, 8829−8834.
(12) Ishige, R.; Osada, K.; Tagawa, H.; Niwano, H.; Tokita, M.;
Watanable, J. Macromolecules 2008, 41, 7566−7570.
(13) Ren, W.; Mcmullan, P. J.; Griffin, A. C. Macromol. Chem. Phys.
2008, 209, 1896−1899.
(14) Hiraoka, K.; Kobayasi, M.; Kazama, R.; Finkelmann, H.
Macromolecules 2009, 42, 5600−5604.
(15) Terentjev, E. M.; Wamer, M. Eur. Phys. J. B 1999, 8, 595−601.
(16) Kelly, S. M. J. Mater. Chem. 1995, 5, 2047−2073.
(17) Yang, H.; Buguin, A.; Taulemesse, J.-M.; Kaneko, K.; Mery, S.;
Bergeret, A.; Keller, P. J. Am. Chem. Soc. 2009, 131, 15000−15004.
(18) Ohm, C.; Serra, C.; Zentel, R. Adv. Mater. 2009, 21, 4859−4862.
(19) Sanchez-Ferrer, A.; Fischl, T.; Stubenrauch, M.; Wurmus, H.;
Hoffmann, M.; Finkelmann, H. Macromol. Chem. Phys. 2009, 210,
1671−1677.
CONCLUSIONS
■
In summary, a series of side-chain LCEs with binaphthalene
derivatives as crosslinkings based on polysiloxane were
synthesized and characterized. The phase transition temper-
atures, helical twisting behaviors, and reflective behaviors of the
elastomers were investigated. The elastomers with short interim
alkyl chain length, E-C4, E-C6, and E-C8, formed Ch phases,
while E-C10 with longer interim alkyl chain length formed Ch
(20) Bufuin, A.; Li, M.-H.; Silberzan, P.; Ladoux, B.; Keller, P. J. Am.
Chem. Soc. 2006, 128, 1088−1089.
(21) Ohm, C.; Kapernaum, N.; Nonnenmacher, D.; Giesselmann, F.;
Serra, C.; Zentel, R. J. Am. Chem. Soc. 2011, 133, 5305−5311.
5565
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566

Macromolecules
Article
(22) Ahn, S.; Deshmukh, P.; Gopinadhan, M.; O.Osuji, C.; M.Kasi, R.
NANO 2011, 5, 3085−3095.
(23) Burke, K. A.; Mather, P. T. J. Mater. Chem. 2010, 20, 3449−
3457.
(24) Chambers, M.; Verduzco, R.; Gleeson, J. T.; Sprunt, S.; Jakli, A.
Adv. Mater. 2009, 21, 1622−1626.
(25) Hiraoka, K.; Sagano, W.; Nose, T.; Finkelmann, H. Macro-
molecules 2005, 38, 7352−7357.
(26) Schmidtke, J.; Kniesel, S.; Finkelmann, H. Macromolecules 2005,
38, 1357−1363.
(27) Cicuta, P.; Tajbakhsh, A. R.; Terentjev, E. M. Phys. Rev. E 2002,
65, 051704.
(28) Bermel, P. A.; Warner, M. Phys. Rev. E 2002, 65, 056614.
(29) Ohm, C.; Brehmer, M.; Zentel, R. Adv. Mater. 2010, 22, 3366−
3387.
(30) Mirfakhrai, T.; Madden, J. D. M.; Baughman, R. H. Mater.
Today 2007, 10, 30−38.
(31) Agez, G.; Mitov, M. J. Phys. Chem. B 2011, 115, 6421−6426.
(32) Fan, B.; Vartak, S.; Eakin, J. N.; Faris, S. M. Appl. Phys. Lett.
2008, 92, 061101.
(33) Xiao, J. M.; Zhao, D. Y.; Cao, H.; Yang, H. Liq. Cryst. 2007, 34,
473−477.
(34) Zografopoulos, D. C.; Kriezies, E. E.; Mitov, M.; Binet, C. Phys.
Rev. E 2006, 73, 061701.
(35) Johm, W. D. S.; Fritz, W. J.; Lu, Z. J.; Yang, D. K. Phys. Rev. E
1995, 51, 1191.
(36) Broer, D. J.; Lub, J.; Mol, G. N. Nature 1995, 378, 467−469.
(37) Hu, W.; Zhao, H. Y.; Song, L.; Yang, Z.; Cao, H.; Cheng, Z. H.;
Liu, Q.; Yang, H. Adv. Mater. 2010, 22, 468−472.
(38) Bian, Z. Y.; Li, K. X.; Huang, W.; Cao, H.; Yang, H. Appl. Phys.
Lett. 2007, 91, 201908.
(39) Guo, R. W.; Li, K. X.; Cao, H.; Wu, X. J.; Wang, G. J.; Cheng, Z.
H.; Wang, F. F.; Zhang, H. Q.; Yang, H. Polymer 2010, 51, 5990−
5996.
(40) Akagi, K. Chem. Rev. 2009, 109, 5354−5401.
(41) Barnett, D. S.; Schaus, S. E. Org. Lett. 2011, 13, 4020−4023.
(42) Han, Y.; Pacheco, K.; Bastiaansen, C. W. M.; Broer, D. J.;
Sijbesma, R. P. J. Am. Chem. Soc. 2010, 132, 2961−2967.
(43) Guo, R. W.; Cao, H.; Liu, H. J.; Li, K. X.; Huang, W.; Xiao, J.
M.; Yuan, X. T.; Yang, Z; Yang, H. Liq. Cryst. 2009, 36, 939−946.
(44) Broer, D. J.; Boven, J.; Mol, G. N. Makromol. Chem. 1989, 190,
2255−2268.
(45) Mao, Y.; Warner, M. Phys. Rev. Lett. 2000, 84, 5335−5338.
(46) Kahn, F. J. Appl. Phys. Lett. 1973, 22, 386−388.
(47) Warner, M.; Terentjev, E. M.; Meyer, R. B.; Mao, Y. Phys. Rev.
Lett. 2000, 85, 2320−2323.
(48) Kumar, G.; Neckers, D. Chem. Rev. 1989, 89, 1915−1937.
(49) Cano, R.; Soc, B.; Minearal, F. Crystallography 1968, 91, 20−27.
(50) Xu, J.; Toh, C. L.; Liu, X.; Wang, S.; He, C.; Lu, X.
Macromolecules 2005, 38, 1684−1690.
(51) Vashchenko, V.; Drushlyak, T.; Shkolnikova, N.; Kutulya, L.
Mol. Cryst. Liq. Cryst. 1999, 328, 245−253.
(52) Januszko, A.; Kaszynski, P.; Drzewinski, W. J. Mater. Chem.
2006, 16, 452−461.
5566
dx.doi.org/10.1021/ma300618t | Macromolecules 2012, 45, 5556−5566