Novel supramolecular side-chain banana-shaped liquid crystalline polymers containing covalent- and hydrogen-bonded bent cores

Article abstract of DOI:10.1021/ma901960c

Novel supramolecular side-chain banana-shaped liquid crystalline (LC) polymer complexes AmBn-N bearing various (m/n) molar ratios of hydrogen- and covalent-bonded bent-core components were acquired by the free radical polymerization, where the hydrogen-bonded (H-bonded) structures were executed via mixing equimolar portions of proton donor (H-donor) polymers AmBn (homopolymers/ copolymers) and pyridyl proton acceptor (H-acceptor) bent cores (small molecules). The influences of the molar ratios of bent-core H-bonded components in side-chain banana-shaped LC polymers and their corresponding polymer complexes on mesomorphic and electro-optical properties were first investigated, The voltage-dependent antiferroelectric properties of spontaneous polarization (Ps) values in the polar smectic phase of the supramolecular side-chain banana-shaped copolymers were also reported. The nematic and tilted smectic phases were verified by XRD measurements, and the SmCP phase was further confirmed by the triangular wave method. Surprisingly, a novel enantiotropic polar smectic (SmCPA) phase was generated in some bent-core side-chain polymer complexes AmBn-N. Therefore, a special approach to constructing (or stabilizing) the SmCP phase was first developed in this study by copolymerization of bent-core covalent- and H-bonded units in side-chain polymer complexes (with proper m/n molar ratios of 16/1 and 10/1) from both bent-core covalent- and H-bonded monomers (i.e., B and A-N units, respectively) without the SmCP phase.

Full text of DOI:10.1021/ma901960c

Macromolecules 2010, 43, 1277–1288 1277
DOI: 10.1021/ma901960c
Novel Supramolecular Side-Chain Banana-Shaped Liquid Crystalline
Polymers Containing Covalent- and Hydrogen-Bonded Bent Cores
Ling-Yung Wang, Hsin-Yi Tsai, and Hong-Cheu Lin*
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, ROC
Received September 2, 2009; Revised Manuscript Received December 15, 2009
ABSTRACT: Novel supramolecular side-chain banana-shaped liquid crystalline (LC) polymer complexes
AmBn-N bearing various (m/n) molar ratios of hydrogen- and covalent-bonded bent-core components were
acquired by the free radical polymerization, where the hydrogen-bonded (H-bonded) structures were
executed via mixing equimolar portions of proton donor (H-donor) polymers AmBn (homopolymers/
copolymers) and pyridyl proton acceptor (H-acceptor) bent cores (small molecules). The influences of the
molar ratios of bent-core H-bonded components in side-chain banana-shaped LC polymers and their
corresponding polymer complexes on mesomorphic and electro-optical properties were first investigated.
The voltage-dependent antiferroelectric properties of spontaneous polarization (Ps) values in the polar
smectic phase of the supramolecular side-chain banana-shaped copolymers were also reported. The nematic
and tilted smectic phases were verified by XRD measurements, and the SmCP phase was further confirmed by
the triangular wave method. Surprisingly, a novel enantiotropic polar smectic (SmCPA) phase was generated
in some bent-core side-chain polymer complexes AmBn-N. Therefore, a special approach to constructing (or
stabilizing) the SmCP phase was first developed in this study by copolymerization of bent-core covalent- and
H-bonded units in side-chain polymer complexes (with proper m/n molar ratios of 16/1 and 10/1) from both
bent-core covalent- and H-bonded monomers (i.e., B and A-N units, respectively) without the SmCP phase.
Introduction
also developed to investigate the influence of molecular config-
urations on mesomorphic and electro-optical properties. How-
Liquid crystalline (LC) materials bearing bent-shaped meso-
gens become interesting topics due to their special electro-optical
properties, such as spontaneous polarized capabilities and non-
linear optics.1-5 Since the first example of bent-core molecules,
which possessed achiral configurations but with chiral characteri-
stics, was published and revealed antiferroelectric effects, bent-
shaped LC derivatives with banana-shaped (or bent-core) meso-
gens were developed and conferred fascinating optical and
electrical properties.6 Consequently, their particular mesophases,
including columnar stacking, tilted smectic phases, and three-
dimensional structures, named B1 to B7 phases were explored
and identified. The most prevailingly investigated B2 phase
revealed ferroelectric (F)/antiferroelectric (A) properties, which
possessed identical/inverse polarizations, and synclinic (S)/anti-
clinic (A) arrangements with alike/opposite molecular tilted
aspects between layer to layer, respectively.6,7 Hence, depending
on the polar directions and molecular tilted directions in neigh-
boring layers, four kinds of different molecular architectures were
categorized to homochiral (SmCAPA and SmCSPF) and racemic
(SmCSPA and SmCAPF) conditions, respectively.
In general, banana-shaped LC configurations are appropriate
lengths of flexible terminal chains attached to mesogenic bent
cores containing a central core with a suitable bent angle linked
through polar functional groups. The structural variations of
achiral molecular designs, such as the central parts, lateral
substituents, linking groups, terminal chains, and the number
of rings, would affect their physical properties to different extents
in small molecular systems. Recently, polymolecular systems, i.e.,
dimeric,8-13 polymeric,14-18 and dendritic19,20 frameworks, were
ever, the most interesting issue of bent-core molecules is to retain
the lamellar organization with spontaneous polarization and
electric-optical switching properties which need to be further
realized due to their possible applications in fast responsive LCD
devices. Moreover, some novel supramolecular bent-core inter-
actions or their nanocomposite architectures have been inte-
grated into organic or inorganic parts to display special electro-
optical characteristics, for instance, bent-core derivatives em-
bedded with nanoparticles,21 H-bonded bent-core supra-
molecules,22-28 and bent-core structures with silyl and siloxyl
linkages.29-31
Concerning the fully covalent-bonded bent-core polymers,
since the example of the bent-core main-chain polymer with a
polar smectic mesophase was synthesized,15 the polar switching
behavior has been declared to exist in the polymeric framework.
Up to now, even if the first case of the bent-core side-chain
polymer, where the bent-core units were connected by siloxyl
spacers, displayed clear ferroelectric switching properties,14 just
only scarce cases of bent-core side-chain polymers were achieved
with barely detectable polar switching properties.17 With regard
to H-bonded bent-core structures, different molecular designs in
terms of small molecules24,25,27,28 and polymers (side-chain poly-
mers)26 have been developed and reported, but very few H-
bonded bent-core structures with ferroelectric or antiferroelectric
properties have been measured and analyzed.25,27 Therefore,
more detailed researches of H-bonded bent-core molecules (as
well as polymers) with special ferroelectric or antiferroelectric
properties may be beneficial for the electro-optical applications of
supramolecular materials.
In our previous studies, the singly H-bonded five-ring banana-
shaped supramolecule (complex H12)32a showed lower meso-
phasic transition temperatures and enthalpies than those of the
*Author for correspondence: Tel 8863-5712121 ext 55305; Fax 8863-
5724727; e-mail linhc@cc.nctu.edu.tw.
r 2010 American Chemical Society
Published on Web 01/05/2010
pubs.acs.org/Macromolecules

1278 Macromolecules, Vol. 43, No. 3, 2010
Wang et al.
covalent-bonded monomer) as well as H-acceptor N are demon-
strated in Scheme 1. The synthetic details of all compounds in
Scheme 1 are shown in the following descriptions.
12-Bromododecanol (1). Doecan-1,12-diol (20.2 g, 100 mmol)
and HBr (8.1 g, 100 mmol) were dissolved in toluene solvent to
react at 60 °C for 24 h, and side product H2O could be removed
by Dean Stark installation. After then, the reacted solution was
extracted by ethyl acetate (EA) and water, and the organic liquid
layer was purified by column chromatography to give a liquid
1
product (14.9 g, 56 mmol). Yield: 56%. H NMR (300 MHz,
CDCl3) δ (ppm): 3.57 (t, J=6.6 Hz, 2H, -OCH2-), 3.39 (t, J=
6.9 Hz, 2H, Br-CH2-), 3.19 (s, 1H, -OH), 2.04-1.80 (m, 2H,
Br-CH2CH2-), 1.56-1.49 (m, 2H, HO-CH2CH2-),
1.44-1.21 (m, 16H, -CH2-).
Figure 1. Chemical structures and formation procedures of bent-core
side-chain polymer complexes (AmBn-N) with covalent- and H-bonded
components (B and A-N units, respectively).
Compound (Cpd) 2. 12-Bromododecanol (1) (14.9 g, 56
mmol), methyl 4-hydroxybenzoate (7.76 g, 51 mmol), and
potassium carbonate (K2CO3) (10.6 g, 76.5 mmol) were dis-
solved in acetone solvent to react at reflux temperature for 20 h.
After that, water was added to dissolve the inorganic salt, and a
white precipitation was produced. Subsequently, the white
powder was washed by hexane to get a pure product (15.6 g,
46.4 mmol). Yield: 91%. 1H NMR (300 MHz, CDCl3) δ (ppm):
7.95 (d, J=9.0 Hz, 2H, Ar-H), 6.87 (d, J=9.0 Hz, 2H, Ar-H),
3.97 (t, J=6.3 Hz, 2H, -OCH2-), 3.85 (s, 3H, -OCH3), 3.61
(m, 2H, -CH2OH), 1.79 (s, 1H, -OH), 1.26 (m, 20H, -CH2-).
Compound (Cpd) 3. Cpd 2 (15.6 g, 46.4 mmol) and potassium
hydroxide (KOH) (10.4 g, 185.6 mmol) were dissolved in
ethanol solvent to reflux and react for 16 h. After cooling reacted
liquid to room temperature, HCl (10 vol % in water) solution
was added to react 30 min. The precipitation was filtered, and
a white powder was formed. The powder was recrystallized
by ethanol and hexane (1:3 vol) to collect a pure white product
(14.2 g, 44.1 mmol). Yield: 95%. 1H NMR (300 MHz, CDCl3) δ
(ppm): 7.92 (d, J=8.7 Hz, 2H, Ar-H), 6.92 (d, J=8.7 Hz, 2H,
Ar-H), 4.00 (t, J=6.6 Hz, 2H, -OCH2-), 3.45 (t, J=6.3 Hz,
2H, -CH2OH), 2.06 (s, 1H, -OH), 1.78 (m, 2H,
-CH2CH2OH), 1.29 (m, 18H, -CH2-).
fully covalent-bonded five-ring banana-shaped analogue
(compound S12)32b as shown in Figure S1 of the Supporting
Information, which suggested that the H-bonded framework
exhibited a softer mesogenic arrangement than the covalent-
bonded architecture. On the other hand, the H-bonded rodlike
(or banana-shaped) molecules may be stabilized by the fully
covalent-bonded counterparts (or as dopants) to have more steady
electro-optical properties. Considering both merits of covalent-
and H-bonded molecular designs, there might be some intermedi-
ate or even premium properties can be achieved by blending
or copolymerizing two types of covalent- and H-bonded ana-
logues.33,26b Therefore, H-bonded bent-core units would behave as
softer skeletons to tune the suitable molecular arrangements in
harmony with the fully bent-core covalent-bonded units in poly-
meric side-chain structures. Hence, our molecular designs of
incorporating bent-core covalent-bonded and H-bonded moieties
in various molar ratios were proceeded in this study of bent-core
side-chain polymers (see Figure 1) to modulate the molecular
organization and optimize the polar switching behavior.
H-Donor Monomer (A). The addition of terminal acryl group
on cpd 2 was proceeded by the reaction of acryloyloxy chloride
(6.0 g, 66.2 mmol) and cpd 2 (14.2 g, 44.1 mmol) in 1,4-dioxane
solvent with an organic base of dimethylaniline (DMA) (5.88 g,
48.5 mmol) under nitrogen to react at room temperature for
24 h. When the reaction was finished, a dilute HCl solution (10
vol % in water) was added to the reacted solution to form a
white powder. The product was purified by column chromato-
graphy to give a white product (9.13 g, 24.3 mmol). Yield:
55%. 1H NMR (300 MHz, CDCl3) δ (ppm): 8.03 (d, J=9.0 Hz,
2H, Ar-H), 6.91 (d, J=9.0 Hz, 2H, Ar-H), 6.41 (d, J=18 Hz,
1H, -CHdCH2), 6.35 (m, 1H, =CH-), 6.07 (d, J=9.0 Hz, 1H,
-CHdCH2), 4.13 (t, J=6.6 Hz, 2H, Ar-OCH2-), 4.00 (t, J=6.3
Hz, 2H, CdC-OCH2-), 1.79 (m, 2H, Ar-OCHH2CH2-), 1.63
(m, 2H, CdC-OCHH2CH2-), 1.26 (m, 16H, -CH2-). MS (EI):
m/z [Mþ] 377; calcd m/z [Mþ] 376.5. EA: Calcd for C22H32O5:
C, 70.18; H, 8,57. Found: C, 70.33; H, 8.52.
Compound (Cpd) 4. Cpd 3 (4.27 g, 10 mmol), resorcinol (1.1 g,
10 mmol), N,N-dicyclohexylcarbodiimide (DCC) (2.27 g, 11
mmol), and a catalytic amount of 4-(N,N-dimethylamino)-
pyridine (DMAP) (50 mg) were dissolved in dry dichloro-
methane (DCM) under nitrogen to react at room temperature
for 15 h, where the starting reactant 3 was a well-known
structure and was synthesized by following the literature pro-
cedure.34 The precipitated dicyclohexylurea (DCU) was filtered
off and washed with an excess of DCM (20 mL). The filtrate was
extracted with water and DCM, and the organic liquid layer was
dried over anhydrous magnesium sulfate. After removal of the
solvent by evaporation under reduced pressure, the residue was
recrystallized from ethanol to give a white solid (2.28 g, 4.4
mmol). Yield: 44%. 1H NMR (300 MHz, CDCl3) δ (ppm): 8.25
(d, J=8.7 Hz, 2H, Ar-H), 8.14 (d, J=9.0 Hz, 2H, Ar-H), 7.40
(d, J=8.7 Hz, 2H, Ar-H), 7.22 (t, J=8.1 Hz, 1H, Ar-H), 7.03
Experimental Section
1
Characterization Methods. H NMR spectra were recorded
on a Varian Unity 300 MHz spectrometer using d6-dioxane and
CDCl3 as solvents, and mass measurements were determined on
a Micromass TRIO-2000 GC-MS. Elemental analyses (EA)
were performed on a Heraeus CHN-OS RAPID elemental
analyzer. Gel permeation chromatography (GPC) analyses were
conducted on a Waters 1515 separation module using polysty-
rene as a standard and THF as an eluant. Mesophasic textures
were characterized by polarizing optical microscopy (POM)
using a Leica DMLP equipped with a hot stage. Infrared (IR)
spectra were investigated by a Perkin-Elmer Spectrum 100
instrument. Temperatures and enthalpies of phase transitions
were determined by differential scanning calorimetry (DSC,
model: Perkin-Elmer Pyris 7) under N2 at a heating and cooling
rate of 10 °C min-1. Synchrotron powder X-ray diffraction
(XRD) measurements were performed at beamline BL17A of
the National Synchrotron Radiation Research Center
(NSRRC), Taiwan, where the wavelength of X-ray was
˚
1.333 66 A. The powder samples were packed into capillary
tubes and heated by a heat gun, whose temperature controller
was programmable by a PC with a PID feedback system. The
scattering angle theta was calibrated by a mixture of silver
behenate and silicon. The electro-optical properties were deter-
mined in commercially available ITO cells (from Mesostate
Corp., thickness=4.25 μm, active area=1 cm2) with rubbed
polyimide alignment coatings (parallel rubbing direction). A
digital oscilloscope (Tektronix TDS-3012B) was used in these
measurements.
Synthesis. Synthesis of Monomers. All synthetic proce-
dures of monomers A (H-donor monomer) and B (bent-core

Article
Macromolecules, Vol. 43, No. 3, 2010 1279
Scheme 1. Synthetic Routes of Monomers A and B along with Pyridyl H-Acceptor Na
a Conditions and reagents: (i) HBr, toluene, (ii): methyl 4-hydroxybenzoate, K2CO3, acetone; (iii) KOH, ethanol; (iv) acryloyloxy chloride, DMA,
1,4-dioxane; (v) DCC, DMAP, DCM; (vi) isonicotinoyl chloride hydrochloride, triethylamine, DCM; (vii) benzyl bromide, K2CO3, acetone; (viii) Pd/C,
H2, THF.
(d, J=9.0 Hz, 2H, Ar-H), 6.71-6.66 (m, 3H, Ar-H), 4.06 (t,
J=6.6 Hz, 2H, OCH2), 1.80 (m, 2H, OCH2CH2), 1.47-1.28 (m,
18H, CH2), 0.88 (t, J=6.3 Hz, 3H, CH3).
pressure, water was added and a precipitate was produced
immediately. The crude product was recrystallized by acetone
and hexane (1:4 vol) to give a white solid (4.7 g, 19.4 mmol).
Yield: 97%. 1H NMR (300 MHz, CDCl3): δ 7.03 (d, J=9.0 Hz,
2H, Ar-H), 6.63-6.50 (m, 5H, Ar-H), 6.35 (d, J = 9.0 Hz,
Ar-H), 4.38 (s, 2H, OCH2), 2.49 (s, 3H, OCH3).
Compound (Cpd) 8. Cpd 7 (4.7 g, 19.4 mmol) and KOH (4.35
g, 77.6 mmol) were dissolved in ethanol and reacted at reflux
temperature for 10 h. HCl solution (10 vol % in water) was
added to produce a precipitate, and the crude product was
recrystallized by THF and hexane (1:10 vol) to give a
white solid (4.34 g, 19.0 mmol). Yield: 98%. 1H NMR
(300 MHz, DMSO) δ 7.87 (d, J = 9.0 Hz, 2H, Ar-H),
7.46-7.33 (m, 5H, Ar-H), 7.07 (d, J = 9.0 Hz, 2H, Ar-H),
5.17 (s, 2H, OCH2).
Compound (Cpd) 9. Cpd 8 (4.34 g, 19.0 mmol) and cpd 4
(9.85 g, 19.0 mmol) were dissolved in dry DCM solvent and reacted
with a catalytic amount of DMAP (0.46 g, 3.8 mmol) and DCC
(4.31 g, 20.9 mmol) under nitrogen for 24 h. The organic solution
was extracted by DCM and water (1:1 vol) and recrystallized by
DCM and ethanol (1:10 vol) to yield a white solid (7.89 g, 10.8
mmol). Yield: 57%. 1H NMR (300 MHz, d-dioxane) δ (ppm): 8.26
(d, J = 9.0 Hz, 2H, Ar-H), 8.13 (d, J = 9.0 Hz, 2H, Ar-H),
7.44-7.29 (m, 10H, Ar-H), 6.97 (d, J = 9.0 Hz, 2H, Ar-H),
6.91-6.81 (m, 7H, Ar-H), 5.06(s, 1H, -Ar-O-CH2-Ar),
4.04(t, J = 6.6 Hz, 2H, OCH2), 1.81(t, J = 6.3 Hz, 2H,
Pyridyl H-Acceptor (N). A mixture of cpd 4 (2.28 g, 4.4
mmol), isonicotinoyl chloride hydrochloride (0.86 g, 4.84
mmol), and triethylamine (0.53 g, 5.3 mmol) were dissolved in
dry DCM under nitrogen to react at room temperature for 8 h.
After workup, the solvent was extracted with water and DCM,
and organic liquid layer was dried over anhydrous magnesium
sulfate. After removal of the solvent by evaporation under
reduced pressure, the residue was purified by column chromato-
graphy and recrystallized by DCM and hexane (1:4 vol) to give a
white solid (2.62 g, 4.2 mmol). Yield: 95%. 1H NMR (300 MHz,
CDCl3): δ 8.89 (d, J=4.2 Hz, 2H, Ar-H), 8.22 (d, J=8.7 Hz,
2H, Ar-H), 8.08 (d, J=8.7 Hz, 2H, Ar-H), 8.01 (d, J=4.2
Hz, 2H, Ar-H), 7.59 (t, J=8.1 Hz, 1H, Ar-H), 7.51 (d, J=9.0
Hz, 2H, Ar-H), 7.41 (s, 1H, Ar-H), 7.32 (br, 2H, Ar-H), 7.10
(d, J=9.0 Hz, 2H, Ar-H); 4.07 (t, J=6.3 Hz, 2H, OCH2), 1.74
(br, 2H, OCH2CH2), 1.23 (br, 18H, CH2), 0.84 (t, J=6.3 Hz, 3H,
CH3). MS (EI): m/z [Mþ] 624; calcd m/z [Mþ] 623.7. EA: Calcd
for C38H41NO7: N, 2.25 C, 73.17; H, 6.63. Found: N, 2.44 C,
73.25; H, 6.75.
Compound (Cpd) 7. Methyl 4-hydroxybenzoate (cpd 6) (3.0 g,
20 mmol), benzyl bromide (3.76 g, 22 mmol), and K2CO3 (4.15 g,
30 mmol) were dissolved in acetone solvent and reacted at reflux
temperature for 10 h. After removing acetone at reduced

1280 Macromolecules, Vol. 43, No. 3, 2010
Wang et al.
OCH2CH2), 1.46-1.25(m, 18H, -CH2-), 0.86 (t, J=6.3 Hz, 3H,
CH3).
Scheme 2. Synthetic Approaches of Side-Chain Polymers AmBn
(Homopolymers/Copolymers) and Their Corresponding Bent-Core
Side-Chain Polymer Complexes AmBn-N
Compound (Cpd) 10. Cpd 9 (7.89 g, 10.8 mmol) and Pd/C
catalyst (0.5 g) were mixed in THF solvent under hydrogen to
react at room temperature for 20 h. The catalyst was removed by
filtration through Celite and washed with THF. The solvent was
removed by evaporation under reduced pressure, and the crude
product was recrystallized by THF and hexane (1:10 vol) to
produce a white solid (5.52 g, 8.64 mmol). Yield: 80%. 1H NMR
(300 MHz, d-dioxane): δ (ppm): 8.28 (d, J=9.0 Hz, 2H, Ar-H),
8.13 (d, J=9.0 Hz, 2H, Ar-H), 8.05 (d, J=8.7 Hz, 2H, Ar-H),
7.47 (t, J=8.1 Hz, 1H, Ar-H), 7.41 (d, J=8.7 Hz, 2H, Ar-H),
7.22 (s, 1H, Ar-H), 7.19-7.14 (m, 4H, Ar-H), 7.03 (d, J=9.0
Hz, 2H, Ar-H), 6.86 (d, J=8.7 Hz, 2H, Ar-H), 4.05 (t, J=6.3
Hz, 2H, -OCH2-), 1.80(m, 2H, -OCHH2CH2-), 1.28 (m,
18H, -CH2-), 0.88 (t, J=6.3 Hz, 3H, -CH3).
Bent-Core Covalent-Bonded Monomer (B). Cpd A (3.58 g, 9.50
mmol), cpd 10 (5.52 g, 8.64 mmol), DCC (1.96 g, 9.5 mmol), and
DMAP (0.21 g, 1.73 mmol) were dissolved in THF solvent under
nitrogen to react at room temperature for 24 h. The solution was
extracted by DCM and water and purified by column chromato-
graphy to acquire a white solid (5.17 g, 5.18 mmol). Yield: 60%. 1H
NMR (300 MHz, d-dioxane) δ (ppm): 8.25 (d, J=9.0 Hz, 2H,
Ar-H), 8.10 (d, J=8.7 Hz, 2H, Ar-H), 7.48 (d, J=8.1 Hz, 1H,
Ar-H), 7.38 (d, J=9.0 Hz, 2H, Ar-H), 7.25(s, 1H, Ar-H), 7.17
(d, J=8.1 Hz, 1H, Ar-H), 7.01 (d, J=8.7 Hz, 2H, Ar-H), 6.29 (d,
J=17.1 Hz, 1H, -CHdCH2), 6.08 (m, 1H, -CH=), 5.77 (d, J=
10.2 Hz, 1H, -CHdCH2), 4.08-4.00 (m, 6H, -OCH2-),
1.78-1.71 (m, 4H, -OCH2CH2-), 1.59-1.56 (m, 2H,
-OCHH2CH2-), 1.43-1.26 (m, 34H, -CH2-), 0.84 (t, J=6.3
Hz, 3H, -CH3). MS(EI):m/z[Mþ] 998; calcd m/z[Mþ] 997.2. EA:
Calcd for C61H72O12: C, 73.47; H, 7.28. Found: C, 73.82;
H, 6.95.
Polymerization. As shown in Scheme 2, the polymerizations
of side-chain polymers AmBn with various molar ratios were
carried out by free radical reactions in dry THF via different
input molar ratios (see Table 1) of monomers A and B with 2,20-
azobis(isobutyronitrile) (AIBN) as an initiator. All reactions
were performed under N2 at reflux temperature for 24 h. The
produced organic liquids were dropped into fast stirring diethyl
ether (EA) solvent to precipitate products and purified again by
THF and EA (1:10 vol) to obtain white solids. Yield: 59-73%.
For example, cpd A (1.0 g, 2.65 mmol) and cpd B (2.65 g, 2.65
mmol) were dissolved in dry THF solvent and reacted with an
AIBN initiator (44.3 mg, 0.27 mmol) under nitrogen for 24 h.
The produced organic liquids were recrystallized by THF and
EA (1:10 vol) to yield a white solid (2.37 g). According to similar
manufactured procedures, a series of side-chain polymers AmBn
(m/n=1/0, 16/1, 10/1, 4/1, 1/2, 1/4, 1/13, 0/1) were prepared by
various input molar ratios of monomers A and B. Furthermore,
the extents of polymerization and output molar ratios (m/n) of
polymer products were determined by 1H NMR spectra.
Preparation of Polymer Complexes. All bent-core side-chain
polymer complexes AmBn-N were constructed by mixing appro-
priate molar ratios of H-donor polymers (AmBn, excluding
A0B1) and pyridyl H-acceptor (N) in the solutions of chloro-
form/THF (ca. 1:1 vol), which were self-assembled into supra-
molecules by evaporating solvents slowly. For example,
homopolymer A1B0 (20 mg) and pyridyl H-acceptor (N) (33.1
mg) were dissolved in a mixed solvent of chloroform/THF (ca.
1:1 vol) and self-assembled into supramolecules by evaporating
solvents slowly. When the solvent were evaporated completely, a
white polymer complex of A1B0-N was formed. In the same
vein, the other polymer complexes A16B1-N, A10B1-N, A4B1-
N, A1B2-N, A1B5-N, and A1B13-N were also provided.
Table 1. Chemical Compositions and Molecular Weights of Side-
Chain Polymers
input molar
ratio A:B
output molar
ratio A:B (m:n)
polymer
Mn (ꢀ103)
PDI
A1B0
A16B1
A10B1
A4B1
A1B2
A1B5
A1B13
A0B1
1:0
15:1
10:1
5:1
1:1
1:5
1:0
16:1
10:1
4:1
1:2
1:5
5.1
5.8
7.2
7.1
10.5
9.1
12.7
12.1
1.13
1.29
1.25
1.26
1.20
1.21
1.17
1.16
1:10
0:1
1:13
0:1
designed and synthesized. The bent-core covalent-bonded five-
ring monomer was connected by polar ester groups, and its
H-bonded analogue was established as a five-ring supramolecule
by blending two complementary components of an acidic proton
donor (H-donor with a terminal acrylate) and bent-core pro-
ton acceptor (H-acceptor with a terminal pyridine). Then, the
H-donor monomer (A) and bent-core covalent-bonded monomer
(B) with different molar ratios were copolymerized to obtain
H-donor side-chain copolymers/homopolymers AmBn (where m
and n are repeating units of A = H-donor structure and B =
covalent-bonded bent-core structure, respectively), and then they
were blended with pyridyl H-acceptor N to form H-bonded bent-
core polymer complexes AmBn-N. Therefore, H-donor side-
chain copolymers/homopolymers AmBn with various molar
ratios of A and B units were synthesized, where m/n molar ratios
are 1/0, 16/1, 10/1, 4/1, 1/2, 1/5, 1/13, and 0/1 as shown in Figure 1
and Table 1. In addition, the bent-core side-chain LC copolymers
bearing both bent-core covalent- and H-bonded components
were developed in this study via their corresponding H-bonded
polymer complexes AmBn-N, which consisted of H-donor side-
chain copolymers/homopolymers (AmBn) and pyridyl H-accep-
tor (N). The variations of mesomorphic and electro-optical
Results and Discussion
According to our previous conception, H-donor and bent-core
covalent-bonded monomers with acrylate terminal groups were

Article
Macromolecules, Vol. 43, No. 3, 2010 1281
Figure 2. NMR spectra of monomers A and B.
Figure 3. NMR patterns of side-chain polymers A1B2 (copolymers), A1B0 (homopolymers), and A0B1 (homopolymers).
properties influenced by the molar ratios of bent-core covalent-
and H-bonded structures in bent-core side-chain polymer and
H-bonded polymer complexes were mainly investigated, and
their mesomorphic and electro-optical properties were exami-
ned and characterized by polarizing optical microscopy
(POM), differential scanning calorimetry (DSC), powder X-ray
diffraction (XRD), and electro-optical (EO) switching current
experiments.
copolymers, all side-chain polymers AmBn and monomers A
and B were investigated by 1H NMR measurements. As
shown in Figure 2, both monomers A and B possessed the
resonant peaks in the chemical shift range of 5.7-6.4 ppm
belonging to the signal of acryl groups, which disappeared in
the corresponding homopolymers A1B0 and A0B1 (see
Figure 3). Meanwhile, the resonant peaks in the range of
6.6-8.5 ppm (attributed to the aromatic rings) are contri-
buted from the benzoic acid groups of structure A (peaks a
and b) and the five phenyl rings of structure B (peaks c, d, e, f,
Synthesis and Characterization of Polymers. In order to
identify the polymers (or copolymers) and the molar ratio of

1282 Macromolecules, Vol. 43, No. 3, 2010
Wang et al.
Table 2. Phase Transition Temperatures and Enthalpies of Side-
Chain Polymersa
phase transition temperature/°C [enthalpy/kJ/g]
heating (top)/cooling (bottom)
polymer
A1B0
K 71.2 [1.3] K0 96.3 [1.7] SmC1 162.2 [22.4] I
I 155.1 [-27.5] SmC1 76.2 [-4.5] K
K 141.2 [1.3] SmC1 159.7 [10.4] I
I 153.6 [-12.9] SmC1 140.9 [-1.8] K
K 140.2 [6.4] SmC1 154.3 [1.7] I
I 153.3 [-7.6]b SmC1 138.7bK
K 112.3 [0.6] N 129.8 [4.5] I
I 129.7 [-3.6] N 105.3 [-1.0] K
K 71.3 [3.5] SmC2 96.0 [5.7] I
I 90.1 [-2.8] SmC2 74.3 [-0.7] K0 59.2 [-1.4] K
K 75.9 [6.9] SmC2 98.8 [2.5] I
A16B1
A10B1
A4B1
A1B2
A1B5
A1B13
A0B1
I 88.7 [-4.69] SmC2 74.8 [-4.5] K
K 120.4 [18.5] SmC2 140cI
I 135c SmC2 115.4 [-15.3] K
K 136.3 [23.5] SmC2 150cI
I 148c SmC2 130 [-19.4] K
Figure 4. IR spectra of polymer A10B1, pyridyl H-acceptor N, and
polymer complex A10B1-N.
a The phase transitions were measured by DSC at the second cooling
scan with a cooling rate of 5 °C min-1. I = isoptropic state; N = nematic
phase; SmC1 and SmC2 = tilted smectic phases; K = crystalline state.
b Means the enthalpy values of two cover transition peaks. c Means the
temperature data is observed in POM only. Phase transitions of mono-
mer A was obtained as I 106.4 [20.6] SmC 55.4 [8.59] K. Phase transition
of monomer B was obtained as I 90.3 [34.8] K.
g, h, and i). To recognize the molar (m/n) ratios of copoly-
mers, the integral values of 1H NMR peaks from structures A
and B in each copolymers were calculated the integral values
of NMR peaks a-b (from structure A) along with paeks c-d
and i (from structure B). Based on this calculating way,
copolymers A16B1, A10B1, A4B1, A1B2, A1B5, and A1B13
and homopolymers A1B0 and A0B1 were characterized. In
addition, the number-average molecular weights (Mn) and
polydispersity index (PDI) values of all polymers were
acquired by GPC experiments as shown in Table 1, where
the PDI values were in the range of 1.13-1.29 and Mn values
were in the range of (5.1-12.7) ꢀ 103. The Mn values were
increased at higher values of n (part B ratio) due to the higher
molecular weight of part B.
instance, the schlieren texture and grainy domain of
polymers A1B0 and A10B1 are demonstrated in parts a
and b of Figure 5, respectively. However, polymer A4B1
revealed a nematic phase in both heating and cooling
processes, and the POM texture of polymer A4B1 is shown
in Figure 5c. Regarding the mesophases of polymers
A1B2, A1B5, A1B13, and A0B1 with lower m/n molar ratios
(higher densities of covalent-bonded bent-core units), the
same enantiotropic smectic phase (SmC) was obtained,
where one of the POM texture of A1B13 is shown in
Figure 5d.
IR Characterization. The existence and stability of H-
bonds in polymer complexes were characterized by IR
spectra, and the IR spectra of H-donor polymer A10B1
(with acidic groups) and pyridyl H-acceptor (N) were com-
pared with that of complex copolymer A10B1-N to examine
the existence of H-bonds as shown in Figure 4. In contrast to
the O-H bands of pure A10B1 at 2666 and 2568 cm-1, the
weaker O-H band observed at 2514 and 1952 cm-1 in
complex A10B1-N was indicative of hydrogen bonding
between the pyridyl group of N and acidic group of A. On
the other hand, a CdO stretching vibrations appeared at
1728 cm-1 (shoulder) and 1687 cm-1 in complex A10B1-N,
which showed that the carbonyl group is in a less associated
state than in pure A10B1 with weaker CdO stretching
Comparing the phase transition temperatures of all side-
chain polymers AmBn, homopolymers A1B0 and A0B1
revealed the highest isotropization temperatures for poly-
mers AmBn with higher and lower m/n molar ratios (lower
and higher densities of covalent-bonded bent-core units),
respectively. Higher isotropization temperatures of homo-
polymers A1B0 and A0B1 indicated that the tighter mole-
cular stacking of intermolecular H-bonded linear cores or
bent cores in homopolymeric systems, which also suggested
that the looser molecular stackings were formed in copoly-
mers due to the disorder arrangements of both H-bonded
linear cores and covalent-bonded bent cores. Especially,
copolymer A4B1 reached the largest randomness to lose
the lamellar packings for both H-bonded linear cores and
covalent-bonded bent cores, and the nematic phase was
preferred instead. Hence, three cartoon diagrams are drawn
in Figure 6 to explain possible intermolecular arrangements
in polymers AmBn. Based on the molar ratios of bent-core
units, polymers A1B0, A16B1, and A10B1 with the high
density of benzoic acidic groups displayed the smectic stack-
ing by the intermolecular acidic H-bonds (with H-bonded
cross-linking structures) as shown in Figure 6a, and
the stacking order was reduced by decreasing m/n molar
ratio. As m/n ratio reached 4/1 (polymer A4B1), the acidic
H-bonded linear cores (H-bonded cross-links) would be
separated into a more random stacking by the introduction
of covalent-bonded bent-core unit B as shown in Figure 6b.
Afterward, to the other extreme of more covalent-bonded
bent-core units (B), polymers A1B2, A1B5, A1B13, and
A0B1 demonstrated another smectic arrangement due to
vibrations appeared at 1687 and 1671 cm .
-1 25,35 The results
suggested that H-bonds of polymer complex A10B1-N are
formed between copolymer A10B1 and H-acceptor N. In
addition, the other polymer complexes were also confirmed
to exhibit H-bonded frameworks as polymer complex
A10B1-N, so the supramolecular structures were established
in all polymer complexes.
Mesophasic and Thermal Properties. (1) Side-Chain Poly-
mers AmBn. In order to understand the influence of the
molar ratio of covalent-bonded bent-core units on the
mesomorphic, molecular stacking, and thermal properties,
side-chain polymers AmBn were investigated by POM, DSC,
and XRD measurements. The thermal properties and phase
behaviors of side-chain polymers AmBn are illustrated in
Figure 7a and Table 2. Polymers A1B0, A16B1, and
A10B1 with higher m/n molar ratios (lower densities of
covalent-bonded bent-core units) possessed the tilted smectic
(SmC) phases, which were verified by POM to show the
enantiotropic schlieren texture and grainy domain. For

Article
Macromolecules, Vol. 43, No. 3, 2010 1283
Figure 5. POM textures at the cooling process: (a) the tilted smectic phase with schlieren texture of polymer A1B0 at 150 °C; (b) the tilted smectic phase
with grainy domain of polymer A10B1 at 150 °C; (c) the nematic phase with schlieren texture of polymer A4B1 at 125 °C; (d) the tilted smectic phase
with grainy domain of polymer A1B13 at 130 °C.
Figure 6. Cartoon diagrams of possible intermolecular arrangements
of (a) polymers A1B0, A16B1, and A10B1 with larger m/n molar ratios
mainly contributed from the self H-bonded acidic dimers, (b) polymer
A4B1 with a medium m/n molar ratio, and (c) polymers A1B2, A1B5,
A1B13, and A0B1 with smaller m/n molar ratios mainly contributed
from the major component of covalent-bonded bent cores.
the major intermolecular stackings of bent-core units (see
Figure 6c).
(2) Bent-Core Side-Chain Polymer Complexes AmBn-N.
The influence of molar ratios of bent-core covalent- and
H-bonded units on the mesomorphic, molecular stacking,
and thermal properties of bent-core side-chain polymer
Figure 7. Phase diagrams (upon second cooling) of (a) side-chain
complexes AmBn-N were also investigated by POM, DSC,
and XRD measurements. The thermal properties and phase
behaviors of bent-core side-chain polymer complexes AmBn-
N are illustrated in Figure 7b and Table 3. According to
Figure S1 of the Supporting Information, compound S12
polymers AmBn and (b) bent-core side-chain polymer complex
AmBn-N.
and supramolecular analogue H12 (H-bonded complex)
both exhibited the SmCP phase, so bent-core side-chain

1284 Macromolecules, Vol. 43, No. 3, 2010
Wang et al.
Table 3. Phase Transition Temperatures and Enthalpies of Bent-Core
Side-Chain Polymer Complexesa
phase transition temperature/°C
[enthalpy/kJ/g] heating (top)/cooling (bottom)
polymer complex
A1B0-N
K 125.6 [43.3] SmC1 158.0 [2.5] I
I 138.7 [1.9] SmC1 97.3 [36.8] K
A16B1-N
A10B1-N
A4B1-N
A1B2-N
A1B5-N
A1B13-N
K 80.0 [2.7] K0 112.7 [13.3] SmCP 145.5 [15.0] I
I 140.1 [-12.2] SmCP 85.6 [-1.8] K0 59.4 [-9.0] K
K 85.4 [2.8] K0 116.1 [18.7] SmCP 143.0 [3.2] I
I 135.8 [-17.0] SmCP 87.7 [-2.3] K0 66.7 [-10.6] K
K 78.5 [5.4] SmC1 117.3 [11.4] I
I 112.1 [-8.4] SmC1 66.8 [-2.7] K
K 77.4 [6.0] SmC1 110.8 [14.3] I
I 107.6 [-7.0] SmC1 75.5 [-14.7] K
K 79.9 [9.9] SmC2 95.7 [17.1] I
I 90.0 [-19.7] SmC2 60.1 [-9.0] K
K 75.9 [1.6] SmC2 115.2 [12.9] I
I 108.9 [-13.9] SmC2 61.7 [-1.2] K
a The phase transitions were measured by DSC at the second cooling
scan with a cooling rate of 5 °C min-1. I = isoptropic state; SmCP =
polar smectic phase; SmC1 and SmC2 = tilted smectic phases; K =
crystalline state. Phase transitions of complex A-N was obtained as I 76.7
[36.4] K.
polymer complexes AmBn-N via the copolymerization of
these two units (S12 and H12) were prepared and surveyed
for the generation of the SmCP phase. However, because of
the addition of acrylate termini in their similar structures, B
and A-N units did not possess any SmCP phase, where the
phase transition temperatures of monomers A and B along
with complex A-N were obtained as A: I 106.4 °C SmC
55.4 °C K, B: I 90.3 °C K, and A-N: I 76.7 °C K, respectively.
In comparison with side-chain polymers AmBn, bent-core
side-chain polymer complexes AmBn-N have lower iso-
tropization temperatures due to their H-bonded pendants
assembled by pyridyl and acidic groups, which have less
intermolecular acidic H-bonds (with less H-bonded cross-
links). Therefore, the novel enantiotropic polar smectic
(SmCP) phase was surprisingly generated in some composi-
tions of bent-core side-chain polymer complexes AmBn-N.
Regarding the mesophasic types, the enantiotropic tilted
smectic phase was observed in polymer complexes A1B0-
N, A4B1-N, A1B2-N, A1B5-N, and A1B13-N, and the
enantiotropic polar smectic (SmCP) phase was achieved
in polymer complexes A16B1-N and A10B1-N. The meso-
phasic textures were observed by POM experiments; for
instance, polymer complex A10B1-N revealed the polar
smectic phase with a fanlike texture in Figure 8a, and
polymer complex A1B13-N exhibited the tilted smectic
(SmC) phase with a grainy domain in Figure 8b, which were
the characteristics of the tilted smectic phases.
With regard to the variation of mesophasic transition
temperatures of polymer complexes AmBn-N, the isotropi-
zation temperatures and mesophasic ranges were reduced as
the m/n molar ratio decreased (except A1B13-N). Side-chain
copolymers AmBn with higher m/n ratios possessed more
H-donor groups exhibited more extensive mesophasic ranges
and higher isotropization temperatures, which indicated
that the acidic H-bonded linear-cores (H-bonded cross-
links) would extend and stabilize the mesophase. However,
because of the intermolecular acidic H-bonds (with
H-bonded cross-linking structures) of side-chain copolymers
AmBn being replaced with side-chain H-bonded pendants of
the analogous polymer complexes AmBn-N, bent-core side-
chain polymer complexes AmBn-N with higher m/n molar
ratios did not exhibit more extensive mesophasic ranges but
still possessed higher isotropization temperatures. Com-
pared with side-chain copolymers AmBn, the corresponding
polymer complexes AmBn-N generally exhibited more
Figure 8. POM textures at the cooling process: (a) the polar smectic
phase with fanlike texture of polymer complex A10B1-N at 130 °C; (b)
the tilted smectic phase with grainy domain of polymer complex A1B13-
N at 85 °C.
extensive mesophasic ranges and lower transition tempera-
tures, except polymer complexes A1B2-N and A1B5-N. In
addition, the nematic phase in copolymer A4B1 was replaced
by a tilted smectic phase in polymer complex A4B1-N. More
excitingly, the polar smectic phase (the switching current
behaviors will be demonstrated later) was achieved in poly-
mer complexes A16B1-N and A10B1-N, though the indi-
vidual components of H-donor side-chain copolymers
A16B1 and A10B1 as well as H-acceptor N did not possess
the SmCP phase (see Tables 2 and 3). Hence, it suggested that
the mesomorphic and thermal properties of polymer com-
plexes AmBn-N were strongly dependent on the m/n molar
ratios of bent-core covalent- and H-bonded units (i.e., B and
A-N units, respectively), where the bent-core H-bonded
units were formed by the acidic H-donor groups (A groups
from side-chain polymers AmBn) incorporated with H-acce-
ptor N. Therefore, we have discovered a special technique
that the construction (or stabilization) of the SmCP phase
can be acquired by copolymerization of bent-core covalent-
and H-bonded units in side-chain polymer complexes (with
proper m/n molar ratios) from both bent-core covalent- and
H-bonded monomers (i.e., B and A-N units, respectively)
without the SmCP phase (see Figure 9).
Powder XRD Analyses. (1) Side-Chain Polymers AmBn.
The molecular arrangements of side-chain polymers AmBn
in different mesophases were investigated by XRD measure-
ments at various temperatures upon cooling (see Figures 10
and 11). As shown in Figure 10a (also see Figures S3a of the
Supporting Information), the 2D XRD pattern of polymer
A16B1 at 150 °C during the cooling process revealed a diffuse
peak at wide angles corresponding to a d-spacing value of
˚
4.6 A, which demonstrated that similar liquidlike in-plane
orders with average intermolecular distances were pre-
valent inside the layers of bent-core units. Two single sharp
peaks were observed at corresponding d-spacing values of

Article
Macromolecules, Vol. 43, No. 3, 2010 1285
Table 4. Powder XRD Data of Side-Chain Polymers
˚
d-spacing (A)
polymer
cooling temp (°C)
2θ (deg)
A1B0
140
2.24
4.47
2.16
4.33
2.12
4.25
4.37 (br)
2.06
2.70
3.82
4.09
2.00
2.83
3.78
6.04
2.04
3.08
3.80
4.45
2.10
3.14
3.85
4.48
5.20
34.1
17.1
35.4
17.7
36.1
18.0
17.5
37.1
28.3
20.0
18.7
38.2
27.0
20.2
12.7
37.5
24.8
20.1
17.2
36.4
24.3
19.9
17.1
14.7
A16B1
A10B1
150
140
A4B1
A1B2
120
90
Figure 9. SmCP phase was introduced by copolymerized frameworks
bearing both bent-core covalent- and H-bonded monomers (B and A-N
units with proper m/n molar ratios) without the SmCP phase.
A1B5
A1B13
A0B1
90
120
140
lower than 130 °C, and the orthogonal arrangement of the
crystalline phase or highly ordered smectic phase was gene-
rated. Polymers A1B0 and A10B1 illustrated similar XRD
results as shown in the Supporting Information (see Figures
S2a and S4a) to indicate the analogous smectic mesophase.
Polymer A4B1 did not obtain any sharp diffraction peak
at small angle regions in the mesophasic temperature
(120 °C) to reveal one dimension order of nematic phase as
shown in Figure S5 of the Supporting Information, but two
broad peaks were observed at the corresponding d-spacing
˚
values of 17.1 and 4.6 A. Until the temperature reaching the
˚
crystalline state (100 °C), a d-spacing value of 66.5 A was
produced to indicate the orthogonal arrangement of the
crystalline phase or highly ordered smectic phase. The
powder XRD results of polymer A4B1 in various tempera-
tures was also provided in Figure S5a of the Supporting
Information to reveal its phase transition in the cooling
process from the isotropic to crystalline states.
As the shown pattern of polymer A1B13 at 120 °C (see
Figure S8a of the Supporting Information), several sharp
˚
peaks were detected at corresponding values of d1=37.5 A,
˚
˚
d2=25.4 A, and d3=19.1 A in small angle regions (along with
some other undefined sharp peaks). The ratio of d1 to d3 was
2:3:4 to index (002), (003), and (004), and a d-spacing value
˚
ca. 76 A was correspondent to the essential peak indexed as
(001), which might be lost due to the limitation of the XRD
instrument. A broad peak was gained at the wide angle
regions to account for the natural mesogenic stacking width.
This similar result was reported in the literature17 to mean
the long-range ordered smectic structure of SmC2. The XRD
investigations of polymer A1B13 at various temperatures
from the isotropic to crystalline states were performed in
Figure S7a of the Supporting Information, and polymers
A1B2, A1B5, and A0B1 exhibited similar XRD results with
those of A1B13 in the Supporting Information (see Figures
S6a, S8a, and S9).
In comparison the variation of d-spacing values in all
side-chain polymers AmBn as shown in Table 4 (also see
Figures S10a of the Supporting Information), the d-spacing
values of copolymers were larger than those of homopoly-
mers to indicate that more tilted smectic arrangements were
produced in both homopolymers A1B0 and A0B1, which
Figure 10. Powder X-ray data of polymer A16B1: (a) 2D pattern in the
tilted smectic phase (150 °C); (b) powder X-ray diffraction intensity
against angle profiles at various temperatures upon cooling from the
isotropic to crystalline phases.
˚
˚
d1 =35.4 A and d2 =17.7 A in small angle regions, where
the longest d-spacing value d1 was indexed as (001). The
d-spacing value (d1) is shorter than the theoretical coplanar
˚
molecular length (L) (about 47 A) of self H-bonded benzoic
acidic dimer to indicate the tilted smectic arrangement. In
addition, temperature-dependent XRD results of polymer
A16B1 were also provided in Figure 10b. Two sharp peaks
appeared during the cooling process from the isotropic to
mesophasic states. An additional peak with a corresponding
˚
d-spacing value (∼46 A) similar to its theoretical molecular
length was obtained as the temperature was equivalent to or

1286 Macromolecules, Vol. 43, No. 3, 2010
Wang et al.
Table 5. Powder XRD Data of Bent-Core Side-Chain Polymer
Complexes
˚
d-spacing (A)
polymer complex
cooling temp (°C)
2θ (deg)
A1B0-N
140
2.19
4.43
1.77
3.54
1.71
3.40
1.70
3.40
2.16
4.32
1.76
2.65
4.42
5.32
2.01
3.04
3.73
4.39
34.9
17.3
43.2
21.6
44.7
22.5
45.0
22.5
35.4
17.7
43.4
28.8
17.3
14.4
38.0
25.1
20.5
17.4
A16B1-N
A10B1-N
A4B1-N
A1B2-N
A1B5-N
130
120
100
100
70
A1B13-N
65
meant that less tilted smectic arrangement existed in co-
polymers with both H-bonded acidic dimers and covalent-
bonded bent cores. Hence, the variations of molecular
arrangements, including two kinds of tilted smectic orders
(i.e., SmC1 and SmC2), in side-chain polymers were further
identified by the XRD experiments.
(2) Bent-Core Side-Chain Polymer Complexes AmBn-N.
The molecular arrangements of bent-core side-chain poly-
mer complexes AmBn-N were also surveyed by XRD mea-
surements, and their related results are illustrated in Table 5.
Compared with side-chain copolymers AmBn, the corre-
sponding polymer complexes AmBn-N generally exhibited
larger d-spacing values (except polymer complex A1B2-N),
which might be due to the coexistence of bent-core covalent-
and H-bonded units in side-chain polymer complexes, and
thus to have less ordered smectogenic packings and to induce
lower phase transition temperatures. Similar to side-chain
copolymers AmBn, most polymer complexes AmBn-N in
Table 5 (also see Figures S10b of the Supporting In-
formation) generally demonstrated larger d-spacing values
than homopolymer complex A1B0-N (with bent-core
H-bonded units only), which might have better and homo-
geneous packing of bent-core H-bonded units in the tilted
smectic arrangement of the homopolymer complex. Simi-
larly, smaller d-spacing values were observed in A1B13 (d1=
Figure 11. Powder X-ray data of polymer complex A16B1-N: (a) 2D
pattern in the tiltedsmectic phase (130 °C);(b) powder X-ray diffraction
intensity against angle profiles at various temperatures upon cooling
from the isotropic to crystalline phases.
A4B1-N, and A1B2-N revealed similar X-ray diffraction
patterns (see Figures S4b, S5b, and S6b of the Supporting
Information) to indicate the analogous type of the tilted
smectic mesophase. Polymer complex A1B13-N manifested
the long-range ordered smectic organization in mesophasic
and crystalline temperatures due to the exhibition of several
sharp diffraction peaks (see Figure S7b of the Support-
ing Information). In addition, polymer complex A1B5-N
revealed X-ray diffraction patterns (see Figure S8b of the
Supporting Information) similar to that of A1B13-N, which
suggested the analogous type of the tilted smectic phase in
both polymer complexes.
˚
˚
˚
37.5 A), A1B13-N (d1 =38.0 A), and A0B1 (d1 =36.4 A),
which might be attributed to the major component of bent-
core covalent-bonded structure B, and the influence of
costacking effect contributed from bent-core H-bonded
structure A-N was much less.
Polymer complex A16B1-N displayed two sharp peaks at
˚
Switching Current Behaviors and Spontaneous Polarization
(Ps) of Bent-Core Side-Chain Polymer Complexes. In order
to evaluate the polar switching properties of the SmCP phase
in all side-chain polymers and bent-core side-chain polymer
complexes, the triangular wave method36 was applied to
measure the switching current behavior (i.e., the sponta-
neous polarization, Ps) in parallel rubbing cells with a cell
gap of 4.25 μm. The triangular voltages were applied on all
polymers and polymer complexes, and only bent-core side-
chain polymer complexes A10B1-N and A16B1-N possess
the switching current behaviors with specific Ps values. For
instance, as shown in Figure 12a, polymer complex A10B1-N
responded under a simple (continuous) triangular voltage to
give a single current peak per half-period in the switching
current response (Vpp =310 V and f=150 Hz, at T=100 °C).
However, as shown in Figure 12b, the current response was
separated into two repolarization peaks under the modified
˚
the associated d-spacing values of d1=43.2 A and d2=21.6 A
in small angle regions and a broad peak at the related d-
˚
spacing value d=4.5 A at 130 °C (upon cooling) as shown in
Figure 11a (also see Figures S3b of the Supporting
˚
Information). The largest d-spacing value (d1 = 43.2 A) is
less than the theoretical length of bent-core H-bonded
˚
structure A-N (about 58 A) to indicate the tilted smectic
arrangement of polymer complex A16B1-N. The XRD
results of A16B1-N at various temperatures upon cooling
from the isotropic to crystalline phases are demonstrated in
Figure 11b. Two sharp peaks of a characteristic smectic
mesophase appeared as the temperature reached 140 °C
during the cooling process. Afterward, an additional peak
developed when the temperature was lower than 80 °C,
˚
where the new d-spacing value of 35.1 A was correspond-
ent to the crystalline state. Polymer complexes A10B1-N,

Article
Macromolecules, Vol. 43, No. 3, 2010 1287
Figure 13. (a) Ps values of polymer complex A10B1-N as a function of
appliedvoltages(atf = 60Hz and T = 100 °C). (b) Psvalues ofpolymer
complex A10B1-N as a function of temperatures (at Vpp = 200 V and
f = 200 Hz).
Figure 12. Switching current responses of polymer complex A10B1-N
under (a) the triangular wave method (at Vpp = 310 V, f = 150 Hz,
and T = 100 °C) and (b) the modified triangular wave method
(at Vpp = 310 V, f = 30 Hz, and T = 100 °C).
triangular wave (i.e., a single pulsed triangular wave, Vpp
=
SmCP phase was mainly contributed from bent-core
H-bonded component A-N rather than from bent-core
covalent-bonded component B (due to a large molar ratio
of m/n in A10B1-N). Hence, the novel example of bent-core
side-chain polymer complex A10B1-N was evidenced to
possess the voltage-sensitive switching polar behavior,
which was provided by the major soft bent-core skeleton
(H-bonded unit) and the minor rigid bent-core skeleton
(covalent-bonded unit). In addition, as shown in
Figure 13b, the Ps values of polymer complex A10B1-N at
various temperatures (except the transition teperatures) were
acquired as a constant value around Ps=60 nC/cm2 in the
SmCP phase. However, the switching current phenomena
were not clearly acquired in bent-core H-bonded homo-
polymer complex (A1B0-N), covalent-bonded homopoly-
mer (A0B1), and the other copolymer complexes (A4B1-N,
A1B2-N, A1B5-N, and A1B13-N), which indicated that the
suitable A-N/B (i.e., m/n) molar ratio in the tilted smectic
phases should be in the range of m/n=16/1 to 10/1 to induce
the polar switching behavior by the favorable molecular
stackings of bent-core H-bonded (major) and covalent-
bonded (minor) components with proper molar ratios of
m/n (ca. 16/1-10/1).
310 V and f = 30 Hz, at T = 100 °C), where a plateau
equivalent to a triangular wave period is introduced at zero
voltage, and antiferroelectric switching current responses
were observed in both polymer complexes A10B1-N and
A16B1-N. Here, the characteristic behavior of a sequential
electric response was due to a ferroelectric state switched into
an antiferroelectric ground state and back to the opposite
ferroelectric state, which confirmed the SmCPA (A=anti-
ferroelectric behavior) structure of the B2 phase,35 and the
existing SmCPA state was hidden under the continuous
triangular wave measurements due to the quick exchange
of SmCPF f SmCPA f SmCPF.
According to the triangular wave method, the Ps values
(the saturated values at high voltages) of polymer complexes
A16B1-N and A10B1-N could be calculated as 15 and 60 nC/
cm2, respectively. As shown in Figure 13, the spontaneous
polarization (Ps) values of polymer complex A10B1-N in the
SmCP phase at various applied electric fields and tempera-
tures were surveyed. With respect to Ps values as a function
of applied voltages (at f = 60 Hz and T = 100 °C) in
Figure 13a, the Ps values were steeply enhanced to reach a
maximum at Vpp ∼130-180 V by increasing the applied
electric fields, and the Ps values were gradually dropped as
the applied electric fields were above Vpp ∼200 V, which were
reproducible for several cycles. It was speculated that the
reduction of Ps values at high applied voltages was due to the
weak H-bonds of bent-core H-bonded component A-N in
polymer complex A10B1-N, and the Ps behavior of the
Conclusions
In summary, several novel side-chain banana-shaped liquid
crystalline copolymers with various molar ratio of covalent- and
H-bonded bent-core components were developed by the free

1288 Macromolecules, Vol. 43, No. 3, 2010
Wang et al.
radical polymerization, and their polymer complexes were self-
assembled by appropriate molar ratios of proton donor
(H-donor) polymers and pyridyl proton acceptor (H-acceptor)
bent cores. The mesomorphic and electro-optical properties in
the side-chain banana-shaped liquid crystalline polymers and
their corresponding polymer complexes were influenced by the
molar ratios of bent-core H-bonded components effectively. The
voltage-dependent antiferroelectric properties of spontaneous
polarization (Ps) values in the polar smectic phase of the
supramolecular side-chain banana-shaped copolymers were also
first observed in this study. Several kinds of nematic and tilted
smectic phases were obtained in bent-core side-chain homopoly-
mers/copolymers and polymer complexes, which depended on
the m/n molar ratio (i.e., hydrogen- and covalent-bonded units).
The nematic and tilted smectic phases were verified by XRD
measurements, and the SmCP phase was further identified by the
triangular wave method. Overall, the antiferroelectric behaviors
of the polar semctic phase were introduced in bent-core side-
chain polymer complexes AmBn-N by tuning the suitable m/n
molar ratios in the range of 16/1 to 10/1. It would be seemingly
summarized that strict packing conditions between each bent-
core covalent-bonded unit were present to reduce molecular
oscillating, but loose packing conditions between each bent-core
H-bonded unit would induce molecular fluctuations and become
dynamically unstable under electric fields. The polar switching
behaviors were diminished if just only either bent-core covalent-
bonded or H-bonded structures were organized in the side chains
of polymers. Therefore, rigid bent-core covalent-bonded compo-
nents uniformly dispersed and copolymerized among soft bent-
core H-bonded ingredients in the side-chain polymers are nece-
ssary for the polar switching behaviors. This study offers some
valuable information to achieve the polar switching properties by
blending bent-core host-guest supramolecular systems with a
combination of low molecular weight molecules (as H-acceptors)
and polymers (homopolymers/copolymers as H-donors), which
could be utilized for supramolecular mixtures in the future.
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Acknowledgment. We thank the financial support from the
National Science Council of Taiwan (ROC) through NSC 96-
2113-M-009-015. We are also grateful to the National Center for
High-performance Computing for computer time and facilities.
The powder XRD measurements were supplied by beamline
BL17A (charged by Dr. Jey-Jau Lee) of the National Synchro-
tron Radiation Research Center (NSRRC) in Taiwan.
Supporting Information Available: Chemical structures
(covalent-bonded compound S12 and H-bonded complex
H12), XRD patterns of polymers A1B0, A16B1, A10B1,
A4B1, A1B2, A1B13, A1B5, and A0B1 as well as and polymer
complexes A1B0-N, A16B1-N, A10B1-N, A4B1-N, A1B2-N,
A1B13-N, and A1B5-N (at various temperatures). This
material is available free of charge via the Internet at http://
pubs.acs.org.
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