Liquid-crystalline binary systems with nonmesomorphic comb-shaped polymer component

Article abstract of DOI:10.1080/15421406.2012.688618

Binary liquid-crystalline systems were prepared by mixing a nonmesomorphic comb-shaped polymer (CSP) and low-molecular-weight liquid crystal. CSP exhibited a glass-isotropic phase transition. The binary liquid-crystalline systems consisting of CSP and polar molecule formed smectic A and smectic B phases. The induction of liquid crystalline phases is due to interactions between the side chain of CSP and low-molecular-weight liquid crystals. Taylor and Francis Group, LLC.

Full text of DOI:10.1080/15421406.2012.688618

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Liquid-Crystalline Binary Systems with
Nonmesomorphic Comb-Shaped Polymer
Component
Takenori Kojo a , Masanori Nata a & Seiji Ujiie a
a Department of Applied Chemistry , Faculty of Engineering, Oita
University , 700 Dannoharu, Oita , 870-1192 , Japan
Published online: 02 Aug 2012.
To cite this article: Takenori Kojo , Masanori Nata & Seiji Ujiie (2012) Liquid-Crystalline Binary
Systems with Nonmesomorphic Comb-Shaped Polymer Component, Molecular Crystals and Liquid
Crystals, 563:1, 75-82, DOI: 10.1080/15421406.2012.688618
To link to this article: http://dx.doi.org/10.1080/15421406.2012.688618
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Mol. Cryst. Liq. Cryst., Vol. 563: pp. 75–82, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.688618
Liquid-Crystalline Binary Systems with
Nonmesomorphic Comb-Shaped
Polymer Component
TAKENORI KOJO, MASANORI NATA, AND SEIJI UJIIE∗
Department of Applied Chemistry, Faculty of Engineering, Oita University,
700 Dannoharu, Oita 870-1192, Japan
Binary liquid-crystalline systems were prepared by mixing a nonmesomorphic comb-
shaped polymer (CSP) and low-molecular-weight liquid crystal. CSP exhibited a glass-
isotropic phase transition. The binary liquid-crystalline systems consisting of CSP and
polar molecule formed smectic A and smectic B phases. The induction of liquid crys-
talline phases is due to interactions between the side chain of CSP and low-molecular-
weight liquid crystals.
Keywords Amorphous polymer; induced smectic phase; liquid-crystalline binary
system; polar molecule
Introduction
Thermotropic liquid-crystalline systems are formed by mesogenic compounds and mix-
tures. One of a method to improve liquid-crystalline properties is to mix two or more
components [1,2]. It is known that the noncovalent interactions between distinct molecules
can lead to the formation of liquid-crystalline phases with enhanced thermal stability
[3,4]. For instance, a binary mixture of electron-donor and electron-acceptor molecules can
form induced smectic phases by a charge-transfer effect even if the components show only
a nematic phase or no liquid-crystalline phase [1,2, 5–10].
In this study, binary liquid-crystalline systems consisting of a nonmesomorphic comb-
shaped polymer and a nematic liquid crystal were prepared. Their thermal and orientational
properties were examined. This paper describes the formation of induced smectic A and
smectic B phases in the liquid-crystalline binary systems.
Experimental
Materials
The structures of mixing components are shown in Fig. 1. A methacrylate monomer was
synthesized following the previous method [11,12].
∗Address correspondence to Prof. Seiji Ujiie, Department of Applied Chemistry, Faculty of
Engineering, Oita University, 700 Dannoharu, Oita 870-1192, Japan. Tel: (+81)97-554-7903. Fax:
(+81)97-554-7903. E-mail: seujiie@oita-u.ac.jp
75

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T. Kojo et al.
Figure 1. Structures of CSP and 5CyCB.
3(1-(Hydroxy)hexyloxy)benzoic acid (m6B)
3-Hydroxybenzoic acid, 6-chloro-1-hexanol and potassium hydroxide were dissolved in
ethanol, and the solution was refluxed for 24 h. After the reaction, ethanol was evaporated
and a crude product was obtained. The crude product was dissolved in water, and the
solution was acidized with hydrochloric acid. 3-(1-(Hydroxy)hexyloxy)benzoic acid (m6B)
was filtered off.
3-(1-Methacryloyloxy)hexyloxy)benzoic acid (MABA)
m6B and excess methacrylic acid were dissolved in chloroform at 60◦C, and the solution was
refluxed for 15 h. After the reaction, the chloroform solution was washed with water, and the
chloroform solution was dried with magnesium sulfate. Chloroform was evaporated, and
the crude product of 3-(1-methacryloyloxy)hexyloxy)benzoic acid (MABA) was purified
by recrystallization using ethanol.
4-(3-(6-Methacryloyloxy)hexyloxy)benzoyloxy-4ꢀ-butylazobenzene (mBu)
MABA was reacted with excess thionyl chloride, and after the reaction, thionyl chloride was
evaporated. The crude product was dissolved in tetrahydrofuran, and the solution was added
in the tetrahydrofuran solution of 4-(4-(butyl)phenylazo)phenol and triethylamine. The
solution was reacted at room temperature for 12 h. After the reaction, tetrahydrofuran was
evaporated, and the crude was dissolved in chloroform. The chloroform solution was washed
with water, and the chloroform solution was dried with magnesium sulfate. Chloroform
was evaporated, and crude product was recrystallized from 2-propanol. The methacrylate
monomer 4-(3-(6-methacryloyloxy)hexyloxy)benzoyloxy-4ꢀ-butylazobenzene (mBu) was
obtained.
1H NMR(CDCl3), δ: 7.99 (d, 2H, Ar-H), 7.83 (m, 4H, Ar-H), 7.71 (s, 1H, Ar-H), 7.42
(t, 1H, Ar-H), 7.35 (m, 4H, Ar-H), 7.18 (d, 1H, Ar-H), 6.10 (s, 1H, CH2=C), 5.54 (s, 1H,
CH2=C), 4.17 (t, 2H, -COOCH2-), 4.03 (t, 2H, -CH2CH2O-), 2.70 (t, 2H, Ar-CH2-), 1.94
(s, 3H, CH2=C(CH3)-), 1.84-1.38 (m, 12H, -CH2-), 0.95 (t, 3H, -CH2CH3).

Binary Systems with Nonmesomorphic CPS Component
4-Pentyl-4ꢀ-cyanobiphenylyl cyclohexanoate (5CyCB)
77
4-Pentyl-4ꢀ-cyanobiphenylyl cyclohexanoate (5CyCB) was synthesized by esterification.
trans-4-Pentylcyclohexanecarboxylic acid reacted with excess thionyl chloride, and af-
ter the reaction, thionyl chloride was evaporated. The crude product was dissolved in
tetrahydrofuran, and the solution was added in the tetrahydrofuran solution of 4-cyano-
4ꢀ-hydroxybiphenyl and triethylamine. The solution was reacted at room temperature for
12 h. After the reaction, tetrahydrofuran was evaporated, and the crude was dissolved in
chloroform. The chloroform solution was washed with water, and the chloroform solution
was dried with magnesium sulfate. Chloroform was evaporated, and crude product was
recrystallized from methanol.
1H NMR(CDCl3), δ: 7.73-7.56 (m, 6H, Ar-H), 7.17 (d, 2H, Ar-H), 2.51 (m, 1H,
-CH(AX)), 2.13 (m, 2H, -CH(AX)), 1.87 (m, 2H, -CH(EQ)), 1.62-1.51 (m, 2H, -CH(EQ)),
1.32-1.22 (m, 9H, -CH(AX), -CH2-), 1.01 (m 1H, -CH(EQ)), 0.92 (t, 3H, -CH2CH3).
Side Chain Polymer (CSP)
mBu and AIBN were dissolved in tetrahydrofuran, and dry nitrogen gas. The mixture was
maintained at 60◦C for 24 h. After the reaction, the solution was poured into methanol,
and the precipitate was filtered off. The purification of the polymer was carried out by
soxhlet extraction using methanol for 24 h, and gave rise to the comb-shaped polymer
(CSP: poly(4-(3-(6-methacryloyloxy)hexyloxy)benzoyloxy-4ꢀ-butylazobenzene)).
Binary Liquid Crystals
Binary liquid-crystalline systems were prepared by mixing CSP and nematic liquid crystal
(5CyCB).
Measurement
The liquid-crystalline properties and phase transition temperatures were examined by po-
larizing microscopy (a Nikon polarizing microscope with a Mettler thermosystem 900
equipped with a Mettler hot stage HT84) and DSC measurement (a Shimadzu DSC60).
The orientational behavior was examined by the temperature-variable X-ray diffraction
measurement (a Shimadzu XRD 6100 with an Anton Parr heating system). The molecular
weight was measured by GPC measurement (a Shimadzu CTO-20A), calibrated standard
polystyrenes.
Results and Discussion
Phase Transitions
A side chain polymer (CSP : Mn = 22900, Mw/Mn = 2.20), having 4-(4-(butyl)phenylazo)-
phenylbenzoate (BAB) side groups, exhibited only a glass transition and did not reveal a
liquid-crystalline phase (see Fig. 2). A low-molecular-weight 5CyCB with a cyanobiphenyl
group is a nematic liquid crystal. The binary liquid crystals (CSP/5CyCB(X), X: mole
fraction of 5CyCB), consisting of CSP and 5CyCB, show induced smectic A and smectic
B phases, which were formed by CSP or 5CyCB (see Fig. 2). It is expected that an
interaction between 4-cyanobiphenylylbenzoate (strong polar group) of 5CyCB and BAB

78
T. Kojo et al.
Figure 2. Phase diagram of binary liquid crystals CSP/5CyCB(X). X : mole fraction of 5CyCB,
g : glassy, k : solid, SmB : smectic B, SmA : smectic A, I : isotropic. d and 2 denote interdigitated
bilayer and bilayer structures, respectively.
side group (nonpolar group) of CSP led to the formation of the induced smectic phases. In
previous researches, the formation of induced smectic phases was reported in the binary
mixtures, consisting of a strong polar compound and a nonpolar compound [1,2].
In the smectic A and smectic B phases of CSP/5CyCB(X), fan textures were observed
(Fig. 3). However, the fan texture in the smectic A phase is not obviously different
from the fan texture in the smectic B phase. Therefore, it is difficult to determine the
smectic A-smectic B phase transition by polarizing microscopy. However, DSC and
X-ray diffraction measurements clearly revealed the existence of the smectic A-smectic B
phase transition in CSP/5CyCB(X) except CSP/5CyCB(0.3). The smectic phases formed
by CSP/5CyCB(0.3) are a frustrated smectic phase. The two types of layer structures
were found in the smectic phases of CSP/5CyCB(X). The orientational structures of the
smectic phases depended on the composition of low-molecular-weight liquid crystals.
An interdigitated bilayer structure (X = 0.2) and a bilayer structure (X is more than
0.4) were formed. Both the interdigitated layer and bilayer structures were coexisted in
CSP/5CyCB(0.3). The same coexistence of two smectic layer structures was also found
for binary mixtures with polar components [13,14].
X-Ray Diffractions
The temperature-variable X-ray diffraction measurement in the liquid-crystalline phase was
performed in order to investigate the orientational behavior of the binary liquid crystals. The
X-ray diffraction patterns of CSP/5CyCB(X) were shown in Fig. 4. In the smectic A phase
(X = 0.7, 0.9), the inner sharp reflections and the outer broad reflection were measured. The
inner sharp reflection corresponds to the layer spacing of the smectic A phase and the outer
broad reflection shows a short range order within the smectic layer. On the other hand, the
X-ray diffraction pattern of the smectic B phase (X = 0.2, 0.3 and 0.5) are characterized
by the sharp inner and outer reflections. The fact that the outer reflection is sharp indicates
the existence in a long range order within the smectic layer, having a hexatic packing.

Binary Systems with Nonmesomorphic CPS Component
79
Figure 3. Optical textures observed for CSP/5CyCB(0.5). (a) : smectic A, 150◦C, (b) : smectic B,
30◦C. The photographs of both (a) and (b) were taken in the same position.
At X = 0.3, the interdigitated layer and bilayer structures coexist, showing the X-ray inner
reflections corresponding to the length of interdigitated layer and bilayer periodicities.
From the relationship between a layer spacing and molecular lengths, possible packing
models for the smectic phases were proposed (see Fig. 5). In the smectic A phase, there is a
segregation between polymer backbones and mesognic groups. The mesogenic groups have
an orientational order and no positional order within the layer. The smectic B phase has the
hexatic order within the layer. The intermolecular distance within the smectic B layer is 4.4
Å. The fully-extended side chain length of CSP is 28.4 Å, while the molecular length of
5CyCB is 21.7 Å. In CSP/5CyCB(0.2), the smectic layer spacing is 35.2 Å, corresponding
to the interdigitated bilayer structure. In CSP/5CyCB(0.5) and CSP/5CyCB(0.9), the layer
spacings were 54.0 Å and 53.9 Å, respectively, corresponding to twice the side chain

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T. Kojo et al.
Figure 4. XRD patterns of CSP/5CyCB(X). X = 0.2, 0.3, 0.5 : smectic B, X = 0.7, 0.9 : smectic A.
Figure 5. Possible packing models for induced smectic A phases of CSP/5CyCB(X). X = 0.2 :
interdigitated bilayer, X = 0.5, 0.9 : bilayer. In the smectic A phases, the position of the center
of gravity of the mesogenic groups is random within the layer. The smectic B phase has a hexatic
packing within the layer.

Binary Systems with Nonmesomorphic CPS Component
81
Figure 6. Schematic illustrations for image of liquid crystal formation.
length of CSP. CSP/5CyCB(0.5) and CSP/5CyCB(0.9) formed the bilayer structure that
partially overlapped terminal alkyl chains. In the X-ray diffraction patterns for the bilayer
structure, the peak intensity of the second order reflection was stronger than that of first
order reflection. The distance for the second order reflection corresponds to the periodicity
of mesogenic groups. The image of the liquid crystal formation in CSP/5CyCB(X) was
schematically illustrated in Fig. 6. The interdigitated layer is formed by an influence of CSP
as shown in X = 0.2. In contrast, the formation of the bilayer structure is mainly influenced
by 5CyCB.
Conclusions
The induced smectic A and smectic B phases were shown in the binary liquid crystals
consisting of the nonmesomorphic side chain polymer and the nematic liquid crystal. In
the orientational structures of the induced smectic phases, both the interdigitated layer and
bilayer structures were formed. Furthermore, even a small amount of CSP acts effectively
in forming layer structure.
References
[1] Ujiie, S., Uchino, H., & Iimura, K. (1995). J. Mater. Chem., 5, 2229.
[2] Ujiie, S., Sato, M., Uchino, H., & Iimura, K. (1998). Mol. Cryst. Liq. Cryst., 309, 283.
[3] Sauer, C., Diele, S., & Tschierske, C. (1997). Liq. Cryst., 23, 911.
[4] Pratibha, R., Madhusudana, N. V., & Sadashiva, B. K. (2001). Mol. Cryst. Liq. Cryst., 365, 755.
[5] Demus, D., Pelzl, G., Sharma, N. K., & Weissflog, W. (1981). Mol. Cryst. Liq. Cryst., 76, 241.
[6] Fukui, M., & Matsunaga, Y. (1981). Bull. Chem. Soc. Jpn., 54, 3137.
[7] Matsunaga, Y., Kamiyama, N., & Nakayasu, Y. (1987). Mol. Cryst. Liq. Cryst., 147, 85.

82
T. Kojo et al.
[8] Imrie, C. T., Karasz, F. E., & Attard, G. S. (1991). Liq. Cryst., 9, 47.
[9] Ujiie, S., Uchino, H., & Iimura, K. (1995). Chem. Lett., 195.
[10] Ujiie, S., Uchino, H., Iimura, K., & Sato, M. (1999). Kobunshi Robunshu, 56, 341.
[11] Ujiie, S., Maekawa, K., Takahashi, S., & Iimura, K. (1993). Mol. Cryst. Liq. Cryst., 237, 477.
[12] Ujiie, S., Fukui, T., Higaki, K., Takahashi, S., & Iimura, K. (1993). Kobunshi Robunshu 50, 687.
[13] Levelut, A. M. (1984). J. Phys. Lett. (Paris), 45, L–603.
[14] Sigaud, G., Hardouin, F., Achard, M. F., & Levelut, A. M. (1981). J. Physique, 42, 107.