九州大学大学院総合理工学府報告第 40 巻 第 2 号 6-10 頁 平成 31 年 2 月

Engineering Sciences Reports, Kyushu University
Vol. 40, No. 2, pp. 6-10, FEB, 2019

Synthesis and Characterization ofMono-acryl Liquid crystalline Functional Monomer
Daisuke YOSHIZAWA*1, Yasushi OKUMURA*2 and Hirotsugu KIKUCHI*2†
E-mail of corresponding author: kikuchi@cm.kyushu-u.ac.jp†(Received December 8, 2018, accepted December 11, 2018)
We newly synthesized a mono-acryl liquid crystalline monomer (mono-acryl RM257) andinvestigated the phase behavior and the liquid crystallinity of it. The temperature range of liquid
crystalline phase was broadened compering to a conventional di-acryl monomer (RM257). This result
suggests that the alkylation of acryl group of RM257 increases the liquid crystallinity because lesssteric hindered of alkyl group enhances the interaction i.e. van der Waals and π－π interaction.
Key words: Liquid crystal, Liquid crystalline monomer, thermal analysis, optical texture

1.

Introduction

Liquidcrystals(LCs)
aretypicalself-organizedmaterials
with
a
high
sensitivity to external fields such as an electricfield, a magnetic field, a temperature change,a mechanical strain and so on.1 They haveplayed significantly important roles indeveloping flat panel displays, optical or
photonic materials, as well as other functional
materials.1 The introduction of chirality into a
LC has a tremendous impact in arrangementof LC molecules. A nematic (N) phasetransforms to a chiral N (N*) phase with ahelical supramolecular structure by dopingwith a chiral molecule.2 Blue phases are also akind of a chiral LC phase existing between a
N* phase and an isotropic liquid.3 Threedifferent blue phases are distinguished anddenoted as BP III (nearly amorphous), BP II(simple cubic) and BP I (body center cubic),
which corresponding to the sequence coolingfrom an isotropic phase. BPs show unique
optical characteristics owing to their nature ofstructure, such as Bragg reflectance,
non-birefringence and large electro-optical
Kerr effect.4 However, their extremely small
temperature range (typically less than afew °C) was a barrier of practical use of BPs.
Our previous studies have demonstrated in*1 Department of Applied Science for Electronics andMaterials*2 Institute for Materials Chemistry and Engineering

expanding the temperature range of BP I by
more
than
60
ºC
via
in
situ
photo-polymerization of approximate amountofmonomersinBPstate.5Thepolymer-stabilized BP (PSBP) is expected to be
applied to next-generation LC display
materials because they exhibit sub-millisecond
electro-optic response. Nevertheless, PSBP
requires high operating voltage because of theshort coherence length due to the lattice
structure on a few 100 nm, the highly twisted
molecular alignment of the LC and the strong
interaction between the polymer and LC
molecules. The investigation of the interaction
between the polymer and LCs plays a key rolein lowering the operating voltage of the PSBP.
Preparing the substrate surface coated with apolymer allows us to evaluate the interaction
between the polymer and LC molecules. The
PSBP precursor mixture usually consists ofhost NLC, chiral molecule, mono-acryl
monomer, di-acryl cross linker (RM257) andphoto initiator.5,6 Therefore, we can prepare
the polymer-coated substrate surface by using
the monomers as mentioned above. However, it
is difficult to produce the smooth surface using
cross linker monomer RM257 because thepolymer prepared with RM257 is rheologicallyrigid owing to their highly cross-linked
network structure.
The aim of this study is to provide a material
which is feasible for conducting a modelexperiment
systemtoevaluatethe平成 30 年度

九州大学大学院総合理工学報告

(a)

(b)

Fig. 1 Chemical structure of (a) RM257 and(b) mono-acryl RM257
intermolecular interaction between thepolymer and LC molecules. In such experiment
system, a monomer having simultaneously
both of a targeted molecular core structure anda polymerizable mono-functional group isnecessary. Therefore, we newly synthesized themono-acryl RM257 monomer (Fig. 1b) andcharacterized the liquid crystallinity of thesynthesized monomer by differential scanningcalorimetry (DSC) measurement and bypolarized
opticalmicroscopy(POM)
observation.

2.

Experimental procedure

2.1 General procedure
All chemical reagents were obtained fromcommercial suppliers and were used without

第 40 巻第2号

7

further purification. Silica gel column
chromatography was performed using silica
gel 60N from Wako Pure Chemical Industries(irregular, 63–212 μm). 1H and 13C NMR
spectra were recorded on a JEOL JNM-LA400
spectrometer. Tetramethylsilane was used as
an internal standard (δ 0.00) for 1H and CHCl3(δ 77.06) for 13C. The coupling constants, J, arereported in hertz (Hz). Mass spectra wereconducted at Kyushu University.
The phase behavior and the mesomorphic
properties of synthesized monomer werecharacterized by DSC (DSC 1 STAR System,
Mettler Toledo Inc.) and by the observation of
optical textures using a polarizing optical
microscope, POM (ECLIPSE E600 POL,
Nikon).
2.2 Synthesis
Fig. 2 shows synthesis route of mono-acryl
RM257.
2.2.1 Synthesis of compound 2
Compound 1 (1.50 g, 12.0 mmol) and Et3N
(2.51 mL, 18.0 mmol) were dissolved in THF(10 mL) at 0 ºC under N2. Then, ethyl
chloroformate (1.37 mL) was added dropwise
over 10 min to a solution and stirred at 0 ºC for
2 hours. The reaction mixture was filtered. The
NaBH4 (1.12g, 48.0 mmol) solution (15 mL)

Fig. 2 Synthesis route of mono-acryl RM257

8Synthesis and Characterization of Mono-acryl Liquid Crystalline Functional Monomer

was added slowly over 45 min to a filtrate at 0ºC and then resulting mixture was stirred at
RT for 90 min. After stirring, distilled waterand 2M HCl was added to adjust the pH < 2.
The organic layer was extracted with ethyl
acetate and dried over Na2SO4, filtrate, andevaporation to give a crude product, which was
purifiedbycolumnchromatography(CH2Cl2/hexane = 1/1) to yield compound 2(994 mg, 60%). 1H NMR (400 MHz, CDCl3); δ
6.70 (d, J = 8.7 Hz, 2H), 6.63 (m, 1H), 4.33 (s,1H), 3.75 (s, 3H), 2.24 (s, 3H) 13C NMR (100MHz, CDCl3); δ 116.79, 115.71, 112.04, 55.92,
16.27.
2.2.2 Synthesis of compound 3
2-hydroxy-5-methoxytoluene 2 (801 mg, 5.79mmol), 4-butoxy benzoic acid (1.35 g, 6.95mmol), EDC ・ HCl (1.67 g, 8.69 mmol), andDMAP (71.7 mg, 0.58mmol) were dissolved in
CH2Cl2 (30 mL) at RT under N2. After stirringfor 20 hours, reaction mixture was washedwith distilled water (30 mL), sat. NaHCO 3 aq.
(30 mL), and brine (30 mL). The collectedorganic layer was dried over Na2SO4, filtrate,and evaporation to give a crude product, which
was purified by column chromatography(CH2Cl2) to yield compound 3 (1.51 g, 83%). 1H
NMR (400 MHz, CDCl3); δ 8.15 (d, J = 8.7 Hz,
2H), 7.03 (d, J = 8.7 Hz, 1H), 6.97 (d, J = 8.7 Hz,
2H), 6.78 (m, 2H), 4.05 (t, J = 6.3 Hz, 2H), 3.81
(s, 3H), 2.19 (s, 3H), 1.78-1.85 (m, 2H),
1.47-1.55 (m, 2H), 1.00 (t, J = 7.2 Hz, 3H) 13C
NMR (100 MHz, CDCl3); δ 165.04, 163.52,
157.24, 143.25, 132.25, 131.43, 122.73, 121.63,
116.28, 114.33, 111.89, 68.04, 55.58, 31.18,
19.24, 16.58, 13.86.
2.2.3 Synthesis of compound 4
A suspension of aluminum chloride (6.38 g,
47.7 mmol) and NaI (7.15 g, 47.7 mmol) in
CH3CN (10 mL) was stirred at 0 ºC under N2and compound 3 in CH3CN was added
dropwise to a stirred mixture. The reaction
mixture was refluxed for 15 hours. Aftercooling to RT, cold water was added to a
resulting mixture and extracted with CH2Cl2.
The separated organic layer was washed withsat. Na2S2O3 aq. (30 mL) and brine (30 mL).
The collected organic layer was dried over
Na2SO4, filtrate, and evaporation to give acrude product. The spot of row material was
removed by column chromatography (CH2Cl2)
and purified by reprecipitation from ethyl
acetate to yield compound 4 (524 mg, 33%). 1H
NMR (400 MHz, CDCl3); δ 8.10 (m, 2H),

6.93-7.00 (m, 3H), 6.67-6.74 (m, 1H), 4.05 (q, J= 7.1 Hz, 2H), 2.18 (s, 2H), 1.82 (m, 2H),
1.48-1.58 (m, 2H), 1.00 (td, J = 7.5, 3.5 Hz, 3H)
13C NMR (100 MHz, CDCl3); δ 163.64, 153.42,
143.12, 132.38, 132.32, 131.55, 122.81, 121.50,
117.70, 114.39, 114.26, 113.64, 68.08, 68.03,
31.17, 19.23, 16.35, 13.84.
2.2.4 Synthesis of compound 6
4-(3-hydroxybutoxy)benzoic acid（0.66 g, 3.36mmol） and NaOH aq. (0.36 g, 9 mmol) 6 mL
was stirred at 0 ºC and acryloyl chloride (0.54mL, 6.68 mmol) in dioxane (10 mL) was added
dropwise over 10 min. After stirring 17 hours
at RT, reaction mixture was evaporated andwarm water was added before filtration. The
residue was collected and purified by column
chromatography (ethyl acetate/toluene = 1/1)
to yield compound 6. 1H NMR (400 MHz,CDCl3); δ 8.05 (d, J = 8.7 Hz, 2H), 6.94 (d, J =9.7 Hz, 2H), 6.42 (d, J = 17.4 Hz, 1H), 6.13 (dd,J = 17.4, 10.6 Hz, 1H), 5.85 (d, J = 10.6 Hz, 1H),
4.77 (s, 1H), 4.38 (t, J = 6.3 Hz, 2H), 4.14 (t, J =5.8 Hz, 2H), 2.17-2.23 (m, 2H) 13C NMR (100MHz, CDCl3); δ 163.22, 132.39, 131.03, 128.32,
114.25, 64.68, 61.22, 30.66, 28.58.
2.2.5 Synthesis of compound mono-acryl
RM257
Compound 4 (293 mg, 0.977 mmol),compound 6 (232 mg, 0.925 mmol), EDC・HCl(274 mg, 1.43 mmol), and DMAP (11.3 mg,
0.105 mmol) were dissolved in dry CH2Cl2 andstirred at RT for 16 hours under N2. The
resulting mixture was washed with sat.
NaHCO3 aq. (30 mL), distilled water (30 mL)
and brine (30 mL). The collected organic layer
was dried over Na2SO4, filtrate, andevaporation to give a crude product, which was
purified by column chromatography (CH2Cl2)
to yield target compound (mono-acryl RM257).
1H NMR (400 MHz, CDCl 3); δ 8.15 (q, J = 4.8
Hz, 4H), 7.07-7.19 (m, 3H), 6.98 (dd, J = 8.7,
1.9 Hz, 4H), 6.43 (dd, J = 17.4, 1.9 Hz, 1H),
6.14 (dd, J = 17.4, 10.6 Hz, 1H), 5.84-5.87 (m,1H), 4.39 (t, J = 5.8 Hz, 2H), 4.17 (t, J = 6.3 Hz,
2H), 4.06 (t, J = 6.8 Hz, 2H), 2.19-2.28 (m, 5H),
1.78-1.85 (m, 2H), 1.48-1.59 (m, 2H), 1.00 (t, J= 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3); δ
166.13, 164.87, 164.57, 163.65, 163.12, 148.42,
147.10, 132.33, 132.32, 131.81, 130.97, 128.33,
124.12, 122.95, 122.00, 121.39, 120.04, 114.40,
114.33, 68.06, 64.72, 61.20, 31.17, 28.58, 19.23,
16.46, 13.84. High resolution mass spectrum;
HRMS (EI) m/z cald for C31H32O8 (M+ ･ ),532.2097; found, 532.2096.

平成 30 年度

3.

九州大学大学院総合理工学報告

The mono-acryl RM257 was chemicallysynthesized through 5 steps (Fig. 2). The
methylation of aldehyde of compound 1 using
ethyl chloroformate resulted compound 2.
Dehydration condensation between compound
2 and 4-butoxy benzoic acid gave compound 3.
Next, we conducted the demethylation ofcompound 3. It is known that BBr3 is a good
reagent for demethylation reaction. However,the compound was broken when BBr3 was used
for demethylation reaction in this study. It isconsidered that hydrogen bromine was formedby adding water at the quench of the reaction
and hydrolysis of the material occurred.
Therefore,
demethylation
reactionofcompound 3 was conducted via mild condition
using aluminum chloride and sodium iodide in
CH3CN. The Schotten-Baumann reaction ofcompound 5 resulted compound 6. Finally, we
successfully obtained mono-acryl RM257 via
dehydration condensation between compound
4 and 6. The total yield was 3.0%.
The liquid crystallinity of mono-acryl RM257
was characterized by DSC measurement andPOM observation. As a reference experiment,
DCS measurement and POM observation of
the conventional cross linker monomer RM257
was conducted. The DSC charts were shown in
Figs. 3a and b. The DSC chart of RM257
exhibits two major endothermic peaks at 71.7
and 126.2 ºC and weak minor peak at around
42 ºC. The weak broad peak at 42 ºC was
attributed to be a non-equilibrium melting of
crystal. The optical texture of RM257 weredisplayed in Fig. 3c. The crystalline, nematic,
and isotropic phase can be identified at 40.1,
1st cooling4.

In conclusion, we have newly synthesized aliquid crystalline mono-acryl RM257. The
temperature range of nematic phase inmono-acryl RM257 is broadened comparing to
the conventional cross linker RM257. We
believe that the mono-acryl RM257 will beapplied to a monomer for preparation of asmooth substrate surface modified with a
1st cooling

152.7 ºC

Iso

N

9

Conclusion(b)

125.7 ºC

第2号

105, and 129 ºC, respectively. This observationsuggests that the peak at 71.7 ºC corresponds
to the crystal — nematic transition, and thehighest peak at 126.2 ºC is due to nematic－
isotropic transition. The supercooling wasobserved in the measurement temperature
range. In contrast, the optical textures ofmono-acryl RM257, crystalline, nematic, andisotropic phase can be identified at 47.3, 80.0,
and 165 ºC, respectively. This observationsuggests that mono-acryl RM257 exhibits thenematic phase between 72.0 and 153.0 ºC andsupercooling of the nematic phase wasobserved below 152.7 ºC in the measurement
temperature range. The crystal － nematictransition temperature is mostly the same
between RM257 and mono-acryl RM257.
However, interestingly, the temperature rangeof nematic phase of mono-acryl RM257 wassignificantly larger than that of RM257. Thisbehavior could be due to alkylation of one sideof acryl group of RM257. This implies that lackof the symmetry of the molecular structure andless of the steric hindered of alkyl groupincrease molecular interaction i.e. van der
Waals and π － π interaction between alkyl
chains and aromatic moieties, respectively.

Results and discussion(a)

第 40 巻

IsoN
Iso41.9 ºC

153.0 ºC

IsoN
126.2 ºC

Cry

N
Cry

1st heating(c)72.0 ºC

71.7 ºC
1st heating(d)Fig. 3 DSC chart of (a) RM257 and (b) mono-acryl RM257 and POM images of (c) RM257 and (d)mono-acryl RM257

10Synthesis and Characterization of Mono-acryl Liquid Crystalline Functional Monomer

target polymer feasible for investigating theinteraction between the polymer and LC
molecules.
Acknowledgments
This work was partially supported the by aGrant-in-Aid for Scientific Research (A) JSPS
KAKENHI Grant Number JP25248021 and
18H03920 from the Japan Society for the
Promotion of Science, Dynamic Alliance forOpen
Innovation
Bridging
Human,
Environment and Materials from the Ministryof Education, Culture, Sports, Science andTechnology, Japan (MEXT), the Cooperative
Research Program of "Network Joint ResearchCenter for Materials and Devices." and CREST,
JST (JPMJCR1424).

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3) P. P. Crooker, Liq. Cryst., 1989, 5, 751–775.
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Kajiyama, Nat. Mater., 2002, 1, 64–68.
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