Synthesis of side-chain liquid-crystalline cinnamide polymers based on post polymer reaction

Article abstract of DOI:10.1080/15421406.2012.689142

We prepared novel photoreactive liquid crystalline (LC) polymer via polymer reaction. The cinnamic acid activated ester easily converted to amide by mixing with amine derivative and solubility of the polymer reduced due to hydrogen bonding. Upon exposure

Full text of DOI:10.1080/15421406.2012.689142

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Synthesis of Side-Chain Liquid-
Crystalline Cinnamide Polymers Based on
Post Polymer Reaction
Mizuho Kondo a , Yoshiyuki Dozono a , Kohei Goto a & Nobuhiro
Kawatsuki a
a Department of Materials Science and Chemistry, Graduate School
of Engineering, University of Hyogo, 2167 Shosha Himeji, Hyogo,
671-2280, Japan
Published online: 02 Aug 2012.
To cite this article: Mizuho Kondo , Yoshiyuki Dozono , Kohei Goto & Nobuhiro Kawatsuki (2012)
Synthesis of Side-Chain Liquid-Crystalline Cinnamide Polymers Based on Post Polymer Reaction,
Molecular Crystals and Liquid Crystals, 563:1, 121-130, DOI: 10.1080/15421406.2012.689142
To link to this article: http://dx.doi.org/10.1080/15421406.2012.689142
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Mol. Cryst. Liq. Cryst., Vol. 563: pp. 121–130, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.689142
Synthesis of Side-Chain Liquid-Crystalline
Cinnamide Polymers Based on Post
Polymer Reaction
MIZUHO KONDO,∗ YOSHIYUKI DOZONO, KOHEI GOTO,
AND NOBUHIRO KAWATSUKI
Department of Materials Science and Chemistry, Graduate School of
Engineering, University of Hyogo, 2167 Shosha Himeji, Hyogo 671-2280, Japan
We prepared novel photoreactive liquid crystalline (LC) polymer via polymer reaction.
The cinnamic acid activated ester easily converted to amide by mixing with amine deriva-
tive and solubility of the polymer reduced due to hydrogen bonding. Upon exposure to
linearly polarized ultraviolet light and subsequent annealing, the LC cinnamide exhib-
ited axis selective photoreaction and following thermally amplification of molecular
alignment. However, photoreactivity, LC stability and thermal amplification behavior of
the cinnamide group were lower than that of original cinnamic acid group, suggesting
that the lateral hydrogen bonding disturbs molecular reorientation behavior.
Keywords Axis selective photoreaction; polymer reaction; hydrogen bonding;
cinnamide
Introduction
Introducing low molecular weight (LMW) functional materials into simple polymer via
polymer reaction or noncovarent bonding is a useful method because it can add electrical
[1], optical [2,3], and photomechanical [4] functions originated from LMW materials. We
have previously studied on enhancement of processibility of π-conjugated LMW combined
with photoreactive polymer liquid crystal (PLCP) materials [5,6] and reported that fuluorene
derivatives can be aligned along the director of PLCP film by using LC property [5] or
hydrogen bonding [6]. PLCPs induce a large photoinduced molecular reorientation when
a thin film of them is exposed to linearly polarized UV (LPUV) light and subsequent
annealing. PLCPs also change their crosslinking density, acidity and dielectric properties
just by tuning the polarization direction and exposing time of the actinic beam. In this
work, we focused on activated ester to enhance the reactivity and thermal stability for
polymer functionalization. It can be connected to carboxylic molecular terminal and and
we can functionalize PLCP by LMW compounds containing amine at molecular terminal
because it convert to amide bonding by using amine compounds under a mild condition.
We synthesized PLCP containing activated ester at molecular terminal and explored their
functionalization with primal phenyl amine derivatives and photoresponsive behavior.
∗Address correspondence to Assistant Prof. Mizuho Kondo, Department of Materials Science and
Chemistry, Graduate School of Engineering, University of Hyogo, 2167, Shosha Hi, meji, Hyogo 671-
2280, Japan. Tel: (+81)79-267-4014. Fax: (+81)79-267-4014. E-mail: mizuho-k@eng.u-hyogo.ac.jp
121

122
M. Kondo et al.
Experimental
Figure 1 shows chemical structure of the polymers used in this study. We used phenyl
amine to evaluate the effect of liquid crystal property on axis-selective photoreaction of
cinnamide group. Synthetic route of the cinnamide polymers are described in Scheme 1.
The photoreactive cinnamide was prepared from activated photoreactive polymer ester
(P6CAM-S) and mixed with various liquid amines to convert to cinnamide derivatives
(P6CAM-A1, A2). The cinnamic acid polymer (P6CAM) was synthesized according to
the literature as a reference [7].
Scheme 1. Synthetic route for cinnamide polymers.
4-(6-Hydroxyhexyloxy) cinnamic Acid (1)
A mixture of trans-p-coumaric acid (25.0 g, 0.15 mol) and 6-chloro-1-hexanol (52 g,
0.38 mol) was dissolved in 25 g of N,N-dimethylimidazoridinone, potassium carbonate
(25 g, 0.18 mol) and a trace amount of potassium iodide were added to the solution.
The resulting solution was heated at 130◦C for 17 h. After the reaction mixture was
cooled to 70◦C, 40 ml of water, 30 g (0.53 mol) of potassium hydroxide and 40 ml of
methanol was added to the mixture and reflux for 1 h. The resultant solution was cooled
to room temperature. After concentrated aqueous hydrochloric acid solution was added to
the reaction mixture to give pH 3, the precipitated solid was collected and washed with
water. The crude product was recrystalized from a mixture of n-hexane and tetrahydrofrane
(THF) to give 1 (6.8 g, 22 mmol) in 47 % yield.

Synthesis of Cinnamide LC Polymers
123
Figure 1. Chemical structure of polymers used in this study.
1H-NMR (DMSO): δ(ppm) 1.34–1.36 (d, J = 6.6 Hz, 3H), 1.40–1.46 (m, 5H),
1.70–1.73 (t, J = 7.3 Hz, 3H), 4.01 (s, 2H), 4.38 (s, 1H), 6.36–6.39 (d, J = 16 Hz,
1H), 6.95–6.97 (d, J = 8.8 Hz, 2H), 7.53–7.56 (d, J = 16 Hz, 1H), 7.62–7.63 (d, J =
8.8 Hz, 2H)
4-(6-Methacryloyloxy-1-hexyloxy)-cinnamic Acid (2)
14 g (50mmol) of 1 and 4.3 g (40 mmol) of p-toluene sulfonic acid was dispersed in a
mixture of 5 ml of chloroform and 5.2 g of methacrylic acid (38 mmol). The mixture was
reflux at 85◦C for 4 h. After the resulting solution was cooled down to room temperature,
40 ml of diethyl ether was added and washed with water for 20 times. After the solvent
was removed, a yellow solid obtained was purified by column chromatography on silica gel
(chloroform) and recrystallized from ethyl acetate and methanol to give 2 (3.2 g, 6.6 mmol)
in 19 %.
1H-NMR (DMSO): δ(ppm) 1.40–1.45 (m, 4H), 1.63–1.66 (m, 2H), 1.72–1.74 (m, 2H),
1.89 (s, 3H), 4.01 (s, 2H), 4.10 (s, 2H), 5.66–5.67 (t, J = 1.6 Hz, 1H), 6.02 (s, 1H) 6.36–6.39
(d, J = 16 Hz, 1H), 6.95–6.97 (d, J = 8.8 Hz, 2H), 7.52–7.56 (d, J = 16 Hz, 1H), 7.61–7.63
(d, J = 8.7 Hz, 2H)
4-(6-Methacryloyloxy-1-hexyloxy)-cinnamic Acid N-Succimide (3)
2.0 g (6.0 mmol) of 2, 0.83 g (7.2 mmol) of N-hydroxysuccinimide, trace amount of
4-dimethylaminopyridine (DMAP), and 1.5 g (7.2 mmol) of dicyclohexyl carbodiimide
(DCC) was put in 100 ml flask. Then, 40 mL of dried THF was slowly added. The reaction
mixture was kept under stirring at room temperature for 19 h. The precipitate formed
during the reaction was filtered off and the organic solution was washed with and water.

124
M. Kondo et al.
The mixture was dried over sodium sulfate and evaporated under vacuum. The crude
product was purified by silica gel column chromatography (ethyl acetate: n-hexane = 7:3)
and finally recrystallized from n-hexane/THF to give 3 (1.3 g, 0.22 mmol) in 50 % yield.
1H-NMR (CDCl3): δ(ppm) 1.49–1.56 (m, 4H), 1.63 (s, 2H), 1.73–1.76 (t, J = 7.2 Hz
2H), 1.83–1.86 (t, J = 7.3 Hz 3H), 1.96 (s, 4H), 2.91 (s, 4H), 4.03 (s, 2H), 4.18 (s, 2H),
5.57(s, 1H), 6,12 (s, 1H), 6.45–6.48 (d, J = 16 Hz, 1H), 6.93–6.94 (d, J = 8.7 Hz, 2H),
7.53–7.54 (d, J = 8.7 Hz, 2H), 7.89–7.91 (d, J = 16 Hz, 1H).
Polymerization of 3
0.8 g (1.9 mol) of 3 and 3.6 mg (0.022 mol) of AIBN were dissolved in chloroform and
placed in a polymerization tube. The tube was sealed under nitrogen atmosphere after
bubbling with nitrogen for 40 min. Then, the tube was kept at 60◦C for 24 h. The resulting
solution was cooled to room temperature and poured into diethylether with vigorously
stirring to precipitate the polymer. The polymer obtained was purified by repeated repre-
cipitation from THF into a large excess of diethylether and dried under vacuum to yield
0.52 g of P6CAM-S in 65wt% conversion.
GPC (chloroform) : Mn= 29,000, Mw/Mn= 3.7
Polymer Functionalization
40 mg of P6CAM-S and 100mg of phenylamine was mixed at room temperature for 3 h
and washed with aqueous hydrochloric acid.
Measurements
1H-NMR spectra of synthesized compounds were taken on a Bruker DRX500. Thin films
of cinnamic acid derivatives were prepared by spin-coating of polymer solutions onto a
quartz substrate. The film was irradiated by UV-light from a 250 W high-pressure Hg-UV
lamp (Ushio, spotcure UIS 20102) that was passed through Glan-Taylor polarizing prisms
with a cut-off filter below 290 nm. The light intensity was about 150 mWcm2 at 365 nm.
After exposing, the film was annealed at elevated temperatures for 10 min. The optical
anisotropy of the film was evaluated with polarizing microscope (POM: OLMPUS, BX-
51P) and polarized absorption spectroscopy (Hitachi, U3010). Conversion of succimide
into amide terminal was confirmed with 1H-NMR, FT-IR spectrometer (Jasco, FT/IR-410)
and ATR FT-IR spectrometer (Jasco, FT-IR-480 plus). The thermodynamic properties of
the polymers were analyzed using differential scanning calorimetry (DSC; Seiko I&E
SSC-5200 and DSC220C) at heating and cooling rates of 10◦C min−1. The molecular
weight of the polymer was determined by gel permeation chromatography (GPC; Sugai,
U-620 column, Jasco UV-2075, RI-8020, TOSOH Gskgel 4000H, Gskgel α5000; eluent,
chloroform) calibrated with standard polystyrenes.
Results and Discussion
Preparation of Cinnamide Group
In the previous work, Zhang et al. has been demonstrated a novel method for preparation
of crosslinked liquid-crystalline polymers by using N-hydroxysuccinimide carboxylate,
activated ester, that can react with primary amines easily under mild reaction conditions

Synthesis of Cinnamide LC Polymers
125
Figure 2. Change in IR spectrum of the activated ester by adding amine derivatives.
[8]. In this work, we applied the activated ester structure for PLCP. Figure 2 shows IR spectra
of the P6CAM-S, P6CAM-A1 and P6CAM-A2 respectively. It is clearly observed that
peak around 1739 cm−1 for FT-IR spectrometry originating from imide group was reduced
and 1700–1650 cm−1 was increased after the reaction. Moreover, the phenyl cinnamide
group showed low solubility for chloroform, which can dissolve P6CAM-S, indicating that
the activated ester converted amide group effectively in a polymer state. Figure 3 shows
DSC thermogram of the compounds. P6CAM and P6CAM-A1 showed LC phase while
the others showed no mesophase at relevant temperature. In addition, no obvious peak of
glass transition was found in P6CAM-A1 due to strong hydrogen bonding though it became
viscous when they were heated above 100◦C. Figure 4 displays absorption spectrum of the
cinnamic acid derivatives used in this study. The absorbance was normalized in 314 nm,
which was a peak of P6CAM. It was found that the peak red shifted for the succinimide
group while it blue shifted for amide group.
Photoreactivity of the Cinnamide Group
It was known that irradiating a copolymer film with LPUV light induced an axis-selective
[2+2] photodimerization reaction of the cinnamic acid groups. Additionally, irradiating a
cinnamate-containing polymeric film with LPUV light leads an axis-selective photoreac-
tion, resulting in an induction of small negative optical anisotropy of the film. Change in
absorption spectrum of P6CAM-A1 film and change in absorbance at 320 and 280 nm was
displayed in Figure 5. A peak around 320 nm reduced upon exposure with UV light, the
Figure 3. DSC thermogram of the polymers. The inset photograph represents the POM image of the
P6CAM-A1 at 110◦C.

126
M. Kondo et al.
Figure 4. Absorption spectra of the polymer film on quarts substrate.
Figure 5. Change in Absorption spectrum of the P6CAM-A1 film (a) and value of absorbance at
280 nm and 380 nm upon exposure with LPUV light (b).

Synthesis of Cinnamide LC Polymers
127
Figure 6. Change in degree of photoreaction of the polymers as a function of dosed energy.
increase in absorbance at longer region (≈300 nm) owing to photo-Fries rearrangement was
not observed in the polymers [9]. We defined degree of photoreaction as following equation,
(A + A⊥)initial − (A + A )
||
||
⊥ exposure
ꢀP =
× 100
(1)
(A + A )
||
⊥ initial
where A and A are the absorbance at 314 nm parallel and perpendicular to electric vector
ꢀ
⊥
of linearly polarized light, respectively. Degree of the photoreaction of cinnamic acid films
as a function of exposure doses is described in Fig. 6. It was found that the photoreaction
of cinnamide groups use larger dose than that of P6CAM and P6CAM-S indicating that
structure of molecular terminal strongly affected photorecativity of PLCPs.
Figure 7 plots the photoinduced dichoroism, ꢀA = A − A , of cinnamic acid and
ꢀ
⊥
their derivative films as a function of the exposure doses. All the films show a generation
of a negative ꢀA due to the axis-selective photoreaction though P6CAM-S showed small
Figure 7. Change in photoinduced optical anisotropy of the polymers.

128
M. Kondo et al.
Figure 8. Polarized absorption spectrum of P6CAM-A1 films before photoirradiation after photoir-
radiation and subsequent annealing.
dichoroism. It was well known that the annealing process enhanced the photoinduced
optical anisotropy of cinnamic LC polymers. Figure 8 shows polarized absorption spectrum
of PLCP films before and after photoirradiation and subsequent annealing. In this case, the
degree of the photoreaction was fixed to 3% (30 mJcm−2) that induces largest value for
P6CAM under thermal amplification. It was found that the optical anisotropy between
A and A became larger on annealing. Additionally, the absorption of A and A after
ꢀ
⊥
ꢀ
⊥
annealing was smaller than that after exposure. These results indicate that the cooperative
effect in P6CAM-A1 is not large enough to reorient the mesogenic side group in the
in-plane direction after the annealing procedure even it showed LC phase and containing
hydrogen bonding.
The annealing temperature affects the efficiency of the thermal amplification of the
molecular alignment of the film. The amplified molecular alignment is evaluated as follow-
ing equation,
A − A
||
⊥
S =
(2)
2Asmall + Alarge
Figure 9. Thermally enhance in-plane order parameter of cinnamide film as a function of annealing
temperature. The degree of photoreaction was fixed in 3%.

Synthesis of Cinnamide LC Polymers
129
Figure 10. Thermally enhanced S values of P6CAM-A1 film when the annealing time is varied.
and Alarge is the larger value of A and A , and Asmall is the smaller one. Figure 9
ꢀ
⊥
represents the amplified S values of the P6CAM-A1 and A2, when the exposed film
is annealed at various temperatures. It is observed that the amplification occurred for
P6CAM-A1 films when the annealing temperature was between 130 and 150◦C while
P6CAM-A2 showed no amplification. Although the amplification in P6CAM-A1 film
was induced when the film was heated over 4 minutes, we fixed the annealing time to
unify the experimental condition to the previous work (Fig. 10). Additionally, the am-
plified value was smaller than that of, previous work, P6CAM. It can be presumed
that the hydrogen bonding perpendicular to the director axis affects the reorientation
behavior.
Finally, we dipped P6CAM-S film into liquid 4-alkylaniline whether cinnamide group
directly convert from succiimide film. P6CAM-S showed a strong peak at 1739 cm−1
,
originating from C O bond at succinic imide. On the other hand, the peak was erased
and new broad peaks around 1700–1650 cm−1 was detected alternatively when the reac-
tion proceeded similar to reaction in the powder state. These peaks are originating from
phenylamide ring indicating that the imide group converted to amide group in a film state
(Fig. 11).
Figure 11. ATR-IR spectra of the P6CAM-A1, A2 and P6CAM-S film.

130
M. Kondo et al.
Conclusions
We prepared novel photoreactive LC polymer via polymer reaction. The cinnamic acid
activated ester easily converted to amide by mixing with amine derivative and solubility of
the polymer reduced due to hydrogen bonding. Upon exposure to UV light and subsequent
annealing, the LC cinnamide exhibited axis selective photoreaction and following thermally
amplification of molecular alignment. However, photoreactivity, LC stability and thermal
amplification behavior of the cinnamide group were lower than that of original cinnamic
acid group, suggesting that the lateral hydrogen bonding disturbs molecular reorientation
behavior.
Acknowledgment
The authors are grateful to Dr. Yusuke Daiko for important discussions. This work was
supported in part by a Grant-in-Aid for scientific research in priority areas “new frontiers
in photochromism” from the ministry of education culture sports science and technology
and research grant from University of Hyogo.
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