Preparation of conducting liquid crystalline polymer based of poly(2-ethanol aniline)

Article abstract of DOI:10.1080/15533174.2012.750345

The authors prepared a novel conducting liquid crystalline polymer based poly(2-ethanol aniline) by chemical and electrochemical methods. First, 2-anilinoethyl-3-chloropropionate was synthesized by reaction of 2-ethanol aniline and 3-chloropropionate in presence of dicyclohexylcarbodiimide (DCCI) and (dimethylamino)pyridine (DMAP). Then, {2-[ethyl[4-[(4-nitrophenyl)azo] phenyl]amino]ethanol}, Disperse Red-I, (Red1) was prepared from addition of 2-(N-ethyl-N-phenylamine) with the 4-nitrobenzenamine. Potassium salt Red1 was prepared by reaction of potassium and Red1 in THF. Then added to 2-anilinoethyl-3-chloropropionate for chemically synthesis of poly[2-anilino-{3-[2-[ethyl[4-[(4-nitrophenyl)azo]phenyl]amino] propanoate]}], Poly(2AECP-Red1). Produced polymer was characterized using FT-IR, UV-visible, and ¹H, ¹³C-NMR spectroscopies. The thermal and liquid crystalline properties of polymer were studied by thermogravimetric and differential scanning calorimetry. Scanning electron microscopy images supported the formation of polymer and showed morphology feature and homogeneous structure on polymer. Electrical conductivity of Poly(2AECP-Red1) has been studied by four-point probe method and produced 4.9 × 10^-3 S/cm conductivity for it.

Full text of DOI:10.1080/15533174.2012.750345

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Preparation of Conducting Liquid Crystalline Polymer
Based of Poly(2-ethanol aniline)
S. Hossein Hosseini a , Y. Sarrafi b & S. A. Hosseini b
a Department of Chemistry, Faculty of Science, Islamic Azad University, Islam-Shahr Branch,
Tehran, I. R. Iran
b Department of Chemistry, Faculty of Science, Mazandaran University, Babolsar, I. R. Iran
Accepted author version posted online: 04 Mar 2013.
To cite this article: S. Hossein Hosseini , Y. Sarrafi & S. A. Hosseini (2013): Preparation of Conducting Liquid Crystalline
Polymer Based of Poly(2-ethanol aniline), Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry,
43:7, 838-846
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 43:838–846, 2013
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2012.750345
Preparation of Conducting Liquid Crystalline Polymer Based
of Poly(2-ethanol aniline)
S. Hossein Hosseini,1 Y. Sarrafi,2 and S. A. Hosseini2
1Department of Chemistry, Faculty of Science, Islamic Azad University, Islam-Shahr Branch, Tehran,
I. R. Iran
2Department of Chemistry, Faculty of Science, Mazandaran University, Babolsar, I. R. Iran
be used to study the photoisomerization, and chiral groups
can be introduced into polymers easily by the method of
copolymerization. Up to now some side chain liquid crystalline
chiral copolymers with azo groups have been prepared and
investigated.[4,5] For example, Niesel et al.[6] studied poly-{4-ω-
methacryloxyhexyloxy-4ꢀ-butyloxyazobenzene}-co-{(S)-4-(ω-
methacryloxyhexyloxy)phenyl-4-(2-methylbutyloxy)benzoa-
te}, which showed nematic and metastable SA phases. Gui
et al.[7] investigated the preparation liquid crystalline side-chain
azo copolymers poly(2-ethynylpyridinium bromide) which
showed cholesteric and smectic phases. In previous works,
we synthesized a new liquid single crystal[8] and reported
liquid crystalline polymer-based N-substituted pyrrole.[9] This
polymer exhibit liquid crystalline and electrically conductivity
properties, as well. In the present article, we report the studies
on the synthesis of a novel conjugated ionic polymer, poly[2-
anilino-{3-[2-[ethyl[4-[(4-nitrophenyl)azo]phenyl]amino] pro-
panoate]}], Poly(2AECP-Red1), having the side chain liquid
crystalline moiety and the characterization of the resulting
conjugated ionic polymer. Figure 1 vividly demonstrates the
opportunity of the molecular design of widespread LC polymer
containing mesogenic group in main chain (poly-2anilino
ethanol), and side chains (side chain liquid crystalline moiety).
The authors prepared a novel conducting liquid crystalline
polymer based poly(2-ethanol aniline) by chemical and elec-
trochemical methods. First, 2-anilinoethyl-3-chloropropionate
was synthesized by reaction of 2-ethanol aniline and 3-
chloropropionate in presence of dicyclohexylcarbodiimide (DCCI)
and (dimethylamino)pyridine (DMAP). Then, {2-[ethyl[4-[(4-
nitrophenyl)azo]phenyl]amino]ethanol}, Disperse Red-I, (Red1)
was prepared from addition of 2-(N-ethyl-N-phenylamine) with the
4-nitrobenzenamine. Potassium salt Red1 was prepared by reac-
tion of potassium and Red1 in THF. Then added to 2-anilinoethyl-
3-chloropropionate for chemically synthesis of poly[2-anilino-
{3-[2-[ethyl[4-[(4-nitrophenyl)azo]phenyl]amino] propanoate]}],
Poly(2AECP-Red1). Produced polymer was characterized using
FT-IR, UV-visible, and 1H, 13C-NMR spectroscopies. The thermal
and liquid crystalline properties of polymer were studied by ther-
mogravimetric and differential scanning calorimetry. Scanning
electron microscopy images supported the formation of polymer
and showed morphology feature and homogeneous structure on
polymer. Electrical conductivity of Poly(2AECP-Red1) has been
studied by four-point probe method and produced 4.9 × 10–3 S/cm
conductivity for it.
Keywords: conducting polymers, liquid crystalline, poly(2-ethanol
aniline), preparation
INTRODUCTION
Side-chain liquid crystalline polymers have caused interest
because of their theoretical aspects and potential uses in
electro-optical and information-storage devices.[1,2] Particular
interest in preparation and investigation of azodye containing
liquid crystalline polymers has increased recently because of
their potential application in optical storage devices due to
both the reversibility of the isomerization and the large steric
difference between the two isomeric states.[3] On the other
hand, functional groups such as the azo group, which can
EXPERIMENTAL
Reagents and Materials
2-Anilinoethanol (Merck, Germany, 99%) was distilled un-
der reduced pressure from CaH2 prior to use, 4-nitroaniline
(Merck, 98%), dicyclohexyl carbodiimide (DCC) (Merck,
98%), 4-(dimethylamino) pyridine (DMAP) (Merck, 99%),
3-chloropropionic acid (Merck, 98%), natriumnitrit (NaNO2)
(Merck, 99%), methanol (Fluka, USA), and tetrahydrofuran
(Merck) were distilled and dried with molecular sieves (4 Å)
prior to use, methylene chloride (CH2Cl2) was distilled and dried
with CaCl2 prior to use, 2-(N-ethyl aniline) ethanol (Merck,
99%). All the other materials used in this work were purchased
from Merck chemicals and purified, or prepared according to
literature methods.
Received 27 August 2012; accepted 13 November 2012.
Address correspondence to S. Hossein Hosseini, Department of
Chemistry, Faculty of Science, Islamic Azad University, Islamshahr
Branch, Tehran, I. R. Iran. E-mail: dr.shhosseini@gmail.com
838

LIQUID CRYSTALLINE POLYMERS
839
Synthesis of 2-anilinoethyl-3-chloropropionate
A total of 14 mmol of 3-chloropropionic acid and 12 mmol
of 2-ethanol aniline were dissolved in 80 mL of dry CH2Cl2.
Then 2.59 g (13 mmol) of dicyclohexylcarbodiimide and 0.22 g
(1.8 mmol) of (dimethylamino)pyridine were added to the vig-
orously stirred solution. The stirred was continued for 24 h. The
mixture was then filtered and the solvent was removed by rotary
evaporator under vacuum. The product was purified on silica
gel using methylene chloride (yield 89%, red crystals).
UV (THF); λmax = 285 nm (1.31 intensity), 360 nm (1.79
intensity). FT-IR (KBr): 3390, 3080, 2985, 1740, 1510, 1460,
1410, 1330, 1100, 810, 660 cm–1. 1H NMR (CDCl3); 2.7 (2H,
t), 3.5 (2H, t), 3.7 (2H, t), 3.8 (2H, t), 6.3–7.5 (5H, m) ppm.
13C NMR (CDCl3); 26.1, 45.5, 49.6, 62.1, 63.3, 123.3, 136.5,
146.5, 148.1, 165.1 ppm.
FIG. 1. Schematic representations of macromolecule of LC Poly(2AECP-
Red1) with mesogenic group.
Instrumentals
Synthesis of 2-anilinoethyl-3-chloropropionate-{2-[ethyl
[4-[(4ꢁ-nitrophenyl)azo]phenyl]amino] ethanol},
Conductivity changes were measured with four-probe de-
vice (ASTM Standards, USA, F 43–93). A Fourier transform
infrared spectrometer (8101 M-Shimadzu, Japan) was used in
spectral studies of the films. Vibrational transition frequencies
(Bruker, Germany) were reported in wave number (cm–1). Proton
and carbon nuclear magnetic resonance [FT-(1H & 13C) NMR]
spectra were recorded at 250 MHz on a Bruker (Germany),
and NMR data were reported in the following order: chemi-
cal shift (ppm), spin multiplicity (s = singlet, d = doublet, t
= triplet, q = quartet, m = multiplet), and integration. Visible
spectra were obtained by Perkin-Elmer Lambda 15 spectropho-
tometer (USA). The Perkin-Elmer (DSC-4) and Perkin-Elmer
pyris-1 were used for thermal analyzes (USA) and the PHILIPS
XL30 (Netherlands) was used for scanning electron microscopy
(SEM).
(2AECP-Red1)
In the three-neck flask equipped with condenser, magnetic
stirrer, nitrogen contact, 6.36 g (0.02 mol) {2-[ethyl[4-[(4ꢀ-
nitrophenyl)azo]phenyl]amino] ethanol} (Red1) was dissolved
in 80 mL THF. In the nitrogen atmosphere 0.83 g (0.02 mol)
potassium was added, thenrefluxedfor 5hat 75◦C. After cooling
to room temperature, the solution of 0.02 mol 2-anilinoethyl-
3-chloropropionate in 80 mL THF was dropped slowly from a
funnel. The solution was stirred for 24 h at room temperature
then refluxed for 4 h at 75◦C. The solution was concentrated
until most of THF was distilled out 100 mL methanol as added.
The red deposit was collected, washed with water, and extracted
in a soxhlet extractor with acetone for four days. The product
was dried in vacuum, yield: 55%.
UV (THF); λmax = 290 nm (1.52 intensity), 370 nm (1.39
intensity), 465 nm (0.85 intensity). FT-IR (KBr): 3405, 3100,
2990, 1760, 1550, 1510, 1420, 1320, 1250, 1115, 1010, 910,
Preparation of 2-[N-ethyl-N-[4-[(4-nitrophenyl)azo]-
phenyl]amino]ethyl (Red1) [9]
1
850, 790, 680 cm–1. H NMR (CDCl3); 0.9 (3H, t), 2.5 (2H,
A total of p-nitroaniline (7 g, 0.05 mol) was dissolved in a
solution of H2O (150 mL) and HCl (25 mL). The mixture was
then heated to 30◦C for 15 min and allowed to be cooled. In
the next step 3.6 g of NaNO2 (0.05 mol) in H2O (5 mL) was
added and stirred for 30 min. A solution of N-ethyl-N-hydroxy
ethyl aniline (10 g, 0.03 mol) in HCl (10%) was prepared in
the other container at 0◦C simultaneously. The latter was added
dropwise to the initial solution. The reaction was stirred for
30min and then neutralized by adding NaOH (10%). Finally
filtration was followed by evaporation of the solvent that led to
a red solid, which recrystallized with isopropanol. Yield: 85%,
red crystals. UV (ethanol); λmax = 280 nm (2 intensity), 360 nm
(0.5 intensity), 470 nm (1.25 intensity). FT-IR (KBr): 3250,
3100, 2979, 1594, 1512, 1469, 1320, 780, 650 cm–1. 1H NMR
(CDCl3); 1.26 (3H, t), 1.75 (1H, s), 3.56 (2H, q), 3.62 (2H, t),
3.90 (2H, t), 6.81 (2H, d), 7.88 (2H, d), 7.92 (2H, d), 8.32 (2H,
d) ppm. 13C NMR (CDCl3); 12.1, 25.8, 46.4, 61.1, 112.3, 122.5,
124.7, 126.6, 143.8, 145.6, 151.6, 155.7 ppm.
m), 2.8–3.2 (4H, m), 3.5–4.1 (8H, m), 6.5 (2H, d), 6.9 (2H, d),
7.1–8.5 (6H, m), 8.8 (2H, t) ppm. 13C NMR (CDCl3); 13.2, 23.4,
25.8, 29.5, 38.9, 45.5, 59.5, 65.1, 112.3, 117.6, 120.6, 122.5,
124.7, 127.5, 130.1, 146.5, 148.6, 151.5, 155.2, 165.2 ppm.
Synthesis of Chemical Polymerization of 2-anilinoethyl-3-
chloropropionate-{2-[ethyl[4-[(4ꢁ-nitrophenyl)azo]
phenyl]amino]ethanol}, Poly(2AECP-Red1)
0.5 g (2AECP-RED1) is completely dissolved in 30 mL of
dimethylsulfoxide (DMSO). 0.5 g p-toluensulfonic acid is added
to the solution, then mixture is vigorously stirred and reduced
temperature to 5◦C. In a separate container 2 g (0.0088 mmol)
(NH4)2S2O8 (ammonium peroxydisulfate) is dissolved in 10 mL
tosic acid solution. The oxidant solution is slowly added at a
rate of approximately 5 mL per minute to the mixture. After the
mixture is allowed to stir for 10 min, a solution containing 1 g
sodium sulfite in 5 mL water/DMSO is added to the mixture.

840
S. H. HOSSEINI ET AL.
SCH. 1. Schematic of chemical synthesis of Poly(2AECP-Red1).
1
1250, 1150, 1050, 1000, 875, 810, 610, 590 cm–1. H NMR
The mixture is stirred for about 2 h and polymer solution is
filtered using G2 sintered glass filter, then precipitated into ice
methanol. The product was washed successively by distilled
water and methanol and dried at 60◦C for 24 h.
UV (DMSO); λmax = 290 nm (1.5 intensity), 360 nm (0.89
intensity), 480 nm (0.68 intensity), 650 nm (0.35 intensity).
FT-IR (KBr): 3100–3500, 3050, 2990, 1750, 1610, 1500, 1400,
(d6-DMSO); 1.1, 2.3, 3.6, 3.7, 4.2, 4.9, 5.6 (2H, d), 6.9 (2H,
d), 7.3 (2H, d), 7.4 (2H, d), 7.8 (2H, d), 8.0 (4H, m), 8.3 (2H,
d), 8.4 (2H, d), ppm. 13C NMR (d6-DMSO); 11.2, 37.2, 37.6,
44.5, 45.6, 51.2, 57.5, 106.5, 110.3, 119.5, 121.7, 121.8, 124.2,
125.4, 125.5, 127.2, 132.8, 133.2, 141.8, 146.0, 151.2, 155.6,
170.1 ppm.

LIQUID CRYSTALLINE POLYMERS
841
RESULTS AND DISCUSSION
FT-IR Spectroscopy
The FT-IR spectrum of poly(2AECP-Red1) is shown in Fig-
ure 2. In this figure, polymer show the amine N-H and O-H
bonds stretching (3100–3500 cm–1) frequencies. Instead, the
C C stretching frequency peak of conjugated polymer back-
bone at 1610 and 1400 cm–1. The C-H aromatic and aliphatic
and C O and N N stretching frequency peaks at 3050, 2990,
1750, and 1500 cm–1 related to 2-anilinoethyl backbone and
azobenzene moieties, respectively.
Polymerization Reactions and UV-Visible Spectroscopy
The 2-anilinoethyl-3-chloropropionate-{2-[ethyl[4-[(4ꢀ-nit-
rophenyl)azo] phenyl]amino] ethanol}, (2AECP-Red1), can
be synthesized as shown in Scheme 1, where the resulting
monomer has substituted 2-anilinoethyl-3-chloropropionate and
Red1 units. The existed 2-anilinoethanol in 2AECP-Red1 can
be oxidatively polymerized by APS. Resulted polymer included
both conducting backbone polymer and mesogenic side chain
group. The polymerization occurs readily, although the reaction
has steric interactions.
NMR Spectroscopy
The FT1H-NMR spectrum of poly(2AECP-Red1) are pre-
sented in Figure 3. On the basis of the comparison with the
spectrum of the monomer, the following lines were assigned
corresponding to the protons of the chromophore: 1.1 (-CH3),
2.3 (-CH2-COO-), 2.5 (DMSO), 3.5 (H2O), 3.6 (-CH2-CH3),
3.7 (-CH2-N), 4.2 (-O-CH2-), 4.9 (CH2-N-) 6.9–8.5 ppm (pro-
tons of azo benzene and phenylene groups). The satellite peaks
probably overlaps with -CH2- groups at 3.2–3.8 ppm. The
FT13C-NMR spectrum of poly(2AECP-Red1) was show in Fig-
ure 4. The 11.2–57.5 ppm lines were assigned correspond-
ing to the aliphatic protons of mesogenic side chain group
and some of peaks probably overlap with solvent assigns.
The 106.5–170.1 ppm lines were assigned corresponding to
the aromatics protons of azobenzene and phenylene groups.
Here is more few peaks that probably related to cis and trans
conformations.
UV-visible spectrum of poly(2AECP-Red1) in DMSO as a
solvent was investigated. Upon UV irradiation, a trans-cis iso-
merization is induced, leading to three absorption bands cen-
tered near 290, 360, and 480 nm, respectively. The first and
third absorption bands are related to the π-π∗ transition of trans
configuration of the azobenzene moieties. Second absorption
bond was related to a π-π∗ transition while the latter is asso-
ciated with a n-π∗ transition. This phenomenon could occur to
UV-visible data for monomer, as well. Therefore, poly(2AECP-
Red1) exhibits a abroad absorption bands around 550–750 nm
which can be related to the π-π∗ transition of the highly conju-
gated polymer units. So, UV-visible spectrum of poly(2AECP-
Red1) showed a peak in the visible region characteristic of a
conjugated polymer system; these spectral data indicated that
the polymer has a conjugated backbone system having liquid
crystalline moieties.
FIG. 2. FT-IR spectrum of Poly(2AECP-Red1).

842
S. H. HOSSEINI ET AL.
FIG. 3. 1HNMR Spectra of Poly(2AECP-Red1).
FIG. 4. 13CNMR spectrum of Poly(2AECP-Red1).

LIQUID CRYSTALLINE POLYMERS
843
FIG. 5. DSC thermogram analysis of poly(2AECP-Red1) (color figure available online).
FIG. 6. TGA thermogram analysis of poly(2AECP-Red1).

844
S. H. HOSSEINI ET AL.
FIG. 7. Cross-polarized optical micrograph of poly(2AECP-Red1). (a,b) Crystalline to nematic phase at 40–50◦C and (c,d) nematic texture at 160–170◦C (color
figure available online).
Differential Scanning Calorimetry
Thermogravimetry Analysis
Differential scanning calorimetry (DSC) measurement of the
The thermogravimetric analysis (TGA) of poly(2AECP-
polymer was carried out as shown in Figure 5. The DSC ther- Red1) (Figure 6) shows that it has thermal resistance lower
mogram of poly(2AECP-Red1) showed two endothermic peaks than polyaniline. This curve exhibits a softening temperature
that appear at 45◦C and 165◦C in heating. During the thermal in 100◦C and degradation initiation at more than 110◦C. This
examination of poly(2AECP-Red1) it was found that first glassy polymer was heated first at 20◦C; it approximately lost 5%
polymer should be heated up to 45◦C. The curve shows a phase of its weight up to 100–170◦C which due to the humidity
transition, crystalline phase changed to nematic phase (C→N) at and existence of solvent in the polymer chain. poly(2AECP-
45◦C. Another transition phase from nematic to isotropic phase Red1) is stable to below 110◦C and in the range of 170–230,
(N→I) occurred at 165◦C. Mesophase of this polymer would 230–270, 270–350, 350–450, and 450–680◦C approximately
be assigned to nematic phase owing to the transition enthalpy lost 5.6, 4.1, 9.2, 9.3 and 10.9% of its weights, which are due
change from mesophase to isotropic fluid. Besides, these results to degraded azobenzene moiety and polymer backbone. Poly-
were confirmed by optical polarizing studies. DSC curves do mer has started to completely decompose over 200◦C. In addi-
not show any peak after cooling.
tion the TGA curve of poly(2AECP-Red1) illustrates that initial

LIQUID CRYSTALLINE POLYMERS
845
FIG. 8. SEM Images of Poly(2AECP-Red1) film. (a,b) Surface, (c) mesoporous surface, and (d) cross cut section.
decomposition temperature (IDT), polymer decomposition tem- nanoporous poly(2AECP-Red1) with agglomerated sphere was
perature (PDT) and the maximum polymer decomposition tem- observed (Figure 8). In figures cases spongy/spherical morphol-
perature (PDTmax) are 180◦C, 350◦C, and 680◦C, respectively. ogy were quite clear. Similar morphology was also observed pre-
The residual weight (γ c) of the polymer is 60% at 680◦C.
viously for the polyaniline nanomaterials[10] and mesoporous[11]
synthesized by other methods. Figure 8 shows the cross cut of
this film, which shows the homogeneity and preparation of LC
Optical Polarizing Microscopy
The optical properties of liquid crystals such as birefrin- substituted on polymer was successfully.
gence are not only interesting but also lead to vividly visi-
Electrical Conductivity
ble effects. The combination of anisotropy of the shape of the
molecules and director configurations varying on a scale equal
to wavelength produces a wide variety of marvelous color pat-
terns which can be observed in a polarizing microscope, by
placing the sample between crossed-polarizer. This property is
utilized by all commercial liquid crystal devices. In the first
and the second transitions, the stability of liquid crystalline
mesophase is about 110◦C. Images of polarizing optical mi-
croscope of poly(2AECP-Red1) demonstrate the three phases,
crystalline, nematic, and isotropic liquid crystalline phases in
the ranges 40–50◦C, 160–170◦C, and above 170◦C temper-
atures, respectively. This indicates the poly(2AECP-Red1) is
a isotropic compound. Cross-polarized optical micrographs of
poly(2AECP-Red1) are shown in Figure 7. The polymer showed
crystalline to nematic phase at 40–50◦C and nematic texture at
160–170◦C. This observation is in good agreement with the re-
sults of the DSC experiment. It shows the isotropic transition
above at ∼170◦C.
Electrical conductivity of poly(2AECP-Red1) was studied
by the four-probe method. The conductivity obtained was 4.9 ×
10–3 Scm–1. This value is several times lower than conductivity
of polyaniline. This low conductivity can be related to the intro-
ducing azobenzene moiety in the polymer chain. The introduc-
tion of azobenzene moiety in to the polymer tends to decrease
the average conjugation length in the polymer backbone.
CONCLUSION
In this article we have described the preparation and in-
vestigation of a series of conducting liquid crystalline polymer
with azobenzene group based poly(2AECP-Red1) as conducting
polymer. This polymer exhibited conductivity and mesophase
behaviors. The phase transition temperatures recorded by
DSC and optical polarizing microscopy. Images of polariz-
ing optical microscope of poly(2AECP-Red1) demonstrate the
three phases, crystalline, nematic, and isotropic liquid crys-
talline phases in the ranges 40–50◦C, 160–170◦C, and above
170◦C temperatures, respectively. Electrical conductivity of
poly(2AECP-Red1) was obtained 4.9 × 10–3 Scm–1. They are
expected to have good long term optical storage properties, fur-
ther investigation is in progress.
Scanning Electron Microscopy
Scanning electron microscopy (SEM) images of poly
(2AECP-Red1) prepared using ammonium peroxydisulfate as
the oxidizing agent are shown in Figure 8, which had been pre-
pared by chemically method (casting method). Images of Fig-
ure 8 show the surface this polymer. SEM micrographs clearly
show that poly(2AECP-Red1) is in the form of spongy shape
and homogenous texture. However with the azobenzene moiety
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