Synthesis and properties of liquid-crystalline-conjugated polymers

Article abstract of DOI:10.1246/bcsj.80.649

We have synthesized novel liquid-crystalline (LC)-conducting polymers by introducing LC groups into acetylene monomers and polymerizing them with Ziegler-Natta, metathesis, and rhodium-based catalysts. All polymers prepared were soluble in organic solvents and had a thermotropic liquid crystallinity characterized with fan-shaped texture in polarizing optical microscopy. Phase transitions and the corresponding enthalpy changes were also evaluated by means of differential scanning calorimeter (DSC). High-order structures of the polymers were investigated by means of X-ray diffraction (XRD) analyses. XRD measurements showed that the polymers had layered structures in the LC state to give smectic A phases, which is in agreement with the results from the polarizing optical microscope. We found that the LC side chains alternate on both sides of the polyene chain, giving rise to a stereoregular sequence, such as head-head-tail-tail linkage. Macroscopic alignments of the polymers were performed in the liquid-crystalline phase by shear stress or a magnetic force field of 0.7-1.0 Tesla, which resulted in an enhancement by two orders of magnitude in the electrical conductivity of iodine-doped cast films. Orientation behaviors of the polymers as well as the monomers were investigated using fused-state ¹³CNMR measurements with proton dipolar decoupling. Analysis of chemical shift tensors was also carried out to evaluate the order parameter and shielding anisotropy in the LC phase. As a result, we demonstrated that LC-conjugated polymers uniaxially aligned due to the magnetically forced alignment of the LC side-chain, giving rise to a monodomain structure.

Full text of DOI:10.1246/bcsj.80.649

Ó 2007 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 80, No. 4, 649–661 (2007)
649
Accounts
Synthesis and Properties of Liquid-Crystalline-Conjugated Polymers
Kazuo Akagi
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Katsura, Nishikyo-ku, Kyoto 615-8510
Received March 7, 2006; E-mail: akagi@star.polym.kyoto-u.ac.jp
We have synthesized novel liquid-crystalline (LC)-conducting polymers by introducing LC groups into acetylene
monomers and polymerizing them with Ziegler–Natta, metathesis, and rhodium-based catalysts. All polymers prepared
were soluble in organic solvents and had a thermotropic liquid crystallinity characterized with fan-shaped texture in po-
larizing optical microscopy. Phase transitions and the corresponding enthalpy changes were also evaluated by means of
differential scanning calorimeter (DSC). High-order structures of the polymers were investigated by means of X-ray dif-
fraction (XRD) analyses. XRD measurements showed that the polymers had layered structures in the LC state to give
smectic A phases, which is in agreement with the results from the polarizing optical microscope. We found that the LC
side chains alternate on both sides of the polyene chain, giving rise to a stereoregular sequence, such as head–head–tail–
tail linkage. Macroscopic alignments of the polymers were performed in the liquid-crystalline phase by shear stress or a
magnetic force field of 0.7–1.0 Tesla, which resulted in an enhancement by two orders of magnitude in the electrical
conductivity of iodine-doped cast films. Orientation behaviors of the polymers as well as the monomers were investi-
gated using fused-state 13C NMR measurements with proton dipolar decoupling. Analysis of chemical shift tensors
was also carried out to evaluate the order parameter and shielding anisotropy in the LC phase. As a result, we demon-
strated that LC-conjugated polymers uniaxially aligned due to the magnetically forced alignment of the LC side-chain,
giving rise to a monodomain structure.
situation means that a monodomain structure of the LC phase
can be constructed on a macroscopic level. Thus, the polymer
should have a higher electrical conductivity, compared with
the case of random orientation. At the same time, one can con-
trol the molecular orientation, and hence the electrical conduc-
tivity of the polymers with an external force. Figure 1 shows
schematically both spontaneous orientation and externally
forced macroscopic alignment of side chain type LC-conjugat-
ed polymers, where the former and the latter generate multi
and mono domains of LC phases, respectively. Currently, a
series of LC polyacetylene derivatives have been synthesized
and characterized from aspects of thermal and electrical prop-
erties.4 For these novel LC-conducting polymers, the macro-
scopic alignment has been first achieved under magnetic force
field.4e Since it is possible to prepare a variety of LC-conduct-
ing polymers, it is straightforward to study other kinds of con-
jugated polymers. In fact, following LC polyacetylene deriva-
tives, which are to be reviewed in more details, various types
of LC polymers have been synthesized over the last few dec-
ades. Scheme 1 shows representative LC-conducing polymers,
e.g., LC polyene derivatives with a six-membered cyclic back-
bone structures, such as poly(1,6-heptadiyne) and poly(dipro-
pargylamine),5 polythiophene derivatives with mesogenic
groups at 3-position of thiophene rings,6 LC polypyrrole deriv-
atives with mesogenic groups at 3-position or N-position of
1. Introduction
Among a variety of electrically conducting polymers report-
ed so far, polyacetylene is the most typical conjugated polymer
that has been studied,1 and it has the highest electrical conduc-
tivity in the order of 104–105 S cmꢀ1 upon an iodine doping.2
However, it is insoluble and infusible, which makes it difficult
to determine its molecular weight and chemical structure and
to process the polymer in solution, such as casting. Introduc-
tion of alkyl or aromatic substituents onto the polyacetylene
chain makes the polymer soluble in organic solvents, when
the alkyl chain length is sufficiently long, i.e., hexyl, pentyl,
and octyl groups.3 Electrical conductivity of substituted poly-
acetylene, however, is significantly lower than that of non-sub-
stituted polyacetylene. This is due to less coplanarity of the
main chain arising from steric repulsions between substituents
as well as a higher ionization potential and a lower electron
affinity. In addition, even in the substituted polyacetylene,
the main chain is still randomly oriented, which suppressed
the observed electrical conductivity of the polymer.
If the substituent is a liquid-crystalline (LC) group, the poly-
mer is not only soluble in organic solvents, but also easily
aligned by spontaneous orientation of the LC group. Besides,
it could be macroscopically aligned by an external perturba-
tion, such as shear stress, electric or magnetic force field. This
Published on the web April 13, 2007; doi:10.1246/bcsj.80.649

650 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
ACCOUNTS
tography (GPC) using polystyrene standards, and electrical
conductivities upon iodine doping of cast films of the polymers
were measured by using a four-probe method. Morphologies
were examined through measurements of scanning electron
microscopy (SEM).
Domain of LC
2. Preparation
2.1 Syntheses of Monomers. (i) The PCHn03A was syn-
thesized by reacting para-(trans-4-alkylcyclohexyl)phenol and
5-chloro-1-pentyne in sodium ethoxide by using potassium
iodide as a catalyst (Scheme 3). (ii) Four steps to synthesize
BP503A were necessary. First, 4-methoxy-40-pentanoylbi-
phenyl (1) was synthesized through a Friedel–Crafts reaction
between 4-methoxybiphenyl and pentanoyl chloride in nitro-
benzene using aluminium chloride as a catalyst. The carbonyl
moiety of 1 was reduced to a methylene group by hydrazine
and potassium hydroxide in diethylene glycol to yield 4-
methoxy-40-pentylbiphenyl (2). The methoxy group of 2 was
changed into a hydroxy group using hydrogen bromide in ace-
tic acid and tetra-n-butylammonium bromide (TBAB). Etheri-
fication of the product 40-pentyl-4-biphenylol (3) was carried
out by coupling it with 5-chloro-1-pentyne in sodium ethox-
ide using potassium iodide as a catalyst, yielding BP503A
(Scheme 3).
Multidomain
External force
Monodomain
Spontaneous
orientation
2.2 Polymerizations of Monomers. Polymerizations of
PCHn03A and BP503A were carried out by using a Ziegler–
Natta catalyst,19 Fe(acac)3–AlEt3, and a metathesis catalyst,20
MoCl5–Ph4Sn, in toluene for 21 h at room temperature. For
some of the monomers, a chlorine-bridged rhodium complex,21
[Rh(NBD)Cl]2, was used with NEt3 as a co-catalyst, and the
polymerization time was within 6 min at room tempera-
ture.4f–g The polymerizations were terminated by pouring the
reaction mixture into a large amount of methanol. The poly-
mers were filtered off, washed with methanol and then dried
under vacuum. The yields and molecular weights evaluated
from GPC are summarized in Table 1. The MoCl5–Ph4Sn cat-
alyst gave higher yields of the polymers than the Fe(acac)3–
AlEt3 catalyst. The number-average molecular weight of
(Mn ¼ 105) was higher for Fe-based PPCH803A. Although
Fe-based PBP503A was insoluble in tetrahydrofuran (THF)
and benzene in the range of room temperature to 90 ꢁC, it
was soluble in cumene upon heating up at 120 ꢁC for 30 min.
The dissolved polymer had a low viscosity and relatively small
molecular weight (3000 < Mn < 4000). This may be due to
decomposition during the heating process.
Fig. 1. Schematic representation of spontaneous and mag-
netically forced orientations of side chain LC-conjugated
polymer.
pyrrole rings,7 LC poly(para-phenylene) derivatives,8 LC
poly(para-phenylenevinylene) derivatives,8 LC polythienyl-
enevinylene derivatives with mesogenic groups at phenylene
or thiophene rings,9 LC polyaniline derivatives with mesogen-
ic groups at ortho-position of aniline ring.10 In addition, small-
band gap LC-conjugated polymers11 based on benzonoid and
quinoid resonance structures were synthesized. Subsequently,
ferroelectric LC (FLC)-conjugated polymers12 consisting of
acetylene, thiophene, phenylene, or phenylenevinylene unit
cell were synthesized in order to achieve highly quick response
to an electric force field during macroscopic alignment. FLC-
conjugated polymers are reviewed elsewhere.
1.1 LC Polyacetylene Derivatives.4,13–18 The LC substitu-
ent on the monomer was composed of a phenylcyclohexyl
(PCH) moiety as a mesogenic core, methylene chain linked
with an ether-type oxygen atom, –(CH2)3O, as a spacer, and
an alkyl chain (–CnH2nþ1, n ¼ 2, 3, and 5–8) as a terminal
group, and the monomer is abbreviated as PCHn03A, where
A stands for acetylene segment. Another LC substituent con-
sists of a biphenyl (BP) mesogenic core, a methylene chain
linked with oxygen as a spacer, and an n-pentyl group as a
terminal moiety. In this case, the monomer is abbreviated
as BPn03A (n ¼ 5). The monomers were polymerized with
Ziegler–Natta, metathesis, and rhodium-based catalysts. The
corresponding polymers are abbreviated as PPCHn03A and
PBPn03A, as shown in Scheme 2.
3. Properties
3.1 LC Phases of Monomers.
Liquid crystallinity of
PCHn03A was determined with a miscibility test. Figure 2
shows a phase diagram of a mixture of PCH803A and 1-hex-
yloxy-4-(trans-4-propylcyclohexyl)benzene, PCH306. The lat-
ter is known to have a nematic LC phase and, therefore, is used
as a reference. In the miscibility phase diagram, the mixture is
homogeneous irrespective of the mole ratio between the two
compounds. This indicates that the LC phase of PCH803A is
nematic. The result is supported by the experimental facts that
PCH803A had a mesophase in DSC and it had a Schlieren tex-
ture characteristic of a nematic phase under a polarizing opti-
cal microscope. Similarly, PCHn03A with n ¼ 5{7 were also
The present monomers and polymers were characterized by
1
means of infrared (IR), UV–vis, H and 13C nuclear magnetic
resonance (NMR) spectroscopies, elemental analyses, DSC,
and polarizing optical microscopy. Molecular weights of the
polymers were evaluated by means of gel-permeation chroma-

K. Akagi
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
651
R
R
R
R
CH
C
x
x
x
x
R
R
1
2
4
3
R
R
R
R
x
S
S
x
x
x
R
x
7
8
5
6
R
NH
R
C
C
R
C
C
N
R
S
N
x
S
x
R'
R'
R
R
9
10
11
R
x
y
x
12
13
R
R
C H
R :
(O) (CH ) O
R :
R :
(O) (CH ) O
n
2n+1
l
2 m
CN
CN
l
2 m
(l = 0, 1; m = 3 ~ 6, 8, 10; n = 2, 3, 5 ~ 8)
(l = 0, 1; m = 3, 6, 8, 10)
R :
R :
CH COO(CH ) O
2 2 m
C H
CH O(CH ) O
5
11
2
2 m
(m = 10)
(m = 10)
O(CH ) O
C H
5 11
2 m
(m = 6)
Scheme 1.
found that the domain size of the LC phase increased with
an increase in terminal alkyl chain length of the side-chain
of the PCH polymer. In addition, the domain size of the Mo-
based PBP503A polymer was larger that of the Fe-based poly-
mer. This is consistent with the experimental fact that the latter
is thermally more stable than the former.
H
CnH2n+1
O(CH2)3
-(C=CH) -
x
PPCHn03A, n = 2, 3, 5 ~ 8
CnH2n+1
O-(CH2)3
DSC measurements of the polymers were carried out, as
shown in Fig. 4. It has been recently reported that the PCH
and BP polymers prepared with a Ziegler–Natta catalyst, such
as Fe(acac)3–AlEt3, assume a cis form, while those obtained
with a metathesis catalyst, such as MoCl5–Ph4Sn, exhibit a
trans form.13 Fe-based PPCH803A exhibited a large exother-
mic peak due to a cis–trans isomerization between 150 and
190 ꢁC in the first heating process. An endothermic peak
around 170 ꢁC was hidden by the isomerization peak. During
the first cooling period, a peak corresponding to an isotropic
to liquid crystal phase transition was observed at 146 ꢁC, and
that corresponding to liquid crystal to solid phase transition
at 98 ꢁC. During the second heating period, the liquid-crystal
phase was observed in the temperature range of 100–128 ꢁC.
Phase-transition temperatures and enthalpy changes of some
-(C=CH) -
x
PBPn03A, n = 5
Scheme 2.
confirmed to have nematic LC phases. It should be noted that
the above-mentioned mesophases of the monomers were ob-
served only during the cooling process, indicating that the
monomers are monotropic liquid crystals.
3.2 Liquid-Crystalline Phases of Polymers. All PCH and
BP polymers with LC groups in the side chain had fan-shaped
textures and uniaxial conoscopic patterns under a polarizing
optical microscope that are characteristic of a smectic A phase.
Typical fan-shaped textures of the polymers prepared with
Fe-based and Mo-based catalysts are shown in Fig. 3. It was

652 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
ACCOUNTS
EtOH, KI
reflux
ONa
+
CnH2n+1
Cl(CH2)3C≡CH
O(CH2)3C≡CH
+
NaCl
CnH2n+1
PCHn03A ( n = 2, 3, 5 ~ 8 )
AlCl3
+
C4H9COCl
OCH3
OCH3
C4H9CO
nitrobenzene
1
KOH
+
+
N2H4 H2O
OCH3
1
2
C5H11
diethylene glycol
2
CH3COOH
HBr
OH + CH3Br
C5H11
TBAB
3
TBAB = tetra-n-butylammonium bromide
EtOH
+ Cl(CH2)3C≡CH
O(CH2)3C≡CH
3
C5H11
Na, KI
4
BPn03A ( n = 5 )
Scheme 3.
Table 1. Polymerization Yields and Molecular Weights of PPCHn03A and PBP503A Prepared with Fe(acac)3–
AlEt3 and MoCl5–Ph4Sn Catalysts (acac = acetylacetonate)
bÞ
Fe(acac)3–AlEt3
MoCl5–Ph4SncÞ
PolymeraÞ
Yield
/%
Mn
Mw
Mw=Mn
Yield
/%
Mn
Mw
Mw=Mn
PPCH303A
PPCH503A
PPCH803A
PBP503A
71
70
67
65
5:5 ꢂ 105
4:5 ꢂ 105
5:2 ꢂ 105
3:5 ꢂ 103
2:6 ꢂ 106
1:8 ꢂ 106
2:6 ꢂ 106
1:0 ꢂ 104
4.7
4.0
5.0
2.9
61
67
73
85
1:5 ꢂ 104
1:4 ꢂ 104
1:2 ꢂ 104
7:5 ꢂ 103
3:4 ꢂ 104
3:3 ꢂ 104
2:7 ꢂ 104
6:8 ꢂ 104
2.3
2.4
2.3
9.1
a) Polymerized in toluene for 21 h at room temperature. [Monomer] = 3 mmol, [Fe(acac)3] = 0.01 mol Lꢀ1
,
[AlEt3]/[Fe(acac)3] = 6, [MoCl5] = 0.01 mol Lꢀ1, [Ph5Sn]/[MoCl5] = 0.5. b) Polymers are soluble in organic
solvents such as CHCl3, THF, and benzene at 50–60 ꢁC. For the measurements of GPC spectra, the polymers were
first dissolved in THF with heating and then allowed to cool to room temperature. c) Polymers are soluble in the
same solvents as mentioned above at room temperature.
representative polymers are listed in Table 2. In the PCH poly-
mer, the enthalpy change due to the smectic to isotropic phase
transition increased with an increase in the terminal alkyl chain
length. This means that the liquid-crystal state is more stabi-
lized with longer the alkyl chains as the terminal moiety of
the LC group. However, the stabilization of the liquid-crystal
state of the BP polymer was relatively small compared with
the PCH polymer. Mesophases of the PPCHn03A and
PBP503A were observed in both heating and cooling process-
es. This indicates that the polymers, irrespective of the catalyst
used in the polymerization, are enantiotropic liquid crystals.
Here, it should be emphasized that PCHn03A monomers
(n ¼ 5{8) had nematic phases, while all of the polymers had
smectic phases of which the ordering was higher than that in

K. Akagi
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
653
Fig. 2. Phase diagram of mixture of PCH803A and PCH306 (I = isotropic; N = nematic; C = crystalline).
the nematic phase. This can be rationalized by involving the
so-called polymerization effect, i.e., higher ordering in molec-
ular arrangement occurs due to the polymerization of the LC
monomer.16
with respect to the intervening double bond.17 As shown in
Table 3, all of the polymers have the side-chain separations
˚
of 4.6–4.8 A. This implies that the side-chain separations are
irrespective of differences in the LC substituents. Meanwhile,
the inter-layer distance increased as the terminal alkyl chain or
˚
the methylene chain became longer; it increased by 6.4 A from
3.3 Higher Order Structure and Stereospecific Con-
figuration.
Figure 5 shows an XRD pattern of Fe-based
˚
Mo-based PPCH503A to PPCH803A, or by 5.6 A from Rh-
PPCH503A. Two diffraction peaks, sharp and broad ones,
were observed in small- and wide-angle regions, respectively.
Such a XRD profile is usually observed for a smectic LC
phase. Similar XRD patterns were also observed for the other
LC polyacetylene derivatives studied here. The results of XRD
analyses are summarized in Table 3. Diffractions of sharp and
broad peaks were observed at 2.35 and 18.6ꢁ in 2ꢀ, respective-
ly. These diffraction angles correspond to periodic distances of
based PPCH503A to PPCH506A. This also supports the pres-
ent assignment that the sharp peak in the small angle region is
due to diffraction between the inter-layers of smectic A form.
As a typical example, a comparison of the inter-layer distances
between Mo-based PPCH503A and PPCH803A is shown in
Fig. 6c. It is clear that the increase in the inter-layer distance
˚
˚
by 6.4 A, which is twice the value of 3.2 A, is due to the differ-
ence in length between the terminal pentyl and octyl groups of
the side chains in the bi-layer type smectic A (SA2) phase.
Here, it is worthwhile to determine how the above-men-
tioned stereoregular configuration is formed. Previous studies
˚
37.5 and 4.76 A, respectively. Namely, the former and the lat-
ter correspond to an inter-layer distance in the smectic state
and the separation between side chains, respectively, as shown
in Fig. 6a. These assignments were supported by molecular
mechanics calculations based on finite systems of LC polyacet-
ylene derivatives; the inter-layer distance and the side-chain
using H NMR, DSC, and ESR13b have confirmed that as-pre-
1
pared LC polyacetylene derivatives with Fe- or Rh-based cat-
alyst and Mo-based catalyst have cis and trans forms, respec-
tively. The cis form is thermally unstable and is easily isomer-
ized into the trans form during the first heating process in the
DSC or polarizing optical microscope measurements. Taking
this into account, we propose a possible polymerization and
cis–trans isomerization mechanism in Fig. 7. The LC-substi-
tuted acetylene monomers approaching to a catalytically active
site are polymerized with a sequence of head–head and tail–
tail linkages, yielding a stereoregular cis form. In cases of
Fe- or Rh-based catalysts, the cis form is a kinetic product,
and hence it is converted into the trans form that is a thermo-
dynamic product. In case of Mo-based catalyst, the cis to trans
isomerization should occur simultaneously during the poly-
merization.
˚
separation were calculated to be 41 and 5 A, respectively.
The present analyses enabled us to draw a polymer structure
of Fe-based PPCH503A where the LC side chains are alterna-
tively located at both sides of polyene chain to form a stereo-
regular configuration of head–head–tail–tail linkage, as shown
in Fig. 6b. At the same time, the polymer structure implied
that the LC side chains are not tilted with respect to the main
chain, leading to a typical picture of smectic A phase. It should
be emphasized that the fully extended side chains are arrayed
perpendicular to the linear backbone, alternatingly on both
sides along it, and the alternating comb-like polymers are
stacked into a layer structure. The terminal alkyl group of
the side chain has a trans conformation. The cyclohexyl group
is in a stable chair conformation. As found in the center and
right sites of Fig. 6b, the chain conformation from C3 through
O to C6 atom is gauche, and as a whole, the side chain is ex-
tended in an almost straight fashion. The side chain is twisted
about the C2–C3 bond, so that the hydrogen atoms attached to
the C3 atom are directed upward from the figure plane (the
plane containing the backbone), so as to release repulsions
with th0e neighboring hydrogens of the backborne. About the
3.4 Absorption Spectra and Chemical Doping. Next,
UV–vis absorption spectra of PCH503A and PPCH503A pre-
pared with Fe-based catalyst were acquired. An absorption
band between 270 and 280 nm for the monomer and the poly-
ꢃ
mer was assigned to the ꢁ ! ꢁ transition of the benzene
moiety of the LC group. The absorption band between 320
and 330 nm in the polymer was assigned to the ꢁ ! ꢁ tran-
ꢃ
sition in the conjugated polyene chain. Broadening of the band
implies that the polymer is composed of finite polyenes with
0
C2 –C3 bond, the side chain is twisted in the opposite direc-
tion, so that the two mesogens are in the antipode arrangement

654 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
ACCOUNTS
(a)
(b)
(c)
(a)
(b)
Fig. 4. DSC curves of PPCH803A polymers prepared with
(a) Fe(acac)3–AlEt3 and (b) MoCl5–Ph4Sn catalysts. The
rate of temperature change in the heating or cooling pro-
cess was 5 ꢁC minꢀ1
.
Fig. 3. Polarizing micrographs of PCH and BP polymers
showing fan-shaped textures. (a) Fe-based PPCH803A at
132 ꢁC; (b) Mo-based PPCH803A at 130 ꢁC; (c) Mo-based
PBP503A at 120 ꢁC.
domly oriented case, such as in solution, probably due to an
increase of co-planarity of the polyene chains. Therefore, from
a view point of enhancement of electrical conductivity, a mac-
roscopic alignment of the polymer that is a so-called mono
domain structure of the LC state must occur via an external
perturbation, as mentioned in the next section (see also Fig. 1).
Absorption spectra of Fe-based PPCH803A, which had been
cast onto an inner wall of a quartz cell, were measured in situ
after iodine doping. The results are shown in Fig. 8. Since the
ionization potential of substituted polyacetylene is generally
larger than that of non-substituted polyacetylene, it might take
more time to complete the iodine doping of the polymers. Ac-
tually, there was no notable change in the absorption spectrum
even after 3 h of exposure to iodine. After about 5 h, the ab-
various conjugation lengths. The results from the absorption
spectra for the representative polymers are summarized in
Table 4. The Mo-based polymer had an absorption band locat-
ed at shorter wavelength (around 300 nm) than the Fe-based
polymer, indicating that the former has a shorter conjugation
length in the polyene chain than the latter. It should be noted
that the microscopic UV–vis measurement of the inside of the
LC domain in Fe-based PPCH803A gave an absorption band at
403 nm, which is shifted by 70 nm towards a longer wave-
length compared to the band observed in solution of the poly-
mer.14 The result demonstrates that the polyene chains are
aligned owing to the spontaneous orientation of the LC side
chains and that the effective conjugation lengths of polyene
chains inside of each domain are longer than those in a ran-
ꢃ
sorption band from 320 to 330 nm, assigned to a ꢁ ! ꢁ tran-
sition in conjugated polyene, slightly decreased in intensity. At
the same time, new bands appeared at 420 and 700 nm. Inter-
estingly, these bands were also observed in gas-phase doping

K. Akagi
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
655
with sulfuric acid. Therefore, the two bands originate from a
chemically doped conjugated polyene chain and can be as-
signed to two kinds of electronically allowed transitions in
positively charged polyene segments. Thus, it is possible to
chemically dope the present polymers.
3.5 Molecular Orientation and Electrical Conductivity.
3.5.1 Orientation by Shear Stress: Figure 9 shows SEM
photographs of Fe-based PPCH503A. Figure 9a shows ran-
domly oriented fibrils. Figures 9b–9d show aligned fibrils that
are generated by a shear stress along the horizontal direction of
the paper in the LC state of the polymer. Figure 10a shows
polarizing micrographs of Mo-based PPCH503A. It is evident
that a batonet optical texture, characteristic of a smectic liquid
crystal, is oriented along the direction of the shear stress. From
these results, we confirmed that the side chain LC-conjugated
polymers are macroscopically aligned by the shear stress as an
external force.
3.5.2 Orientation by Magnetic Field: Electrical conduc-
tivity of the polymers was measured by using the four-probe
method. The polymer was first melted onto a hot substrate
on which gold had been vaporized in the form of four leads,
and it was gradually cooled down to the LC temperature by ap-
plying an external magnetic field of 0.7–1.0 Tesla. After align-
ment of the polymer was completed in the LC state, the poly-
mer was further cooled down to room temperature to give a
solid sample available for conductivity measurements. Sche-
matic representation of the magnetically forced alignment of
the polymer and current direction in the four-probe measure-
ment are shown in Fig. 11, where ꢂ and ꢂ stand for the con-
k
?
ductivities parallel and perpendicular to the direction of the
polymer main chain. The results are summarized in Table 5.
Conductivities of undoped and iodine-doped samples were
10ꢀ11–10ꢀ9 and 10ꢀ8–10ꢀ7 S cmꢀ1, respectively. Through the
magnetically forced alignment, the conductivity of the doped
sample was further enhanced by 1–2 orders of magnitude to
give 10ꢀ6 S cmꢀ1. Especially, the conductivity of the aligned
sample of Fe-based PPCH503A increased 102 times in ꢂ ,
k
i.e., from 10ꢀ8 to 10ꢀ6 S cmꢀ1. As for PBP503A, the increase
due to the alignment was only about 2 times.
Meanwhile, the ꢂ of Mo-based PPCH503A and PBP503A
?
decreased by 102–104, as expected. However, those of Fe-
based PPCH503A increased by 70 times. The difference in
conductivity resulted in a wide range of electrical anisotropy
(ꢂ =ꢂ ) (2{105).
k
?
The increase in ꢂ after macroscopic alignment, as men-
?
tioned in the case of Fe-based PPCH503A may, in part, be
due to an increase in the coplanarity of the conjugated polyene
chain upon alignment. This suggests that in analyzing the
change in conductivity upon the molecular orientation, an in-
plane alignment of the polyene chain must be considered at
the same time, as well as a so-called parallel alignment of
the polyene chain.15
Table 2. Phase-Transition Temperature (ꢁC) and Enthalpy
Changes (J gꢀ1) for PPCHn03A and PBP503A
Figure 10a shows polarizing optical micrographs of Fe-
based PPCH803A after magnetically forced alignment. The
First coolingaÞ
Second heatingaÞ
Cat.bÞ Polymer
k ! SA ! i
k ! SA ! i
Fe
PPCH303A
60 (0.7) 107 (4.5) 70 (0.7) 102 (3.3)
98 (1.1) 146 (6.3) 100 (1.3) 128 (6.2)
81 (3.2) 151 (8.2) 83 (3.3) 142 (5.8)
126 (3.2) 180 (3.1) 129 (4.9) 171 (1.0)
PPCH503A
PPCH803A
PBP503A
Mo
PPCH303AcÞ
PPCH503AcÞ
PPCH803A
PBP503A
133 (4.2)
160 (6.2)
134 (3.7)
160 (4.5)
86 (3.4) 171 (6.7) 91 (3.7) 166 (6.4)
132 (4.4) 189 (4.5) 135 (6.7) 180 (—)
a) k = crystalline, SA = smectic A, i = isotropic. b) Fe and
Mo denote catalysts of Fe(acac)3–AlEt3 and MoCl5–Ph4Sn,
respectively. c) No distinct DSC peak corresponding to the
phase transition between crystalline and smectic A phases
was observed.
Fig. 5. X-ray diffraction pattern of Fe-based PPCH503A.
Table 3. XRD Results for LC Polyacetylene Derivatives
Polymer
TailaÞ
SpaceraÞ
CatalystbÞ
IsomerizationcÞ
LC phase
Inter-layer
˚
distance/A
Side-chain
separation/A
˚
PPCH503A
5
3
Fe
Rh
Mo
(cal.)dÞ
Rh
cis ! trans
cis ! trans
trans
—
cis ! trans
trans
SA
SA
SA
—
SA
SA
37.5
38.0
4.76
4.73
4.55
(5.0)dÞ
4.71
4.75
40.2
(ꢄ41)dÞ
PPCH506A
PPCH803A
5
8
6
3
43.6
46.6
Mo
a) Number of the carbon atoms in the terminal alkyl moiety or methylene spacer moiety of LC side chain. b) Fe,
Mo, and Rh denote catalysts of Fe(acac)3–AlEt3, MoCl5–Ph4Sn, and [Rh(NBD)Cl]2–NEt3, respectively. c) Fe-
and Rh-based catalysts and Mo-based one give cis-rich and trans-rich polyacetylene derivatives, respectively.
d) Values in the parenthesis are based on molecular mechanics calculations for finite systems.

656 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
ACCOUNTS
(a)
22'
21'
22'
21'
19'
20'
18'
20'
19'
18'
15'
15'
16'
17'
12'
14'
13'
16'
17'
14'
13'
12'
9'
9'
10'
11'
8'
7'
8'
7'
10'
11'
6'
5'
6'
5'
4'
4'
3'
3'
2'
(2')
2
(2)
3
3
4
4
5
5
6
6
7
7
8
11
11
10
Fig. 7. Possible polymerization mechanism using Ziegler–
Natta catalyst for LC-substituted acetylene and cis–trans
isomerization.
8
10
9
12
9
12
17
16
13
14
17
13
14
16
15
15
18
18
19
19
20
20
21
21
22
22
Table 4. Absorption Band (ꢃmax) and Intensity ("max) and
Proton Chemical Shift (ꢄ) for PPCHn03A and PBP503A
Front view
Side view
(b)
Catalyst
Polymer
ꢃmax
/nmaÞ
"
ꢄ
max
/ꢂ103 Mꢀ1 cmꢀ1 aÞ /ppmbÞ
Fe(acac)3– PPCH303A 324
AlEt3
2.0
1.9
2.5
5.98
5.97
5.97
PPCH503A 325
PPCH803A 324
PBP503A insoluble
PPCH303A 301
PPCH503A 301
PPCH803A 301
PBP503A 305
MoCl5–
Pn4Sn
1.4
1.4
1.2
2.6
no value
5.94–6.14
ꢃ
polyene chain. b) Chemical shift of olefinic proton in cis form.
a) Absorption band due to ꢁ ! ꢁ transition in conjugated
magnetic field was applied horizontal to photograph. The tex-
ture was aligned parallel to the magnetic field, although the
alignment was not homogeneous. The incomplete alignment
is attributed to an insufficient strength of the magnetic field
(0.7–1.0 Tesla), which may cause a variation in ꢂ and sample
(c)
Fig. 6. (a) Higher order structure of Fe-based PPCH503A
and smectic A structure. (b) Structure of PPCH503A opti-
mized by molecular mechanics (MM) calculation on finite
system (left site) (The red, gray, and purple balls indicate
carbon, hydrogen, and oxygen atoms, respectively). The
ball and stick figures drawn in the center and right sites
are front and side views of the core parts of optimized
structure, respectively (The carbon and hydrogen atoms
in the main chain are expressed as yellow and green
balls, in order to distinguish them from those of the side
chain). (c) Comparison of inter-layer distance between
PPCH503A and PPCH803A.
dependency, especially in the case of ꢂ . In order to achieve
?
complete alignment of the polymer in the highly viscous smec-
tic LC state, a magnetic field strength of more than 2 Tesla is
should be required.
3.6 Spin State and Chemical Doping. Figure 12 shows
ESR spectra of the PCH and BP polymers in non-doped and
iodine-doped states.16b The results are also summarized in
Table 6. In the non-doped state, the Fe-based PCH and BP
polymers showed no signal, meanwhile the Mo-based PCH
polymer showed two kinds of signals with g-values of 2.014

K. Akagi
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
657
(a)
Fig. 8. Changes of UV–vis absorption spectra upon gas-
phase iodine doping for the cast film of Fe-based
PPCH503A. (a) intact; (b) 30 min; (c) 171 min; (d) 291
min; (e) 1131 min.
(b)
Fig. 10. Polarizing micrographs of (a) Mo-based
PPCH503A aligned using shear stress, and (b) Fe-based
PPCH803A aligned using a magnetic force field of 0.7
Tesla where magnetic field is parallel to the horizontal
direction.
Fig. 9. SEM photographs of Fe-based PPCH503A. (a) no
shear stress; (b)–(d) aligned with shear stress.
and 2.005. This is consistent with the above-mentioned result
that the Fe-based Ziegler–Natta and the Mo-based metathesis
catalysts produce cis and trans forms of mono-substituted poly-
acetylenes, respectively. Namely, the cis form is a kinetically
favored product, and it easily isomerizes into a thermally more
stable trans form during a thermal heating, chemical doping, or
even polymerization using the metathesis catalyst. Such a cis–
trans isomerization should cause defects in polyene chains,
giving rise to unpaired electrons that are responsible for the
paramagnetic behavior. In practice, upon the iodine doping,
Fig. 11. Schematic representation of magnetically forced
alignment of the side chain LC mono-substituted polyacet-
ylene and sample cell for the four-probe method of electri-
cal conductivity measurement (H is magnetic field).
the Fe-based PCH and BP polymers showed sharp ESR signals
with g-values of 2.006 and 2.003, respectively. On the other
hand, with the doped Mo-based polymer, the lower field signal
(g ¼ 2:014) slightly decreased in intensity and the higher field

658 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
ACCOUNTS
Table 5. Electrical Conductivities (ꢂ/S cmꢀ1) for PPCH503A and PBP503A before and after
Iodine Doping and Macroscopic Alignment
CatalystaÞ
Polymer
Undoped
Iodine doped
ꢂ
ꢂrandom
ꢂ
ꢂ
?
k
Fe
Mo
Fe
PPCH503A
PPCH503A
PBP503A
10ꢀ11–10ꢀ10
10ꢀ11–10ꢀ9
10ꢀ11–10ꢀ9
1:0 ꢂ 10ꢀ8
1:3 ꢂ 10ꢀ7
1:0 ꢂ 10ꢀ8
1:3 ꢂ 10ꢀ6
1:5 ꢂ 10ꢀ6
2:3 ꢂ 10ꢀ8
7:2 ꢂ 10ꢀ7
1:4 ꢂ 10ꢀ11
1:2 ꢂ 10ꢀ10
a) Fe: Fe(acac)3–AlEt3, Mo: MoCl5–Ph4Sn.
Table 6. ESR Results of the Iodine-Doped LC Polyacetylene Derivatives
aÞ
Catalyst
Polymer
g-Value
ꢀHpp
/gauss
ꢀH1=2=ꢀHpp
Spin density
/spins gꢀ1
y-ValuebÞ
Fe
Fe
Mo
PPCH503A
PBP503A
PPCH503A
2.006
2.003
2.014, 2.005
15.1
11.0
—
2.05
2.36
—
3 ꢂ 1015
1 ꢂ 1015
2 ꢂ 1017
0.065
0.097
0.028
cÞ
cÞ
a) ꢀHpp means a full width at maximum slope, corresponding to a peak to peak width in differential
curve of signal. ꢀH1=2 means a full width at half maximum. b) Dopant concentration defined as
[(CHCR)þ3y(I3ꢀ)y]x, where R is a liquid-crystal group. c) Two peaks are overlapped.
Measurements of the fused state 13C NMR spectra were car-
ried out on Bruker AMX-40 equipped with a high magnitude
proton decoupler. The strength of magnetic field was 9.4 Tesla.
The sample was first melted by heating and measured in the
isotropic state. Then by applying the magnetic field, the sam-
ple was gradually cooled down with a temperature controller
and measured in the LC state.
Figure 13 shows 13C NMR spectra of PCH803A monomer
in the isotropic and nematic phases. Upon the phase transition
from the isotropic to LC phase, chemical shifts of aromatic
carbons (C6–C9) of phenyl ring shifted to a lower magnetic
field, down-field shift. Especially, those of C6 and C9 carbons
showed relatively larger down-field shifts. The results are de-
scribed in Fig. 14. On the other hand, chemical shifts of alky-
nyl carbons of acetylene segments (C1 and C2) shifted to a
higher magnetic field, up-field shift. The up-field shifts are also
found in alkyl carbons of terminal group and methylene chain,
although the degrees of the shifts are quite small. These ten-
dencies in chemical shift become more remarkable as temper-
ature decreases from 307 to 305 K, indicating an increase in
degree of molecular orientation. Interestingly, the methylene
carbon (C5) neighboring with the phenoxy moiety shows al-
most no change in chemical shift even after the phase transi-
tion. This suggests that the C5 carbon atom might be located
in an axis which forms an angle of about 53.5ꢁ (magic angle)
to the molecular axis.
Figure 15 shows 13C NMR spectra of PPCH803A in the iso-
tropic and smectic phases. The polymer in the smectic phase
has a high viscosity and low fluidity, which causes a broaden-
ing of the signals. Upon the phase transition, the phenyl car-
bons (C6–C9) also show the down-field shifts. It is intriguing
that the down-field shifts in the polymer are larger than in the
case of the monomer, as summarized in Table 7. That is, the
down-field shifts of C6, C9, and C7, C8 carbons of the poly-
mer are 48–50 and 19–20 ppm, respectively. Whereas, those
of the monomer are 37–40 and 15–17 ppm, respectively. The
results imply that the LC state of the polymer gives a larger
anisotropic environment than that of the monomer. This can
Fig. 12. ESR spectra measured at room temperature.
(a) I2-doped PPCH503A (Fe); (b) I2-doped PBP503A
(Fe); (c) non-doped PPCH503A (Mo); (d) I2-doped
PPCH503A (Mo).
signal (g ¼ 2:005) increased, resulting in overlapped signals as
seen in Fig. 12.
The peak width, ꢀHpp, was 3–5 times larger, and the spin
density was 2–4 orders of magnitude smaller than those of io-
dine-doped polyacetylene.22 Such a large peak width suggests
that the unpaired electrons in the substituted polyacetylene
tend to be more localized, probably due to a decrease in the
planarity of the polyene chain. From the view point of electri-
cal transport phenomenon, it can be argued that the present
polymers have lower mobility and lower concentration of car-
riers. This may account for the lower electrical conductivity of
the substituted polyacetylenes including the present PCH and
BP polymers.
3.7 Orientation Behavior and Anisotropy under Magnet-
ic Field. We measured fused state 13C NMR spectra of side-
chain LC polyacetylene derivatives as well as a LC acetylene
monomer in isotropic and liquid-crystalline states to eluci-
date their orientation behaviors and anisotropies in chemical
shifts.16

K. Akagi
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
659
Fig. 13. 13C NMR spectra of PCH803A in the isotropic
(upper) and nematic (lower) states.
Fig. 15. 13C NMR spectra of PPCH803A in the isotropic
(upper) and smectic (lower) states.
Table 7. Changes of Chemical Shifts (ppm) upon Transition
from the Isotropic to LC Phase for PCH803A and Fe-
Based PPCH803A
Terminal
(Alkyl)
C6
C7
C8
C9
ꢂaniso
ꢂiso
206.6 135.0 148.4 190.5
158.3 115.8 127.7 140.2
12.4
14.1
ꢀ1:7
ꢀ0:5
ꢀꢂaÞ
48.3
36.6
19.2
15.5
20.7
17.0
50.3
39.5
ꢀꢂaÞ (Monomer)
a) ꢀꢂ ¼ ꢂaniso ꢀ ꢂiso
.
be rationalized with a difference of LC phase between the
polymer and the monomer where the former and the latter
are respectively smectic and nematic phases. In other words,
higher order and hence larger anisotropy are generated in the
smectic phase, compared with the nematic phase.
We evaluated chemical shifts semi-quantitatively in the
isotropic and anisotropic states by using the shielding tensors
of a di-substituted benzene, 1-alkoxy-4-alkylbenzene, used as
Fig. 14. 13C NMR chemical shifts of phenylene ring of
PCH803A in the isotropic and nematic states.

660 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
ACCOUNTS
a model compound. The calculated isotropic (ꢂiso) and aniso-
tropic (ꢂaniso) chemical shifts were 157.4 and 191.3 ppm, re-
spectively. The difference between them, defined as ꢀꢂ ¼
ꢂaniso ꢀ ꢂiso, was 39.6 ppm. The down-field shift and its
magnitude are consistent with the experimental results for
PCH803A, where ꢄ of the C6 carbon for instance was 36.6
ppm. Taking into account the electron density distributions
of sp3, sp2, and sp hybrid carbon atoms in cartesian coordi-
nates and chemical shift tensors reported so far, the largest
shielding for aromatic carbons is perpendicular to the aromatic
ring. For aliphatic carbons, however, the smallest shielding is
perpendicular. The anisotropy in the shielding produces
changes of chemical shifts observed upon the phase transition
from the isotropic to LC states. The changes in the chemical
shifts indicate that the monomer and the side chain of the poly-
mers are oriented parallel to the direction of magnetic field em-
ployed in NMR measurement, which means that LC domains
macroscopically aligned to give a mono domain structure as
shown in Fig. 1.
ESR measurements, Prof. A. Kawaguchi (Ritsumeikan Univer-
sity) for XRD analyses, and Dr. T. Nishizawa and Dr. K.
Masuda (Kobe Steel Ltd.) for the fused state 13C NMR mea-
surements. This work was supported by a Grant-in-Aid for Sci-
ence Research in a Priority Area, ‘‘Super-Hierarchical Struc-
tures’’ (No. 446) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
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ð1Þ
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4. Conclusion
5
a) S.-H. Jin, S.-J. Choi, W. Ahn, H.-N. Cho, S.-K. Choi,
We synthesized two kinds of liquid-crystalline polyacet-
ylene derivatives by using Fe-based Ziegler–Natta, Mo-based
metathesis and Rh-based catalysts. The polymers had enantio-
tropic smectic A phases by virtue of a spontaneous orientation
of LC side chain composed of phenylcyclohexyl or biphenyl
mesogenic moieties. It was found from XRD measurements
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chain, giving rise to a stereoregular sequence, such as head–
head–tail–tail linkage. Electrical conductivities measured us-
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doping of the cast films of the polymers. The alignment of the
main chain accompanied with the side chain orientation using
an external magnetic force of 0.7–1.0 Tesla enhanced the elec-
trical conductivity up to 10ꢀ6 S cmꢀ1 and gave rise to a notable
electrical anisotropy. It was shown from the fused state
13C NMR measurements using a superconducting magnet of
9.4 Tesla that the LC side chains of the polymer were com-
pletely oriented along the magnetic field, giving a mono-
domain structure.
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and Dr. H. Goto (University of Tsukuba) and Dr. K. Araya
(Hitachi Ltd.) for their collaborations. Acknowledgements
are also given to Prof. J. Isoya (University of Tsukuba) for
9
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T. M. Cooper, J. D. Gresser, Marcel Dekker, 1998, Chap. 28,
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Professor Kazuo Akagi graduated from the Department of Hydrocarbon Chemistry of Faculty of
Engineering at Kyoto University and earned a Doctoral degree in 1980. He became a Research
Associate at Fukui University in 1982. He became an Assistant Professor in the Institute of
Materials Science at University of Tsukuba in 1984, and then was promoted to Associate Professor
in 1991 and Professor in 1998. He became a Director of Tsukuba Research Center of Interdisci-
plinary Materials Science in 2003 and a Professor of the Graduate School of Pure and Applied
Sciences in 2004. He has been a Professor of the Graduate School of Engineering, Kyoto Univer-
sity since 2006. He is studying Materials Science, Polymer Chemistry, and Liquid Crystal Chem-
istry. Prof. Akagi was awarded The Divisional Award of The Chemical Society of Japan (1999),
NISSAN Science Prize (2000), The Award of the Japanese Liquid Crystal Society for Outstanding
Paper (2000), Tsukuba Prize (2001), The Award of the Society of Polymer Science, Japan (2002),
The Commendation for Science and Technology by the Minister of Education, Culture, Sports,
Science and Technology, Prizes for Science and Technology (2005). He is a Head Investigator
of Scientific Research in Priority Area entitled ‘‘Control of Super-Hierarchical Structures and
Innovative Functions of Next-Generation Conjugated Polymers,’’ Grants-in-Aids for Scientific
Research in Japan.