Side-chain liquid-crystalline polymers based on flexible rod-like mesogen directly attached to backbone

Article abstract of DOI:10.1002/pola.26337

In this article, we report the synthesis and characterization of a new end-on side-chain liquid crystalline polymer (SCLCP), poly[4-(4′- alkoxyphenyloxymethylene)styrene] [denoted as Poly(n-POMS), where n is the carbon number of the alkyl tail, n = 2, 4, 6, 8, 12, 16], with the flexible rod-like mesogenic side-chain directly attached to the polymer backbone without flexible spacer. The polymer was obtained by using free radical polymerization. The chemical structures of Poly(n-POMS) and the corresponding monomer were characterized using various techniques with satisfactory analysis data. A combination analysis of differential scanning calorimetry, polarized light microscopy, small angle X-ray scattering, and wide-angle X-ray diffraction has been conducted to investigate the phase behavior of Poly(n-POMS). Poly(2-POMS), Poly(4-POMS), and Poly(6-POMS) are amorphous. Poly(8-POMS) develops partially into the liquid crystal phase, and Poly(12-POMS) and Poly(16-POMS) self-assembly into the smectic A (SmA) phase. Upon increasing temperature, the phase transition of Poly(16-POMS) follows the sequence of SmA1 ? SmA2 ? isotropic (I), which may be attributed to the conformation isomerization of the flexible rod-like mesogens.

Full text of DOI:10.1002/pola.26337

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Side-Chain Liquid-Crystalline Polymers Based on Flexible Rod-Like
Mesogen Directly Attached to Backbone
Jun-Feng Zheng,1 Zhen-Qiang Yu,2 Xin Liu,1 Xiao-Fang Chen,1
Shuang Yang,1 Er-Qiang Chen1
1Beijing National Laboratory for Molecular Sciences, Department of Polymer Science and Engineering and the
Key Laboratory of Polymer Chemistry and Physics of the Ministry of Education, College of Chemistry and
Molecular Engineering, Peking University, Beijing 100871, China
2Shenzhen Key Laboratory of Functional Polymers and School of Chemistry and Chemical Engineering,
Shenzhen University, Shenzhen 518060, China
Correspondence to: E.-Q. Chen (E-mail: eqchen@pku.edu.cn) or X.-F. Chen (E-mail: chenxiaofang@pku.edu.cn)
Received 30 May 2012; accepted 7 August 2012; published online
DOI: 10.1002/pola.26337
ABSTRACT: In this article, we report the synthesis and charac-
terization of a new end-on side-chain liquid crystalline polymer
(SCLCP), poly[4-(40-alkoxyphenyloxymethylene)styrene] [denoted
as Poly(n-POMS), where n is the carbon number of the alkyl
tail, n ¼ 2, 4, 6, 8, 12, 16], with the flexible rod-like meso-
genic side-chain directly attached to the polymer backbone
without flexible spacer. The polymer was obtained by using
free radical polymerization. The chemical structures of
Poly(n-POMS) and the corresponding monomer were charac-
terized using various techniques with satisfactory analysis
data. A combination analysis of differential scanning calorim-
etry, polarized light microscopy, small angle X-ray scattering,
and wide-angle X-ray diffraction has been conducted to
investigate the phase behavior of Poly(n-POMS). Poly(2-
POMS), Poly(4-POMS), and Poly(6-POMS) are amorphous.
Poly(8-POMS) develops partially into the liquid crystal phase,
and Poly(12-POMS) and Poly(16-POMS) self-assembly into
the smectic A (SmA) phase. Upon increasing temperature,
the phase transition of Poly(16-POMS) follows the sequence
of SmA1 $ SmA2 $ isotropic (I), which may be attributed
to the conformation isomerization of the flexible rod-like
C
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mesogens.
2012 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 000: 000–000, 2012
KEYWORDS: liquid crystalline polymers (LCP); phase behavior;
radical polymerization; s(LCP)
INTRODUCTION Liquid crystalline polymers (LCPs) have
been studied for several decades in both industrial and aca-
demic research because they combine the functionality of
conventional liquid crystals (LCs) with the advantages of
polymer systems. Several molecular design-related concepts
have been proposed when constructing various LCPs for dif-
ferent functional properties. In general, mesogens, polymer
backbones, and their linkage strategy are mostly considered
as the three structural factors of LCP molecular engineering.
When designing a side-chain LCP,1 rod-like, disk-like, or
other shaped mesogens were frequently introduced into the
side-chain with different attachment method. Typically, for
rod-like mesogenic side-chain, end-on or side-on type side-
chain LCPs (SCLCPs) could be achieved. It should be noted
that the thermodynamic behaviors of mesogenic side-chain
and polymer backbone are quite different. The chain back-
bone tends to be disordered and coil-like driven by maximi-
zation of conformational entropy, whereas the mesogenic
side-chains tend to self-assembly into ordered structures
driven by maximization of their enthalpic interaction. There-
fore, in case of mesogenic side-chain directly attached to the
polymer backbone, the coil conformation of polymer back-
bone may disturb the mesogenic side-chain to form ordered
LC phases to some extent. Thus, flexible spacers are pur-
posefully introduced to decouple the dynamics of the poly-
meric backbone and the mesogenic side-chain to maintain
the liquid crystallinity of side-chains.2,3 This ‘‘decoupling con-
cept’’ suggested by Ringsdorf and Finkelmann has become an
useful guideline for the molecular design of SCLCPs. Accord-
ingly, nematic or semctic LC phases can be readily obtained
from end-on SCLCPs. Percec and coworkers first introduced
the concept of microphase separation between the backbone
and side groups into end-on SCLCP systems by using immis-
cible polymer backbone and side groups.4–6 Consequently,
highly or even completely decoupled end-on SCLCP can be
realized. On the other side, it has been found that, in side-on
type SCLCPs, attaching the mesogenic side-chains to the
polymer backbone with short or no spacers can induce a
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the polyethylene backbone, it will give us a good opportu-
nity to investigate how the conformation isomerism of
flexible mesogenic side-chain interplays with polymer
backbone thermodynamically.
Although this kind of directly linkage sounds not good to LC
formation, we first intend to observe if the flexibility owned
by the mesogen itself can facilitate the formation of LC
phases. We presume that the mesogens with the majority of
trans conformation at low temperatures may favor smectic
structures. Moreover, considering that the gauche conforma-
tion of mesogen may bring the 40-alkoxyphenyl group much
closer to the backbone, we are also interested in if the chain
backbone can feel strong ‘‘jacketing effect’’ when more and
more side-chains adopt gauche conformation with increasing
temperature. If it is the case, Poly(n-POMS) may form supra-
molecular columnar phase, and thus, the sample will display
a phase transition of smectic-to-columnar. We investigated
the phase behavior of Poly(n-POMS) using differential scan-
ning calorimetry (DSC), polarized light microscopy (PLM),
and wide-angle X-ray diffraction (WAXD). It is found that
Poly(n-POMS) with reasonably long alkyl tails can render
stable smectic A (SmA) phase at low temperatures, showing
the tail length influence on the formation of LC phases.
Although the smectic-to-columnar transition which we
desired was not realized, we observed that Poly(16-POMS)
SCHEME 1 Chemical structure and conformational isomerism
of Poly(n-POMS).
strong ‘‘jacketing effect’’ of side-chains to the backbone espe-
cially, resulting in the SCLCP called mesogen-jacketed LCP
(MJLCP) vividly.7–9 In this case, the mesogen jacket covered
around the polymer backbone forces the flexible backbone
stretching to a great extent. So each jacketed polymer could
be considered as a rod-like polymer chain, which can pack
parallel to others forming supramolecular columnar
LC structure.10 When increasing the rigidity of the mesogen
or the length of rod-like mesogens of MJLCP, those side-
chains could overwhelm the disturbance from the polymer
backbone and self-organize into smectic layer-like
mesophase.11,12
From the previous SCLCP research work, we can be aware
of that the mechanism of LC formation in polymeric sys-
tem is really not as direct as we thought, especially con-
sidering that the side-chain and polymer backbone have
complex and subtle interaction between each other. None-
theless, if we could take advantage of the interaction
between them, we may realize novel self-assembled LC
structure through rational molecular design. In this article,
we design and synthesize a series of end-on SCLCP con-
taining rod-like benzyl ether mesogens directly attached to
polyethylene backbone without any flexible spacer [see
Scheme 1, denoted as Poly(n-POMS), where n is the car-
bon number of the alkyl tail]. Because of the free rotation
around the ether bonds, the mesogenic side-chain incorpo-
rated in Poly(n-POMS) presents conformational isomerism
(Scheme 1). On the basis of the difference between the
rotational energy barrier of different configurational iso-
mers or conformers of calamitic mesogens, rod-like meso-
gens could be classified into three categories: rigid shape,
semi-rigid, or flexible rod-like mesogens.13–16 Percec and
coworkers have introduced the flexible mesogen
into SCLCPs,13,14,16,17 main-chain LCPs,15,18–26 as well as
polymers containing mesogens with more complex topol-
ogy based on conformational isomerism27 and systemati-
cally studied their phase behaviors.28–34 When compared
with other rigid calamitic mesogens, the flexible rod-like
mesogen can adjust its conformation. For Poly(n-POMS),
because the benzyl ether mesogen is attached directly to
SCHEME 2 Synthetic route of monomers (n-POMS) and corre-
sponding polymers (Poly(n-POMS)).
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TABLE 1 Molecular Weight Characterization of Poly(n-POMS)a
PLM. No further phase structural studies of those monomers
were performed due to their easily thermal polymerization.
n
Poly(n-POMS) was obtained by conventional free radical
polymerization. Number average molecular weights (Mn) of
these polymers ranged from 5.4 ꢁ 104 to 7.8 ꢁ 104 g/mol,
with the polydispersity of 2.0–2.4 were measured by gel per-
meation chromatography (GPC) using polystyrene (PS)
Poly(n-POMS)
2
4
6
8
12
16
Mw ꢁ 10ꢃ5b
Mn ꢁ 10ꢃ4c
Mw/Mn
1.87
7.80
2.40
1.69
6.61
2.56
1.74
7.02
2.47
1.25
5.42
2.30
1.40
7.05
1.99
1.46
6.48
2.26
1
standards (Table 1). The H NMR spectrum of 12-POMS and
a
corresponding polymer Poly(12-POMS) are shown in Figure
1. In Figure 1(a), representative resonances of the vinyl
group of 12-POMS at 5.24–5.28 and 5.74–6.77 ppm can be
seen clearly. After polymerization, these signals completely
disappear [see Fig. 1(b)]. The resonance peaks of the spec-
trum of polymer were broad due to the slower motion of
the protons. All other monomers and polymers were charac-
terized similarly, and the results were in accordance with
the desired structures.
Molecular weights and polydispersity were measured by GPC, using
tetrahydrofuran as an eluent at 35 ꢀC, polystyrene as the standard.
b
M
w, weight average molecular weight.
c
Mn, number average molecular weight.
exhibits a transition of SmA1 $ SmA2, which should be
largely related to the conformational isomerism of the flexi-
ble rod-like mesogens.
RESULTS AND DISCUSSION
Synthesis and Characterization of Monomers and
Polymers
Phase Transitions and Phase Structures of Polymers
Phase transitions of Poly(n-POMS) were first examined by
DSC. Figure 2(a) shows the DSC traces of the six samples
recorded during the second heating at a rate of 10 ꢀC/min.
For n ¼ 2, 4, and 6, typical glass transitions are observed in
the temperature range from 30 to 60 ꢀC, of which the glass
transition temperature (Tg) decreases with increasing n.
Poly(n-POMS) can also be viewed as a derivate of PS. When
compared with that of PS, the lower Tg’s of Poly(n-POMS)
implies that the directly attached flexible mesogen enhance
the chain mobility, and moreover, increasing the length of
alkyl tail depresses more the Tg of Poly(n-POMS). Poly
(8-POMS) exhibits a broad and weak endotherm peaked at
Monomers n-POMS were prepared as shown in Scheme 2
using two subsequent etherification reactions. Monoalkoxy
substituted 4-alkoxyphenols were first produced by etherifi-
cation of bromoalkane and hydroquinone. The second etheri-
fication step of the obtained 4-alkoxyphenol with a 10%
excess amount of vinylbenzyl chloride in the presence of a
catalytic amount of tetrabutylammonium bromide (TBAB)
afforded monomers n-POMS in 80–90% yield. The unreacted
vinylbenzyl chloride is easy to remove by recrystallization
from corresponding solvents. The structures of the mono-
mers and precursors were confirmed by 1H NMR, 13C NMR,
and elemental analysis. All the monomers exhibited as white
crystals at ambient temperature and could melt into iso-
tropic state around 60–70 ꢀC, which were detected under
ꢀ
ꢂ50 C right after the glass transition. This implies that liq-
uid crystallinity of the sample may be partially developed.
The DSC curve of Poly(12-POMS) displays an endothermic
FIGURE 1 1H NMR spectra of 12-POMS (a) and Poly(12-POMS) (b).
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heating and cooling rate dependence. This can be taken as
an indicative of LC transitions.
We used PLM to study the LC behavior of Poly(n-POMS). The
results confirmed that the samples with n ¼ 2, 4, and 6
were amorphous. Although a sort of LC structure of Poly(8-
POMS) might be partially developed as suggested by the DSC
result [see Fig. 2(a)], no clear birefringence of the sample
could be observed. Figure 3(a,b) depicts the PLM pictures of
Poly(12-POMS) and Poly(16-POMS), respectively, which were
taken after the samples were cooled slowly from their iso-
tropic state at a rate of 1 ꢀC/min. Thread-like texture [Fig.
3(a)] of Poly(12-POMS) and sanded-like texture [Fig. 3(b)] of
Poly(16-POMS) indicate the existence of LC structures.
The phase structures of the polymers were further charac-
terized by X-ray diffraction experiments. Sets of one-dimen-
sional (1D) WAXD profiles recorded at room temperature of
FIGURE 2 Differential scanning calorimetry thermograms of
Poly(n-POMS) at a rate of 10 ꢀC/min (a) and Poly(16-POMS) at
different heating and cooling rate (b).
transition peaked at 75 ꢀC. For Poly(16-POMS), a relatively
broad and strong endotherm appears in the temperature
range of ꢂ20 to 50 ꢀC. Afterward, two highly overlapped
endothermic transitions between 65 and 80 ꢀC can be
observed. The DSC results demonstrate clearly that some or-
dered structure of Poly(12-POMS) and Poly(16-POMS) are
melted during heating. The transition is in fact enantiotropic,
which could be also detected upon cooling from the isotropic
state. It is interesting to note that Poly(16-POMS) with the
longest alkyl tails we investigated possesses multiple transi-
tions and the glass transition could not be observed directly.
The broad melting endothermic peak and the plot shifting
upward slightly indicate the possibility of a combination of
Tg and melting endotherm. Figure 2(b) presents a set of
cooling and subsequent heating DSC curves of Poly
(16-POMS), showing that the transitions exhibit almost no
FIGURE 3 Polarized light microscope pictures of Poly
(12-POMS) at 72 ꢀC (a) and Poly(16-POMS) at 79 ꢀC (b).
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which is less than twice the calculated side-chain length of
3.0 nm. In addition, a bump peaked at q ¼ 15.4 nmꢃ1 is
superimposed on the high-angle amorphous halo, which
should arise from the partial crystallization of the long alkyl
tails. It should be reasonable to assume that Poly(16-POMS)
also possesses a smectic phase at low temperatures.
Two-dimensional (2D) WAXD experiments were carried out
to study the polymer mesophase structure as well, to get
more information of the phase structure. Specimens were
obtained by mechanical shearing the sample at temperatures
slightly lower than that of the isotropic transition. The ori-
ented films were annealed at the shear temperature for sev-
eral hours and then quenched to room temperature. Figure
5(a,b) shows the 2D-WAXD pattern of the sheared films of
Poly(12-POMS) and Poly(16-POMS) obtained at room tem-
perature with the X-ray incident beam perpendicular to the
shear direction, respectively. For both of the polymers, the
2D-WAXD results elucidate the existence of SmA structure.
With the shear direction along the meridian, the low-angle
diffractions with the q-ratio of 1:2:3 appear on the equator,
indicating that the smectic layer normal is perpendicular to
the shear direction. On the other hand, the high-angle scat-
tering halo is more or less concentrated on the meridian.
Therefore, the side-chains should be largely parallel to the
layer normal. We found that mechanical shear could greatly
enhance the smectic ordering of Poly(16-POMS). As shown
in Figure 5(b), the layer diffractions up to the third order
can be seen. When compared with that of Poly(12-POMS),
the high-angle scattering of Poly(16-POMS) is stronger. A
pair of diffraction arc with d-spacing of 0.41 nm can be
found on the meridian [pointed by the arrow in Fig. 5(b)],
which should be associated with the partially crystallization
of the long alkyl tails. Considering that the layer spacing is
nearly twice the side-chain length, the SmA phase of
Poly(12-POMS) and Poly(16-POMS) should be a bilayer
structure with slight interdigital.
FIGURE 4 1D-WAXD profiles of Poly(n-POMS).
Poly(n-POMS) after heating and subsequent cooling proc-
esses are presented in Figure 4. Poly(2-POMS) and Poly
(4-POMS) at room temperature display a broad halo both in
the low angle region and high angle region, representing the
amorphous state. For Poly(6-POMS), we notice that the low-
angle scattering halo possesses a smaller full-width of half
maximum (FWHM) compared with that of the samples with
smaller n. This may suggest that some ordered molecular
packing tends to develop in Poly(6-POMS). However, the
sample should be still most likely amorphous. The WAXD
pattern of Poly(8-POMS) displays a rather strong diffraction
peak at q of 1.65 nmꢃ1 (q ¼ 4psinh/k, where k is the X-ray
wavelength and 2h the scattering angle) in the low angle
region. Careful examination can reveal a weak and small
bump at q ¼ 3.24 nmꢃ1, which can be assigned as the sec-
ond-order diffraction. In this case, although clear LC texture
of the sample was absence under PLM, Poly(8-POMS) may
form a smectic structure. Here, we observe the tendency to
develop LC phase with increasing the tail length. We con-
sider that when the alkyl tails are short the motion of the
polyethylene backbone dominates the dynamics of whole
molecule and hence prevents the formation of LC phase of
flexible mesogens. Increasing the alkyl tail length may
enhance the degree of microphase separation between the
backbones and side-chains. Consequently, the smectic phase
can be achieved in Poly(n-POMS) with large n.
The WAXD pattern of Poly(12-POMS) shows clearly two dif-
fraction peaks in the low angle region with q-ratio of 1:2,
indicating a smectic structure. The d-spacing of 4.6 nm cor-
responding to the first-order diffraction is comparable with
twice the length of the side chain estimated under the
assumption that the alkyl tail adopts an all-trans conforma-
tion which is 2.4 nm. For Poly(16-POMS), we observe a very
strong low-angle diffraction with a d-spacing of 5.28 nm,
FIGURE 5 2D-WAXD patterns collected from the sheared sam-
ple of Poly(12-POMS) (a) and Poly(16-POMS) (b) at RT and (c)
is the shear geometry of polymer film.
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FIGURE 6 Set of 1D-WAXD powder patterns in the low 2h angle region (a) and in the high 2h angle region (b) of Poly(16-POMS)
obtained during the first heating of the as-cast film.
Mesophase Phase Behavior of Poly(16-POMS)
mainly due to the thermal expansion of the smectic layers.
The value of FWHH of the low-angle diffraction decreases
during the melting of tails. This may be due to that the
increased tail mobility promotes a better smectic packing.
As shown in Figure 2(a), the DSC result reveals that the
phase transition of Poly(16-POMS) is more complicated than
other samples. We performed thermal 1D-WAXD experiments
to follow the phase transition process during heating, of
which the result is shown in Figure 6. After the sample was
slowly cooled from isotropic state to room temperature fol-
lowed by prolonged annealing, we can see clearly a diffrac-
tion peaked at 2h of 21.5ꢀ [see Fig. 6(b), 30 ꢀC], which can
be taken as an indicative of the crystalline parking of the
long alkyl tails. Upon heating to 60 ꢀC, this diffraction com-
pletely disappears, and only a typical amorphous halo can be
observed in the high-angle region. Combining the DSC and
1D-WAXD results, we can conclude that the low temperature
endotherm is associated with the melting of the alkyl tails.
However, this transition does not affect the smectic structure
too much. As shown in Figure 6(a), the low-angle diffraction
looks largely unchanged. In Figure 7, we plot the d-spacing
and FWHM of the low-angle diffraction as functions of tem-
perature measured upon heating. With heating from 35 to
60 ꢀC, accompanying with the continuous melting of tails,
the d-spacing increases from 5.1 to 5.3 nm, which should be
For Poly(16-POMS), of particular interesting is that the two
transitions occur in the high temperature range, which are
largely overlapped with each other. Figure 6(a) shows that
the low-angle diffraction is remained until the temperature
becomes higher than 80 ꢀC. Afterward, the diffraction peak
becomes diffused, indicating that the sample enters into iso-
tropic state (I). In the case, we presume that before the iso-
tropization the sample keeps the smectic structure. As
shown in Figure 7, after entering the temperature range of
the middle transition, the FWHM shows a maximum at ꢂ75
ꢀC, which is the peak temperature of corresponding endo-
therm of Poly(16-POMS) (see Fig. 2). On the other hand, the
d-spacing of the low-angle diffraction decreases monotoni-
ꢀ
ꢀ
cally from 5.3 nm at 65 C to 4.2 nm at 80 C. It sounds eas-
ily to assign that the middle transition leads the SmA to
SmC. However, if it is the case, the phase transition sequence
of SmA-SmC-I would be contrary to the normal one of
most LCs which shall be SmC-SmA-I. We suggest that
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on a Bruker ARX400 spectrometer using deuterated chloro-
form (CDCl3) as the solvent and tetramethylsilane (TMS) as
the internal standard. GPC was carried out on a Waters 515
pump combined with Waters 2410 refractive-index detector
at 35 ꢀC, and THF was used as the eluent at a flow rate of
1.0 mL/min. Three Water Styragel columns with 10 lm bead
size were connected in series. All GPC data were calibrated
with PS standards.
DSC (Perkin-Elmer Pyris I) was used to examine the thermal
behaviors of polymers. The temperature and heat flow were
calibrated with benzoic acid and indium. The samples were
encapsulated in hermetically sealed aluminum pans, with a
typical sample weight of ꢂ3.5 mg.
LC textures of the polymers was examined under PLM (Leica
DMLP) coupled with a Mettler-Toledo hot stage (FP82HT).
The thickness of film samples was kept several micrometers.
FIGURE 7 d-Spacing and FWHM data of the low angle peak as
functions of temperature measured during heating of Poly(16-
POMS).
To identify the LC structures of the polymers, WAXD experi-
ments were performed with several X-ray instruments. 1D-
WAXD experiments were carried out with a high-flux SAXS
instrument (SAXSess, Anton Paar) and a PANalytical X’Pert
Pro diffractometer. For SAXSess, the diffraction pattern was
recorded on an imaging-plate, which covers the q range from
0.06 to 29 nmꢃ1. The X’Pert Pro is equipped with an X’cele-
rator detector and a temperature control unit (Anton Paar
TTK450). 2D-WAXD experiments were carried out using a
Bruker D8 Discover diffractometer in a transmission mode
using a GADDS detector. The macroscopically oriented sam-
ples prepared by mechanical shear were mounted on the
sample stage with the point-focused X-ray incident beam
perpendicular the shear direction. For all the X-ray instru-
ments we used, the X-ray sources (Cu Ka) were provided by
3 kW ceramic tubes. The diffraction peak positions were cali-
brated with silicon powder (2h > 15ꢀ) and silver behenate
(2h < 10ꢀ). The background scattering was recorded and
subtracted from the sample patterns.
Poly(16-POMS) remains the feature of SmA during heating
until the isotropization, and the transition sequence is
SmA1-SmA2-I. Considering the flexible nature of the rod-like
mesogen incorporated in this polymer, we propose that the
middle transition is associated with the fact that more and
more gauche conformers of mesogenic groups prefer to exist
with increasing temperature. The bended gauche conforma-
tion certainly brings the side-chain tails to be more closed to
the chain backbone, resulting in the decrease of the smectic
layer spacing. It is worth to mention here that Poly(12-
POMS) only exhibits the transition of SmA-I, which takes
place in the same temperature range of the middle transition
of Poly(16-POMS). Seemingly, the long alkyl tail of Poly(16-
POMS) can retard the trans-to-gauche conformational iso-
merism to some degrees, and thus let the sample to form
the additional SmA2 with smaller layer spacing. Following
the picture of ‘‘microphase separation’’ of SCLCP, we consider
that the nano-segregation between the mesogen core and the
alkyl tail can help to stabilize the layer-like self-assemble
structure.
Synthesis of Monomers
The monomers n-POMS were synthesized by etherification of
hydroquinone with 1-bromoalkane followed by etherification
with vinylbenzyl chloride in the presence of K2CO3 and a
catalytic amount of TBAB (Scheme 1). 4-Alkoxyphenol was
synthesized according to the ref. 35. The monomers were
synthesized as in the following example of 4-(40-dodecoxy-
phenyloxymethylene)styrene (12-POMS).
EXPERIMENTAL
Materials
Vinylbenzyl chloride (Aldrich) and hydroquinone (Beijing
Chemical Reagent Company) were used as received. Ethyl
bromide, bromobutane (98%), bromohexane (98%), bro-
mooctane (98%), bromododecane (98%), and bromohexade-
cane (98%) were all purchased from Alfa Aesar and used as
received. Benzoyl peroxide (BPO) was recrystallized from
chloroform and methanol. Chlorobenzene was washed with
concentrated H2SO4, then with aqueous NaHCO3 and H2O,
drying first with CaCl2 and then distilling from CaH2 under
N2 atmosphere. All other solvents and reagents were
obtained commercially and used without further purification.
Synthesis of 12-POMS
Into a single-necked 100 mL round-bottom flask equipped
with a condenser, 1.39 g (5 mmol) of 4-dodecoxyphenol, 0.88
g (5.75 mmol) of vinylbenzyl chloride, 0.69 g (5 mmol) of
K2CO3, a catalytic amount of TBAB, and 40 mL of acetone
were added. The reaction mixture was refluxed until 4-dode-
coxyphenol was completely exhausted by TCL analysis under
an atmosphere of nitrogen. After the mixture was cooled to
room temperature, acetone was removed by a rotary evapora-
tor. The residue was dissolved in dichloromethane (200 mL)
and washed three times in total with 150 mL of aqueous
NaCl solution. The organic phase was dried over MgSO4 and
Instruments and Measurements
Elemental analysis was performed with an Elementar Vario
EL instrument. 1H NMR (400 MHz) spectra were recorded
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filtered, and the solvent was removed by rotary evaporator to
yield the crude product. Recrystallization from absolute etha-
nol gave 1.82 g of 12-POMS as white crystals (yield: 92%).
(m, 1H, CHH¼¼CHAr), 5.03 (s, 2H, OCH2Ar), 3.94–3.91 (t, 2H,
OCH2CH2), 1.81–1.75 (m, 2H, OCH2CH2), 1.49–1.40 (m, 2H,
O(CH2)2CH2), 1.41–1.20 (m, 24H, O(CH2)3(CH2)12), 0.92–0.90
(t, 3H, CH3). Anal. Calcd. for C31H46O2: C, 82.61; H, 10.29;
Found: C, 82.73; H, 10.17.
2-POMS
White solid; yield 88%. 1H NMR (400 MHz, CDCl3, 25 ꢀC,
TMS): d (ppm) ¼ 7.46–7.30 (m, 4H, CH2¼¼CHArH), 6.91–6.86
(m, 2H, 2-H, 3-H), 6.84–6.79 (m, 2H, 1-H, 4-H), 6.76–6.68 (m,
1H, CH2¼¼CHAr), 5.78–5.72 (m, 1H, CHH¼¼CHAr), 5.27–5.23
(m, 1H, CHH¼¼CHAr), 5.00–4.99 (d, 2H, OCH2Ar), 4.00–3.94
(m, 2H, OCH2CH2), 1.39–1.36 (t, 3H, CH3). Anal. Calcd. for
Polymer Synthesis
All polymers [Poly(n-POMS) in Scheme 1] were obtained by
conventional solution free radical polymerization with the ratio
of monomer to initiator being 200. A typical experimental pro-
cedure for the polymerization of 12-POMS is given below. A
total of 200 mg (0.506 mmol) of 12-POMS, 80 lL of chloroben-
zene solution of 5 mg/mL BPO, 0.8 mL of chlorobenzene, and a
magnetic stir bar were added into a polymerization tube. After
three freeze-pump-thaw cycles, the tube was sealed off under
vacuum. Polymerization was carried out at 90 ꢀC for 12 h. The
tube was then opened, and the reaction mixture was diluted
with 5 mL of THF. Then, the solution was dropped slowly into
80 mL of the mixture of methanol/THF (3/1). The dissolution
and precipitation were repeated three times. After drying
under vacuum, 0.1 g of polymer was obtained. Yield: 50%.
C17H18O2: C, 80.28; H, 7.04; Found: C, 80.27; H, 7.04.
4-POMS
White solid; yield 80%. 1H NMR (400 MHz, CDCl3, 25 ꢀC,
TMS): d (ppm) ¼ 7.46–7.30 (m, 4H, CH2¼¼CHArH), 6.91–6.87
(m, 2H, 2-H, 3-H), 6.85–6.80 (m, 2H, 1-H, 4-H), 6.76–6.68 (m,
1H, CH2¼¼CHAr), 5.79–5.72 (m, 1H, CHH¼¼CHAr), 5.27–5.23
(m, 1H, CHH¼¼CHAr), 5.00 (s, 2H, OCH2Ar), 3.92–3.89 (m,
2H, OCH2CH2), 1.77–1.70 (m, 2H, OCH2CH2), 1.53–1.43 (m,
2H, O(CH2)2CH2), 0.98–0.95 (t, 3H, CH3). Anal. Calcd. for
C19H22O2: C, 80.82; H, 7.85; Found: C, 80.43; H, 7.73.
CONCLUSIONS
6-POMS
White solid; yield 79%. 1H NMR (400 MHz, CDCl3, 25 ꢀC,
TMS): d (ppm) ¼ 7.46–7.29 (m, 4H, CH2¼¼CHArH), 6.92–6.86
(m, 2H, 2-H, 3-H), 6.84–6.79 (m, 2H, 1-H, 4-H), 6.76–6.68 (m,
1H, CH2¼¼CHAr), 5.79–5.72 (m, 1H, CHH¼¼CHAr), 5.27–5.23
(m, 1H, CHH¼¼CHAr), 5.00 (s, 2H, OCH2Ar), 3.92–3.88 (m,
2H, OCH2CH2), 1.78–1.71 (m, 2H, OCH2CH2), 1.50–1.39 (m,
2H, O(CH2)2CH2), 1.38–1.25 (m, 4H, O(CH2)3(CH2)2), 0.92–
0.88 (t, 3H, CH3). Anal. Calcd. for C21H26O2: C, 81.25; H, 8.44;
Found: C, 81.04; H, 8.34.
In summary, we synthesized a series of SCLCP, Poly(n-POMS)
with the flexible rod-like benzyl ether mesogens attached
directly onto the polyethylene backbone. We find that the liq-
uid crystallinity of Poly(n-POMS) is dependent on the length
of alkyl tail. With short alkyl tails, that is, n ¼ 2, 4, and 6, the
polymers are amorphous. For n ꢄ 8, the sample without flexi-
ble spacer between the mesogen and the backbone can form
smectic phases at low temperatures, which is partially attrib-
uted to the flexible rod-like mesogens can adjust properly
their conformation to fit in the mesophase. Our 2D-WAXD
experiments reveal the SmA packing of Poly(12-POMS) and
Poly(16-POMS). We also observe that Poly(16-POMS) pos-
sesses a rich phase transition behavior. At sufficiently low
temperatures, the alkyl tails can partially crystallize inside the
smectic structure. Upon heating, the smectic structure
remains until the isotropization. We suggest that Poly(16-
POMS) can possess two SmA phases, and the trans-to-gauche
conformational isomerism of the side-chain results in the sec-
ond SmA with smaller layer spacing. As mentioned in ‘‘Intro-
duction’’ section, we intend to see if the conformational iso-
merism of flexible rod-like mesogen can lead to smectic-to-
columnar phase transition. This idea is not realized in this
study. However, as Poly(16-POMS) provides some insights
that the long alkyl tail contributes to stabilize additional LC
phase, we may propose that further increasing the tail length
or the number of tails may lead to a stable columnar phase of
such a kind of SCLCP when the gauche conformation of the
flexible mesogen becomes dominant at high temperatures.
Detailed experiments and the mechanism study of the LC for-
mation in this series of polymer were still ongoing.
8-POMS
White solid; yield 80%. 1H NMR (400 MHz, CDCl3, 25 ꢀC,
TMS): d (ppm) ¼ 7.46–7.30 (m, 4H, CH2¼¼CHArH), 6.92–6.86
(m, 2H, 2-H, 3-H), 6.84–6.80 (m, 2H, 1-H, 4-H), 6.76–6.68 (m,
1H, CH2¼¼CHAr), 5.79–5.72 (m, 1H, CHH¼¼CHAr), 5.27–5.23
(m, 1H, CHH¼¼CHAr), 5.00 (s, 2H, OCH2Ar), 3.92–3.88 (m,
2H, OCH2CH2), 1.78–1.71 (m, 2H, OCH2CH2), 1.49–1.40 (m,
2H, O(CH2)2CH2), 1.39–1.20 (m, 8H, O(CH2)3(CH2)4), 0.90–
0.87 (t, 3H, CH3). Anal. Calcd. for C23H30O2: C, 81.61; H, 8.93;
Found: C, 81.19; H, 8.81.
12-POMS
White solid; yield 92%. 1H NMR (400 MHz, CDCl3, 25 ꢀC,
TMS): d (ppm) ¼ 7.47–7.32 (m, 4H, CH2¼¼CHArH), 6.93–6.87
(m, 2H, 2-H, 3-H), 6.85–6.80 (m, 2H, 1-H, 4-H), 6.77–6.69 (m,
1H, CH2¼¼CHAr), 5.79–5.74 (m, 1H, CHH¼¼CHAr), 5.28–5.24
(m, 1H, CHH¼¼CHAr), 5.00 (s, 2H, OCH2Ar), 3.92–3.88 (t, 2H,
OCH2CH2), 1.79–1.72 (m, 2H, OCH2CH2), 1.49–1.40 (m, 2H,
O(CH2)2CH2), 1.39–1.20 (m, 16H, O(CH2)3(CH2)8), 0.90–0.87
(t, 3H, CH3). Anal. Calcd. for C27H38O2: C, 82.18; H, 9.71;
Found: C, 82.16; H, 9.73.
16-POMS
ACKNOWLEDGMENTS
White solid; yield 95%. 1H NMR (400 MHz, CDCl3, 25 ꢀC,
TMS): d (ppm) ¼ 7.49–7.33 (m, 4H, CH2¼¼CHArH), 6.95–6.90
(m, 2H, 2-H, 3-H), 6.87–6.80 (m, 2H, 1-H, 4-H), 6.79–6.72 (m,
1H, CH2¼¼CHAr), 5.82–5.76 (m, 1H, CHH¼¼CHAr), 5.34–5.27
This work was supported by the National Natural Science Foun-
dation of China (NNSFC Grant 20990232 and 21104001) and
the MOST (2011CB606004).
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17 Percec, V.; Rodriguezparada, J. M.; Ericsson, C. Polym. Bull.
1987, 17, 347–352.
REFERENCES AND NOTES
1 McArdle, C. B. Side Chain Liquid Crystal Polymers; Blackie
and Son Ltd: Glasgow, and Chapman and Halk: New York, 1989.
18 Percec, V.; Rodriguezparada, J. M.; Ericsson, C.; Nava, H.
Polym. Bull. 1987, 17, 353–359.
2 Finkelmann, H.; Ringsdorf, H.; Wendorff, J. H. Makromol.
Chem. 1978, 179, 273–276.
19 Percec, V.; Yourd, R. Macromolecules 1988, 21, 3379–3386.
20 Percec, V.; Yourd, R. Macromolecules 1989, 22, 3229–3242.
3 Finkelmann, H.; Rehage, G. Adv. Polym. Sci. 1984, 60-1,
21 Percec, V.; Yourd, R. Makromol. Chem. Macromol. Chem.
Phys. 1990, 191, 25–48.
97–172.
4 Hsu, C. S.; Percec, V. Polym. Bull. 1987, 17, 49–54.
22 Percec, V.; Yourd, R. Makromol. Chem. Macromol. Chem.
Phys. 1990, 191, 49–69.
5 Hahn, B.; Percec, V. Macromolecules 1987, 20, 2961–2968.
6 Percec, V.; Pugh, C. In Side Chain Liquid Crystal Polymers;
McArdle, C. B., Ed.; Chapman and Hall: New York, 1989; pp 30–
105.
23 Percec, V.; Tsuda, Y. Macromolecules 1990, 23, 5–12.
24 Percec, V.; Tsuda, Y. Macromolecules 1990, 23, 3509–3520.
25 Ungar, G.; Feijoo, J. L.; Keller, A.; Yourd, R.; Percec, V. Mac-
romolecules 1990, 23, 3411–3416.
7 Zhou, Q. F.; Li, H. M.; Feng, X. D. Macromolecules 1987, 20,
233–234.
26 Percec, V.; Kawasumi, M. Macromolecules 1991, 24, 6318–6324.
8 Zhou, Q. F.; Zhu, X. L.; Wen, Z. Q. Macromolecules 1989, 22,
491–493.
27 Percec, V.; Heck, J.; Lee, M.; Ungar, G.; Alvarezcastillo, A. J.
Mater. Chem. 1992, 2, 1033–1039.
9 Chen, X. F.; Shen, Z. H.; Wan, X. H.; Fan, X. H.; Chen, E. Q.;
Ma, Y. G.; Zhou, Q. F. Chem. Soc. Rev. 2010, 39, 3072–3101.
28 Percec, V.; Tomazos, D. Adv. Mater. 1992, 4, 548–561.
10 Ye, C.; Zhang, H. L.; Huang, Y.; Chen, E. Q.; Lu, Y. L.; Shen,
D. Y.; Wan, X. H.; Shen, Z. H.; Cheng, S. Z. D.; Zhou, Q. F. Mac-
romolecules 2004, 37, 7188–7196.
29 Percec, V.; Heck, J.; Johansson, G.; Tomazos, D.; Ungar, G.
Macromol. Symp. 1994, 77, 237–265.
30 Percec, V.; Heck, J.; Johansson, G.; Tomazos, D.; Kawasumi,
M.; Chu, P.; Ungar, G. J. Macromol. Sci. Pure Appl. Chem.
1994, A31, 1719–1758.
11 Chen, S.; Gao, L. C.; Zhao, X. D.; Chen, X. F.; Fan, X. H.; Xie,
P. Y.; Zhou, Q. F. Macromolecules 2007, 40, 5718–5725.
12 Chai, C. P.; Zhu, X. Q.; Wang, P.; Ren, M. Q.; Chen, X. F.;
Xu, Y. D.; Fan, X. H.; Ye, C.; Chen, E. Q.; Zhou, Q. F. Macromo-
lecules 2007, 40, 9361–9370.
31 Percec, V.; Heck, J.; Johansson, G.; Tomazos, D.; Kawasumi,
M.; Ungar, G. J. Macromol. Sci. Pure Appl. Chem. 1994, A31,
1031–1070.
13 Hsu, C. S.; Percec, V. J. Polym. Sci. Part A: Polym. Chem.
1987, 25, 2909–2923.
32 Percec, V. Pure Appl. Chem. 1995, 67, 2031–2038.
33 Rudick, J. G.; Percec, V. Acc. Chem. Res. 2008, 41, 1641–1652.
14 Hsu, C. S.; Percec, V. J. Polym. Sci. Part A: Polym. Chem.
1989, 27, 453–466.
34 Rosen, B. M.; Wilson, C. J.; Wilson, D. A.; Peterca, M.;
Imam, M. R.; Percec, V. Chem. Rev. 2009, 109, 6275–6540.
15 Percec, V.; Yourd, R. Macromolecules 1989, 22, 524–537.
16 Percec, V.; Zuber, M. Polym. Bull. 1991, 25, 695–700.
35 Zhang, D.; Liu, Y. X.; Wan, X. H.; Zhou, Q. F. Macromole-
cules 1999, 32, 5183–5185.
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