Structure-property relationship of a series of novel mesogen-jacketed liquid-crystalline polymers containing semirigid side chain with different numbers of alkoxy terminal groups

Article abstract of DOI:10.1016/j.polymer.2009.12.004

A series of vinyl monomers, 2, 5-bis [(4-methoxy benzyl) oxycarbonyl] styrene (MBCS); 2, 5-bis [(3, 5-dimethoxy benzyl) oxycarbonyl] styrene (DMBCS) and 2, 5-bis [(3, 4, 5-trimethoxy benzyl) oxycarbonyl] styrene (TMBCS) were synthesized and polymerized vi

Full text of DOI:10.1016/j.polymer.2009.12.004

Polymer 51 (2010) 422–429
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Polymer
journal homepage: www.elsevier.com/locate/polymer
Structure–property relationship of a series of novel mesogen-jacketed
liquid-crystalline polymers containing semirigid side chain with different
numbers of alkoxy terminal groups
,
b
Chang-An Yang a, Qian Tan a, GuanQun Zhong a, HeLou Xie a, HaiLiang Zhang a , Er-Qiang Chen ,
*
Qi-Feng Zhou b
a Key Laboratory of Polymeric Materials & Application Technology of Hunan Province, Key Laboratory of Advanced Functional Polymer Materials of Colleges and Universities
of Hunan Province, College of Chemistry, Xiangtan University, Xiangtan 411105, Hunan Province, PR China
b Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry and Molecular
Engineering, Peking University, Beijing 100871, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of vinyl monomers, 2, 5-bis [(4-methoxy benzyl) oxycarbonyl] styrene (MBCS); 2, 5-bis [(3, 5-
dimethoxy benzyl) oxycarbonyl] styrene (DMBCS) and 2, 5-bis [(3, 4, 5-trimethoxy benzyl) oxycarbonyl]
styrene (TMBCS) were synthesized and polymerized via free radical polymerization. The terminal groups
of the semirigid side chain were systematically varied to investigate the effects of their numbers on the
ability of mesophase formation of the resultant polymers. The chemical structures of the monomers were
confirmed by elemental analysis, 1H NMR and 13C NMR. The characterization of the polymers was per-
formed with 1H NMR, gel permeation chromatography (GPC). The phase structures and transition
behaviors were studied using differential scanning calorimetry (DSC), polarized light microscopy (PLM)
and one- and two-dimensional wide-angle X-ray diffraction (WAXD). The experimental results suggested
that the ability of mesophase formation of the polymers decreased as the rigidity of side-chain group
decreased and increased as the number of the alkoxy terminal group increased, and that all the polymers
with high molecular weight showed stable columnar nematic phase (FN).
Received 29 July 2009
Received in revised form
3 December 2009
Accepted 6 December 2009
Available online 16 December 2009
Keywords:
Mesogen-jacketed liquid-crystalline
polymer
Mesogen
Columnar nematic phase
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
side-chain mesogenic units were connected at their gravity center
to the main chain without or with only very short spacers, which
In recent years, liquid-crystalline polymers have attracted
longstanding attention for their potential applications in many
fields, including optical data storage, optic, electro-optic,
nonlinear optic devices, photomechanical, and so on [1–10].
Generally, liquid-crystalline polymers can be divided into main-
chain liquid-crystalline polymers (MCLCPs) and side-chain liquid-
crystalline polymers (SCLCPs) according to the positions of
mesogens [11]. For SCLCPs, the mesogenic groups incorporated in
the SCLCPs can be linked to the backbone via either ‘‘terminal’’ or
‘‘lateral’’ attachment, and the flexible spacers are needed to
decouple motions between the main chain and the mesogenic
side groups [12,13]. However, when flexible spacers are absent,
the phase structures may become more intriguing.
could also show liquid-crystalline behavior [14–20]. In the past
several years, the MJLCPs have been widely researched by Finkle-
mann [21], Percec [22], Pugh [23,24], Keller [25], Gray [26], Ober
[16], and Zhou [15,17–19,27–43]. In these cases, the main chain of
the polymer were forced to adopt a more extended conformation
because of a strong steric interaction between polymer backbones
and bulky side chains, and the conformation of the polymers were
similar to that of main-chain liquid-crystalline polymers (MCLCPs),
which was different from the conventional SCLCPs with long
spacers and their liquid-crystalline behaviors were not absolutely
determined by the mesogenic groups. Therefore, MJLCPs exhibited
some unique LC phase structures and could form hexatic columnar
nematic (FHN) phases [41,43], columnar nematic (FN) [44] and
smectic A (SA) phase [45,46]. Presently, most of the studies are
concentrated on the synthesis of MJLCPs and the investigation of
the chemical structures of rigid or flexible side-chain effect on the
phase structure [27–46]. However, few reposts are found to study
the effects of semirigid side chain on the phase structure and on the
ability of mesophase formation. Moreover, the effects of number of
A
class of ‘‘mesogen-jacketed liquid-crystalline polymers’’
(MJLCPs) was reported by Zhou et al. in 1987 [14]. In MJLCPs, the
* Corresponding author. Tel.: þ86 731 58293377; fax: þ86 731 58293264.
E-mail address: hailiangzhang@xtu.edu.cn (H.L. Zhang).
0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2009.12.004

C.-A. Yang et al. / Polymer 51 (2010) 422–429
423
the terminal flexible substituents in the semirigid side chain on the
phase structure and on the ability of mesophase formation of
mesogen-jacketed liquid-crystalline polymers have not been
reported.
being dried with anhydrous calcium chloride and then distilled.
THF (AR; Beijing Chemical Co.) and Triethylamine (Acros, 99%) were
heated under reflux over calcium hydride for at least 8 h and
distilled before use. 4-Dimethylaminopyridine (DMAP) was
purchased from Aldrich Chemical Co. Anhydrous magnesium
sulfate was used to dry all organic extracts. All other reagents were
used as received from commercial sources.
In this work, we report the synthesis and characterization of
a series of vinyl monomers with different numbers of alkoxy
terminal groups and their corresponding homopolymers. We try to
add one methylene unit between the alkoxybenzene unit and the
oxycarbonyl styrene unit of poly {2, 5-bis [(4-methoxyphenyl)
oxycarbonyl] styrenes} (PMPCS) to break the rigidity of side-chain
mesogen and investigate the effects of the semirigid side chain on
the phase structure and the ability of mesophase formation.
Moreover, we add different number of alkoxy terminal groups to
change spatial steric hindrance, and investigate the effects of the
spatial steric hindrance on the ability of mesophase formation. The
structures of the monomers and the corresponding polymers and
their abbreviations are depicted in Scheme 1. As evidenced by the
results of DSC, PLM, and WAXD, all the high molecular weight
polymers show stable columnar nematic phase (FN), and the subtle
structural change or the number change of terminal groups all lead
to a remarkable impact on the ability of mesophase formation.
2.1.1. Synthesis of monomers
The synthetic route of MBCS, DMBCS and TMBCS was shown in
Scheme 1. The experimental details of the monomers synthesis and
characterization are described below.
2.1.1.1. 2, 5-Bis [(4-methoxy benzyl) oxycarbonyl] styrene
(MBCS). An amount of vinyl terephthalic acid (1.92 g, 10 mmol) was
mixed with thionyl chloride (40 ml). The mixture was stirred for
about 4 h at 50 ꢀC till a clear solution was obtained. The excess
thionyl chloride was removed by evaporation under reduced
pressure. The residue was washed twice by petroleum ether, then,
dissolved in dried THF (20 mL). 4-Methoxybenzalcohol (2.76 g,
20 mmol), DMAP (3.67 g, 30 mmol) and triethylamine (4 mL) were
dissolved in dried THF (50 mL). Under intense stirring at the
temperature of the ice bath, the solution of vinylterephthal chloride
was slowly dropped into the solution over a 0.5 h time period. A
vigorous reaction occurred, leading to a white suspension. The
mixture was further stirred at room temperature for 24 h, and then
most of the THF was evaporated under reduced pressure. Then,
water and dilute HCl were added to dissolve the precipitate, and the
product was extracted with CH2Cl2. The extracts were dried over
anhydrous magnesium sulfate (anhydrous MgSO4), and condensed
to give a solid. Afterward, the raw product dissolved in dichloro-
methane was purified first by column chromatography (silica gel,
2. Experimental section
2.1. Materials
The compound of vinyl terephthalic acid was synthesized using
the method previously reported [47]. Azobisisobutyronitrile (AIBN)
was purified by recrystallization from ethanol. Chlorobenzene was
purified by washing with concentrated sulfuric acid to remove
residual thiophenes, followed by washing twice with water, once
with 5% sodium carbonate solution, and again with water before
Scheme 1. Synthetic route of the monomers and polymers.

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C.-A. Yang et al. / Polymer 51 (2010) 422–429
4H, –OCH2–); 3.88 (s, 12H, –OCH3). 13C NMR (
d, ppm, CDCl3): 55.39
(–OCH3); 67.03, 67.10 (–OCH2–); 100.23, 100.29, 106.04, 106.22,
128.25, 128.50, 130.51, 132.36, 133.21, 137.87, 137.99, 139.76, 161.06
(Ar); 117.86 (CH2]); 134.90 (]C–); 165.50, 166.45 (C]O). Anal.
Calcd for C28H28O8: C, 68.28; H, 5.73. Found: C, 68.13; H, 5.68.
2.1.1.3. 2, 5-Bis [(3, 4, 5-trimethoxy benzyl) oxycarbonyl] styrene
(TMBCS). 1H NMR (
d, ppm, CDCl3): 8.28–7.93 (m, 3H, Ar–H); 7.44–
7.39 (q, 1H,]CH–); 6.68–6.66 (m, 4H ,Ar–H); 5.78–5.74 (dd,
1H,]CH2); 5.44–5.41 (dd, 1H,]CH2); 5.31, 5.29 (s, 4H, –OCH2–);
3.88, 3.85 (s, 18H, –OCH3). 13C NMR (
d, ppm, CDCl3): 56.19, 60.82
(–OCH3); 67.40, 67.44 (–OCH2–); 105.71, 105.95, 128.22, 128.44,
130.42, 131.13, 131.24, 132.48, 133.21, 138.23, 139.61, 153.43 (Ar);
117.79 (CH2]); 134.84 (]C–); 165.50, 166.52 (C]O). Anal. Calcd for
C30H32O10: C, 65.21; H, 5.84. Found: C, 65.13; H, 5.81.
2.2. Polymerization
All polymers were obtained by conventional solution radical
polymerization (see Scheme 1). A typical polymerization procedure
was carried out as follows. For example, MBCS (0.5 g, 1.16 mmol),
0.01 M chlorobenzene solution of AIBN (300 mL,) and chloroben-
zene (1.2 mL) were transferred into a polymerization tube. After
three freeze-pump-thaw cycles, the tube was sealed off under
vacuum. Polymerization was carried out at 60 ꢀC for 24 h. The tube
was then opened, and the reaction mixture was diluted with THF
(10 mL), and then reprecipitated in methanol. After purification, the
polymers were dried to a constant weight.
Fig. 1. 1H NMR spectra of (a) the monomer MBCS and (b) the polymer PMBCS in
CDCl3–d.
2.3. Measurement and characterization
dichloromethane) and then recrystallized from diethyl ether/ethyl
alcohol to MBCS. 1H NMR (
d, ppm, CDCl3): 8.23–7.87 (m, 3H, Ar–H);
Elemental analysis was carried out with an Elementar Vario EL
instrument. 1H and 13C NMR spectra were recorded on a Bruker
ARX400 spectrometer at room temperature, using deuterated
chloroform (CDCl3) as the solvent and tetramethylsilane (TMS) as
the internal standard.
The apparent number-average MW (Mn) and MW distribution
(Mw/Mn) were measured on a GPC (WATERS 1515) instrument with
a set of HT3, HT4 and HT5. The m-Styragel columns used THF as an
eluent, and its flow rate was 1.0 mL/min at 35 ꢀC. Calibration was
made with polystyrene standards (PSt). The TGA was performed on
a TA SDT 2960 instrument at a heating rate of 20 ꢀC/min in nitrogen
atmosphere.
7.42–7.36 (q, 1H, ¼ CH–); 7.39–7.36 (m, 4H, Ar–H); 6.93–6.90 (m,
4H, Ar–H); 5.75–5.70 (dd, 1H, ¼ CH2); 5.41–5.38 (dd, 1H, ¼ CH2);
5.31, 5.29 (s, 4H,–OCH2–); 3.82 (s, 6H, –OCH3). 13C NMR (
d, ppm,
CDCl3): 55.32 (–OCH3); 67.05, 67.07 (–OCH2–); 114.07,114.17, 127.77,
127.87, 128.20, 128.41, 129.96, 130.26, 132.49, 133.29, 139.65, 159.83
(Ar); 117.78 (CH2 ¼ ); 134.89 (¼C–); 165.70, 166.66 (C]O). Anal.
Calcd for C26H24O6: C, 72.21; H, 5.59. Found: C, 72.12; H, 5.56.
All other monomers were prepared in a similar way. The spec-
tral data were as follows.
2.1.1.2. 2, 5-Bis [(3, 5-dimethoxy benzyl) oxycarbonyl] styrene
(DMBCS). 1H NMR (
d, ppm, CDCl3): 8.28–7.95 (m, 3H, Ar–H); 7.47–
7.40 (q, 1H, ¼ CH–); 6.60–6.57 (m, 4H ,Ar–H); 6.44 (m, 2H ,Ar–H);
5.77–5.73 (dd, 1H, ¼ CH2); 5.44–5.40 (dd, 1H, ¼ CH2); 5.32, 5.30 (s,
Table 1
GPC, DSC, and TGA results and thermotropic properties of PMBCSs, PDMBCSs and
PTMBCSs.
Samplea Mnb(ꢁ10ꢂ4
)
PDIb DPb Tgc(ꢀC) Td (ꢀC) Liquid crystallinitye
d
P1
P2
P3
P4
P5
P6
P7
P8
13.49
16.17
21.37
5.68
9.66
24.19
2.82
2.23 312 52.7
2.26 374 53.2
2.17 495 55.1
1.72 115 49.8
2.27 196 51.3
1.96 492 52.9
359.6
371.9
374.5
397.0
397.5
392.7
364.3
368.5
No
Yes
Yes
No
Yes
Yes
Yes
Yes
2.25
51 79.6
10.12
2.29 183 82.2
a
P1, P2 and P3 represented PMBCS; P4, P5 and P6 represented PDMBCS; P7 and
P8 represented PTMBCS.
b
Based on GPC measurements.
Glass-transition temperature obtained from the second-heating DSC experi-
c
ments and heating rates were 10 ꢀC/min.
Fig. 2. The second-heating DSC curves of all polymers at a heating rate of 10 ꢀC/min
(P1, P2 and P3 represented PMBCS; P4, P5 and P6 represented PDMBCS; P7 and P8
represented PTMBCS).
d
Temperature at which the weight loss of the polymers reached 5%.
Determined by PLM.
e

C.-A. Yang et al. / Polymer 51 (2010) 422–429
425
Fig. 3. Representative textures of (a) PMBCS (P3), (b) PDMBCS (P6) and (c) PTMBCS (P8) at 220 ꢀC with PLM.
DSC examination was carried out on a TA DSC Q100 calorimeter
3. Results and discussion
with a programmed heating procedure in nitrogen. The tempera-
ture and heat flow were calibrated, using standard materials
(indium and zinc) at cooling and heating rates 10 ꢀC/min. Samples
with a typical mass of 3–10 mg were encapsulated in sealed
aluminum pans.
LC texture of the polymers was examined under PLM (Leica DM-
LM-P) coupled with a Mettler-Toledo hot stage (FP82HT). The films
with thickness of 10 mm were casted from THF solution and slowly
3.1. Synthesis of the monomers
As shown in Scheme 1, all the monomers MBCS, DMBCS and
TMBCS were successfully synthesized through multistep reactions.
The structures of the monomers have been confirmed by elemental
analysis, 1H NMR, and 13C NMR. Fig. 1a gave the 1H NMR spectra of
the monomer MBCS.
dried at room temperature.
One-dimensional (1D) wide-angle X-ray diffraction (WAXD)
experiments were performed on a Philips X0 Pert Pro diffractometer
with a 3 kW ceramic tube as the X-ray source (Cu KR) and an X0
celerator detector. The reflection peak positions were calibrated
3.2. Synthesis of the polymers
Fig. 1b showed the 1H NMR spectra of the polymer PMBCS. The
characteristic resonance peaks of the vinyl substituent of monomer
MBCS were presented at 5.75–5.38 and 7.42–7.36 ppm, respec-
tively. After polymerization, these signals disappeared completely,
and the chemical shifts of polymers were quite broad, consistent
with the expected polymer structure.
GPC analysis was performed to determine the apparent MW
and molecular weight distributions of the polymers. Table 1
summarized the results of the characterization of PMBCSs,
PDMBCSs and PTMBCSs. For the three monomers MBCS, DMBCS
and TMBCS, we endeavored to synthesize the polymers via the
atomic transfer radical polymerization (ATRP), and different
ligands and different initiators were used in the ATRP system.
However, we found that it was very difficult to obtain the high
molecular weight polymers via the ATRP, probably because of the
chain transfer reactions with the multi-benzylic protons in the
side groups during atomic transfer radical polymerization. In this
study, we synthesized a series of the polymers with different MWs
with silicon powder (2q q
> 15ꢀ) and silver behenate (2 < 10ꢀ). The
sample stage is set horizontally, and a wtemperature control unit
(Paar Physica TCU 100) in conjunction with the diffractometer was
utilized to study the structure evolutions as a function of temper-
ature. The heating and cooling rates in the WAXD experiments
were 10 ꢀC/min.
Two-dimensional wide-angle X-ray diffraction (2D WAXD) fiber
patterns were recorded on a Bruker D8 Discover diffractometer
equipped with a general area detector diffraction system (GADDS)
as a 2D detector, in a transmission mode at room temperature.
Again, calibrations were made against silicon powder and silver
behenate. Samples were mounted on the sample stage, and the
point-focused X-ray beam was aligned either perpendicular or
parallel to the mechanical shearing direction. Fibers were drawn at
a stretching rate of about 1 m sꢂ1 at 200 ꢀC and quenched to room
temperature for measurements.

426
C.-A. Yang et al. / Polymer 51 (2010) 422–429
Fig. 4. Sets of WAXD powder patterns in both 2
q
angle region of 2–30PoP. (a) PMBCS (P3), (b) PDMBCS (P6), (c) PTMBCS (P8) all obtained during the heating of the as-cast films.
by radical polymerization and all the polymers had approximately
the same MW distributions (Table 1).
transition are influenced by the situation of the alkoxy terminal
group and the number of the alkoxy terminal group simulta-
neously. Moreover, compared with PMPCS, the glass transition
temperature of PMBCS was obviously lower than 60 ꢀC. For
example, the glass transition temperature of the PMPCS samples
reached a plateau of 116 ꢀC when the Mn exceeded approximately
1.0 ꢁ 104 [48]. It indicated that the glass-transition temperature
obviously decreased as the rigidity of side-chain group decreased.
Birefringence of the polymers was observed by PLM with the
samples cast from THF solution and slowly dried at room temper-
ature. For the polymer PMBCS (P1), no birefringence could be
observed under PLM in the consecutive heating and cooling
process, and for the polymers PMBCSs (P2, P3), focal conic fanlike
textures appeared in the heating process and the textures still
retained before decomposed temperature, while, the textures could
be maintained during the cooling process (Fig. 3a). The birefrin-
gence of the polymer PDMBCS (P4) did not appear in the consec-
utive heating and cooling process, and birefringence could be
3.3. Thermal properties and mesomorphic properties
TGA was employed to characterize the thermal stabilities of the
polymers. As could be seen from Table 1, all the polymers were
quite stable with the temperatures at 5% weight loss above 350 ꢀC
in nitrogen atmosphere. The phase transitions of the polymers
were studied by DSC. To eliminate the effect of thermal history, we
first heated all the samples from 0 to 240 ꢀC at a rate of 10 ꢀC/min.
The DSC thermal diagrams were recorded at 10 ꢀC/min during the
second-heating process, of which the DSC traces were shown in
Fig. 2. From Fig. 2, we could observe that each of the polymers
showed only a glass transition, and that the temperatures of glass
transition of PTMBCSs were obviously greater than those of PMBCSs
and PDMBCSs, and the temperatures of glass transition of PDMBCSs
were the lowest. The reason may be that the temperatures of glass

C.-A. Yang et al. / Polymer 51 (2010) 422–429
427
Fig. 5. (a, b and c) 2D WAXD patterns of the oriented PMBCS (P3), PDMBCS (P6) and PTMBCS (P8) recorded at room temperature, respectively. The X-ray incident beam was
perpendicular to the fiber axis.
observed in the polymers PDMBCSs (P5, P6), when the samples
were heated to a temperature much higher than Tg (Fig. 3b). For the
polymers PTMBCSs (P7, P8), focal conic fanlike textures appeared
and the textures retained before decomposed temperature, and the
textures remained in consecutive cooling (Fig. 3c).
diffraction evolved during the first heating all remained upon
cooling. Moreover, the similar results could be observed in the 1D
WAXD patterns of PDMBCS (P6, Fig. 4b) and PTMBCS (P8, Fig. 4c).
For the three samples (P3, P6 and P8), the changes and positions of
the two scattering halos in the high 2
q
region of 10–30ꢀ were
region
To elucidate the phase structures and transitions clearly, we
performed WAXD experiments under different temperatures. All
the samples exhibited similar results, although the testing
temperature was different. Herein, we will use the WAXD
measurement results of the typical sample PMBCS (P3) as the
example to elucidate the evolution. Contrast to common MJLCPs, it
was interesting that the PMBCS (P3) obviously exhibited two
similar. However, the d spacing of the polymers in the low 2
q
slightly increased as the number of the alkoxy terminal group
increased, for example, at 200 ꢀC, the d spacing of the polymer P3
was 17.3 Å (2
q
¼ 5.12ꢀ), but for polymer P6 the one was 18.4 Å
(2
q
¼ 4.80ꢀ), and for the polymer P8 it was 18.5 Å (2
q
¼ 4.77ꢀ) (as
shown in Fig. 4). The difference of the d-spacing suggests that the
main chain of polymer may take more extended conformation with
the number of the alkoxy terminal group increased. On the other
hand, all the previous MJLCPs only exhibits one scattering halo in
scattering halos at 2
(d spacing of 4.0 Å) during the heating in the high 2q region in 1D
q
¼ 15.5ꢀ (d spacing of 5.7 Å) and at 2
q
¼ 22.5ꢀ
WAXD patterns (as shown in Fig. 4a). Moreover, with increasing
the high 2 region, however, we can observe two scattering halos at
q
temperatures, the center of the two halos slightly shifts to lower 2
q
the high 2q regions of the polymers in the 1D WAXD patterns. This
phenomenon hardly was investigated in MJLCPs. In general, the
angles, then, followed by sudden jump to 2
q
¼ 14.9ꢀ (d spacing of
5.9 Å) and at 2
q
¼ 21.5ꢀ (d spacing of 4.1 Å) at 200 ꢀC, respectively.
halo at 2
q
¼ 21.5ꢀ (d spacing of 4.1 Å) presented the lateral packing
Above 200 ꢀC, the two center positions continuously and slightly
of the mesogens [18,32,41,46]. However, for the scattering halo at
shifts to lower 2
same time, the scattering halo of the sample in the low 2
q
angles caused by the thermal expansion. At the
region of
2
q
¼ 15.5ꢀ (d spacing of 5.7 Å), we still do not get a reasonable
q
interpretation about the packing.
3.0–6.5ꢀ was observed when the temperature was below 200 ꢀC.
Upon heating, a diffraction peak gradually developed at the right
side of the scattering halo, of which the intensity increased and the
peak position slightly shifted toward a lower angle. At 200 ꢀC, the
To further confirm the structures of the polymers, 2D WAXD
experiments needed to carry out. Parts a, b and c of Fig. 5 were the
2D WAXD patterns of the oriented PMBCS (P3), PDMBCS (P6) and
PTMBCS (P8) samples at room temperature with the X-ray inci-
dent beam perpendicular to the shear direction, respectively. In
these three figures, only the higher angle amorphous scattering
halos are observed to be more or less concentrated on the
meridians with rather broad azimuthal distributions, which shall
diffraction peak positions were at the 2
q
¼ 5.12ꢀ with a d spacing of
17.3 Å (Fig. 4a). Further heating the samples led to a substantial
enhancement of the reflection peak intensity, and the peak position
continuously and slightly shifted to lower 2q angles. The low-angle

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C.-A. Yang et al. / Polymer 51 (2010) 422–429
be ascribed to the short-range orders existing along the fiber
direction. On the other hand, a pair of strong diffraction arcs can
PMBCSs, PDMBCSs and PTMBCSs, the samples could show liquid-
crystalline behaviors when DPGPC exceeded 312, 115 and 51,
respectively. It indicated that the ability of mesophase formation of
the polymers increased as the number of the alkoxy terminal group
increased.
be seen on the equators at 2
q
¼ 5.12ꢀ (d-spacing was 17.3 Å), 4.80ꢀ
(d-spacing was 18.4 Å) and 4.77ꢀ (d-spacing was 18.5 Å) for PMBCS
(P3), PDMBCS (P6) and PTMBCS (P8), respectively, indicating that
the order structures have developed along the direction perpen-
dicular to the fiber axis on the nanometer scale. Therefore, the LC
phase in PMBCS (P3), PDMBCS (P6) and PTMBCS (P8) shall be a FN
phase, respectively [48].
Acknowledgment
This research was financially supported by the New Century
Excellent Talents in University (NCET-05-0707), the Scientific
Research Fund of Hunan Provincial Education Department
(06A068), the Key Project of Chinese Ministry of Education for
Science and Technology (NO.207075) and the National Nature
Science Foundation of China (20874082).
From all these results, we found that the mesophase formation
of the polymers all showed remarkable MW dependence (see Table
1). Compared with those MJLCPs, the side chains based on a more
rigid and straight mesogen core, the ability of mesophase formation
of the polymers with the semirigid side groups were lower. For
example, when the MWs of the PMPCS samples were higher than
10,200 (DPGPC ¼ 25), the amorphous samples cast from solution
developed into an LC phase above the glass-transition temperature
upon the first heating [31,48]. However, when we added one
methylene unit between the alkoxybenzene unit and the oxy-
carbonyl styrene unit of PMPCS to break the rigidity of side-chain
mesogen, we found the PMBCS samples with MWs higher than
13.5 ꢁ104 (DPGPC ¼ 312) could form LC phase. So, we presumed that
the ability of mesophase formation of the PMBCSs was obviously
lower than the PMPCSs and the ability of mesophase formation of
the polymers decreased as the rigidity of side-chain group
decreased. As could be seen from Table 1 in combination with the
results of PLM, the ability of mesophase formation of the polymers
increased as the number of the alkoxy terminal group increased.
For example, for PMBCSs, PDMBCSs and PTMBCSs, the samples
could show liquid-crystalline behaviors when DPGPC exceeded 312,
115 and 51, respectively. It meant that the samples were much
easier to form liquid-crystalline state with the number of the
methoxy terminal group increased. We presumed that for MJLCPs,
because of the spatial requirement of bulky mesogenic units, the
main chain had to take an extended and stiffened conformation and
the steric hinderance caused by the number of methoxy terminal
group increased. So the ability of mesophase formation increased
with the steric hinderance increasing due to the increase of the
number of the methoxy terminal group. And all the polymers with
high molecular weight showed stable columnar nematic phase
References
[1] Ikeda T, Tsutsumi O. Science 1995;268:1873–5.
[2] Natansohn A, Rochon P. Chem Rev 2002;102:4139–76.
[3] Yoneyama S, Yamamoto T, Tsutsumi O, Kanazawa A, Shiono T, Ikeda T.
Macromolecules 2002;35:8751–8.
[4] Tamai N, Miyasaka H. Chem Rev 2000;100:1875–90.
[5] Yu Y, Nakano M, Ikeda T. Nature 2003;425:145.
[6] Yu HF, Iyoda T, Ikeda T. J Am Chem Soc 2006;128:11010–1.
[7] Bubulac TV, Hamciuc C. Polymer 2009;50:2220–7.
[8] Bhowmik PK, Han H, Nedeltchev AK, Mandal HD, Jimenez-Hernandez JA,
McGannon PM. Polymer 2009;50:3128–35.
[9] Rodrı´guez-Hidalgo MDR, Soto-Figueroa CS, Martı´nez-Magada´n JM, Luı´s-
Vicente. Polymer 2009;50:4596–601.
[10] Kawatsuki N, Koezuka Y. Polymer 2009;50:2349–56.
[11] Zhou QF, Li HM, Feng XD. Synthesis of a new class of side chain liquid crystal
polymers. In: International conference on liquid crystak polymers. Bordeaux,
France: 1987. p. 401.
[12] Finkelmann H, Wendorff HJ. Structure of nematic side chain polymers. In:
Blumstein A, editor. Polymeric liquid Crystals. New York: Plenum Press; 1985.
p. 295.
[13] Hessel F, Finkelmann H. Polym Bull 1985;14:375–8.
[14] Zhou QF, Li HM, Feng XD. Macromolecules 1987;20:233–4.
[15] Zhou QF, Zhu XL, Wen ZQ. Macromolecules 1989;22:491–3.
[16] Pragliola S, Ober CK, Mather PT, Leon HG. Macromol Chem Phys 1999;200:
2338–44.
[17] Zhang D, Zhou QF, Ma YG, Wan XH, Feng XD. Polym Adv Technol 1997;8:
227–33.
[18] Zhang D, Liu YX, Wan XH, Zhou QF. Macromolecules 1999;32:5183–5.
[19] Yu ZN, Wan XH, Zhang HL, Chen XF, Zhou QF. Chem Commun 2003:974–5.
[20] Chen XF, Tenneti KK, Li CY, Bai YW, Zhou R, Wan XH, et al. Macromolecules
2006;39:517–27.
[21] Hessel F, Herr RP, Finkelmann H. Makromol Chem 1987;188:1597–661.
[22] Percec V, Tomazos DJ. Matter Chem 1993;3:643–50.
[23] Pugh C, Schrock RR. Macromolecules 1992;25:6593–604.
[24] Pugh C, Liu Y, Arehart SV, Narayannan R. Macromol Symp 1995;98:293–310.
[25] Keller P, Hardouin R, Mauzac M, Achard M. Mol Cryst Liq Cryst 1988;155:
171–8.
[26] Gray GW, Hill JS, Lacey D. Mol Cryst Liq Cryst 1991;197:43–55.
[27] Zhou QF, Wan XH, Zhu XL, Zhang F, Feng XD. Mol Cryst Liq Cryst 1993;231:
107–17.
(FN).
It is of interest to further examine the alkoxy length of alkoxy
terminal group effect on the phase structure. We speculate that
increasing the length of the alkoxy tails will gradually increase the
side-chain mobility. Once the steric hindrance can be overcome, the
polymers with long alkoxy tails shall pack into more intriguing
structures. The results will be reported in the near future.
[28] Zhou QF, Wan XH, Zhu XL, Zhang D, Feng XD. In: Isayev AI, Kyu T, Cheng SZD,
editors. Liquid crystalline polymer Systems-Technological Advances. ACS
Symposium Book series 632. Washington, DC: American Chemical Society;
1996. p. 344–57.
4. Conclusion
[29] Tu YF, Wan XH, Zhang D, Zhou QF, Wu C. J Am Chem Soc 2000;122:10201–5.
[30] Tu YF, Wan XH, Zhang HL, Fan XH, Chen XF, Zhou QF, et al. Macromolecules
2003;36:6565–9.
[31] Zhang H, Yu Z, Wan X, Zhou QF, Woo EM. Polymer 2002;43:2357–3261.
[32] Guan Y, Chen XF, Shen ZH, Wan XH, Zhou QF. Polymer 2009;50:936–44.
[33] Wang P, Chuai YT, Chai CP, Wang FZ, Zhang GL, Ge GP, et al. Polymer
2008;49:455–60.
[34] Zhang HL, Sun XY, Wang XY, Zhou QF. Macromol Rapid Commun
2005;26:407–11.
[35] Wang XZ, Zhang HL, Shi M, Wang XY, Zhou QF. J Polym Sci Part A Polym Chem
2005;43:733–41.
[36] Xie HL, Hu TH, Zhang HL, Chen EQ, Zhou QF. J Polym Sci Part A Polym Chem
2008;46:7310–20.
[37] Yu ZN, Tu HL, Wan XH, Chen XF, Zhou QF. J Polym Sci Part A Polym Chem
2003;41:1454–64.
[38] Fan XH, Dong HC, Chen XF, Wan XH, Zhou QF. Acta Polym Sin 2004;4:620–4.
[39] Tu HL, Zhang D, Wan XH, Chen XF, Liu YX, Zhang H, et al. Macromol Rapid
Commun 1999;20:549–51.
[40] Wan XH, Tu HL, Liu YX, Zhang D, Chen XF, Zhang H, et al. Chin J Polym Sci
2003;21:21–7.
In summary, we synthesized a series of vinyl monomers with
different numbers of alkoxy terminal groups. Upon using conven-
tional radical polymerization, we further obtained their corre-
sponding homopolymers. The chemical structures of the
monomers and polymers were confirmed by various character-
ization techniques. The phase transition behaviors were studied
using DSC, and the phase structures and the ability of mesophase
formation have been investigated by PLM and WAXD. DSC results
revealed that each of the polymers showed only a glass transition
and the Tg of PTMBCSs were obviously greater that those of PMBCSs
and PDMBCSs, and those of PDMBCSs were the lowest. Compared
with PMPCS, the glass-transition temperatures of the polymers
obviously decreased as the rigidity of side-chain group decreased.
Moreover, the ability of mesophase formation of the polymers
decreased as the rigidity of side-chain group decreased. For

C.-A. Yang et al. / Polymer 51 (2010) 422–429
429
[41] Tu HL, Wan XH, Liu YX, Chen XF, Zhang D, Zhou QF, et al. Macromolecules
2000;33:6315–20.
[45] Chai CP, Zhu XQ, Wang P, Ren MQ, Chen XF, Xu YD, et al. Macromolecules
2007;40:9361–70.
[42] Yin XY, Chen EQ, Wan XH, Zhou QF. Chin J Polym Sci 2003;21:9–14.
[46] Chen S, Gao LC, Zhao XD, Chen XF, Fan XH, Xie PY, et al. Macromolecules
2007;40:5718–25.
[47] Liu YX, Zhang D, Wan XH, Zhou QF. Chin J Polym Sci 1998;16:283–8.
[48] Ye C, Zhang H, Huang Y, Chen EQ, Lu YL, Shen DY, et al. Macromolecules
2004;37:7188–96.
[43] Yin XY, Ye C, Ma X, Chen EQ, Qi XY, Duan XF, et al.
2003;125:6854–5.
J Am Chem Soc
[44] Li CY, Tenneti KK, Zhang D, Zhang H, Wan X, Chen EQ, et al. Macromolecules
2004;37:2854–60.