Influence of alkoxy tail length on the phase behaviour of mesogen-jacketed liquid crystalline polymers with fan-shaped pendants

Article abstract of DOI:10.1016/j.polymer.2010.08.007

A series of new monomers of 2, 5-bis [(3, 4, 5-trialkoxy benzyl) oxycarbonyl] styrene (denoted as M-tri-OC_mH_{2m + 1}, m = 1, 2, 4, 6, 8, 10, 12, where m indicated the number of carbon atoms in the alkoxy group) were designed and synthesized. Then, their corresponding polymers P-tri-OC_mH_{2m + 1} (m = 1, 2, 4, 6, 8, 10, 12) were synthesized by free radical polymerization. The chemical structure of the monomers was confirmed by elemental analysis, ¹H NMR and ¹³C NMR. The molecular characterization of polymers was performed with ¹H NMR, gel permeation chromatography (GPC). The thermal stability of polymers was investigated by thermogravimetric analysis (TGA). The phase structure and transition behaviours were studied using differential scanning calorimetry (DSC), polarized light microscopy (PLM), one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction (WAXD). We found that P-tri-OC_mH_{2m + 1} (m = 1, 2) with short n-alkoxy substituents as the tail form columnar nematic (Φ_N) phase; that with the increasing length of alkoxy tails, P-tri-OC_mH_{2m + 1} (m = 4, 6, 8) can demonstrate the hexagonal columnar (Φ_H) phase; however, when the length of alkoxy tails exceeded a threshold, P-tri-OC_mH_{2m + 1} (m = 10, 12) only develop into columnar nematic (Φ_N) phase instead of Φ_H phase.

Full text of DOI:10.1016/j.polymer.2010.08.007

Polymer 51 (2010) 4503e4510
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Influence of alkoxy tail length on the phase behaviour of mesogen-jacketed
liquid crystalline polymers with fan-shaped pendants
*
Chang-An Yang, Guo Wang, He Lou Xie, Hai Liang Zhang
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
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new monomers of 2, 5-bis [(3, 4, 5-trialkoxy benzyl) oxycarbonyl] styrene (denoted as
M-tri-OCmH2m þ 1, m ¼ 1, 2, 4, 6, 8, 10, 12, where m indicated the number of carbon atoms in the alkoxy
group) were designed and synthesized. Then, their corresponding polymers P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4,
6, 8, 10, 12) were synthesized by free radical polymerization. The chemical structure of the monomers
was confirmed by elemental analysis, 1H NMR and 13C NMR. The molecular characterization of polymers
was performed with 1H NMR, gel permeation chromatography (GPC). The thermal stability of polymers
was investigated by thermogravimetric analysis (TGA). The phase structure and transition behaviours
were studied using differential scanning calorimetry (DSC), polarized light microscopy (PLM), one- and
Received 18 April 2010
Received in revised form
27 July 2010
Accepted 5 August 2010
Available online 12 August 2010
Keywords:
Mesogen-jacketed liquid crystalline
polymer (MJLCP)
Phase structure
Hexagonal columnar phase (FH
two-dimensional (1D and 2D) wide-angle X-ray diffraction (WAXD). We found that P-tri-OCmH2m
þ
1
(m ¼ 1, 2) with short n-alkoxy substituents as the tail form columnar nematic (FN) phase; that with the
increasing length of alkoxy tails, P-tri-OCmH2m þ 1 (m ¼ 4, 6, 8) can demonstrate the hexagonal columnar
)
(
FH) phase; however, when the length of alkoxy tails exceeded a threshold, P-tri-OCmH2m þ 1 (m ¼ 10, 12)
only develop into columnar nematic (FN) phase instead of FH phase.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
hexagonal columnar phase (FH) [35], smectic A (SA) phase [36,37],
and so on. Their phase structure and transition depended strongly
on the chemical structure of side chain, such as the length or type of
the terminal flexible substituents, nature of the polymer backbone,
tacticity, and so on [33,34,38,39].
Mesogen-jacketed liquid crystalline polymers (MJLCPs) have
been attracting increasing interests for its novelties in the structure
and properties since these compounds were first investigated by
Zhou et al. in the 1987 [1]. Compared with conventional side-on
fixed side chain liquid crystalline polymers (side-on fixed SCLCPs),
the mesogenic pendants of a MJLCP were connected laterally to the
polymer backbones without or with very short spacers, leading to
the extended main chain conformation and giving some properties
similar to main chain liquid crystalline polymers (MCLCPs) by
virtue of the spatial requirement of the bulky and rigid mesogenic
units [2e4].
In the past several years, the MJLCPs have been researched in
a few research groups including Finklemann [5], Pugh [6,7], Ober
[8], Percec [9], Gray [10], Keller [11] and Zhou [12e24]. Unlike
conventional SCLCPs with a spacer of a certain length that formed
nematic phase [25e27] and smectic phases [28e31], MJLCPs could
Recently, three new MJLCPs, poly {2, 5-bis [(4-methoxy benzyl)
oxycarbonyl] styrene} (PMBCS), poly {2, 5-bis [(3, 5-dimethoxy
benzyl) oxycarbonyl] styrene} (PDMBCS) and poly {2, 5-bis [(3, 4,
5-trimethoxy benzyl) oxycarbonyl] styrene} (PTMBCS) with the
semi-rigid side chain have been synthesized, and the ability of
mesophase formation of these polymers was investigated [24]. To
further investigate the relationship between the flexibility and
phase structure of the liquid crystalline polymer, the model, poly
{2, 5-bis [(3, 4, 5-trimethoxy benzyl) oxycarbonyl] styrene} with
trialkoxy as terminal substituent, was chosen, and the length of
polymer’s terminal flexible substituent was changed without
changing all the others. In this article, a series of monomers with
different lengths of the terminal alkoxy, 2, 5-bis [(3, 4, 5-trialkoxy
benzyl) oxycarbonyl] styrene} (denoted as M-tri-OCmH2m þ 1, m ¼ 1,
2, 4, 6, 8, 10, 12, where m indicated the number of carbon atoms in
the alkoxy group) were designed and synthesized. Then, their
corresponding polymers were synthesized by free radical poly-
merization. The chemical structure of the monomers and their
corresponding polymers is depicted in Scheme 1. The structure of
develop into columnar nematic
nematic (FHN) phases [33,34], hexatic columnar phase (FHex),
(FN) [32], hexatic columnar
* Corresponding author. Tel.: þ86 731 58293377; fax: þ86 731 58293264.
E-mail address: hailiangzhang@xtu.edu.cn (H.L. Zhang).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.08.007

4504
C.-A. Yang et al. / Polymer 51 (2010) 4503e4510
Scheme 1. Synthetic route of the monomers M-tri-OCmH2m
(m ¼ 1, 2, 4, 6, 8, 10, 12) and their corresponding polymers P-tri-OCmH2m
þ 1
(m ¼ 1, 2, 4, 6, 8, 10, 12).
þ
1
the monomers was confirmed by elemental analysis, 1H NMR
and 13C NMR, and their corresponding polymers were character-
ized with 1H NMR, gel permeation chromatography (GPC), thermo
gravimetric analysis (TGA), differential scanning calorimetry (DSC),
polarized light microscopy (PLM), and wide-angle X-ray diffraction
(WAXD).
6, 8, 10, 12) is shown in Scheme 1. The experimental details of the
monomer synthesis and characterization are described below using
M-tri-OCH3 (m ¼ 1) as an example.
2.2.1. Synthesis of methyl 3, 4, 5-trimethoxybenzoate
Methyl 3, 4, 5-trihydroxybenzoate (18.4 g, 0.1 mol), dimethyl
sulfate (37.8 g, 0.3 mol) and K2CO3 (82.8 g, 0.6 mol) were dissolved
in acetone (250 mL) and refluxed for 24 h. The floating salt was
filtrated and the solvent was evaporated under reduced pressure,
and then, it was precipitated in ice water. The mixture was filtrated,
and the obtained white solid was washed with ice water and dried
2. Experimental section
2.1. Materials
The compound of vinylterephthalic acid was synthesized using
the method previously reported [40]. Azobisisbutyronitrile (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
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 (MgSO4) was used to dry all organic extracts. All other
reagents were used as received from commercial sources.
to yield 14.1 g (62.4%) of solid. 1H NMR (
d, ppm, CDCl3): 7.30e7.28
(m, 2H,AreH); 3.91 (s, 12H, eOCH3).
2.2.2. Synthesis of 3, 4, 5-trimethoxybenzalcohol
LiAlH4 (3.8 g, 0.1 mol) was suspended in dry THF (20 mL), and the
solution of methyl 3, 4, 5-trimethoxybenzoate (22.6 g, 0.1 mol) in
THF (50 mL) was added slowly dropwise at room temperature. After
all of the THF solution had been added, the mixture was reacted for
another 2h. Water was then added slowly with vigorous stirring to
terminate the reaction, and then diluted HCl was added to dissolve
the precipitate. The product was extracted with CH2Cl2. The extracts
were dried over Anhydrous MgSO4, and condensed to yield 17.5 g
(88%) of liquid. 1H NMR (
d, ppm, CDCl3): 6.60e6.57 (m, 2H, AreH);
4.64 (s, 2H, eCH2OH); 3.87 (s, 6H, eOCH3); 3.84 (s, 3H, eOCH3).
2.2. Synthesis of monomers
2.2.3. Synthesis of vinylterepthaloyl chloride
The synthetic route of the monomers of 2, 5-bis [(3, 4, 5-tri-
alkoxy benzyl) oxycarbonyl] styrene} (M-tri-OCmH2m þ 1, m ¼ 1, 2, 4,
An amount of vinylterephthalic acid (1.92 g, 10 mmol) was mixed
with thionyl chloride (20 mL) in a round-bottom flask (100 mL). The

C.-A. Yang et al. / Polymer 51 (2010) 4503e4510
4505
mixture was refluxed for about 2 h to get a clear solution. The excess
thionyl chloride was removed by evaporation under reduced pres-
sure. The residue was washed twice by petroleum ether. A pale
yellow liquid of vinylterepthaloyl chloride was obtained.
5.76e5.71 (dd, 1H, eCH]CHH); 5.41e5.38 (dd, 1H, eCH]CHH);
5.26, 5.25 (s, 4H, eCOOCH2e); 3.96e3.92 (m, 12H, eOCH2e);
1.82e1.70 (m, 12H, eCH2e); 1.45e1.41 (m, 12H, eCH2e); 1.26e1.24
(m, 72H, eCH2e); 0.88e0.85 (m,18H, eCH2CH3). Anal. Calcd for
C84H140O10: C, 77.01; H, 10.77. Found: C, 77.16; H, 10.89.
2.2.5.6. M-Tri-OC12H25. d, ppm, CDCl3). 8.24e7.88 (m,
1H NMR (
2.2.4. Synthesis of 2, 5-bis [(3, 4, 5-trimethoxy benzyl)
3H, AreH); 7.38e7.34 (q, 1H, eCH]CH2); 6.61e6.60 (m, 4H, AreH);
5.75e5.72 (dd, 1H, eCH]CHH); 5.37e5.34 (dd, 1H, eCH]CHH);
5.25, 5.23(s, 4H, eCOOCH2e); 3.94e3.91 (m, 12H, eOCH2e);
1.77e1.73 (m, 12H, eCH2e); 1.44e1.40 (m, 12H, eCH2e); 1.24e1.21
(m, 96H, eCH2e); 0.85e0.82 (m,18H, eCH2CH3). Anal. Calcd for
C96H164O10: C, 78.00; H, 11.18. Found: C, 77.75; H, 10.96.
oxycarbonyl] styrene (M-tri-OCH3)
3, 4, 5-Trimethoxybenzalcohol (7.92 g, 20 mmol), DMAP (7.34 g,
60 mmol), and triethylamine (8 mL) were dissolved in dried THF
(50 mL). Vinylterephthal chloride was dissolved in dried THF
(20 mL). Under intense stirring at the temperature of the ice bath, the
solution of vinylterepthaloyl 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 evapo-
rated under reduced pressure. Then, water and dilute HCl was added
to dissolve the precipitate, the product was extracted with CH2Cl2.
The extracts were dried over Anhydrous MgSO4, and condensed to
get a solid. Afterward, the raw product dissolved in dichloromethane
was purified first by column chromatography (silica gel, dichloro-
methane/acetone, 50/1), followed by recrystallization from diethyl
2.3. Polymerization
All polymers were obtained by conventional free radical
solution polymerization (see Scheme 1). For example, M-tri-OCH3
(0.5 g, 0.9 mmol), chlorobenzene solution of 0.01 M AIBN
(300
mL), and chlorobenzene (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 samples were dried to a constant
weight.
ether/ethyl alcohol to yield 2.3 g (42%) of M-tri-OCH3. 1H NMR (
d,
ppm, CDCl3): 8.28e7.93 (m, 3H, AreH); 7.44e7.39 (q, 1H, eCH]
CH2); 6.68e6.66 (m, 4H,AreH); 5.78e5.74 (dd, 1H, eCH]CHH);
5.44e5.41 (dd, 1H, eCH]CHH); 5.31, 5.29 (s, 4H, eCOOCH2e);
2.4. Instruments and measurements
3.88e3.85 (s, 18H, eOCH3). 13C NMR (
d, ppm, CDCl3): 56.19, 60.82
Elemental analysis was carried out with an Elementar Vario EL
instrument.
(eOCH3); 67.40, 67.44 (eOCH2e); 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 (]Ce); 165.50, 166.52 (C]O). Anal. Calcd for
C30H32O10: C, 65.21; H, 5.84. Found: C, 65.13; H, 5.81.
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.
2.2.5. Synthesis of 2, 5-bis [(3, 4, 5-trialkoxy benzyl) oxycarbonyl]
styrene (M-tri-OCmH2mþ1, m¼ 2, 4, 6, 8, 10, 12).
All other monomers were prepared in a similar way. The spectra
data are as follows.
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).
2.2.5.1. M-Tri-OC2H5. 1H NMR (
d, ppm, CDCl3). 8.26e7.90 (m, 3H,
AreH); 7.40e7.35 (q, 1H, eCH]CH2); 6.64e6.62 (m, 4H, AreH);
5.72e5.68(dd,1H, eCH]CHH);5.39e5.34(dd,1H, eCH]CHH);5.28,
5.26 (s, 4H, eCOOCH2e); 4.07e4.05 (m, 12H, eOCH2e); 1.55e1.34
(m,18H, eCH2CH3). Anal. Calcd for C36H44O10: C, 67.91; H, 6.97. Found:
C, 67.63; H, 6.82.
The TGA was performed on a TA SDT 2960 instrument at
a heating rate of 20 ꢀC/min in nitrogen atmosphere.
DSC examination was carried out on a TA DSC Q100 calo-
rimeter with a programed heating procedure in nitrogen. The
temperature and heat flow were calibrated using standard
materials such as indium and benzoic acid. The samples were
encapsulated in hermetically sealed aluminum pans with
a typical sample weight of w5 mg. The cooling and subsequent
heating DSC experiments were carried out at a rate of 10 ꢀC/
min.
2.2.5.2. M-Tri-OC4H9. 1H NMR (
d, ppm, CDCl3). 8.29e7.93 (m, 3H,
AreH); 7.44e7.38 (q, 1H, eCH]CH2); 6.65e6.63 (m, 4H, AreH);
5.75e5.73 (dd,1H, eCH]CHH);5.41e5.38(dd,1H, eCH]CHH); 5.28,
5.25 (s, 4H, eCOOCH2e); 4.01e3.98 (m,12H, eOCH2e); 1.80e1.53 (m,
24H, eCH2e); 0.97e0.93 (m,18H, eCH2CH3). Anal. Calcd for
C48H68O10: C, 71.61; H, 8.51. Found: C, 71.90; H, 8.37.
LC texture of the samples was examined under PLM (Leica
DM-LM-P) coupled with a Mettler-Toledo hot stage (FP82HT). The
films with thickness of w10 mm were casted from THF solution and
2.2.5.3. M-Tri-OC6H13. 1H NMR (
d, ppm, CDCl3). 8.24e7.88 (s, 1H,
AreH); 7.44e7.38 (q, 1H, eCH]CH2); 6.61e6.59 (m, 4H, AreH);
5.75e5.72 (dd, 1H, eCH]CHH); 5.37e5.34 (dd, 1H, eCH]CHH);
5.25, 5.23(s, 4H, eCOOCH2e); 3.94e3.90 (m, 12H, eOCH2e);
1.77e1.72 (m, 12H, eCH2e); 1.44e1.39 (m, 12H, eCH2e); 1.24e1.21
(m, 24H, eCH2e); 0.85e0.80 (m,18H, eCH2CH3). Anal. Calcd for
C60H92O10: C, 74.04; H, 9.53. Found: C,74.02; H, 9.39.
slowly 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 Ka) and an X0
celerator detector. The reflection peak positions were calibrated
with silicon powder (2q q
> 15ꢀ) and silver behenate (2 < 10ꢀ). The
2.2.5.4. M-Tri-OC8H17. d, ppm, CDCl3). 8.26e7.90 (m,
1H NMR (
sample stage is set horizontally, and a temperature control unit
(Paar Physica TCU 100) in conjunction with the diffractometer was
employed to study the structure evolutions as a function of
temperature. The heating and cooling rates in the WAXD experi-
ments were 10 ꢀC/min.
Two-dimensional wide-angle X-ray diffraction (2D-WAXD) fibre
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.
3H, AreH); 7.45e7.38 (q, 1H, eCH]CH2); 6.63e6.62 (m, 4H, AreH);
5.76e5.72 (dd, 1H, eCH]CHH); 5.41e5.38 (dd, 1H, eCH]CHH);
5.27, 5.25 (s, 4H, eCOOCH2e); 3.96e3.92 (m, 12H, eOCH2e);
1.84e1.72 (m, 12H, eCH2e); 1.46e1.44 (m, 12H, eCH2e); 1.31e1.26
(m, 48H, eCH2e); 0.88e0.86 (m,18H, eCH2CH3). Anal. Calcd for
C72H116O10: C, 75.75; H, 10.24. Found: C, 75.87; H, 10.31.
2.2.5.5. M-Tri-OC10H21
3H, AreH); 7.47e7.40 (q, 1H, eCH]CH2); 6.62e6.61 (m, 4H, AreH);
. d, ppm, CDCl3). 8.26e7.92 (m,
1H NMR (

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C.-A. Yang et al. / Polymer 51 (2010) 4503e4510
elemental analysis. Parts a and b of Fig. 1 gave the 1H NMR spectra
of the monomer M-tri-OCH3 and its polymer P-tri-OCH3, respec-
tively. The characteristic resonance peaks of the vinyl substituent
of monomer M-tri-OCH3 were presented at 5.41e5.78 and
7.39e7.46 ppm. After polymerization, these signals disappeared
completely, and the chemical shifts of polymers were quite broad,
consistent with the expected polymer structure. P-tri-OCmH2m þ 1
(m ¼ 1, 2, 4, 6, 8, 10, 12) were completely soluble in regular organic
solvents such as THF, chlorobenzene, chloroform, and so on.
GPC analysis was performed to determine the apparent MW and
molecular weight distributions of polymers. Originally, we tried to
synthesize these polymers via atom transfer radical polymerization
(ATRP) at different conditions, but we found it was very difficult to
obtain the high molecule weight polymers. Therefore, the free
radical polymerization method was used to synthesize the high
molecule weight polymers and a series of the samples with similar
MWs were successfully obtained. Table 1 summarizes the GPC
results of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12).
3.2. Phase transition and phase structure
The thermal stability of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12)
was investigated by TGA in nitrogen and air atmosphere, respec-
tively. As could be seen from Table 1, all polymers were quite stable
with temperature at 5.00% weight loss above 330 ꢀC in nitrogen
atmosphere. Even when the atmosphere was changed from
nitrogen to air, polymers (m ¼ 1, 2, 4, 6, 8,10,12) still possessed very
good thermal stability (see Table 1).
The phase transition of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12)
was studied by DSC. To eliminate the effect of thermal history, all
the samples were first heated from 0 to 240 ꢀC at a rate of
10 ꢀC/min. The DSC thermograms were recorded at 10 ꢀC/min
during the second heating process, of which the DSC traces were
shown in Fig. 2. For P-tri-OCmH2mþ1 (m ¼ 1, 2, 4, 6), only glass
transition could be observed, and the glass transition temperatures
(Tg) of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6) decreased as the length of
the alkoxy tails increased. This phenomenon is similar to some
other MJLCPs systems [33]. When the length of the alkoxy tails (m)
was increased from 8 to 12, no obvious glass transition was
Fig. 1. 1H NMR spectra of (a) the monomer M-tri-OCH3 and (b) its polymer P-tri-OCH3
in CDCl3-d.
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. Fibres were drawn at
a stretching rate of about 1 msꢁ1 at 200 ꢀC and quenched to room
temperature for measurements.
3. Results and discussion
observed. Each of P-tri-OCmH2m
thermic peak, which should correspond to the melting peak of the
(m ¼ 10, 12) had one endo-
þ
1
3.1. Synthesis and characterization of the monomers and polymers
alkyl tails. Tg and melting temperature (Tm) of P-tri-OCmH2m
þ
1
(m ¼ 1, 2, 4, 6, 8, 10, 12) are listed in Table 1.
As shown in Scheme 1, all the monomers M-tri-OCmH2m
Birefringence of polymers was observed with PLM. The samples
were cast from THF solution and slowly dried at room temperature.
When each of the samples P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12)
was heated to a temperature much higher than Tg, the liquid
þ
1
(m ¼ 1, 2, 4, 6, 8, 10, 12) could be easily polymerized via the
conventional free radical polymerization method. The structure of
the monomers has been confirmed by 1H NMR, 13H NMR and
Table 1
GPC, DSC and TGA Results and Thermotropic Properties of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12).
Sample
Yielda (%)
Mn (ꢂ10ꢁ4
)
PDIb
Td(air)f (ꢀC)
Td(N2)f (ꢀC)
LC phaseg
b
c
Tm (ꢀC)
c
Tg (ꢀC)
P-tri-OCH3
87
78
85
76
80
75
62
10.12
12.13
14.91
14.66
9.04
2.29
2.26
2.22
2.00
2.28
1.80
2.30
e
82
54
35
31
e
335
326
324
328
328
317
320
339
331
335
345
355
360
351
FN
FN
FH
FH
FH
FN
FN
P-tri-OC2H5
P-tri-OC4H9
P-tri-OC6H13
P-tri-OC8H17
P-tri-OC10H21
P-tri-OC12H25
e
e
e
ed
ꢁ32.5
7
15.15
9.11
e
ee
a
Polymerized in chlorobenzene at 60 ꢀC for 24 h using azobisisobutyronitrile (AIBN) as initiator; [monomer]:[ AIBN] ¼ 300:1 (molar ratio).
Based on GPC measurements.
b
c
d
e
f
Glass transition temperature (Tg) and melting temperature (Tm) obtained from the second heating DSC experiments and heating rates were 10 ꢀC/min.
No metling temperature could be detected by DSC.
No obvious glass transition could be detected by DSC.
Temperature at which the weight loss of polymers reached 5.00% was obtained from TGA under air [Td(air)] and in nitrogen [Td(N2)] by TGA heating experiments at a rate
of 20 ꢀC/min.
g
LC phase of polymers obtained by WAXD.

C.-A. Yang et al. / Polymer 51 (2010) 4503e4510
4507
narrow reflection peak with centres at 2
q
¼ 4.60ꢀ (d spacing of
ꢀ
ꢀ
ꢀ
19.2 A) and 4.82 (d spacing of 18.3 A), respectively. Further heating
the sample, it led to a substantial enhancement of the reflection
peak intensity, and the peak position continuously and slightly
shifted to lower 2q angles. In the high 2q
region (10e30ꢀ), two
scattering holes shape and intensity kept relatively unchanged
under Tg in the first heating (see Fig. 4a). As the temperature
increased, the two peaks intensity gradually decreased and the
centre of the two halos slightly shifted to lower 2q angles caused by
the thermal expansion. One narrow reflection peak with centres
ꢀ
at 2
centres at 2
q
¼ 4.77ꢀ (d spacing of 18.5 A) and two scattering holes with
ꢀ
¼ 21.5ꢀ (d spacing
ꢀ
q
¼ 15.5 (d spacinꢀg of 5.7 A) and 2
q
ꢀ
of 4.1 A) were observed at 220 C. This suggested a columnar lateral
ꢀ
packing of the rods with the rod diameter of 18.5 A. It is noted that
ꢀ
P-tri-OCH3 rod diameter of 18.5 A in the columnar nematic (FN
)
phase is just slightly less than the calculated length of the
ꢀ
side group (18.7 A). Therefore, the fully semi-rigid side groups of
P-tri-OCH3 are almost perpendicular to theꢀrod long axis with the
ꢀ
Fig. 2. DSC thermograms of P-tri-OCmH2m
(m ¼ 1, 2, 4, 6, 8, 10, 12) during the
þ
1
column. For the scattering halo at 2
q
¼ 21.5 (d spacing of 4.1 A), it
second heating at a rate of 10 ꢀC/min.
should correspond to spacing between the semi-rigid side groups,
ꢀ
ꢀ
and for the scattering halo at 2
q
¼ 15.5 (d spacing of 5.7 A), we still
crystalline birefringence appeared and kept unchanged before
decomposition. During the cooling process, the birefringence could
be maintained. These phenomena were all similar to other MJLCPs
[40]. Herein, the samples P-tri-OCH3 and P-tri-OC4H9 will be used
as the examples. For the sample P-tri-OCH3, a focal-conic fan
texture appeared during the heating and it remained unchanged in
consecutive cooling (see Fig. 3a). When the sample P-tri-OC4H9 was
heated to a temperature much higher than the Tg, a representative
schlieren texture appeared and remained before decomposition
(see Fig. 3b).
do not get a reasonable interpretation about the packing. During
the cooling process, the low-angle diffraction which evolved during
the first heating was remained and the reflection peak intensity
slightly decreased as the temperature decreased.
Fig. 4b showed the structurally sensitive 1D-WAXD patterns of
P-tri-OC4H9 from 30 to 250 ꢀC. Upon the first heating, higher orders
of the diffractions were visible. For the sample P-tri-OC4H9, the
scattering vector ratio of the diffractions followed 1: 31/2: 41/2: 71/2
,
demonstrating
a long-range ordered hexagonal lattice. The
ꢀ
maximum d spacing value (23.4 A) of the sample was almost iden-
tical to the calculated length of the side group in monomers (23.5 A),
ꢀ
The phase transition of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12)
was further verified on the 1D-WAXD instrument. Fig. 4a summa-
rized the d spacing changes with temperatures for P-tri-OCH3 in the
which meant the side chain of the side group was perpendicular to
the main chain. Therefore, we presumed that the sample formed
a hexagonal columnar phase (FH). When the sample was cooled, the
hexagonal columnar phase (FH) remained unchanged.
The other polymers P-tri-OCmH2m þ 1 (m ¼ 2, 6, 8, 10, 12) were
also investigated by the 1D-WAXD instrument from room
temperature to 240 ꢀC during the first heating and the 1D-WAXD
data at 220 ꢀC was summarized in Table 2. When polymers
had shorter n-alkoxy substituent as the tail (for example,
low and high 2q angle regions during the first heating. When the
temperature was below Tg during the first heating, a low-angle
scattering halo was observed and the peak intensity was
unchanged. With further increasing temperature, the peak inten-
sity gradually increased and the position still kept unchanged from
100 ꢀC to 130 ꢀC. When the sample was heated from 130 ꢀC to
190 ꢀC, the peak intensity decreased and the position suddenly
shifted to lower 2
asymmetric and was deconvoluted into one broad halo and one
q
angles. At 200 ꢀC, the scattering halo became
P-tri-OCmH2m
1, m ¼ 1, 2), they formed columnar nematic
þ
(FN) phase (see Fig. 4a and Table 2), and when polymers had
Fig. 3. Representative textures of (a) P-tri-OCH3 and (b) P-tri-OC4H9. Samples were heated to 280 ꢀC at 10 ꢀC/min, then cooled to room temperature at 10 ꢀC/min and pictured
at 220 ꢀC.

4508
C.-A. Yang et al. / Polymer 51 (2010) 4503e4510
Fig. 4. Sets of 1D-WAXD patterns in both low and high 2q angle regions. (a) P-tri-OCH3 and (b) P-tri-OC4H9 all obtained during the heating.
at 220 ꢀC. Fig. 5a shows the 2D-WAXD patterns of the oriented
P-tri-OCH3 sample at room temperature with X-ray incident beam
perpendicular to the fibre direction. A pair of strong diffraction arcs
Table 2
1D-WAXD Results of P-tri-OCmH2m þ 1 (m ¼ 1, 2, 4, 6, 8, 10, 12) at 220 ꢀC.
(ꢀ)
d (A)
q-Ratios
ꢀ
Sample
2
q
ꢀ
was observed on the equator at 2
q
¼ 4.77ꢀ (d spacing was 18.5 A),
P-tri-OCH3
4.77
4.28
18.5
20.6
e
e
P-tri-OC2H5
P-tri-OC4H9
P-tri-OC6H13
P-tri-OC8H17
P-tri-OC10H21 2.92
P-tri-OC12H25 2.86
indicating that the order structure was developed perpendicular to
the fibre axis on the nanometer scale. This was perfectly consistent
with the 1D-WAXD results. Meanwhile, two scattering halos in the
3.77, 6.55, 7.53, 9.93 23.4, 13.5, 11.7, 8.9
3.51, 6.05, 6.95, 9.09 25.2, 14.6, 12.7, 9.7
1: 31/2: 41/2: 71/2
1: 31/2: 41/2: 71/2
3.06, 5.29, 6.18, 8.11 28.9, 16.7, 14.3, 10.9 1: 31/2: 41/2: 71/2
high 2q angle were more or less concentrated on the meridians
30.2
30.9
e
with rather broad azimuthal distributions. This indicated that only
the short-range orders existed along the shear direction. The
2D-WAXD pattern in Fig. 5a proved that P-tri-OCH3 formed
a typical columnar nematic (FN) phase.
e
relatively longer n-alkoxy substituents as the tail (for example,
P-tri-OCmH2m
1, m ¼ 4, 6, 8), they demonstrated hexagonal
Fig. 5b shows the 2D-WAXD patterns of the oriented P-tri-
OC4H9 sample at room temperature with X-ray incident beam
perpendicular to the shear direction. Three pairs of strong diffrac-
tion arcs could be found on the equator at 3.77ꢀ, 7.53ꢀ, 9.93ꢀ
þ
columnar (FH) phase (see Fig. 4b and Table 2). As the length of the
alkoxy tails further increased (for example, P-tri-OCmH2m
,
)
þ
1
m ¼ 10, 12), polymers only developed into columnar nematic (FN
ꢀ
phase and their 1D-WAXD patterns were provided in the Sup-
porting Information (see Fig. S-1 and Table 2).
(d spacing was 23.4, 11.7, 8.9 A, respectively). These three scattering
vector ratios followed 1: 41/2: 71/2, and the diffraction arcs could be
assigned to be the (100), (200) and (210) plane, respectively, indi-
cating that a long-range periodic hexagonal packing along the
To further confirm the structure of these polymers, the
2D-WAXD experiments were carried out. The fibres were spun
Fig. 5. (a) and (b) were the 2D-WAXD patterns of P-tri-OCH3 and P-tri-OC4H9 at room temperature, respectively. The X-ray incident beam was perpendicular to the fibre axis, and
the fibre axis and equator are indexed by the solid and dashed lines, respectively.

C.-A. Yang et al. / Polymer 51 (2010) 4503e4510
4509
Fig. 6. Schematic representation of (a) columnar nematic (FN) and (b) hexagonal columnar phase (FH).
lateral direction perpendicular to the fibre axis was formed. The
Acknowledgment
2D-WAXD pattern in Fig. 5b proved that P-tri-OC4H9 formed
a hexagonal columnar (FH) phase.
This research is financially supported by the National Nature
Science Foundation of China (20874082), the Postgraduate Inno-
vation Fund of Hunan Province (S2008yjscx10), 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 New Century Excel-
lent Talents in University (NCET-05-0707).
In this article, two kinds of columnar packing schemes are
observed in P-tri-OCmH2mþ1 (m ¼ 1, 2, 4, 6, 8, 10, 12) and shown in
Fig. 6. It is envisaged that this difference in packing schemes may be
due to the soft shell of the macromolecular rod surface, which is self-
assembled by multiple terminal n-alkoxy groups. P-tri-OCmH2m þ 1
(m ¼ 1, 2) with short n-alkoxy substituents as the tail form columnar
nematic (FN) phase; with the increasing length of alkoxy tails, P-tri-
OCmH2m þ 1 (m ¼ 4, 6, 8) can demonstrate the hexagonal columnar
Supplementary material
(FH) phase; however, when the length of alkoxy tails exceeded
a threshold, P-tri-OCmH2m
(m ¼ 10, 12) only develop into
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.polymer.2010.08.007.
þ
1
columnar nematic (FN) phase instead of FH phase (see Fig. 6). This
indicates that the flexibility of alkoxy tails is crucial to determine the
LCstructure. Namely, simplychanging the chemical structure of small
portion of the MJLCP may greatly vary the molecular packing
behaviour and thus the molecular shape in LC phase structure. The
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