Effects of main chain and acceptor content on phase behaviors of hydrogen-bonded main-chain/side-chain combined liquid crystalline polymers

Article abstract of DOI:10.1016/j.polymer.2016.01.018

Main-chain/side-chain combined liquid crystalline polymers (MCSCLCPs) are usually difficult to synthesize and their degrees of polymerization are relatively low, which bring difficulties in studying their structure-property relationships. In order to solve this problem, we prepared a new series of MCSCLCPs containing mesogen-jacketed liquid crystalline polymer (MJLCP) main chains via hydrogen-bonding (H-B). A pyridine derivative with a triphenylene (Tp) unit is the H-B acceptor. In addition to the temperature dependence, the phase behavior of the resulting complex is strongly influenced by the content of the H-B acceptor and the rigidity of the side-chain core of the MJLCP. The resulting complexes exhibit different phase structures: (1) a columnar nematic phase or a smectic A (SmA) phase formed by the supramolecular MJLCP chain as a whole; (2) hierarchical nanostructures including a hexagonal columnar phase or a SmA phase of the whole polymer chain plus a discotic nematic phase associated with the Tp moieties.

Full text of DOI:10.1016/j.polymer.2016.01.018

Polymer 84 (2016) 355e364
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Effects of main chain and acceptor content on phase behaviors of
hydrogen-bonded main-chain/side-chain combined liquid crystalline
polymers
a
,
b
,
1, Wei Qu a , Hong-Bing Pan , Yu-Dong Zhang , Shi-Jun Zheng
,
1
,
2
a
a
b, **
Shuai-Qi Yang
,
a
a, *
Xing-He Fan , Zhihao Shen
Beijing National Laboratory for Molecular Sciences, The Key Laborarotary of Polymer Chemistry and Physics of Ministry of Education, Center for Soft
Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Bejing 100871, China
a
b
College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 August 2015
Received in revised form
Main-chain/side-chain combined liquid crystalline polymers (MCSCLCPs) are usually difficult to syn-
thesize and their degrees of polymerization are relatively low, which bring difficulties in studying their
structureeproperty relationships. In order to solve this problem, we prepared a new series of MCSCLCPs
containing mesogen-jacketed liquid crystalline polymer (MJLCP) main chains via hydrogen-bonding (H
eB). A pyridine derivative with a triphenylene (Tp) unit is the HeB acceptor. In addition to the tem-
perature dependence, the phase behavior of the resulting complex is strongly influenced by the content
of the HeB acceptor and the rigidity of the side-chain core of the MJLCP. The resulting complexes exhibit
different phase structures: (1) a columnar nematic phase or a smectic A (SmA) phase formed by the
supramolecular MJLCP chain as a whole; (2) hierarchical nanostructures including a hexagonal columnar
phase or a SmA phase of the whole polymer chain plus a discotic nematic phase associated with the Tp
moieties.
1
January 2016
Accepted 6 January 2016
Available online 8 January 2016
Keywords:
Main-chain/side-chain combined liquid
crystalline polymer
Hydrogen-bonding
Hierarchical structure
©
2016 Elsevier Ltd. All rights reserved.
1
. Introduction
controllable and complex structures [7e10]. Main-chain/side-chain
combined LCP (MCSCLCP), a hybrid structure which combines the
chemical features of both main-chain liquid crystalline polymer
(MCLCP) and side-chain liquid crystalline polymer (SCLCP), may
have more complex phase behaviors compared to conventional
MCLCPs and SCLCPs [11]. Since the first example reported by
Ringsdorf et al. [12], many MCSCLCPs have been synthesized and
investigated [13e16]. Generally, in MCSCLCPs, the main chain is a
rigid rod or rod-like chain composed of mesogenic groups and
flexible spacers, while the side chain usually contains a mesogenic
group linked to the main-chain repeating unit through a flexible
spacer. The typical method to obtain this kind of MCSCLCP is
condensation polymerization, and thus the molecular weight (MW)
and the polydispersity index (PDI) of the polymer are not easily
controllable.
Liquid crystal (LC), a typical soft matter with mesophase struc-
tures between the three-dimensionally ordered crystal and
isotropic liquid state, can exhibit phase structures with one-
dimensional (1D) or two-dimensional (2D) order on the length
scale of about 1e10 nm. Liquid crystalline polymers (LCPs) have
received much attention because of their potential applications in
fields such as electro-optic materials, catalysis, nano-templates, etc.
[1e6]. In the past decades, scientists have paid attention to the
strategies in the design and synthesis of LCPs by selecting different
mesogenic groups, varying the location of the mesogen, changing
the length of the flexible spacer, and so on, in order to obtain more
*
Corresponding author.
Mesogen-jacketed liquid crystalline polymers (MJLCPs) are,
chemically speaking, SCLCPs with a very short spacer or a single
carbonecarbon bond between the backbone and the laterally
attached bulky side group [17,18]. The “jacketing” effect or the steric
effect makes the backbone of the MJLCP more or less extended, and
** Corresponding author.
E-mail addresses: zsj316@zzu.edu.cn (S.-J. Zheng), zshen@pku.edu.cn (Z. Shen).
These two authors contributed equally.
Current address: Research Institute of Wood Industry, Chinese Academy of
1
2
Forestry, CRIWI, No. 2, Dongxiaofu, Xiangshan Road, Haidian District, Beijing
00091, China.
1
http://dx.doi.org/10.1016/j.polymer.2016.01.018
032-3861/© 2016 Elsevier Ltd. All rights reserved.
0

356
S.-Q. Yang et al. / Polymer 84 (2016) 355e364
the polymer chain as a whole acts like a supramolecular rod.
Therefore, MJLCPs are more like MCLCPs rather than SCLCPs from a
physical point of view. Xie et al. investigated an MCSCLCP based on
an MJLCP main chain, poly(2,5-bis{[6-(4-butoxy-40-oxy-biphenyl)
hexyl]oxycarbonyl}styrene) (PBBHCS), which was synthesized us-
ing free radical polymerization [19]. Biphenyl groups are incorpo-
rated into the side chain. At low temperatures PBBHCS exhibits a
hierarchical supramolecular structure with double orderings on
different length scales. The main chain constructs a rectangular
scaffold on the nanometer length scale, and the biphenyl-
containing side chains form a smectic E (SmE)-like structure on
the subnanometer length scale [20]. Zhu et al. studied another
MJLCP-based MCSCLCP PPnV, which incorporates triphenylene (Tp)
units into the side chain [21,22]. PPnV also exhibits hierarchical
supramolecular structures in which the main chain forms the
columnar structure and the Tp units in the side chain form a dis-
with different compositions are denoted as PVTA(PHTC
PBCPS(PHTC (where the value of x indicates the molar ratio of
PHTC to the eCOOH group in the MJPE repeating unit). We mainly
focused on complexes with x ranging from 0.5 to 1, where macro-
phase separation did not occur.
6 x
) and
6 x
)
6
2. Materials and methods
2.1. Materials
Dimethyl formamide (DMF) was refluxed over potassium hy-
droxide and distilled out before use. Tetrahydrofuran (THF) was
refluxed over sodium under argon and distilled before use. Chlo-
robenzene was washed by H SO and then distilled under a
2
4
reduced pressure. All other reagents were used as received from
commercial sources.
D
cotic nematic (N ) phase. However, the MW of the monomer of
PPnV is high, and the fraction of the polymerizable styrene unit is
relatively low in the monomer, both of which will lead to a smaller
degree of polymerization (DP) in preparation by atom transfer
radical polymerization (ATRP). It brings difficulties in studying the
structureeproperty relationship of this and other similar
MCSCLCPs.
Another useful and simple method to building LCPs is via
hydrogen bonding. During the past few decades, main-chain, side-
chain, and network LCPs have been designed and prepared by using
hydrogen bonding [23e28]. Xu et al. synthesized a new series of
MJLCPs, utilizing hydrogen bonding, and the resulting complexes
2
.2. Measurements
All the measurements, such as 1H NMR spectrometry, mass
spectrometry (MS), gel permeation chromatography (GPC), ther-
mogravimetric analysis (TGA), differential scanning calorimetry
(
DSC), FTIR spectroscopy, polarized light microscopy (PLM), small-
angle X-ray scattering (SAXS), and 2D wide-angle X-ray diffraction
WAXD) experiments, were performed according to the procedures
previously described [30,31].
(
2
.3. Synthesis of the MJPEs
n
form a smectic A (SmA) or columnar nematic (Col ) phase [29].
Huang et al. prepared hydrogen-bonded MCSCLCPs with a pyridine
group-containing MCLCP and two ligands having the carboxylic
acid group (ꢀCOOH), and they investigated the influence of the
side-chain mesogen on the phase behavior of the MCSCLCPs [15].
However, to the best of our knowledge, the influence of main-chain
mesogen on the phase behavior of MCSCLCPs prepared via
hydrogen bonding has never been investigated. Therefore, the
design and preparation of new MCSCLCPs based on different MJLCP
main chains using hydrogen bonding are appealing and promising.
In this work, we designed and prepared new hydrogen-bonded
MCSCLCPs (see Chart 1) based on MJLCP main chains. The main
chains, which are used as the hydrogen-bonding donors, are two
mesogen-jacketed polyelectrolytes (MJPEs) containing two eCOOH
groups in the side chain, poly(vinyl terephthalic acid) (PVTA) and
poly[2,5-bis(4-carboxylic phenyl)styrene] (PBCPS). And a pyridine
The chemical structures and synthetic procedures of the
monomers and polymers are illustrated in Scheme 1. The experi-
mental details are described as follows.
2
.3.1. Synthesis of di-tert-butyl 2-vinylterephthalate (TBVT)
2-Vinylbenzene-1,4-dioic acid was synthesized according to the
procedure reported previously [32]. 2-Vinylbenzene-1,4-dioic acid
0
(
1.92 g, 10.0 mmol), 2-methylpropan-2-ol (2.22 g, 30.0 mmol), N,N -
dicyclohexylcarbodiimide (DCC, 10.6 g, 50.0 mmol), N,N-dime-
thylpyridin-4-amine (DMAP, 0.120 g, 1.00 mmol), and 50 mL of dry
dichloromethane were added into a 100 mL round-bottomed flask,
and then the mixture was stirred at ambient temperature for 24 h.
The insoluble material was removed by filtration, and the solvent
was evaporated under a reduced pressure. The product was puri-
fied by passing through a silica gel column with dichloromethane
derivative
containing
a
Tp
unit,
4-(6-(3,6,7,10,11-
and petroleum ether (v:v, 1:3) as the eluent. The obtained mono-
pentakis(hexyloxy)triphenylen-2-yloxy)hexyloxy)pyridine (PHTC
6
,
1
mer was a light yellow liquid. H NMR (400 MHz, CDCl
3
,
d, ppm):
where 6 is the number of the methylene units between pyridine
and Tp) is the hydrogen-bonding acceptor. One of our objectives is
to explore the possibility of preparing MCSCLCPs based on MJLCP
main chains via hydrogen bonding. The other objective is to study
the influences of the main chain and the content of the pyridine
derivative on the phase behaviors of these MCSCLCPs.
1
.67 (s, 18H), 5.37e5.41 (d, 1H), 5.70e5.76 (d, 1H), 7.33e7.43 (p, 1H),
7.80e7.82 (d, 1H), 7.87e7.90 (d, 1H), 8.16 (s, 1H). MS (EI, m/z): 304.2
$þ
(M
).
2.3.2. Synthesis of methyl 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)benzoate
,5-Dibromostyrene was synthesized according to the previ-
ously reported method [33]. 4-(Methoxycarbonyl)phenylboronic
Self-assembled phase structures of the MJPE-ligand complexes
in bulk were investigated using various techniques. The complexes
2
Chart 1. Chemical structures of the supramolecular MCSCLCPs.

S.-Q. Yang et al. / Polymer 84 (2016) 355e364
357
Scheme 1. Synthetic route of PVTA (a) and PBCPS (b).
acid (20.5 g, 114 mmol), 2,3-dimethyl-2,3-butanediol (14.0 g,
was dissolved in 150 mL of anhydrous ether, then potassium tert-
butoxide (11.2 g, 99.8 mmol) was added slowly. The mixture was
stirred at ambient temperature for another 2 h, washed with
1
18 mmol), and 500 mL of dry THF were added into a 1000 mL
ꢁ
round-bottomed flask, and then the mixture was refluxed at 70 C
for 2 h. The solvent was evaporated under a reduced pressure, and
300 mL of water, and dried using anhydrous MgSO
the solvent was evaporated, and the residue was purified by pass-
ing through a silica gel column with CH Cl and petroleum ether
, ppm): 0.5e1.6 (d, 18H),
5.32e5.35 (d, 1H), 5.80e5.85 (d, 1H), 6.62e6.70 (q, 1H), 7.40e7.44
d, 1H), 7.56e7.60 (d, 2H), 7.60e7.64 (q, 1H), 7.82e7.84 (d, 2H),
7.86e7.88 (d, 1H), 7.96e8.00 (d, 2H), 8.00e8.04 (d, 2H). Anal. Calcd.
for C30 (％): C, 78.92; H, 7.06. Found: C, 78.98; H, 7.07. MS (EI,
4
. After filtration,
the residue was purified by passing through an Al
2
O
3
column with
, ppm): 3.89 (s, 3H),
.34 (d, 2H), 5.44 (d, 2H), 7.24e7.446 (d, 1H), 7.57 (q, 1H), 7.66 (d,
1
THF as the eluent. H NMR (400 MHz, CDCl
3
,
d
2
2
1
5
1
3
(v:v, 1:10). H NMR (400 MHz, CDCl , d
H).
(
2.3.3. Synthesis of 2,5-bis(4-methoxycarbonyl phenyl)styrene
2
,5-Dibromostyrene (2.10 g, 4.23 mmol), 4-methyl-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate (2.44 g,
.30 mmol), potassium carbonate (5.84 g, 42.3 mmol), hydroqui-
none (0.130 g, 1.18 mmol), and Pd(PPh (0.150 g, 0.130 mmol)
were added into a 100 mL three-necked flask. Then toluene
32 4
H O
$þ
m/z): 456.2 (M ).
9
3
)
4
2.3.5. Polymerization
The polymers were obtained by ATRP. Taking poly(di-tert-butyl
2-vinylterephthalate) (PTBVT) as an example, the detailed proce-
dure was carried out as follows. The monomer TBVT (1.00 g,
(
30.0 mL) and water (10.0 mL) were injected under a continuous
ꢁ
stream of argon. The mixture was stirred at 110 C for 48 h. The
0
00 00
separated organic layer was dried using anhydrous MgSO
4
. After
3.28
(PMDETA, 5.68 mg, 32.8
6.07 mg, 32.8 mol), CuBr (4.72 mg, 32.8 m
mmol),
N,N,N ,N ,N -pentamethyldiethylenetriamine
mol), (1-bromoethyl)benzene (BEB,
mol), dry chlorobenzene
the solvent was evaporated under a reduced pressure, the product
m
was purified by passing through a silica gel column with ethyl ac-
m
1
etate and petroleum ether (v:v, 1:10) as the eluent. H NMR
(1.5 g), and a magnetic stir bar were added into a polymerization
tube. After three freezeepumpethaw cycles, the tube was sealed
under vacuum and subsequently immerged into an oil bath ther-
(
5
(
7
400 MHz, CDCl
.80e5.85 (d, 1H), 6.62e6.70 (q, 1H), 7.40e7.44 (d, 1H), 7.56e7.60
d, 2H), 7.60e7.64 (q, 1H), 7.82e7.84 (d, 2H), 7.86e7.88 (d, 1H),
.96e8.00 (d, 2H), 8.00e8.04 (d, 2H).
3
, d, ppm): 3.78e3.80 (s, 6H), 5.32e5.35 (d, 1H),
ꢁ
mostated at 110 C for 24 h. The polymerization was stopped when
the tube was quenched in liquid nitrogen and taken out to ambient
conditions. The solution was diluted with THF (5 mL) and then
passed through a neutral alumina column in order to remove
copper salt. At last, the polymer was precipitated out from meth-
anol and dried in vacuum overnight.
2
(
.3.4. Synthesis of 2,5-bis(4-tert-btuoxylcarbonyl phenyl)styrene
TBPS)
,5-Bis(4-methoxycarbonyl phenyl)styrene (3.70 g, 9.94 mmol)
2

358
S.-Q. Yang et al. / Polymer 84 (2016) 355e364
6
Scheme 2. Synthetic route of PHTC .
2
.3.6. Synthesis of MJPEs
After 300 mg of the precursor polymer samples was dissolved in
silica gel column with ethyl acetate and petroleum ether (v:v, 1:15)
as the eluent. Then the resultant product (5.95 g, 6.00 mmol),
pyridin-4-ol (0.685 g, 7.20 mmol), potassium carbonate (2.49 g,
18.0 mmol), potassium iodide (0.100 g, 0.604 mmol), and DMF
(100 mL) were charged in a 250 mL three-necked flask. The mixture
was refluxed for 24 h and then cooled to ambient temperature.
After the resulting mixture was filtered, the solvent in the filtrate
was removed under a reduced pressure. The residue was purified
10 mL of chloroform, 5 mL of trifluoroacetic acid was slowly added
at ambient temperature. The solution was further stirred for 24 h,
followed by the removal of the solvent under a reduced pressure.
The residue was washed with ethyl ether for three times to obtain
the pure product.
by passing through a silica gel column with dichloromethane and
2.4. Synthesis of the Tp-containing pyridine derivative
1
methanol (v:v, 30:1) as the eluent. H NMR (400 MHz, CDCl
3
,
d,
ppm): 0.87e0.97 (t, 15H), 1.32e1.44 (m, 22H), 1.52e1.61 (m, 10H),
.64e1.70 (m, 2H), 1.87e1.98 (m, 14H), 4.20e4.30 (m, 14H),
.47e7.54 (t, 2H), 7.77e7.87 (m, 6H), 8.06e8.13 (s, 2H). Anal. Calcd.
for C59 (％): C, 76.83; H, 9.51; N, 1.52. Found: C, 76.50; H,
The synthetic route of the pyridine derivative is depicted in
Scheme 2. 2-Hydroxyl-3,6,7,10,11-pentakis(hexyloxy)triphenylene
PHT) was synthesized according to the reported procedure [34].
1
7
(
H87NO
7
$þ
9.99; N, 1.56. MS (EI, m/z): 921.7 (M ).
2
.4.1. Synthesis of PHTC
PHT (4.50 g, 6.04 mmol),1,6-dibromohexane (4.42 g,18.1 mmol),
potassium carbonate (1.24 g, 8.98 mmol), potassium iodide
0.100 g, 0.604 mmol), and acetonitrile (100 mL) were charged in a
50 mL three-necked flask. The mixture was refluxed for 24 h and
6
2.5. Preparation of the complexes
(
2
The complexes with different molar ratios of PHTC
eCOOH group in the repeating unit were prepared using the pyr-
idine solution. The MJPE and PHTC were separately dissolved in
6
to the
then cooled to ambient temperature. After the resulting mixture
was filtered, the solvent in the filtrate was removed under a
reduced pressure. The residue was purified by passing through a
6
pyridine solutions until clear solutions were obtained, and then the
solutions were mixed together, followed by mechanical stirring at
Fig. 1. FT-IR spectra of PTBVT and PVTA.
Fig. 2. 1H NMR spectra of PTBVT and PVTA.

S.-Q. Yang et al. / Polymer 84 (2016) 355e364
359
6 0.5
Fig. 3. FT-IR spectrum of PVTA(PHTC ) .
ꢁ
0 C for about 24 h. The solution concentration was about 5 mg/mL
6
to ensure the formation of a homogeneous solution. Afterwards,
ꢁ
the solvent was allowed to slowly evaporate at 50 C for about 3
ꢁ
days. Then the obtained complexes were further dried at 60 C in
vacuum for another 24 h to remove the residual solvent.
3
. Results and discussion
Fig. 5. Representative PLM micrographs of PVTA(PHTC
6
)
1
(a) and PBCPS(PHTC
6
)
1
(b) at
ꢁ
100 C.
3.1. Synthesis and characterization of the polymers and the
hydrogen-bonded complexes
MS spectrometry. Polymers were obtained by ATRP, and the ratio of
the monomer to the initiator was 100:1. Taking poly(di-tert-butyl 2-
vinylterephthalate) (PTBVT) as an example, the GPC curve shows
1
The structures of the monomers were confirmed by H NMR and
n
that the number-averaged MW (M ) of PTBVT is 25.7 kDa and its
PDI value is 1.11 (Fig. S1 in Supplementary Content). The complete
removal of the neopentyl groups is confirmed by FT-IR and NMR
results. For example, Fig. 1 shows the FT-IR spectra of PTBVT and
ꢀ
1
PVTA. The vibration band at 1720 cm
for PTBVT shifts to
for PVTA, indicating that the neopentyl groups are
removed and the eCOOC(CH groups have changed to the eCOOH
ꢀ
1
1695 cm
3 3
)
ꢀ1
groups. The broad band between 2800 and 3700 cm also proves
the existence of the eCOOH groups [29]. In Fig. 2, the signals of the
neopentyl groups in PTBVT at 1.46 ppm in the spectrum of PTBVT
completely disappear in the spectrum of PVTA, demonstrating that
the neopentyl groups are completely removed from PTBVT.
The formation of hydrogen bond between the carboxylic acid
group of the MJPEs and the pyridine nitrogen of PHTC
investigated by FT-IR. For example, the FT-IR result of
PVTA(PHTC 0.5 is shown in Fig. 3. The broad bands at 1950 and
500 cm are indicative of strong hydrogen bonding between the
carboxylic acid group of PVTA and the pyridine nitrogen of PHTC
24,35]. The formation of hydrogen bonds in other complexes are
confirmed by FT-IR (Fig. S4 in Supplementary Content).
6
was also
6
)
ꢀ
1
2
6
[
3.2. Thermal and LC properties of the complexes
The thermal and LC properties of the complexes were studied by
DSC and PLM. Because TGA results show that the degradation
ꢁ
temperatures of PVTA, PBCPS, and PHTC
6
are 276, 281, and 289 C,
respectively, the highest temperature in DSC measurements is only
ꢁ ꢁ ꢁ
40 C. All the samples were first heated to 240 C at a rate of 20 C/
2
min under a nitrogen atmosphere to erase the thermal history.
Then DSC thermographs during the first cooling and second heat-
ꢁ
ing were obtained at a rate of 10 C/min under a nitrogen
atmosphere.
Fig. 4. DSC curves of PVTA(PHTC
6
)
x
(a) and PBCPS(PHTC
6 x
) (b) along with those of
ꢁ
PVTA, PBCPS, and PHTC
atmosphere.
6
during the second heating at a rate of 10 C/min under a N
2
As shown in Fig. 4, two endothermic peaks and a broader

360
S.-Q. Yang et al. / Polymer 84 (2016) 355e364
Fig. 6. SAXS profiles of PHTC
6
, PVTA(PHTC
6
)
x
, and PVTA (a) and those of PVTA
x
in the
6 6 x
Fig. 7. SAXS profiles of PHTC , PBCPS(PHTC ) , and PBCPS (a) and those of
low-angle region (b) with varying x.
PBCPS(PHTC in the low-angle region (b) with varying x.
6 x
)
and 2D WAXD experiments were performed. Samples for SAXS
experiments were the bulk powders embedded in aluminum foils.
In 2D WAXD experiments, oriented film specimens were obtained
by shearing the bulk samples with a relatively large mechanical
force at an appropriate temperature above the glass transition
exothermic peak are observed during the second heating process
for PHTC6. Variable-temperature 1D WAXD results (Fig. S6 in
Supplementary Content) indicate that with the increase of tem-
6
perature the PHTC molecule experiences a transformation from
the crystalline state to the isotropic liquid directly when the tem-
ꢁ
ꢁ
temperature (T ) of the corresponding complex. All samples were
perature is above 100 C. Therefore, the endothermic peak at 90 C
corresponds to the transition from the crystalline state to isotropic
g
thermally annealed overnight before measurements.
ꢁ
ꢁ
The phase behaviors of the complexes show a strong composi-
tion dependence. Figs. 6 and 7 show the SAXS results of
PVTA(PHTC6)x and PBCPS(PHTC6)x at ambient temperature,
respectively, with the profiles of pure PVTA, PBCPS, and PHTC also
6
included for comparison. For PVTA and PBCPS, there are no
diffraction peaks in the high-angle region, which indicates that the
liquid. When the temperature increases from 30 C to 80 C, the
high-angle diffraction peaks indicate crystalline structures. Thus,
the exothermic peak at 50 C corresponds to the transition between
ꢁ
two crystalline phases. The similar transition has been observed in
other triphenylene-based discotic molecules [36]. . However, no
transition peaks are observed in the DSC curves of the complexes
pure PVTA and PBCPS are amorphous. The SAXS result of PHTC
6
also
6 x 6 x
PVTA(PHTC ) and PBCPS(PHTC ) , indicating that there is no
demonstrates that the pure PHTC is crystalline at ambient tem-
6
6
macrophase separation and that no PHTC crystalline phases are
perature. As shown in Figs. 6a and 7a, there are no diffraction peaks
in the profiles of the complexes in the high-angle region, indicating
that PHTC loses its crystalline structure when it is hydrogen-
6
bonded with the MJPEs. On the other hand, there are only a few
low-angle diffraction peaks that should be attributed to the com-
formed in the complexes.
PLM results show that all the complexes exhibit strong bire-
fringence. The typical PLM micrographs of PVTA(PHTC and
PBCPS(PHTC are shown in Fig. 5. However, no characteristic
textures are observed.
6 1
)
6 1
)
6
plexes between the MJPEs and PHTC , revealing their LC nature. The
amorphous halo in the high-angle region represents the charac-
teristic dimensions of the amorphous packing of the alkyl chains
3.3. Phase structure determination
along with the
pep stacking in Tp moieties. Therefore, the
In order to identify the phase structures of the complexes, SAXS

S.-Q. Yang et al. / Polymer 84 (2016) 355e364
361
Two-dimensional WAXD experiments were carried out to
further verify the structures of the complexes. Parts a and b of Fig. 8
show 2D WAXD patterns of PVTA(PHTC )0.5, with the X-ray incident
6
beam parallel to the X and Y directions, respectively. In Fig. 8a, a
sharp diffraction ring is observed near the beam stop. When the X-
ray incident beam is parallel to the Y direction, the diffraction ring
in Fig. 8a becomes two sharp diffraction arcs centered on the
n
equator in Fig. 8b, suggesting a Col phase, which agrees well with
the SAXS result. The position of diffraction arcs also indicates that
the cylinders are parallel to the shear direction after mechanical
shearing. Parts c and d of Fig. 8 show 2D WAXD patterns of
PVTA(PHTC ) . When the X-ray incident beam is parallel to the X
6 1
direction, the first diffraction divided into six arcs with a 6-fold
symmetry is observed near the beam stop in Fig. 8c, which confirms
the existence of the Col
h
phase. The second diffraction split into two
arcs at q ¼ 3.49 nm (d-spacing ¼ 1.80 nm) is originated from the
structure (N phase) of the Tp moieties, and the close-to-ring
ꢀ1
D
pattern suggests the poor orientation of the Tp units in the YZ
plane. When the X-ray incident beam is parallel to the Y direction,
only two pairs of sharp diffraction arcs appear and are centered on
the equator in Fig. 8d. Such a pattern indicates that the MJLCP
columns are oriented parallel to the shear (X) direction, as ex-
pected. The diffraction associated with the characteristic dimension
of the Tp moiety appears as a ring in Fig. 8c and on the equator in
Fig. 8d, suggesting that the Tp discs are oriented with the disc
normal parallel to the shear (X) direction. Considering the weak
ꢀ
1
diffraction at q ¼ 3.50 nm in Fig. 6, the Tp moieties may be in an
or Col phase. However, it is quite difficult for the Tp discs,
which are hydrogen-bonded to the main chain, to be packed into a
Col phase in the matrix of a Col phase formed by the whole su-
pramolecular polymer chain. Therefore, we assign the structure of
the Tp moieties as an N phase. The 2D WAXD patterns of
PVTA(PHTC 0.75 are similar to those of PVTA(PHTC (Fig. S7 in
Supplementary Content). The above results demonstrate that
when x ꢂ 0.75 the complex PVTA(PHTC can form a hierarchical
nanostructure in which the whole polymer chain serves as a cyl-
inder to form the Col phase and the Tp moieties form an N phase
N
D
n
n
h
D
6
)
6 1
)
Fig. 8. 2D WAXD patterns of PVTA(PHTC
ray incident beam parallel to the X (a, c) and Y (b, d) directions, the shearing geometry
e) and the sketch of the polymer chain structure (f).
6 6 1
)0.5 (a, b) and PVTA(PHTC ) (c, d) with the X-
6 x
)
(
h
D
within the columnar structure.
intermolecular hydrogen bonding can prevent the crystallization of
PHTC and induce the ordering of the resultant complexes.
In Fig. 6b, the SAXS profile of PVTA(PHTC
In Fig. 7b, the SAXS profiles of PBCPS(PHTC
6
)
x
with x ¼ 0.5 also
6
ꢀ
1
show only one diffraction peak at q ¼ 1.25 nm , and the fact that it
is a sharp and strong peak indicates the formation of a low-ordered
smectic phase. In the low-angle region, a broad halo is also
6
)
x
, with x ¼ 0.5, shows
ꢀ1
only one diffraction peak at q ¼ 1.33 nm , indicating the possible
presence of a columnar phase. A broad scattering halo is also
ꢀ1
ꢀ1
observed at q z 3.57 nm (d ¼ 1.76 nm), which is the character-
istic size of the Tp moiety. The smectic phase of PBCPS(PHTC
different from the columnar structure of PVTA(PHTC 0.5, which is
observed at about q ¼ 3.50 nm (d ¼ 1.79 nm) in the low-angle
region, which is the characteristic size of the Tp moiety [37,38].
When x is increased to 0.75, four diffraction peaks in the low-angle
6
)0.5 is
6
)
consistent with our previous results that a more rigid side-chain
core and a longer side chain increase the possibility of forming
smectic phases for MJLCPs [39e41] With increasing content of
region are observed in the SAXS profile of PVTA(PHTC
6
)
x
. The halo
0.5 becomes a relatively broad
peak, which means that the structure of the Tp moieties is more
ordered with the increase in the content of PHTC . The peak with
q ¼ q becomes sharper and stronger, and there is a q ratio of
:2:√7 for the three low-angle diffraction peaks except that at
ꢀ1
at q ¼ 3.50 nm in PVTA(PHTC
6
)
ꢀ
1
PHTC , the halo at q z 3.55 nm becomes a diffraction peak,
6
6
*
implying that the Tp moieties in the side chains are packed in a
more ordered fashion. In addition, this diffraction is stronger than
that in Fig. 6, indicating that the degree of order of the structure
formed by the Tp moieties in the PBCPS(PHTC
complex is higher than in the PVTA(PHTC
1
ꢀ1
q ¼ 3.50 nm owing to the ordered packing of the Tp moieties,
6
)
x
(x ¼ 0.75 and 1)
indicating the formation of a hexagonal columnar (Col ) phase with
h
6
)
x
(x ¼ 0.75 and 1)
the lattice parameter a ¼ 5.15 nm that is not far away from the
complex, even if the type of structure is the same. Furthermore, the
q ratio of the other two low-angle diffraction peaks is 1:2, proving
estimated dimension of 6.2 nm (assuming all trans-conformation of
6 x
alkyl chains) of the side chain of PVTA(PHTC ) containing two Tp
that the complexes PBCPS(PHTC
smectic structures. The d-spacing values of the smectic structures
of PBCPS(PHTC 0.75 and PBCPS(PHTC are 4.65 nm, while The
6 6 1
)0.75 and PBCPS(PHTC ) form
moieties, with the consideration of possible interdigitation of alkyl
tails and even the Tp moieties. Therefore, the columnar phase is
formed by the whole MJLCP containing Tp moieties as a supra-
molecular cylinder. When x is further increased to 1, a similar SAXS
6
)
6 1
)
estimated dimension of the side chain of the MJLCP containing two
Tp moieties is about 7.2 nm, which indicates significant interdigi-
tation in the packing.
Fig. 9 shows the 2D WAXD patterns of PBCPS(PHTC
and b show 2D WAXD patterns of PBCPS(PHTC 0.5, with the X-ray
incident beam parallel to the X and Y directions, respectively. There
result to that of PVTA(PHTC
phase of PVTA(PHTC is also Col
.01 nm which is smaller than that of PVTA(PHTC
that the complex with more Tp moieties is packed more closely.
6
)
0.75 is obtained, indicating that the LC
. The lattice parameter a is
0.75, suggesting
6
)
1
h
6 x
) . Parts a
5
6
)
6
)

362
S.-Q. Yang et al. / Polymer 84 (2016) 355e364
6
Fig. 9. 2D WAXD patterns of PBCPS(PHTC )0.5 with the X-ray incident beam parallel to
the X (a) and Y (b) directions and those of PBCPS(PHTC
parallel to the Y (c) and Z (d) directions.
6 1
) with the X-ray incident beam
is a sharp diffraction ring in Fig. 9a, and there are a pair of sharp
diffraction arcs on the equator in Fig. 9b, consistent with a low-
ordered smectic phase. However, there is only an amorphous
diffuse ring in the high-angle region, which is hard to determine
whether the smectic phase is smetic A (SmA) or smetic C (SmC).
6 1
The 2D WAXD patterns of PBCPS(PHTC ) are shown in parts c and
d of Fig. 9, with the X-ray incident beam parallel to the Y and Z
directions, respectively. In both 2D WAXD patterns, three pairs of
sharp diffraction arcs located on the equator are observed. The q
ratio of the two pairs of diffraction arcs other than that at
6 1 6 1
Fig. 10. SAXS profiles of PVTA(PHTC ) (a) and PBCPS(PHTC ) (b) at different tem-
peratures during heating.
ꢀ
1
q ¼ 3.57 nm
(d-spacing ¼ 1.76 nm) is 1:2, demonstrating a
smectic structure. The pair of diffuse arcs in the high-angle region is
centered on the meridian, indicating an SmA phase. Similar to the
case of PVTA(PHTC
also likely to form the N
of the pair of diffraction arcs with q ¼ 3.57 nm on the equator
suggests that the Tp discs are also oriented with the disc normal
parallel to the shear direction. Therefore, the normal of the Tp discs
are perpendicular to the layer normal of the SmA structure. The 2D
6
)
x
(x ¼ 0.75 and 1) complex, the Tp moieties are
6 1
than that at low temperatures, suggesting that PVTA(PHTC )
D
phase in the SmA matrix. The appearance
transforms from the Colh phase to the Coln phase when the Tp
moieties isotropilize. The hydrogen bonds are still present during
the heating process from variable-temperature FT-IR results (Fig. S8
ꢀ
1
*
in Supplementary Content). In Fig. 10b, the peak with q ¼ q re-
mains sharp compared to those at low temperatures, which implies
WAXD patterns of PBCPS(PHTC
Content) are similar to those of PBCPS(PHTC
PBCPS(PHTC
nanostructure in which the whole polymer chain serves as a su-
pramolecular tablet to form the SmA phase and the Tp moieties
6
)
0.75 (Fig. S7 in Supplementary
6 1
that the smectic phase of PBCPS(PHTC ) remains, while the
6
)
1
. Therefore, the
broadening of the peak demonstrates that the degree of order is
decreased when the Tp moieties go to isotropic. Such a difference in
the phase behaviors of PVTA(PHTC ) and PBCPS(PHTC ) can again
6
)
x
(x ¼ 0.75 and 1) complex also forms a hierarchical
6
1
6 1
be attributed to the different rigidities and lengths of the main
chains in these two complexes. In both types of complexes, the
degree of order of the low-temperature larger-scale structure is
higher than that of the phase at high temperatures when Tp goes
develop an N
the SmA phases of PBCPS(PHTC
pose that PBCPS(PHTC 0.5 also forms a SmA phase.
D
phase within the smectic structure. In addition, from
6
)0.75 and PBCPS(PHTC , we pro-
6 1
)
6
)
Because the hierarchical nanostructures of the complexes with
x ꢂ 0.75 are induced by the introduction of the Tp moieties, we
investigated the influence of the isotropization of the Tp moieties
upon heating on the phase behaviors of the complexes. Variable-
D
into isotropic, suggesting that the N phase at low temperatures
improves the structure of the whole supramolecular polymer chain
or that alternatively the more ordered structure of the whole
polymer renders the ordered packing of the Tp moieties. In other
words, the two types of mesogens are promotive to each other, as in
the covalent analogs [21].
6 1 6 1
temperature SAXS results of PVTA(PHTC ) and PBCPS(PHTC )
are shown in parts a and b of Fig. 10, respectively. When the com-
ꢁ
ꢀ1
plexes are heated to 150 C, the diffraction peak at q z 3.50 nm
Fig. 11 depicts the schematic representation of the phase
structures of the hydrogen-bonded complexes at low temperatures
attributed to the ordered structure of the Tp moieties becomes an
amorphous halo, indicating that the Tp moieties are in the isotropic
6
with varying contents of PHTC . As demonstrated by the above-
*
state. In Fig. 10a, the peak with q ¼ q becomes broader and weaker
mentioned results, the complexes exhibit complicated phase

S.-Q. Yang et al. / Polymer 84 (2016) 355e364
363
MCSCLCPs, which is of great importance for fundamental research
in the fields of LCPs and supramolecular chemistry. This supra-
molecular method provides a facile approach to regulating ordered
hierarchical nanostructures and exploring new functional
materials.
Acknowledgment
This work is supported by the National Natural Science Foun-
dation of China (Grants: 21174006 and 20990232).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2016.01.018.
Fig. 11. Schematic drawing of the phase structures of the hydrogen-bonded complexes
at low temperatures.
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