A series of novel side chain liquid crystalline polysiloxanes containing cyano- and cholesterol-terminated substituents: Where will the structure-dependence of terminal behavior of the side chain reappear?

Article abstract of DOI:10.1002/pola.28547

A series of polysiloxane side chain liquid crystal polymers with strong polarity cyano substitution-terminated achiral side chains and cholesterol-terminated chiral side chains was successfully synthesized via thiol-ene click chemistry. ¹H-NMR, FT-IR, and thermogravimetric analysis were used to confirm their chemical structures and thermal stabilities. Their phase transition behaviors and phase structures were systematically investigated by a combination of analysis methods such as differential scanning calorimetry, polarized optical microscopy, and X-ray. Results revealed that attributing to the decisive role of the polarity interaction, all the polymers only developed a monolayer interdigitated SmA phase in which the period arrangement was determined by the cyano-terminated side chains, the increased content of cholesterol-terminated chiral side chains (X_chol) just expanded the distance between neighboring molecules within a layer.

Full text of DOI:10.1002/pola.28547

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A Series of Novel Side Chain Liquid Crystalline Polysiloxanes Containing
Cyano- and Cholesterol-Terminated Substituents: Where will the
Structure-Dependence of Terminal Behavior of the Side Chain Reappear?
1
†
2†
2
1
3
1
Wenhuan Yao, Yanzi Gao, Cuihong Zhang, Chenyue Li, Fasheng Li, Zhou Yang,
2
Lanying Zhang
1
Department of Materials Physics and Chemistry, School of Materials Science and Engineering, University of Science and
Technology Beijing, Beijing 100083, People’s Republic of China
2
Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Department of Materials Science and Engineering,
College of Engineering, Peking University, Beijing 100871, People’s Republic of China
3
College of Medical Laboratory, Dalian Medical University, Dalian, Liaoning Province 116044, People’s Republic of China
Correspondence to: L. Zhang (E-mail: zhanglanying@pku.edu.cn), Z. Yang (E-mail: yangz@ustb.edu.cn), or F. Li (E-mail:
lifasheng@dmu.edu.cn)
Received 27 December 2016; accepted 15 February 2017; published online 00 Month 2017
DOI: 10.1002/pola.28547
ABSTRACT: A series of polysiloxane side chain liquid crystal
polymers with strong polarity cyano substitution-terminated
achiral side chains and cholesterol-terminated chiral side
chains was successfully synthesized via thiol-ene click chemis-
developed a monolayer interdigitated SmA phase in which the
period arrangement was determined by the cyano-terminated
side chains, the increased content of cholesterol-terminated
chiral side chains (Xchol) just expanded the distance between
neighboring molecules within a layer. V 2017 Wiley Periodicals,
Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 00, 000–000
1
C
try. H-NMR, FT-IR, and thermogravimetric analysis were used
to confirm their chemical structures and thermal stabilities.
Their phase transition behaviors and phase structures were
systematically investigated by a combination of analysis meth-
ods such as differential scanning calorimetry, polarized optical
microscopy, and X-ray. Results revealed that attributing to the
decisive role of the polarity interaction, all the polymers only
KEYWORDS: interdigitated smectic A phase; polarity interaction;
polysiloxane polymers; side chain liquid crystal; thiol-ene click
chemistry
1
2–17
Polysiloxanes side-chain liquid crystalline polymers (PSCLCPs),
as one of the most important branches of soft matter materials
that combining the anisotropic characteristics of mesogen
pendants with polymeric properties, have been drawn wide-
spread attention for both fundamental and applied reasons in
core
as well as the linkage groups between the rigid
Beyond that, the polarity of the terminal substitu-
1
8–21
core.
ents in the side chains is also one of the most important fac-
tors. Sołtysiak et al.
different types of polar terminal groups and found that the
polarity reduced the phase transition temperatures of the
2
2,23
prepared cyclic oligosiloxanes with
1
–4
the past few decades.
Among them, the mesogen pendants
formed interdigitated smectic A phase. By replacing the CH
3
with polar substituents such as cyano, fluorine, and so on,
which can be oriented in an electrical field, endows PSCLCPs
with some special interests.
d
2
4
side chain groups with polar CF3 groups, Lee et al. found
2
5–27
28,29
5,6
the similar results. Sudh o€ lter et al.
and Chen et al.
reported that a drastic change in mesogen phase structures
was occurred when cyano group was used instead of methoxy
From the viewpoint of molecular design and structure–prop-
erties–performance relationship, previous results have
revealed that the self-assembly behaviors and phase struc-
tures of SCLCPs can be drastically affected by the polymer
3
0,31
group as the terminal group. Zhou et al.
synthesized a
series of mesogen-jacketed liquid crystalline polymers
(MJLCPs) with asymmetric substitutions and found that car-
boxylic acid terminated asymmetric polymers formed a dou-
ble layer smectic A phase, while the corresponding alkyl
7
,8
9–11
backbone, the length of flexible spacers,
the size and
architecture of the terminal flexible substituents in mesogenic
†
Joint first authors; these authors contributed equally to this study.
Additional Supporting Information may be found in the online version of this article.
2017 Wiley Periodicals, Inc.
V
C
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terminated polymers showed no liquid crystallinity or exhib-
3
2
ited columnar phase. Their later work revealed that the
introduction of fluorinated substituent weakened the liquid
crystallinity of the polymers as well as boosted the glassy
temperature.
3
3
In our previous work, we have synthesized and character-
ized a series of PSCLCPs based on poly-[3-mercaptopropylme-
thylsiloxane] (PMMS) backbone with cholesterol-terminated
chiral side chains and methoxy-terminated achiral side chains
(
3
PMMSs-OCH -based polymers). By virtue of the long polysi-
loxane skeleton and spacer as well as the synergy between
them, smectic E (SmE), which is a high ordered liquid crystal-
line (LC) phase, was self-assembled at low temperatures for
polymers with the molar concentration of chiral cholesteric
unit (Xchol) below 0.3. Furthermore, a strong dependence of
LC phase structures on Xchol, which showed a layer period sal-
tation as Xchol changing from 0.40 to 0.50, was observed. Here
in this work, by replacing the weak polarity methoxy substitu-
tion with strong polarity cyano substitution as the terminal
group of the achiral side chains, we designed and synthesized
a series of novel PSCLCPs based on PMMS backbone. We
anticipate that by subtle changes in the molecular structure
with the polarity alteration of the terminal group in achiral
side chains, the resulting PSCLCPs will bring unexpected vari-
ation of the self-assembly behaviors and LC properties.
EXPERIMENTAL
Materials
SCHEME 1 Synthetic routes of the monomers and polymers.
Cholesterol (A.R. grade, Sinopharm), poly[3-mercaptopropyl-
methylsiloxane] (PMMS, SMS-992, M.W. 4000-7000, 95 cst,
Gelest Inc), ethylparaben (A.R. grade, Sinopharm), acetoni-
trile (A.R. grade, Sinopharm), 3-bromopropene (98%, Beijing
Synthesis of the 4-(Allyloxy) Benzoic Acid
The experimental details of the precursor synthesis are in
3
3
accordance with the literature.
Dominant Technology Co.), dimethylaminopyridine (DMAP)
0
(
99%, Energy Chemical), N,N -dicyclohexylcarbodiimide
2
1
FT-IR (KBr, cm ): 2985–2825 (ACH A, H C@, and @CAH),
2
2
(
DCC) (98%, Energy Chemical), 4-hydroxybenzonitrile (A.R.
2668–2554 (AOH in ACOOH), 1680 (C@O), 1648 (C@C),
grade, Beijing Dominant Technology Co.), potassium hydrox-
ide (A.R. grade, Beijing Chemical Reagents Co.), and anhy-
drous potassium carbonate (A.R. grade, Beijing Chemical
Reagents Co.) were used as purchased. Toluene (A.R. grade,
Beijing Chemical Reagents Co.) was refluxed over sodium
and distilled under nitrogen atmosphere before use. Azodii-
sobutyronitrile (AIBN) (A.R. grade, Beijing Dominant Tech-
nology Co.) was purified by recrystallization from ethanol.
Other chemical reagents were used without any purification.
1
1602, 1575, 1503, 1425 (Ar-), 1251 (CAOAC). H-NMR (400
MHz, DMSO, TMS, d, ppm): 12.61 (1H, s, -COOH), 7.88–7.85
2H, d, Ar-H), 7.02–7.0 (2H, d, Ar-H), 6.08–5.98 (1H, m,
CH @CHACH A), 5.41–5.36 (1H, dd, one of CH @CHACH A),
(
2
2
2
2
5
.28–5.25 (1H, dd, one of CH @CHACH A), 4.63–4.62 (2H, d,
2 2
CH @CHACH A).
2
2
Synthesis of Cholesteryl-4-(Allyloxy) Benzoate (M1)
The experimental details of M1 synthesis are in accordance
with the literature. FT-IR (KBr, cm ): 2946–2884 (ACH3,
Measurements
H-NMR spectra, thermogravimetric analysis (TGA), differential
scanning calorimetry (DSC), polarized optical microscope (POM),
one-dimensional wide-angle X-ray diffraction (1D-WAXD), small
angle X-ray scattering (SAXS), and two-dimensional wide-angle X-
ray diffraction (2D-WAXD) were carried out according to the pro-
33
21
1
ACH A, H C@, and @CAH), 1712 (C@O), 1648 (C@C), 1606,
2
2
1
1
580, 1509, 1464 (ArA), 1274, 1249 (CAOAC). H-NMR (400
MHz, CDCl , TMS, d, ppm): 8.00–7.98 (2H, dt, ArAH), 6.93–
3
6
.91(2H, dt, ArAH), 6.09–6.02 (1H, m, CH @CHACH A), 5.45–
2 2
33
5.42 (1H, dq, one of CH
cholesteryl moiety), 5.33–5.30 (1H, dq, one of CH
4.84–4.80(1H, m, AOACHA in cholesteryl moiety), 4.60–4.59
(2H, d, CH @CHACH A), 2.46–2.44(2H, d, AOACHACH ACA
2
@CHACH
A), 5.40(1H, t, @CHA in
2
cedures as described previously.
2
@CHACH A),
2
Synthesis
The synthetic routes of the monomers and polymers are
shown in Scheme 1. The experimental details are described
below.
2
2
2
in cholesteryl moiety), 2.04–0.86(38H, m, H in cholesteryl moie-
ty), and 0.69(3H, s, ACH in cholesteryl moiety).
3
2
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FIGURE 1 FT-IR spectra of monomers and all the polymers. [Color figure can be viewed at wileyonlinelibrary.com]
1
Synthesis of 4-Cyanophenyl 4-(Allyloxy) Benzoate (M2)
The synthesis of M2 used the same method as described for
the preparation of M1. 4-(allyloxy) benzoic acid (8.40 g, 0.05
mol), 4-hydroxybenzonitrile (7.14 g, 0.06 mol), dimethylami-
nopyridine (DMAP) (0.92 g, 7.50 mmol), and 200 mL
dichloromethane were premixed, then a dichloromethane
compounds were confirmed by FT-IR and H-NMR spectro-
scopic methods.
1
The FT-IR and H-NMR spectra of monomers, PMMS, and all
the polymers are illustrated in Figures 1 and 2, respectively.
The disappearance of the weak vibrational bands at
2552 cm [assigned as the SAH stretching, as shown in Fig.
(a)] as well as the signal of the thiol group in PMMS at
21
0
solution of N,N -dicyclohexylcarbodiimide (DCC) (12.36 g,
1
0.06 mol) was added dropwise slowly to the premixture,
1
.37 ppm (as shown in Figure 2), indicated that hydrogen
and reacted at room temperature for 24 h. After filtration
and removal of the solvent, the coarse products were puri-
fied by silica gel column chromatography with dichlorome-
thane as the eluent to give M2 as a white crystal. FT-IR (KBr,
atoms of all the SAH groups were substituted completely.
The appearance of the vibrational bands, which were derived
from methylene (ACH
(C@O), aromatic (ArA), SiAC, and SiAOASi at 2965–2836,
2229, 1737/1712, 1603–1467, 1260, and 1072–1018 cm
(as shown in Fig. 1), respectively, and the proton peak of
aromatic (as shown in Figure 2), suggested the successful
preparation of polymers via thiol-ene addition reaction.
A), cyanogroup (ACN), ester carbonyl
2
2
1
cm ): 3104–2862 (ACH , ACH A, H C@, and @CAH), 2229
3
2
2
21
(
ACN), 1737 (C@O), 1633 (C@C), 1603, 1579, 1509, 1467
1
(ArA), 1275, 1261 (CAOAC). H-NMR (400 MHz, CDCl3,
TMS, d, ppm): 8.2A8.12 (2H, dt, ArAH), 7.79A7.72 (2H,dt,
ArAH), 7.41A7.35 (2H, dt, ArAH), 7.08A7.00 (2H, td,
21
ArAH), 6.16A6.03 (1H, m, CH
2
@CHACH
2
A), 5.52–5.43 (1H,
Additionally, the weak vibrational bands at 1633 cm
dq, one of CH @CHACH A), 5.40–5.34 (1H, dq, one of
[assigned as the C@C stretching, the partially amplified FT-IR
spectra as shown in Figure 1(b)] and the representative sig-
nals of the vinyl group in monomers at 6.05, 5.43, and 5.31
ppm (as shown in Figure 2) disappeared, indicating the
2
2
CH @CHACH A), 4.70–4.64 (2H, dt, CH @CHACH A).
2
2
2
2
Synthesis of the Polymers
The synthetic routes of all the polymers were similar to
3
3,34
those reported in the literature with minor modification.
Taking the preparation of polymer P-3 as a typical proce-
dure. M1 (361.00 mg, 0.66 mmol), M2 (122.76 mg, 0.44
mmol), PMMS (137.60 mg, 1.00 mmol-SH), AIBN (16.40 mg,
0.10 mmol), and toluene (1.85 mL) were sealed in a poly-
merization tube after degassed via three freeze–pump–thaw
cycles to obtain a vacuum environment, then stirred at 65 8C
for 24 h. After removal of the solvent, the coarse polymer
was purified by several precipitate–dissolve–precipitate
cycles to give P-3 as white powders. Yield: 90.7%.
RESULTS AND DISCUSSION
Synthesis and Characterization of Monomers and
Polymers
The synthetic routes of monomers consisted of Williams
etherification reaction and Steglich esterification reaction in
an efficient sequential order as shown in Scheme 1. AIBN
was used as the initiator in the thiol-ene addition reaction to
obtain the polymers, and the yields of all the polymers were
higher than 86%. The chemical structures of all the above
1
FIGURE 2 H-NMR spectra of monomers and all the polymers.
[Color figure can be viewed at wileyonlinelibrary.com]
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TABLE 1 Thermal Properties and Molecular Characterization of Polymers
a
M1/(M1 1 M2) (MR)
M
n
(g/mol)
Calculated
b
c
c
d
b
d
e
Sample
In feed
Calculated
T
g
(8C)
T
i
(8C)
GPC
800
PDI
T
d
(8C)
Yield (%)
PMMS
P-1
—
—
—
—
6192
2.53
2.84
2.28
2.23
1.67
1.89
2.04
—
—
0.00
0.20
0.40
0.60
0.80
1.00
0.000
0.221
0.425
0.604
0.819
1.000
2.4
92.1
2200
3300
3700
4000
4400
4800
18747
21412
23872
26031
28624
30852
349
302
301
334
329
337
86.2
87.4
89.5
90.7
92.3
91.2
P-2
10.5
18.7
23.6
33.1
35.7
96.3
P-3
111.7
176.8
189.4
204.8
P-4
P-5
f
P-6
a
e
f
Molar ratio.
5% weight loss temperature was evaluated by TGA at a rate of 20 8C/min.
The data of P-6 referenced as PMMS-XChol-1.00 in ref. 33 and listed
b
1
According to the H-NMR results.
c
Evaluated by DSC during the second heating at the rate of 10 8C/min.
Determined by GPC in THF using polystyrene standards.
here for comparison only.
d
completely removal of the excessive allyl ether monomers.
Furthermore, as summarized in Table 1, the actual molar
fraction of M1 based on (M1 1 M2) (assigned as Xchol) in a
specified polymer could be calculated on the basis of recip-
rocal relationship between the integral area of the signals
at 4.82 ppm (AOACHA in cholesteryl moiety) in M1 and
respectively. A focal-conic texture, which was a characteristic of
37,38
smectic phase,
was developed following by isothermal
annealing for a short time, then it maintained to the room tem-
perature. These observations indicated that all the polymers
had at least one smectic phase. Considering the only structure
changes of the terminal groups in achiral monomer, we specu-
lated that these polymers might have the similar period
7.76 ppm (ArAH) in M2 (as remarked by red dotted boxes
in Figure 2), and the variation of Xchol could also be reflected
by the gradually weakened relative intensity of cyano
absorption peak [as shown in Figure 1(a)] as well as the
reciprocal relationship between the vibrational band of C@O
arrangement scale with previously reported PMMSs-OCH -
3
based polymers.
33
As shown in Table 1 and Supporting Information, Figure S2,
the temperatures of all the polymers at 5% weight loss in
nitrogen were all above 300 8C, indicating that the polymers
had good thermal stabilities.
21
21
at about 1712 cm
in M1 and 1737 cm
in M2 [as
remarked in Figure 1(b)]. In agreement with our previously
3
3
reported work, the calculated Xchol were relatively bigger
than that in the feed, indicating that the substituted vinyl
monomer M1 with much larger space and stronger rigid was
DSC experiments were performed to examine the phase transi-
tions of all the polymers. The traces of the first cooling and
the subsequent second heating process were recorded at a
rate of 10 8C/min under nitrogen as shown in Figure 4. As
expected, the synergistic effect of the relatively less rigid side-
chain structure and the flexible polysiloxane backbone
endowed all the samples with low glass transition tempera-
3
5,36
more reactive than M2.
As listed in Table 1 and Supporting Information, Figure S1,
GPC measurement showed that the number-average molecu-
lar weight (M ) of polymers decreased with the increasing
n
content of M2 along with broad molecular weight distribu-
tures (T ) below 33 8C, which was gradually increased with
g
tion of polymers which was derived from parent skeleton
the increasing content of chiral monomer M1. Additionally,
1
molecules PMMS, and the calculated M
n
according to the H-
comparing the glass transition temperatures (T ) of the poly-
g
NMR results also exhibited the similar variation tendency,
which were in line with that the molecular weight of M1 is
greater than that of M2. Furthermore, as a result of the
molecular weight of monomeric unit of sample (413 or
mers in this study with those of the corresponding PMMSs-
OCH -based polymers, the T of the polymers in this study
3
g
was slightly higher except P-1, which might be attributed to
the combined effect of the more rigid side-chain structure and
the strong polarity with the introduction of cyano substitution.
Besides the apparent glass transition, only one endothermic/
exothermic peak at higher temperature in the whole heating/
cooling processes was observed for all the polymers, and dis-
695 g/mol) was much larger than that of polystyrene stand-
ards (104 g/mol), the hydrodynamic volume of former was
smaller than that of the latter, which led to the significant
1
difference between the calculated M based on H-NMR spec-
n
tra and the measured M according to the GPC method.
played a similar evolution tendency as T with altering the
n
g
content of M1, suggesting that there might exist only one LC
phase structure in the whole mesogenic temperature ranges.
Phase Structures and Phase Transition Identification
Figure 3 shows the POM images of all the polymers, which
were obtained by cooling the samples from isotropic state to
room temperature at a rate of 1 8C/min. The birefringence of
P-1, P-2, P-3, P-4, and P-5 appeared rapidly upon cooling
when the temperature reached to 78, 95, 110, 172, and 185 8C,
To systematically investigate whether there were phase tran-
sitions in the mesogenic state and the self-assembly struc-
tures of all the polymers, variable-temperature 1D-WAXD,
SAXS, and 2D-WAXD experiments were carried out.
4
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FIGURE 3 POM textures of (a) P-1, (b) P-2, (c) P-3, (d) P-4, and (e) P-5 were recorded by cooling the samples from isotropic state
to room temperature at a rate of 1 8C/min. [Color figure can be viewed at wileyonlinelibrary.com]
Distinctively, different from the apparent diffraction pattern
variations of PMMSs-OCH -based polymers, the diffraction
patterns of polymers in this work seemed to be simply or
not variety enough. Taking the performance of sample P-4 as
a typical example, parts a and b of Figure 5 show the SAXS
and 1D-WAXD patterns of P-4 during the heating processes,
respectively. There was a scattering halo at high-angle region
with the center position slightly blue shifted during the
whole heating scanning, indicating the absence of nanometer
ordered packing. While only one diffraction peak was
observed (corresponding to a d-spacing of 3.20 nm) [see the
inset of Figure 5(a)], and the intensity gradually weakened
upon heating. When the temperature reached 185 8C, the
sharp diffraction peak at low-angle region vanished, accom-
panied with the amorphous broad high-angle halo becoming
more diffused and the center position shifting to a higher
angle, demonstrating that the sample entered into isotropic
state. Therefore, combining the results of DSC, POM, 1D-
3
FIGURE 5 (a) SAXS (inset shows the enlarged patterns in the
low-angle region) and (b) 1D-WAXD (inset shows the enlarged
patterns in the high-angle region) patterns of P-4 during the
heating process. [Color figure can be viewed at wileyonline-
library.com]
FIGURE 4 DSC thermograms of polymers during (a) the first
cooling and (b) subsequent second heating scans at a rate of
10 8C/min.
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FIGURE 6 2D-WAXD pattern of (a) P-4 and (b) the shear geom-
etry. [Color figure can be viewed at wileyonlinelibrary.com]
WAXD, and SAXS, a low ordered smectic phase structure of
SmA or SmC in the whole mesogenic state was demonstrat-
ed, which was on account of the representative fan-shaped
texture under POM along with the sharp low-angle diffrac-
tion peak and the diffused scattering halo at high-angle
region under SAXS and 1D-WAXD.
FIGURE 8 d(100) and dp–p as a function of Xchol at room temper-
ature. [Color figure can be viewed at wileyonlinelibrary.com]
similar to those of P-4, an SmA phase structure in the whole
mesogenic state could be confirmed consequently.
2
D-WAXD experiments were carried out to remedy the
Dependence of the Phase Structure on the Two LC
Building Blocks and Interplay Between Them
dimensionality absence of the 1D-WAXD and SAXS patterns
to further confirm the smectic structures of polymers. Taking
the 2D-WAXD pattern of P-4 as a representative example, the
sample was mechanically sheared and annealed at 89 8C and
then cooled to room temperature. As depicted in Figure 6(a),
the 2D-WAXD pattern of P-4 was recorded at room tempera-
ture with the X-ray incident beam (along Z direction) per-
pendicular to the shear direction (X direction). A pair of
strong low-angle diffraction arcs, which was originated from
the layer structure, could be observed on the equator (Y
direction). Meanwhile, a pair of scattering halos at q ꢀ
Parts a and b of Figure 7 show the SAXS and 1D-WAXD pat-
terns of all the polymers at room temperature, respectively.
The corresponding d-spacing of the strong diffraction peak
in the low-angle region (assigned as d(100)) and the amor-
phous broad halo (assigned as dp-p) in the high-angle region
as a function of Xchol are shown in Figure 8. The values of
d(100) and dp-p along with the phase transitions of all the pol-
ymers are also summarized in Table 2. Obviously, the posi-
tion of the diffraction peaks in the low-angle region, which
indicated the distance of minimized layer spacing of the peri-
od arrangement, were almost unchanged with the increasing
of Xchol. While the central positions of the amorphous broad
halos in high-angle region, which represented the distance
between the molecules within a layer, were shifted to the
lower angle obviously (blue shift).
2
1
12.56 nm (corresponding to a d-spacing of 0.50 nm) were
more or less concentrated on the meridian (X direction) with
rather broad azimuthal distributions, and its center azimuth-
al had an offset of 908 with that of the low-angle diffraction
arcs. These results proved that a typical SmA phase structure
1
3,39
was formed for P-4 sample.
Comparing the value of d(100) with the calculated length of
the side chains, where the calculated length of the chiral and
achiral side chains from the Si atom in the main chains to
Accordingly, the DSC traces, POM textures, 1D-WAXD, and
SAXS patterns of polymers P-1, P-2, P-3, and P-5 were quite
the last C/N atom of the side chains were 3.09 nm (L ) and
1
2
.33 nm (L ) under the perfect assumption that the alkyl
2
chains were in an all-trans conformation, it could be easily
found that L2 < L1 < d(100) < 2L2 < 2L . Further analysis
1
and probe showed that d(100) ꢀ L
m s s
1 2L , where L
1.07 nm) is the calculated length of the spacers from the O
(
atom in the ether groups to the Si atom in the backbones,
and Lm (1.28 nm) is the calculated length of the achiral
mesogenic cores from the O atom in the ether groups to the
last N atom of the achiral side chains, respectively. Addition-
ally, previous reports have revealed that the dipole interac-
tion of the strong polarity cyano substituent could induce
the side chains to organize in antiparallel pairs to force the
cyano away from each other and to minimize the system
energy, which played a decisive role on the self-organization
FIGURE 7 (a) SAXS and (b) 1D-WAXD patterns of all the poly-
mers at room temperature. [Color figure can be viewed at
wileyonlinelibrary.com]
2
6,27,40
of the molecule.
Combining the comprehensive analy-
sis and judgment of above results, as shown in Scheme 2, we
6
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TABLE 2 d-Spacing and Phase Transitions of Polymers
a
Phase transitions (8C)
Heating
b
b
c
Sample
P-1
Cooling
d
(100) (nm)
d
p-p (nm)
c (nm)
G2.4SmA
s
92.1Iso
-1.4G
96.3 Iso
Iso98.5SmA 8.8G
G18.7SmA 111.7Iso
Iso113.4SmA 16.4G
G23.6SmA 176.8Iso
Iso175.8SmA 19.5G
G33.1SmA 189.4Iso
Iso186.7SmA 29.9G
G35.7SmA 139.9SmA
Iso197.9SmA 136.6SmA
3.20
3.20
3.20
3.20
3.20
6.61
0.44
0.46
0.49
0.50
0.50
–
3.20
3.20
3.20
3.20
3.20
6.61
Iso81.3SmA
s
P-2
P-3
P-4
P-5
G10.5SmA
s
s
s
s
s
s
s
s
d
P-6
d
s
204.8Iso
34.6G
s
d
a
c
According to the DSC results: G, glass state; SmA
s
, smectic A phase
The minimized layer spacing of the periodic arrangement.
d
with single layer; SmA
state.
d
, smectic A phase with double layer; Iso, isotropic
The data of P-6 referenced as PMMS-XChol-1.00 in ref. 33 and listed
here for comparison only.
b
Calculated at room temperature for all the polymers and according to
the XRD results.
speculated that for this series of polysiloxanes-containing
cyano-terminated side chains, a monolayer SmA phase with
side chains partially interdigitated was self-assembled, in
which the layer period was dominated by the achiral side
chains with cyano unit. Moreover, the chiral side chains
with large space volume and steric hindrance were forced
to adopt compression or partially coiled conformation, and
the increased content of chiral cholesteric side chains just
expanded the distance between the molecules within a
layer.
CONCLUSIONS
In summary, a series of novel PSCLCPs based on cholesterol
and benzonitrile groups as side groups was successfully
designed and synthesized via efficient thiol-ene click addition
chemistry reaction. Results indicated that a drastic change in
mesogenic state was observed when the cyano substitution
was used instead of methoxy substitution. With increasing
Xchol, polymers with cyano-terminated side chains in this
work developed a single monolayer interdigitated SmA
phase, while the corresponding PMMS-OCH -based polymers
3
formed abundant LC phase structures including SmE phase,
a monolayered SmA phase as well as a bilayered SmA phase.
Attributing to the decisive role of the polarity interaction, a
strong dependence of LC phase structures on Xchol was not
reappeared in this series of cyano-terminated polymers. This
work reproduced the mysterious force of the polarity termi-
nal groups in construction of the LC phase structures of
SCLCPs.
ACKNOWLEDGEMENTS
Financial support from the National Natural Science Founda-
tion of China (Grant No. 51573003, 51372029, 51373024), the
Fok Ying Tung Education Foundation (Grant No. 142009).
SCHEME 2 Schematic of molecules packing of polymer. [Color
figure can be viewed at wileyonlinelibrary.com]
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