New liquid-crystalline elastomers: 1. Synthesis, structure, and phase behavior of a series of mesogenic crosslinking agents containing reactive bifunctional groups

Article abstract of DOI:10.1080/15421406.2010.526561

The synthesis of eight mesogenic crosslinking agents (1c-8c) containing reactive bifunctional groups is described. The chemical structures were characterized by Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR) spectra. The mesomorphism was investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The compounds 1c, 2c, 3c, 5c, 6c, and 8c showed an enantiotropic nematic phase. In addition, 5c exhibited a smectic A (SmA) phase on cooling; 4c exhibited a smectic C (SmC) phase, a SmA phase, and a nematic phase and a monotropic a smectic B (SmB) phase on cooling. 7c revealed an SmA phase and a nematic phase and a monotropic SmC phase on cooling. Copyright Taylor & Francis Group, LLC.

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New Liquid-Crystalline Elastomers: 1.
Synthesis, Structure, and Phase Behavior
of a Series of Mesogenic Crosslinking
Agents Containing Reactive Bifunctional
Groups
Xiao-Xu Xu a , Zhe Hong a & Fei Liu a
a College of Chemical Engineering and Material, Eastern Liaoning
University , Dandong, People's Republic of China
Published online: 14 Dec 2010.
To cite this article: Xiao-Xu Xu , Zhe Hong & Fei Liu (2010) New Liquid-Crystalline Elastomers:
1. Synthesis, Structure, and Phase Behavior of a Series of Mesogenic Crosslinking Agents
Containing Reactive Bifunctional Groups, Molecular Crystals and Liquid Crystals, 533:1, 52-62, DOI:
10.1080/15421406.2010.526561
To link to this article: http://dx.doi.org/10.1080/15421406.2010.526561
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Mol. Cryst. Liq. Cryst., Vol. 533: pp. 52–62, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421406.2010.526561
New Liquid-Crystalline Elastomers: 1. Synthesis,
Structure, and Phase Behavior of a Series of
Mesogenic Crosslinking Agents Containing
Reactive Bifunctional Groups
XIAO-XU XU, ZHE HONG, AND FEI LIU
College of Chemical Engineering and Material, Eastern Liaoning
University, Dandong, People’s Republic of China
The synthesis of eight mesogenic crosslinking agents (1cꢀ8c) containing reactive
bifunctional groups is described. The chemical structures were characterized by
Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (NMR)
spectra. The mesomorphism was investigated by differential scanning calorimetry
(DSC) and polarizing optical microscopy (POM). The compounds 1c, 2c, 3c, 5c,
6c, and 8c showed an enantiotropic nematic phase. In addition, 5c exhibited a smec-
tic A (SmA) phase on cooling; 4c exhibited a smectic C (SmC) phase, a SmA
phase, and a nematic phase and a monotropic a smectic B (SmB) phase on cooling.
7c revealed an SmA phase and a nematic phase and a monotropic SmC phase on cooling.
Keywords Crosslinking agent; liquid crystalline; nematic phase; reactive bisfunc-
tional group; smectic phase
Introduction
Since liquid-crystalline elastomers (LCEs) were reported by Finkelmann et al. in
1981 [1], they have attracted increasing attention and interest as a new supramolecu-
lar system and liquid-crystalline (LC) materials due to their unique mechanical
properties and potential applications; for example, as sensors and actuators or arti-
ficial muscles [2–11]. The LCEs combine the rubber elasticity of polymer networks
with the anisotropic properties of LCs. Consequently, they not only hold the entro-
pic elasticity but also show a reversible mesophase transition. From a scientific point
of view, the LCEs are fascinating because they allow the study of the interplay of
electrical and mechanical forces in a rubbery material. This happens because the
reorientation of the mesogenic groups in the electric field creates stress in the
network of the polymer chains.
In general, LCEs are composed of two subsystems: (1) the mesogenic units give
the mesomorphic properties and (2) the crosslinking units give weak density of poly-
meric network and lead to rubber elasticity. To date, many nematic [10–16], smectic
[17–23], and cholesteric [24–29] LCEs, have been prepared mostly by adopting LC
Address correspondence to Xiao-Xu Xu, College of Chemical Engineering and Material,
Eastern Liaoning University, Dandong 118004, China. E-mail: 3x.931@163.com
52

Mesogenic Crosslinking Agent
53
monomers and bifunctional crosslinking agents. Most of the crosslinking agents of
the LCEs are nonmesogenic flexible bifunctional monomers, which may influence
the mesophase properties in two ways. (1) The flexible crosslinking chains act as a
diluent and cause a decrease in the clearing temperature; and (2) chemical crosslink-
ing can prevent the motion and orientation of mesogenic molecule at and in the
vicinity of the crosslinking sites. However, little study on the LCEs derived from
mesogenic crosslinking agents is reported; moreover, the low density of the meso-
genic crosslinking units may make some contribution to the formation of meso-
phases in the LCEs [28]. Therefore, it is necessary to design and synthesize some
mesogenic crosslinking agents and the corresponding LCEs to study the effect of
these mesogenic crosslinking units on the mesomorphism of the LCEs.
In this section, eight mesogenic crosslinking agents with central mesogenic
groups, reactive end groups, and the spacers were prepared and characterized. Their
mesomorphic properties and phase behavior were investigated with differential scan-
ning calorimetry (DSC) and polarizing optical microscopy (POM). The structure–
property relationships of the crosslinking agents 1cꢀ8c are discussed.
Experimental
Materials
Allyl bromide was purchased from Beijing Chemical Reagent Co. (Beijing, China)
Undecylenic acid was purchased from Beijing Jinlong Chemical Reagent Co., Ltd.
(Beijing, China) 4-Hydroxybenzoic acid was obtained from Shanghai Wulian
Chemical Plant (Shanghai, China). 4,40-Dihydroxybiphenyl (from Aldrich) was used
as received. All solvents and reagents used were purified by standard methods.
Measurements
Fourier transform infrared (FTIR) spectra were measured on a Perkin-Elmer
1
Spectrum One (B) spectrometer. H NMR spectra were obtained with a Bruker
ARX400 spectrometer. The phase behavior was determined with a Netzsch
DSC 204 equipped with a cooling system. The heating and cooling rates were
10ꢁC=min. A Leica DMRX POM equipped with a Linkam THMSE-600 cool and
hot stage was used to observe the phase transition temperatures and analyze the
mesomorphism through the observation of optical textures.
Synthesis of the Compounds
The synthetic route of compounds 1a–4a and 1b–3b is outlined in Scheme 1.
4-Allyloxybenzoic acid (1a), 4-allyloxy-40-hydroxybiphenyl (2a), 4-hydroxyphenyl-
40-allyloxybenzoate (3a), 4-hydroxybiphenyl-40-allyloxybenzoate (4a), 4-(10-
undecylen-1-yloxy) benzoic acid (1b), 4-hydroxy-40-(10-undecylen-1-yloxy)biphenyl
(2b), and 4-hydroxybiphenyl- 40-(10-undecylen-1-yloxy)benzoate (3b) were prepared
according to the method reported previously [30].
Synthesis of the Mesogenic Crosslinking Agents
The synthetic route of the bis-olefinic mesogenic crosslinking agents 1c–8c is shown
in Scheme 2. The synthesis of compounds 2c–8c is presented by the same method.

54
X.-X. Xu, Z. Hong, and F. Liu
Scheme 1. Synthesis of compounds 1a–4a and 1b–3b.
4,4-0bis(Allyloxybiphenyl) (1c). 4,40-Dihydroxybiphenyl (9.3 g, 0.05 mol) was
dissolved in 60 mL of ethanol, and a solution of KOH (5.6 g, 0.1 mol), a small
amount of potassium iodide, and 15 mL of water were added to the mentioned
above mixture. After dropwise addition of 12 mL of allyl bromide, the mixture
was refluxed for 30 h under stirring. The reaction mixture was poured into a
beaker filled with 1% NaOH solution and then filtered. The crude product was
recrystallized from ethanol. White solid was obtained. Yield 72%. IR (KBr, cmꢀ1):
=
3,076 (¼C–H); 2,950, 2,845 (–CH2–); 1,646 (C C); 1,608, 1,505 (Ar–); 1,256 (C–
1
O–C). H NMR (CDCl3, TMS): d 4.64 [m, 4H, 2(–CH2O–)]; 5.32–5.50 (m, 4H,
2CH2¼); 6.04–6.10 (m, 2H, 2CH2 ¼ CH–); 6.91–7.43 (m, 8H, Ar–H).
4-(P-Allyloxybiphenyl)-40-allyloxybenzoate (2c). Compounds 1a (8.9 g, 0.05 mol)
and 2a (11.3 g, 0.05 mol) were dissolved in 50 mL of tetrahydrofuran (THF) at
30ꢁC. N,N0-Dicyclohexylcarbodiimide (DCC; 10.3 g, 0.05 mol) and a small amount
of 4-dimethylaminopyridine (DMAP) were dissolved in 50 mL of THF and then
added dropwise to the above solution. The reaction mixture was stirred for 24 h at
30ꢁC. Then a small amount of water was added into the resulting solution and

Mesogenic Crosslinking Agent
55
Scheme 2. Synthesis of the mesogenic crosslinking agents 1c–8c.
filtered. The filtrate was poured into cold water, and the crude product obtained was
recrystallized from ethanol=acetone (1:1). White solid was obtained. Yield 79%. IR
(KBr, cmꢀ1): 3,032 (¼C–H); 2,951, 2,862 (–CH2–); 1,726 (C O); 1,645 (C C); 1,602,
=
=
1
1,508 (Ar–); 1,257 (C–O–C). H NMR (CDCl3, TMS): d 4.58–4.65 [m, 4H, 2(–
CH2O–)]; 5.31–5.51 (m, 4H, 2CH2 ¼); 6.04–6.12 (m, 2H, 2CH2 ¼ CH–); 7.02–8.18
(m, 12H, Ar–H).
4-(P-10-Undecylen-1-yloxyphenyl)-40-allyloxybenzoate (3c). Recrystallized from
ethanol. Yield 80%. IR (KBr, cmꢀ1): 3,078 (¼ C–H); 2,921, 2,848 (–CH2–); 1,755,
1
=
=
1,724 (C O); 1,642 (C C); 1,609, 1,463 (Ar–); 1,259 (C–O–C). H NMR (CDCl3,
TMS): d 1.27–2.60 [m, 16H,–(CH2)8–]; 4.65 (t, 2H, –CH2O–); 4.94–5.04 [m, 2H,
CH2 ¼ CH(CH2)8–]; 5.33–5.48 (m, 2H, CH2 ¼ CHCH2O–); 5.78–5.84 [m, 1H,
CH2 ¼ CH(CH2)8–]; 6.02–6.09 (m, 1H, CH2 ¼ CHCH2O–); 6.99–8.16 (m, 8H, Ar–H).
4-(P-10-Undecylen-1-yloxybiphenyl)-40-allyloxybenzoate (4c). Recrystallized from
ethanol=acetone (2:1). Yield 77%. IR (KBr, cmꢀ1): 3,077 (¼C–H); 2,922, 2,849
1
=
=
(–CH2–); 1,756, 1,729 (C O); 1,641 (C C); 1,608, 1,465 (Ar–); 1,257 (C–O–C). H
NMR (CDCl3, TMS): d 1.27–2.62 [m, 16H,–(CH2)8–]; 4.66 (t, 2H, –CH2O–);
4.94–5.05 [m, 2H, CH2 ¼ CH(CH2)8–]; 5.34–5.49 (m, 2H, CH2 ¼ CHCH2O–);

56
X.-X. Xu, Z. Hong, and F. Liu
5.79–5.85 [m, 1H, CH2 ¼ CH(CH2)8–]; 6.04–6.12 (m, 1H, CH2 ¼ CHCH2O–);
7.01–8.20 (m, 12H, Ar–H).
4-(P-Allyloxybiphenyl)-40-(10-undecylen-1-yloxy)benzoate (5c). Recrystallized
from ethanol=acetone (2:1). Yield 79%. IR (KBr, cmꢀ1): 3,080 (¼ C–H);
=
2,918, 2,849 (–CH2–); 1,755, 1,732 (C O); 1,642 (C C); 1,604, 1,464 (Ar–); 1,219
=
1
(C–O–C). H NMR (CDCl3, TMS): d 1.28–2.61 [m, 16H,–(CH2)8–]; 4.64 (t, 2H, –
CH2O–); 4.95–5.04 [m, 2H, CH2 ¼ CH(CH2)8–]; 5.34–5.48 (m, 2H, CH2 ¼
CHCH2O–); 5.78–5.85 [m, 1H, CH2 ¼ CH(CH2)8–]; 6.03–6.10 (m, 1H,
CH2 ¼ CHCH2O–); 7.03–8.22 (m, 12H, Ar–H).
4-(P-Allyloxybenzoyloxyphenyl)-40-(10-undecylen-1-yloxy)benzoate (6c). Recrystal-
lized from ethanol=acetone (2:1). Yield 82%. IR (KBr, cmꢀ1): 3,080 (¼C–H);
=
2,924, 2,849 (–CH2–); 1,748, 1,722 (C O); 1,641 (C C); 1,605, 1,510 (Ar–); 1,256
=
1
(C–O–C). H NMR (CDCl3, TMS): d 1.32–2.63 [m, 16H,–(CH2)8–]; 4.63 (t, 2H,
–CH2O–); 4.93–5.04 [m, 2H, CH2 ¼ CH(CH2)8–]; 5.33–5.49 (m, 2H,
CH2 ¼ CHCH2O–); 5.80–5.87 [m, 1H, CH2 ¼ CH(CH2)8–]; 6.03–6.11 (m, 1H,
CH2 ¼ CHCH2O–); 6.99–8.26 (m, 12H, Ar–H).
4-(P-10-Undecylen-1-yloxybiphenyl)-40-(10-undecylen-1-yloxy)benzoate (7c). Recrystal-
lized from ethanol=acetone (1:1). Yield 78%. IR (KBr, cmꢀ1): 3,075 (¼C–H); 2,925,
1
=
=
2,850 (–CH2–); 1,750, 1,732 (C O); 1,640 (C C); 1,602, 1,495 (Ar–). H NMR
(CDCl3, TMS): d 1.29–2.61 [m, 32H, 2CH2 ¼ CH(CH2)8–]; 4.93–5.02 (m, 4H,
2CH2 ¼ CH–); 5.78–5.82 (m, 2H, 2CH2 ¼ CH–); 6.94–8.28 (m, 12H, Ar–H).
Biphenyl 4, 40-bis(P-10-undecylen-1-yloxybenzoate) (8c). Recrystallized from
ethanol=acetone (1:2). Yield 81%. IR (KBr, cmꢀ1): 3,068 (¼ C–H); 2,975, 2,852
1
=
=
(–CH2–); 1,754, 1,724 (C O); 1,640 (C C); 1,602, 1,508 (Ar–). H NMR (CDCl3,
TMS): d 1.29–2.57 [m, 32H, 2CH2 ¼ CH(CH2)8–]; 4.92–5.03 (m, 4H, 2CH2 ¼);
5.80–5.86 (m, 2H, 2CH2 ¼ CH–); 7.16–8.21 (m, 16H, Ar–H).
Results and Discussion
Syntheses. The synthetic routes of mesogenic crosslinking agents 1cꢀ8c are shown
1
in Scheme 2. Their structures were characterized by FTIR and H NMR, which
were in agreement with the expected prediction. IR spectra of 1cꢀ8c showed
characteristic stretching bands at 1,756ꢀ1,748 cmꢀ1 attributed to the ester C O in
=
the undecylenate and 1,732 ꢀ 1,722 cmꢀ1 attributed to the ester C O in a
=
1
substituted benzoate. H NMR spectra of 1cꢀ8c showed a multiplet at about 6.14
and 5.31 ppm corresponding to olefinic protons in the allyl group and about 5.87
1
and 4.92 ppm corresponding to the olefinic protons in the undecylenyl group. H
NMR spectra of 3c as an example are shown in Fig. 1.
Thermal Properties
The thermal properties of the mesogenic crosslinking agents 1cꢀ8c were investigated
with DSC and POM. The phase transition temperatures, corresponding enthalpy
changes, and mesophase types of 1cꢀ8c are summarized in Table 1. All phase
transitions are reversible, and the transition temperatures noted with DSC are

Mesogenic Crosslinking Agent
57
Figure 1. 1H NMR spectra of 3c.
consistent with those observed by POM. Representative DSC curves of 3c and 4c are
shown in Figs. 2 and 3.
DSC heating thermograms of 1c, 2c, 3c, 5c, 6c, and 8c showed a melting
transition at low temperature and a nematic-to-isotropic phase transition at
high temperature. On the cooling cycle, an isotropic-to-nematic phase transition
and a crystallization transition appeared. In addition, a DSC cooling curve of
5c also showed a smectic A (SmA) phase transition between the nematic and crystal-
lization phase transitions. On heating, 4c showed a melting transition, a smectic
C (SmC)-to-SmA phase transition, an SmA-to-nematic phase transition, and a
nematic-to-isotropic phase transition, respectively. In the cooling cycle, an
Table 1. Phase transition temperature (ꢁC) and enthalpy changes (J ꢂ gꢀ1) of cross
linking agents
Samples
Mesophase and phase transitions, Heating=cooling
1c
2c
3c
4c
K130.4(103.7) N141.4(5.4)I
I121.6(4.2) N108.8(73.6)K
I202.8(2.1) N75.1(40.3)K
I79.8(2.3) N44.8(70.4)K
I202.9(3.5) N115.2(2.4)
SmA95.4(4.5) SmC81.9(0.3)
SmB55.0(19.6)K
K142.2(52.9) N239.5(3.1)I
K62.0(75.7) N82.6(2.5)I
K88.3(21.2) SmC96.4(9.8)
SmA115.3(1.7) N207.2(2.2)I
5c
K107.5(46.0) N206.1(2.6)I
I198.4(2.7) N102.2(0.4)
SmA89.2(35.8)K
6c
7c
K108.7(45.1) N210.2(2.5)I
K84.5(23.5) SmA171.3(2.6)
N178.6(1.3)I
I199.1(1.2) N73.4(36.5)K
I175.1(1.5) N167.4(2.0)
SmA114.8(3.1) SmC72.5(20.2.1)K
I238.7(1.1) N120.2(10.6)K
8c
K136.5(12.5) N240.3(1.2)I
K ¼ crystal, N ¼ nematic, SmA ¼ smectic A phase; SmB ¼ smectic B phase; SmC ¼ smectic
C phase; I ¼ isotropic; D ¼ decomposition.

58
X.-X. Xu, Z. Hong, and F. Liu
Figure 2. DSC thermograms of 3c.
isotropic-to-nematic phase transition, a nematic-to-SmA phase transition, an
SmA-to-SmC phase transition, an SmA-to-smectic B (SmB) phase transition, and
a crystallization transition were seen. In addition, 7c showed an enantiotropic
SmA phase and nematic phase and a monotropic SmC phase.
The Effect of the Rigidity of the Mesogenic Core. As seen from the data listed in
Table 1, the mesogenic core has a considerable influence on the thermal properties
and mesophase types of 1cꢀ8c. In general, with increasing the rigidity of the
Figure 3. DSC thermograms of 4c.

Mesogenic Crosslinking Agent
59
mesogenic core or the number of aryl rings in LC molecules, the corresponding
melting temperature (Tm) and the isotropic or clearing temperature (Ti) increased.
Taking the effect of the number of aryl rings on Ti into account, the equation is
given by Dejeu [31] as follows:
0:084ða== ꢀ a ÞI
?
Ti ¼
ð1Þ
KV2
where K is Boltzman’s constant, I is ionized electric potential, V is molar volume, and
a== ꢀ a is polarizability anisotropy parallel and normal to the molecular axis
?
direction. In the conjugate system of the aryl rings, the a==-value is very great, so
the a==-value will increase with increasing number of rings, and Ti also increases.
Moreover, Ti increased more than Tm, so the mesophase temperature ranges
(DT ¼ T – Tm) also widened. For example, compared with Tm and Ti of 1c, those
i
of 2c increased by 11.8ꢁC and 98.1ꢁC, respectively. DT increased from 11.0ꢁC for
1c to 97.3ꢁC for 2c. Similar results were also seen for 3c and 4c or 7c and 8c.
In addition, the rigidity of the mesogenic core also affected the mesophase types.
For example, with increasing number of aryl rings, the smectic phase could be
induced in addition to the nematic phase. 3c only showed an enantiotropic nematic
phase, whereas 4c showed, in addition to an enantiotropic nematic phase, SmC and
SmA phases on heating, or SmA, SmC, and SmB phases on cooling. However, a con-
verse result was seen for 7c and 8c. This indicates that the smectic phase could not be
induced when the rigidity of the mesogenic core is moderate.
The Effect of the Arrangement of the Mesogenic Core. Although the molecular
formula of 4c and 5c is identical, their phase transition temperatures and phase
types are different due to their different arrangement of the aryl mesogenic core
or the change of the position of the biphenyl or phenyl moiety in the mesogenic
core. (1) Compared with Tm of 4c, that of 5c increased by 19.5ꢁC. However, Ti of
4c and 5c showed little difference. Although the molecular structures of 4c and 5c
are different, they were made up of the same aryl segments and terminal groups.
According to Eq. (1), Ti of 4c and 5c should be nearly the same; and (2) 4c
formed a higher order smectic phase and showed enantiotropic SmC, SmA, and
nematic phases and a monomtropic SmB phase, whereas 5c showed only an
enantiotropic nematic phase and a monomtropic SmA phase.
The Effect of the Ester Linkage Bond in the Mesogenic Core. The ester linkage bond
in the mesogenic core also has an influence on the thermal properties due to the
conjugation action of the ester linkage bond. However, the difference in the phase
transition temperatures was less because the conjugation action of the ester
linkage bond was weaker, According to Table 1, Tm and Ti of 6c increased by
1.2ꢁC and 4.1ꢁC over those of 5c, respectively.
The Effect of the Spacer Length of the Terminal Group. In general, with increasing
the spacer length of the terminal group, the intermolecular forces weaken, which
causes the corresponding phase transition temperatures to decrease. For example,
compared with 2c containing two terminal allyl spacers, Tm and Ti of 4c
containing a terminal allyl spacer and a terminal undecylenyl spacer decreased by
53.9ꢁC and 32.3ꢁC, respectively, and those of 7c containing two terminal
undecylenyl spacers decreased by 57.7ꢁC and 60.9ꢁC, respectively. In addition, the

60
X.-X. Xu, Z. Hong, and F. Liu
Figure 4. Optical textures of 4c (200ꢃ). (a) Schlieren texture of nematic phase on heating to
204.7ꢁC; (b) fan-shaped texture of an SA phase on cooling to 111.0ꢁC; (c) broken fan-shaped
texture of an SC phase on cooling to 89.3ꢁC; and (d) mosaic texture of an SB phase on cooling
to 72.7ꢁC.
spacer length of the terminal group affects the mesophase types. For 2c, 4c, and 7c,
with increased spacer length of the terminal groups, the smectic phase could be
induced. The smectic phase temperature range widened from 27.0ꢁC for 4c to
86.8ꢁC for 7c and the nematic phase temperature range shortened from 97.3ꢁC for
2c to 91.9ꢁC for 4c and to 7.3ꢁC for 7c. However, compared with 4c, the order of
the smectic phase for 7c decreased. For example, 7c with two terminal undecylenyl
spacers showed an SmA phase in addition to a nematic phase on heating, whereas
4c with a terminal undecylenyl spacer and a terminal allyl spacer showed SmC
and SmA phases.
Optical Textures
In general, LC materials show a nematic phase and=or smectic phases, which mainly
depends on the relative strength of the molecular transverse attractive forces and the
terminal attractive forces. When the molecular transverse attractive forces are
predominant, LC materials show smectic phases. Conversely, LC materials show a

Mesogenic Crosslinking Agent
61
Figure 5. Optical textures of 5c (200ꢃ). (a) Thread-like texture of nematic phase on heating to
135.6ꢁC; and (b) droplet texture of nematic phase on cooling to 197.3ꢁC.
nematic phase. However, when the strength of these two kinds of forces is about
equal, both smectic and nematic phases can appear.
The optical textures of 1cꢀ8c are studied by POM with a heating stage. POM
results shows that 1c, 2c, 3c, 5c, 6c and 8c exhibit an enantiotropic nematic
thread-like texture, droplet texture, and Schlieren texture on heating and cooling
cycles. In addition, 5c also exhibits a fan-shaped texture of an SmA phase on cool-
ing. 4c Exhibits an enantiotropic, broken fan-shaped texture of an SmC phase, a
fan-shaped texture of an SmA phase, a Schlieren texture of a nematic phase, and
a monotropic mosaic texture of an SmB phase on cooling. 7c Exhibits an enantiotro-
pic fan-shaped texture of an SmA phase, A thread-like texture of a nematic phase,
and a monotropic, broken fan-shaped texture of an SmC phase on cooling. There-
fore, the mesophases observed with POM are in agreement with those noted by
DSC. The optical textures of 4c and 5c, as examples, are shown in Figs. 4 and 5,
respectively.
Conclusions
Eight new mesogenic crosslinking agents (1cꢀ8c) containing reactive bifunctional
groups were synthesized and characterized. The compounds 1c, 2c, 3c, 5c, 6c, and
8c all show an enantiotropic, nematic thread-like texture, a droplet texture, and a
Schlieren texture. In addition, 5c also exhibits a fan-shaped texture of an SmA phase
on cooling. 4c Exhibits an Enantiotropic, broken fan-shaped texture of an SmC
phase, a fan-shaped texture of an SmA phase, a Schlieren texture of a nematic phase,
and a monotropic, mosaic texture of an SmB phase on cooling. 7c Reveals an enan-
tiotropic SmA phase and a nematic phase, and a monotropic SmC phase on cooling.
With increasing the rigidity of the mesogenic core, Tm and Ti increased; moreover, Ti
increased more than Tm, and the mesophase; temperature ranges widened. In
addition, with increasing the spacer length of the terminal group, both Tm and Ti
decreased, and the different smectic phases could be induced and gradually showed
narrow nematic phase ranges and broader smectic phase ranges.

62
X.-X. Xu, Z. Hong, and F. Liu
Acknowledgment
The authors are grateful to the Educational Development of Liaoning Province,
China for financial support of this work.
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