Dimesogenic liquid crystalline organosiloxanes

Article abstract of DOI:10.1023/A:1025609613210

Liquid crystalline (LC) organosiloxanes with two terminal cyanobiplienylyl groups attached to a linear or cyclic siloxane center through an aliphatic spacer (CH₂)_n with n = 10 were synthesized. The ability of compounds to pass into the LC state was confirmed by thermooptical, X-ray diffraction, and calorimetric measurements. The temperatures and the enthalpies of phase transitions were determined. The types of LC structures and the capability of one compound for polymesomorphism to form the chiral S _mC* phase without a chiral center in the mesogenic group were established. The temperatures and the enthalpies of the reversible phase transitions, crystal ? S_mC ? S_mA ? melt and crystal ? S_mA ? melt, for linear and cyclic LC organosiloxanes, respectively, were determined. Models of molecular packing in the S_mA and S_mC* phases were proposed based on X-ray diffraction data. A specific feature of the S_mA phases of new LC organosiloxanes is a negative gradient of the temperature dependence of the interlayer spacing.

Full text of DOI:10.1023/A:1025609613210

1610
Russian Chemical Bulletin, International Edition, Vol. 52, No. 7, pp. 1610—1620, July, 2003
Dimesogenic liquid crystalline organosiloxanes
a
b
a
a
N. N. Makarova,a L. M. Volkova, E. V. Matukhina, A. V. Kaznacheev, and P. V. Petrovskii
ꢀ
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 135 8550. Eꢀmail: nmakar@ineos.ac.ru
bMoscow State Pedagogical University, Department of Physics,
1, ul. Malaya Pirogovskaya, 119882 Moscow, Russian Federation,
Fax: +7 (095) 245 0310. Eꢀmail: lmatukh@mail.ru
Liquid crystalline (LC) organosiloxanes with two terminal cyanobiphenylyl groups atꢀ
tached to a linear or cyclic siloxane center through an aliphatic spacer (CH2)n with п = 10 were
synthesized. The ability of compounds to pass into the LC state was confirmed by thermooptical,
Xꢀray diffraction, and calorimetric measurements. The temperatures and the enthalpies of
phase transitions were determined. The types of LC structures and the capability of one
compound for polymesomorphism to form the chiral SmC* phase without a chiral center in the
mesogenic group were established. The temperatures and the enthalpies of the reversible phase
transitions, crystal
SmC
SmA
melt and crystal
SmA
melt, for linear and
cyclic LC organosiloxanes, respectively, were determined. Models of molecular packing in the
SmA and SmC* phases were proposed based on Xꢀray diffraction data. A specific feature of the
SmA phases of new LC organosiloxanes is a negative gradient of the temperature dependence of
the interlayer spacing.
Key words: disiloxanes, cyclosiloxanes, liquid crystalline compounds, mesogen, phase tranꢀ
sitions, spatial isomers.
During the last three decades, syntheses of combꢀlike
Results and Discussion
liquid crystalline (LC) polyorganosiloxanes have been perꢀ
formed and their phase behavior has been comprehenꢀ
sively studied depending on the chemical structure of the
mesogen and the length of spacers.1 The number of publiꢀ
cations dealing with monomeric LC siloxanes is much
smaller; these studies consider compounds with linear
siloxane and cyclotetrasiloxane centers and with variable
structure of mesogenic groups.2—5 It was found that an
increase in the length of siloxane units in dimesogenic
α,ωꢀdimethyloligosiloxanes entails a decrease in the temꢀ
peratures of phase transitions.3,4 Dimesogenic compounds
with a hexamethyldisiloxane center and chiral groups exꢀ
hibit enantiotropic mesomosphism, SmA—SmC* (SmA and
SmC are smectic A and C phases) with a change in the
interlayer spacing.2 Spontaneous polarization was found
in dimesogenic hexadecamethylheptasiloxanes with a
chiral center in the terminal group.4
This study is devoted to the structure of linear and
cyclic siloxane centers of molecules with a particular spaꢀ
tial position of terminal cyanobiphenylyl mesogenic
groups connected to the core by an aliphatic (CH2)n spacer
with п = 10. The purpose of the study was to elucidate the
influence of the structure of the central siloxane core on
phase transition temperatures and on the type of LC strucꢀ
tures formed.
Synthesis of liquidꢀcrystalline organosiloxanes. We synꢀ
thesized dimesogenic compounds with different structures
of the siloxane center. Linear tetramethyldisiloxane 1
(Scheme 1) and cyclic decamethylcyclohexasiloxane 2
(Scheme 2) were used as central cores. The mesogenic
group for compounds 1 and 2 was chosen resorting to
published data,1 stating that the use of an aliphatic spacer
with п > 8 decreases the effects related to the oddꢀandꢀ
even structure of the uncoupling; simultaneously, this
creates an additional dipole moment.
Disiloxane 1 was prepared5 by hydrosilylation of unꢀ
saturated ester 3 with chlorodimethylsilane in the presꢀ
ence of a Pt catalyst (the Carsted catalyst) followed by
hydrolysis if the resulting chlorosilane 4 in the presence of
NaHCO3 (see Scheme 1).
Dimesogenic compound 2 with the central cycloꢀ
hexasiloxane fragment was prepared by the reaction
of transꢀ2,8ꢀdihydroxyꢀ2,4,4,6,6,8,10,10,12,12ꢀdecaꢀ
methylcyclohexasiloxane (5) 6 with chlorosilane 4 (see
Scheme 2).
The choice of cyclic cyclohexasiloxane 5 as a core for
an LC monomer is due to the presence of two tetraꢀ
methyldisiloxane groups between two MeSiO3 centers
connected to the mesogenic group. Within this group, the
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1526—1536, July, 2003.
1066ꢀ5285/03/5207ꢀ1610 $25.00 © 2003 Plenum Publishing Corporation

Dimesogenic LQ organosiloxanes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 7, July, 2003
1611
Scheme 1
Scheme 2
Si—O—Si angle can vary from 148° to 178° (the four Si
atoms lie in one plane), which provides a hypothetical
possibility of the formation of LC packings of different
types.
cisꢀ and transꢀisomers in compound 2. A difference
between the chemical shifts, ∆δ ≈ 0.20, has been found for
MeSiO3 groups in the same region for bifunctional
monomers and cyclolinear polymers; however, the nonꢀ
equivalence of silicon in the Me2SiO groups of cycloꢀ
siloxane isomers was not manifested.7
The structures and purity of compounds 1 and 2 were
1
confirmed by TLC, H and 29Si NMR and IR spectrosꢀ
copy, and elemental analysis.
Since the starting cyclosiloxane 5 was a pure transꢀ
isomer according to a previous publication,6 the results
we obtained attest to partial inversion of one silicon atom
during the formation of compound 2.
1
The H NMR spectra of compounds 1 and 2 exhibit
highꢀfield signals for the protons of the alkyl substituents.
The singlet with δ 0.021 in the spectrum of compound 1
refers to the two methyl groups at the silicon atom. The
spectrum of compound 2 contains signals with δ 0.02 and
0.04 (3 H) for the MeSiO3 methyl groups correspondꢀ
ing to transꢀ and cisꢀisomers with the intensity ratio
trans : cis ≈ 3 : 1. The signals of compound 5 in different
solvents ((CD3)2CO, CDCl3—CCl4, C6D6—CCl4) were
assigned to cisꢀ and transꢀisomers on the basis of previꢀ
ously published data.6 Other methylꢀgroup protons reꢀ
lated to Me2SiO in cyclosiloxane and to Me2SiCH2 are
responsible for singlets with δ 0.06 (12 H) and 0.09 (6 H),
respectively. In this case, the nonequivalence of the meꢀ
thyl protons in cisꢀ and transꢀisomers is not observed. The
proton signals of the mesogenic group in compounds 1
and 2 are identical.
The 29Si NMR spectrum of compound 1 contains only
one signal at δ 7.15, i.e., in the region characteristic of
Me2SiCH2 groups. However, in the case of compound 2,
this spectral region contains two signals δ 7.92 and 7.27,
with an intensity ratio of ∼3 : 1, while the region from
δ –66.0 to –67.0, typical of the methylsilsesquioxane
group, exhibits two signals at δ –66.47 and –66.73 with
an intensity ratio of ∼3 : 1, which points to the presence of
The IR spectra of compounds 1 and 2 exhibit absorpꢀ
tion bands typical of SiMe2 groups (791 cm–1); Si—O
(1070 cm–1), Si—CH2CH2 (1135 cm–1), CH2O—C
(1172 cm–1), and Si—Me (1255 cm–1) bonds; C6H4
groups (1495, 1607 cm–1); and C=O (1759 cm–1) and
C≡N (2235 cm–1) bonds. Absorption bands correspondꢀ
ing to asymmetric and symmetric stretching vibrations of
the C—H bonds in methyl and methylene groups are
observed in the 2845—2920 cm–1 region. The bands corꢀ
responding to asymmetric and symmetric bending vibraꢀ
tions of these groups occur at about 1460 and 1390 cm–1
.
Phase behavior. Comparative study of the phase beꢀ
haviors of compounds 1 and 2 was carried out by DSC.
Figure 1 shows the DSC curves recorded at the heating
rate V = 10 °C min–1. It can be seen from these data that
compound 1 undergoes at least two phase transitions at 56
and 116 °C, unlike compound 2, where only one diffuse
transition can be detected. The enthalpy of isotropization
∆Hi =11.0 J g–1 for compound 1 is close to published data
for siloxane polymers with alkoxycyanobiphenylyl side
groups and the (CH2)n alkyl spacer with п = 11 (∆Hi =
9.2 J g–1), which form the SmA phase with a parallel packꢀ

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Russ.Chem.Bull., Int.Ed., Vol. 52, No. 7, July, 2003
Makarova et al.
were observed for polyacrylates with alkoxycyanobiꢀ
phenylyl groups and the (CH2)n spacer with n = 11.9 The
cooling rate (V ) affects appreciably the temperature of
the SmA→SmC transition. Indeed, for V = 3 °C min–1 it is
equal to 28 °C, while for V = 0.5 °C min–1, to 45—52 °C.
Figure 2, b shows the texture of compound 1 during the
SmA→SmC transition at 52 °C. The lowest phase transiꢀ
a
endo
1
2
tion temperature TS
= 8.0 °C was determined by
A→S
C
DSC at V = 10 °C mmin–1.mFigure 2, c shows the texture of
the SmC phase of compound 1 at 26 °C. The temperature
range of existence of the LC state for compound 1 is twice
as wide as that for the initial mesogen 3.5
–50
0
50
100
T/°C
Figure 3, a shows the texture of the rodꢀshaped liquidꢀ
crystalline nuclei obtained on cooling of compound 2
from an isotropic melt at 90 °C. The shape of the nuclei
indicates that the growth rate in the axial direction is
greater than that in the radial direction. When compound 2
is cooled at a rate of V = 0.5 °C min–1 to 80 °C, the
background field is filled with the focal conic texture of
the SmA phase, which remains unchanged down to 20 °C
(see Fig. 3, b). The texture of the SmA phase predomiꢀ
nates for compound 2. However, on further cooling of
compound 2, an additional texture looking as crosses withꢀ
out disruption of each branch was found to appear in the
remaining isotropic melt (in the black field) (see Fig. 3, c).
This is probably due to formation of the texture of the
cisꢀisomer of 2.
Figure 4 shows the Xꢀray diffraction patterns of ester 3
used to prepare compounds 1 and 2. One can see that the
mesogen is crystalline at 20 °C. Compound 3 is known to
pass to the SmA phase at 50 °C.5 The Xꢀray diffraction
pattern for the SmA phase of compound 3 recorded at
54 °C (see Fig. 4, curve 2) contains only one narrow
reflection at 2θ = 2.14° (dl = 41.23 Å) with the halfꢀwidth
endo
b
1
2
–30
0
30
60
90
T/°C
Fig. 1. DSC curves for compounds 1 (a) and 2 (b) at a heating
and cooling rate of 10 °C min–1: (1, 2) are the heating and
cooling curves, respectively.
ing of backbone sections.8 The lower isotropization temꢀ
perature Тi found for 2 is probably due to both the greater
number of tetramethyldisiloxane groups in molecule 2
compared to that in 1 and the fact that compound 2 is a
mixture of two spatial isomers present in ∼3 : 1 ratio.*
During cooling of compound 1, DSC measurements
(see Fig. 1, curve 2) show two transitions at 113.0 and
8.0 °C, while in the case of compound 2, only one
exotherm with a poorly resolved maximum is observed.
The overall enthalpy of phase transitions in compound 2
is much lower than that for compound 1.
∆
= 0.27° and a broad nearly symmetrical amorphous
1/2
halo at 2θa = 19.83° (da = 4.47 Å) with ∆1/2 = 6.0°.
According to previous data,5 the SmA phase exists over a
narrow temperature range (∆TS = 50.0—67.5 °C). The
A
m
Xꢀray diffraction pattern of ester 3 recorded above Тi, at
105 °C, contains only a symmetrical amorphous halo with
a maximum at 2θa = 19.0° (da = 4.67 Å, ∆1/2 = 6.8°).
According to Xꢀray diffraction data, compound 1 is
crystalline at 20 °C (Fig. 5, a). In the Xꢀray diffraction
pattern, transition to the SmA phase was detected at 54 °C
(see Fig. 5, b). The Xꢀray diffraction pattern of the SmA
phase exhibits one narrow intense reflection at 2θ = 1.98°
(d1 = 44.57 Å, ∆1/2 = 0.26°) and a broad amorphous halo.
The position of the halo maximum, 2θа = 19.9°, is virtuꢀ
ally identical to the corresponding value for the mesogen.3
Thus, the amorphous maximum at 2θа is mainly due to
scattering on mesogenic groups. The Xꢀray diffraction
pattern of the melt of compound 1 measured at 120 °C
(see Fig. 5, c) contains only one amorphous halo with a
maximum at 2θа = 16.47° (∆1/2 = 4.1°). The average inꢀ
termolecular distance in the melt calculated for comꢀ
It was found by polarization microscopy that comꢀ
pounds 1 and 2 are crystalline at 20 °C; they exhibit
enantiotropic LC mesomorphism and undergo isotropiꢀ
zation upon temperature rise to 120 and 100 °C, respecꢀ
tively. During cooling of an isotropic melt, the liquid
crystalline isotropic state is retained down to –70 °C with
a cooling rate of 3—10 °C min–1. The crystal structure is
completely restored after 2 days at 20 °C.
Figure 2, a shows the texture of compound 1 at
116.5 °C during cooling the isotropic melt from 120 °C.
As the temperature decreases in the case of compound 1,
the texture of the SmA phase disappears and a new texture
typical of the chiral SmC phase appears instead (see
Fig. 2, c). Similar textures for the SmA and SmC phases
* The introduction of Me2SiO units in LC compounds is known
to result in a sharp decrease in Ti.3,4

Dimesogenic LQ organosiloxanes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 7, July, 2003
1613
a
b
c
a
b
c
100 µm
100 µm
100 µm
100 µm
100 µm
Fig. 2*. Optical photomicrographs of the textures of compound 1
at 116.5 °C in the SmA phase (cooling rate 1.0 °C min–1) (a), in
the instant of the SmA
SmC transition at 52 °C (cooling rate
0.5 °C min–1) (b), and in the SmC phase at 26 °C (cooling rate
3.0 °C min–1) (c).
pound 1, da = 5.38 Å, is substantially greater that the
corresponding value for mesogen 3 for which da = 4.67 Å.
This is indicative of changes introduced by the siloxane
center to the statistics of intraꢀ and intermolecular disꢀ
tances. Comparison of the 2θа values for the SmA phase
and the isotropic melt suggests the possibility of microꢀ
20 µm
Fig. 3*. Optical photomicrographs of the textures of comꢀ
pound 2 in the SmA phase at 90 (a) and 80 °C (b) (cooling rate
0.5 °C min–1) and in the SmA phase at 20 °C (cooling rate
1.0 °C min–1) (c).
* Figures 2 and 3 are available in full color in the onꢀline version of the journal (http://www.wkap.nl/journalhome.htm/1066ꢀ5285)
and on the web site of the journal (http://rcb.ioc.ac.ru).

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Makarova et al.
I/pulse s–1
6000
4000
a
150
100
50
0
5
10
15
20
25
2θ/deg
I/pulse s–1
b
400
200
1
2
0
5
10
15
20
25
2θ/deg
Fig. 4. XꢀRay diffraction patterns of compound 3 at 20 °C (a) and 54 (1) and 105 °C (2) (b).
phase separation between mesogenic groups and the silꢀ
oxane core in the LC phase.
did not show a stepwise change in the d1 parameter on
cooling of compound 1 in the temperature range of existꢀ
ence of the LC phase. This is probably due to the close
positions of the melting point and the SmC→SmA transiꢀ
tion found by DSC (see Fig. 1). It should be emphasized
that the gradient of the d1(Т ) dependence was negative.
On cooling of the melt, the smallꢀangle reflection from
the LC phase gradually shifted to smaller angles, pointing
to an increase in the parameter d1 with a decrease in
temperature (Fig. 6). In the 40—50 °C region correspondꢀ
According to Xꢀray diffraction data, compound 1
does not crystallize immediately after cooling from
120 to 20 °C; crystallization is very slow, the crystal
structure being completely restored only after 48 h
at 20 °C.
As noted above, SmA→SmC transition taking place on
cooling of an isotropic melt was found for compound 1
using polarization microscopy. XꢀRay diffraction analysis

Dimesogenic LQ organosiloxanes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 7, July, 2003
1615
I/pulse s–1
I/pulse s–1
2000
1500
1000
500
1750
a
a
1500
500
1
250
2
3
4
0
5
10
10
10
15
15
15
20
20
20
25 2θ/deg
I/pulse s–1
b
5
2100
1800
6
1.5
d1/Å
2.0
2.5
3.0
2θ/deg
100
50
SmC
SmA
0
44
43
42
5
25 2θ/deg
I/pulse s–1
Melt
2500
2000
c
150
100
50
20
40
60
80
100
T/°C
0
Fig. 6. XꢀRay diffraction characteristics of compound 1 in the
liquidꢀcrystalline state: (а) fragments of Xꢀray diffraction patꢀ
terns obtained by cooling of a melt at 110 (1), 92 (2), 86 (3),
74 (4), 54 (5), and 20 °C (6); (b) the temperature dependence of
the interlayer spacing d1.
5
25 2θ/deg
Fig. 5. XꢀRay diffraction patterns of compound 1 at 20 (a),
54 (b), and 120 °C (c).
ing to the SmA→SmC transition, the parameter d1 was
noted to decrease (by ∼1.5 Å).
reflection at 2θ = 3.07° (d = 28.74 Å) with the halfꢀwidth
Compound 2 is partially crystalline at 20 °C (Fig. 7,
curve 1), the fraction of the crystalline phase being small.
On heating to 30 °C, this compound completely transꢀ
forms in the SmA phase (curve 2). The Xꢀray diffraction
pattern obtained at 30 °C (curve 2) shows one intense
∆
= 0.23° and amorphous scattering. The distribution
1/2
curve for the intensity of amorphous scattering has a comꢀ
plex shape. However, it is possible to distinguish two
maxima at 2θa = 10.08° (da = 8.75 Å) and 2θа = 20.36°
1
1
2
(da = 4.36 Å) located in the third, very broad halo at
2

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Makarova et al.
I
According to Xꢀray diffraction data, isotropization of
compound 2 takes place at 90 °C, which is consistent with
the DSC and optical microscopy data. The Xꢀray diffracꢀ
tion pattern of the melt of compound 2 (see Fig. 7, curve 4)
contains only an amorphous halo of a complex shape.
The intensity distribution curve for the amorphous scatꢀ
tering for the melt of compound 2 differs appreciably
from the diffraction patterns of the melts of mesogen 3
and compound 1 by the presence of a clear maximum at
2θa = 10.0° corresponding to scattering on the siloxane
1
1
2
rings. Thus, the microphase separation between the silꢀ
oxane centers and organic mesogens noted previously
for the SmA phase is retained in the isotropic melt.
The scattering curve from the melt has a maximum at
2θа = 17.40°.
2
The obtained data imply the following sequence
of phase transformations for mesogen 3 and comꢀ
pounds 1 and 2:
3
4
5
10
15
20
25
2θ/deg
Mesogen 3
Fig. 7. XꢀRay diffraction patterns of compound 2 at 20 (1),
30 (2), 81 (3), and 105 °C (4).
Crystal
Crystal
Sm
A
N
Melt
Melt
Compound 1
SmC* SmA
2θа = 17.74°. Comparison of the Xꢀray diffraction patꢀ
3
terns obtained at 30 and 81 °C (see Fig. 7, curves 2 and 3)
shows that the angle position of the first amorphous maxiꢀ
mum depends only slightly on the temperature, unlike
that of the second maximum, which is highly sensitive to
temperature changes. This indicates that the maxima at
Compound 2
Sm
Crystal
A
Melt
2θa and 2θa2 are due to scattering on different molecular
1
fragments.
To summarize the data obtained for mesogen 3 and
compounds 1 and 2, the following conclusions can be
drawn:
(1) the introduction of the cyclic siloxane core beꢀ
tween two mesogenic groups decreases the thermal stabilꢀ
ity of the crystal phase, thus extending the temperature
range of existence of the SmA phase;
The da value is close to the thickness of the siloxane
1
cyclic fragment, which is 7.8 Å.* Hence, the arrangement
of cyclic fragments within the layer is subject to a shortꢀ
range order, the strictest correlation being observed along
the direction normal to the plane of the rings. The angle
position of the second amorphous halo, 2θа , virtually
2
coincides with the 2θа value for mesogen 3 (da = 4.47 Å).
Therefore, it is most likely that the second amorphous
halo at 2θа reflects scattering on mesogenic groups.
(2) the presence of the linear siloxane core has no
influence on the thermal stability of the crystal phase and
leads to pronounced supercooling of the LC phase, giving
rise to the SmC phase in the absence of chiral centers. The
presence of siloxane cores increases the thermal stability
of the mesomorphic state due to additional interactions
caused by microphase separation between the siloxane
and mesogenic organic fragments (the substantial broadꢀ
ening of the isotropization region of cyclic LC organoꢀ
siloxane is due to the presence of cisꢀisomers).
A temp2erature rise results in a substantial shift of 2θа
2
toward smaller scattering angles, indicating an increase in
the average distance between mesogenic groups. Meanꢀ
while, the 2θa value depends only slightly on the temꢀ
1
perature, i.e., the correlation in the mutual arrangement
of cyclic fragments is retained. The high gradient for the
2θа (Т ) dependence found for the temperature range of
2
existence of the SmA phase may attest to the lack of comꢀ
plete overlap of the mesogenic groups at the intermolecuꢀ
lar level.
The interlayer spacing for the linear LC siloxane near
Тi (d1 = 41.62 Å) is close to the analogous parameter for
mesogen 3 (d1 = 41.23 Å). As the temperature decreases,
the interlayer spacing in the SmA phase of linear LC siloxꢀ
ane increases, reaches the maximum value, d1 = 44.79 Å,
* A similar value has been found for the mesophases of cycloꢀ
linear polymethylsiloxanes containing decamethylcyclohexaꢀ
siloxane fragments.10
near the SmA
SmC transition at 54 °C, and decreases
to d1 = 43.04 Å in the SmC phase. Figure 8 shows the

L = 55.6 Å
d1 = 44.6 Å
is the linear siloxane core;
is the C6H4 group of the mesogen;
is the aliphatic spacer (CH2)10
;
is the cyano group;
is the carboxy group
Fig. 8. Model of molecular packing for compound 1 in the SmA phase. (In the smectic C phase, the mesogenic groups are arranged at an angle of ∼15° relative to the
director.)

a
d = 28.8 Å
b
L = 2l + 8 Å ≈ 63.6 Å
l = 27.8 Å
d1 = 57.6 Å
is cyclohexasiloxane;
is the aliphatic spacer (CH2)10
;
is the C6H4 group of the mesogen;
is the cyano group;
is the carboxy group
Fig. 9. Putative models for the packing of compound 2 in the SmA phase (the smectic layers are arranged vertically): (a) packing with full overlap of mesogen groups;
(b) layered packing.

Dimesogenic LQ organosiloxanes
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 7, July, 2003
1619
models of packing in the SmA and SmC phases of comꢀ
pound 1 constructed based on Xꢀray diffraction data and
on the HyperChem 4.5 models designed on a Silicon
Graphics O2 computer.
Experimental
1
H and 29Si NMR spectra were recorded on a Bruker
AMXꢀ400 spectrometer at 20 °C in a CDCl3—CCl4 mixture and
the IR spectra were measured on a Specord Mꢀ82 spectrometer
in КВr pellets. The temperatures and enthalpies of phase transiꢀ
tions in the compounds were determined by differential scanꢀ
ning calorimetry on a PerkinꢀElmer DSCꢀ7 instrument at a
heating rate of 2, 5, or 10 °C min–1. The Xꢀray diffraction
measurements were carried out on a Dronꢀ3M diffractometer.
Prior to the measurements, the samples were maintained at a
constant temperature, to within 1 °C, for 20 min. The phase
state was determined by optical polarization microscopy using
an Axiolab Pol microscope (Zeiss). A Linkam controlled hot
stage was used.
1,3ꢀBis[10ꢀ(4´ꢀcyanobiphenylꢀ4ꢀylcarbonyloxy)decyl]tetraꢀ
methyldisiloxane (1). A solution of chlorosilane 4 (1.9 g,
4.1 mmol) in 10 mL of an Et2O—toluene mixture (1 : 1) was
added over a period of 30 min to a mixture of H2O (0.07 g,
3.9 mmol) and NaHCO3 (0.34 g, 4.0 mmol) in 5 mL of Et2O.
The mixture was heated for 2 h on a water bath. The precipitate
was filtered off and the upper layer was washed with water and
dried with Na2SO4. The solvents were evaporated in vacuo. Fracꢀ
tional crystallization from hot EtOH and subsequent recrystalliꢀ
zation from Et2O gave 1.40 g (78.6%) of compound 1 with Тi
108—110 °C. Found (%): C, 72.70; H, 7.75; N, 3.20; Si, 6.78.
C52H68N2OSi2. Calculated (%): C, 72.90; H, 7.24; N, 3.27; Si,
6.54. 1H (δ: 0.02 (s, 6 H, MeSi); 0.48 (m, 2 H, CH2Si); 1.28 (m,
12 H, CH2CH2CH2); 1.39 (quint., 2 H, CH2CH2CH2, 3J =
7.6 Hz); 1.76 (quint, 2 H, C(O)CH2CH2, J = 7.6 Hz); 2.55 (t,
2 H, C(O)CH2CH2, 3J = 7.6 Hz); 7.15 (d, 2 H, CHCCN,
The results of Xꢀray diffraction measurements may
imply two variants of molecular packing for compound 2
in the SmA phase. First, with known interlayer spacing
calculated from the angle position of the smallꢀangle reꢀ
flection (d = 28.8 Å) and the length of the mesogenic
group (L = 27.8 Å), one can construct the model of
molecular packing with full overlap of the mesogenic
groups (Fig. 9, a). However, within the bounds of this
model, it is difficult to interpret a number of features
inherent in the Xꢀray diffraction patterns of compound 2
in the SmA phase, in particular, the complex pattern of
amorphous scattering and the negative gradient of the
d1(T ) dependence. It follows from Xꢀray diffraction data
that the layer packing with d = 2d002 = 57.44 Å shown in
Fig. 9, b is most probable for compound 2. Indeed, the
presence of amorphous diffraction in the Xꢀray diffracꢀ
tion pattern caused by scattering on the siloxane rings
attests to an increase in the electron density in the center
of the layer. This should result in a decrease in the intenꢀ
sity of odd reflection orders responsible for interlayer peꢀ
riodicity. Therefore, an index of 002 should be ascribed to
the registered interlayer reflection with 2θ = 3.07°, asꢀ
suming that the <001> direction coincides with the norꢀ
mal to the plane of the layer.
The presence of these features in the Xꢀray diffracꢀ
tion characteristics in the case of compound 2 and their
lack for compound 1 is due to a substantial increase in the
volume fraction of the siloxane moiety upon replacement
of the linear central fragment by a cyclic one. The calcuꢀ
lation showed that the ratios of the sums of the increꢀ
ments of the van der Waals volumes of atoms incorporated
in the siloxane and mesogenic fragments, Σ∆ViSi/Σ∆Vim
are 178.3/689.4 ≈ 0.26 and 671.2/689.4 ≈ 0.97 for comꢀ
pounds 1 and 2, respectively.11
3
C6H4CN, J = 8.4 Hz); 7.53 (d, 2 H, CHCHCCN, C6H4CN,
3J = 8.4 Hz); 7.61 (d, 2 H, CHCHCO, J = 8.4 Hz); 7.68 (d,
3
2 H, CHCHCO, C6H4O, 3J = 8.4 Hz). 29Si NMR, δ: 7.15
(s, CH2SiMe2O).
2,8ꢀBis[10ꢀ(4´ꢀcyanobiphenylꢀ4ꢀyloxycarbonyl)decyl(diꢀ
methyl)silyloxy]ꢀ2,4,4,6,6,8,10,10,12,12ꢀdecamethylcyclohexaꢀ
siloxane (2). A solution of chlorosilane 4 (0.16 g, 3.58 mmol) in
2 mL of toluene was placed into an argonꢀfilled flask equipped
with a reflux condenser, a dropping funnel, and a thermometer.
At 20 °C, a mixture of cyclohexasiloxane 5 (0.06 g, 0.145 mmol)
and 0.4 mL of Et3N in 6 mL of toluene was added from a
dropping funnel with stirring over a period of 0.5 h and the
resulting mixture was heated for 12 h at 50 °C. The precipitate
was filtered off, the solution was washed many times with water
and dried with CаCl2, and the solvent was evaporated. The
residue was purified on a column with silica gel (elution with
toluene—acetone, 5 : 1) to give 0.06 g (32%) of compound 2
with Тi 87—89 °C. Found (%): C, 57.60; H, 7.58; N, 2.05;
Si, 17.61. C62H98N2O12Si8. Calculated (%): C, 57.78; H, 7.65;
N, 2.17; Si, 17.43. H NMR, δ: 0.02, 0.04 (both s, 3 H each,
cis and trans MeSiO3); 0.06 (s, 24 H, Me2SiO2); 0.09 (s, 6 H,
CH2(CH3)2SiO); 0.51 (m, 2 H, CH2Si); 1.28 (m, 12 H,
CH2CH2CH2); 1.40 (quint, 2 H, CH2CH2CH2, J = 7.6 Hz);
1.76 (quint, 2 H, C(O)CH2CH2, J = 7.6 Hz); 2.56 (t, 2 H,
C(O)CH2CH2, 3J = 7.6 Hz); 7.16 (d, 2 H, CHCCN, C6H4CN,
3J = 8.4 Hz); 7.55 (d, 2 H, CHCHCCN, C6H4CN, 3J =
8.4 Hz); 7.64 (d, 2 H, CHCHCO, 3J = 8.4 Hz); 7.71 (d,
2 H, CHCHCO, C6H4, 3J = 8.4 Hz). 29Si NMR, δ: 7.92
Thus, in relation to two liquid crystalline organosilicon
compounds with linear and cyclic siloxane centers with
the predominant transꢀposition of the terminal cyanoꢀ
biphenylyl mesogenic groups connected to the core by an
aliphatic (CH2)n spacer (n = 10), it was shown that the
type of packing in the LC state depends on the structure
of the siloxane core. The cyclosiloxane core stabilizes the
layer type of packing in the LC state, while the linear core
in the absence of a chiral center in the mesogenic group
creates conditions for the formation of the SmC chiral
phase with a maximum interlayer distance in the region of
1
3
the SmA
SmC transition. Irrespective of the structure
of the siloxane center, the synthesized liquidꢀcrystalline
methylsiloxanes are characterized by a negative gradient
of the temperature dependence of the interlayer spacing
in the SmA phase.

1620
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 7, July, 2003
Makarova et al.
(s, trans CH2SiMe2O); 7.27 (s, cis CH2SiMe2O) (intensity
ratio, trans : cis ≈ 3 : 1); –22.26 (s, Me2SiO2); –66.47 (s, trans
MeSiO3); –67.73 (s, cis MeSiO3) (intensity ratio,
trans : cis ≈ 3 : 1)).
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 01ꢀ03ꢀ
32585).
(4´ꢀCyanobiphenylꢀ4´ꢀyl)undecꢀ10ꢀenoate (3) was prepared
by a known procedure5 by acylation of 4ꢀcyanobiphenylꢀ4ꢀol
with undecꢀ10ꢀenoyl chloride (m.p. 49.5 °C)5 in dry THF in the
presence of Et3N. The yield of compound 3 was 80% after two
recrystallizations from EtOH, m.p. 49.5 °C; the temperaꢀ
ture of the nematic phase (N)→isotropic melt (I) transition,
TN→I = 75 °C.
References
1. Side Chain Liquid Crystal Polymers, Ed. C. B. McArdle,
Chapman and Hall, New York, 1989.
2. A. Kaeding and P. Zugenmaier, Liq. Cryst., 1998, 25, 449.
3. S. Aquilera and L. Bernal, Polymer Bull., 1984, 12, 383.
4. H. Poths, E. Wischerhoff, R. Zentel, A. Schönfeld, G. Henn,
and F. Kremer, Liq. Cryst., 1995, 18, 811.
5. B. Krucke, M. Schlossarek, and H. Zaschke, Acta Polymer.,
1988, 39, 607.
6. N. N. Makarova and B. D Lavrukhin, Izv. Akad. Nauk SSR,
Ser. Khim., 1985, 1114 [Bull. Acad. Sci. USSR, Div. Chem.
Sci., 1985, 34, 1017 (Engl. Transl.)].
7. B. D. Lavrukhin, N. N. Makarova, and I. M. Petrova, Izv.
Akad. Nauk, Ser. Khim., 1993, 1460 [Russ. Chem. Bull., 1993,
42 (Engl. Transl.)].
8. S. G. Kostromin, and V. P. Shibaev, Vysokomolekulyar.
soedineniya, Ser. A, 1999, 41, 1854 [Polym. Sci., Ser. A,
1999, 41 (Engl. Transl.)].
9. S. G. Kostromin, V. V. Sinitsyn, R. V. Tal´roze, and V. P.
Shibaev, Vysokomolekulyar. soedineniya, Ser. A, 1984, 26,
335 [Polym. Sci. USSR, Ser. A, 1984, 26 (Engl. Transl.)].
4´ꢀCyanobiphenylꢀ4ꢀyl 11ꢀ(dimethylchlorosilyl)undecanoꢀ
ate (4). Ether 3 (3.5 g, 9.7 mmol), dimethylchlorosilane
(2.2 mL, 10.0 mmol), and the Carsted catalyst РCO72
(Aldrich) (3 µL) were placed into an argonꢀfilled tube
equipped with a magnetic stirrer and a reflux condenser.
1
The course of the reaction was monitored by H NMR specꢀ
troscopy. The reaction mixture was heated on a water bath
for 9 h at 60 °C and evacuated for 4 h at 3 Torr to give 4.4 g
(95.0%) of crystalline compound 4, Тi 80 °C. Found (%):
C, 68.20; H, 7.45; N, 2.90; Cl, 7.60; Si, 6.40. C26H34NClO2Si.
Calculated (%): C, 68.46; H, 7.51; N, 3.07; Cl, 7.78; Si, 6.14.
IR, ν/cm–1: 725, 792, 833, 923, 1073, 1140, 1170, 1210, 1254,
1495, 1565, 1608, 1759. 1H NMR, δ: 0.38 (s, 6 H, MeSi);
0.79 (m, 2 H, CH2Si); 1.30 (m, 12 H, CH2CH2CH2); 1.39
(quint, 2 H, CH2CH2CH2, 3J = 7.6 Hz); 1.76 (quint, 2 H,
3
C(O)CH2CH2CH2, J = 7.6 Hz); 2.56 (t, 2 H, C(O)CH2CH2,
3
3J = 7.6 Hz), 7.17 (d, 2 H, CHCCN, C6H4CN, J = 8.4 Hz);
7.64 (d, 2 H, CHCHCO, J = 8.4 Hz); 7.70 (d, 2 H, CHCHCO,
3
C6H4O, J = 8.4 Hz).
transꢀ2,8ꢀDihydroxyꢀ2,4,4,6,6,8,10,10,12,12ꢀdecamethylꢀ
cyclohexasiloxane (5) was synthesized by a known procedure,6
m.p. 97—98 °C.
Received December 4, 2002
in revised form February 17, 2003