Structure of carbosilane amphiphilic liquid-crystalline codendrimers in bulk and in thin (Langmuir) films

Article abstract of DOI:10.1007/s11172-008-0285-3

Amphiphilic carbosilane liquid-crystalline codendrimers with terminal mesogenic butoxybenzoate and phenolic groups have been synthesized for the first time. The structures and compositions of the synthesized codendrimers were characterized by NMR spectros

Full text of DOI:10.1007/s11172-008-0285-3

Russian Chemical Bulletin, International Edition, Vol. 57, No. 10, pp. 2101—2110, October, 2008
2101
Structure of carbosilane amphiphilic liquidꢀcrystalline
codendrimers in bulk and in thin (Langmuir) films
I. D. Leshchiner,a E. V. Agina,a N. I. Boiko,a R. Richardson,b and V. P. Shibaeva
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
1 Leninskie gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 939 0174. Eꢀmail: igleshch@yahoo.com
bH. H. Wills Physics Laboratory, University of Bristol,
Tyndall av., Bristol BS8 1TL, United Kingdom
Amphiphilic carbosilane liquidꢀcrystalline codendrimers with terminal mesogenic butoxyꢀ
benzoate and phenolic groups have been synthesized for the first time. The structures and
compositions of the synthesized codendrimers were characterized by NMR spectroscopy. The
data from polarization optical microscopy, differential scanning calorimetry, and smallꢀangle
Xꢀray scattering demonstrated that all codendrimers possessed mesomorphic properties. They
form thin (Langmuir) films at the water—air interface. The surface pressure—surface area
isotherms were plotted. The Langmuir—Blodgett films of different thicknesses were obtained
by the vertical dipping method on the solid substrate. The film structures were studied by
grazing incidence Xꢀray diffraction analysis.
Key words: dendrimers, codendrimers, carbosilane, liquidꢀcrystalline, amphiphilic,
Langmuir—Blodgett films.
The studies of liquidꢀcrystalline (LC) dendrimers had
long ago attracted attention of researchers working in the
areas of both highꢀmolecularꢀweight compounds and liquid
crystals.1—5 Unusual molecular topology of these systems
that are prone to microsegregation and selfꢀassembling
with the formation of a complicated hierarchy of supramoꢀ
lecular structures evoked increased interest in studying
the structure formation processes of these compounds in
dilute solutions6 and in the solid phase.7 Undoubtedly,
substantial information on the structure of LC dendrimers
could be obtained by the study of their thin films prepared
by the Langmuir—Blodgett method (LB films).
However, to use this procedure, one needs, as a rule,
amphiphilic molecules capable of specific orientation on
the water surface with the polar groups arranged in the
aqueous phase and nonpolar groups, in the organic phase.
Carbosilane dendrimers, which have been studied in deꢀ
tail in our previous works,1,2,7 do not meet, unfortunately,
these requirements. Therefore, we concentrated our
attention on the synthesis of amphiphilic carbosilane LC
codendrimers of the first, third, and fifth generations
containing different ratios of hydrophilic (phenolic YOH)
and hydrophobic (butoxybenzoate, Y´OBu) mesogenic
groups (Fig. 1).
the carbosilane matrix through the aliphatic spacers conꢀ
sisting of ten methylene units.
It should be mentioned that the number of previously
synthesized and studied codendrimers is rather small,
although many LC dendrimers were described.8,9
The following tasks were set in the present work:
(1) to develop a method for the synthesis of the LC
codendrimers based on the carbosilane dendritic matrix;
(2) to study the influence of the composition and genꢀ
eration number of the synthesized codendrimers on the
formation of the LC structures;
(3) to reveal the possibility of formation of the thin LB
films from the synthesized LC codendrimers and to study
their structures.
Results and Discussion
Synthesis of codendrimers. We have developed a genꢀ
eral approach to the synthesis of amphiphilic carbosilane
LC codendrimers, which includes the following main
stages:
(1) synthesis of the reactive component (Scheme 1)
containing the terminal reactive Si—H group, an aliphatic
spacer, and a protected ester of paraꢀhydroxybenzoic acid;
(2) attachment of the synthesized protected fragment
to the carbosilane dendritic matrix with the terminal allyl
groups followed by removal of methoxycarbonyl protectꢀ
ing groups (Scheme 2);
As can be seen from Fig. 1, a dendrite molecule with
random distribution of mesogenic and phenolic terminal
fragments, in essence, is a biphilic codendrimer in which
heterogeneous terminal groups are chemically bound to
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2063—2072, October, 2008.
1066ꢀ5285/08/5710ꢀ2101 © 2008 Springer Science+Business Media, Inc.

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Leshchiner et al.
Gꢀ5ꢀ(Y´OBu)x(YOH)128–x
Gꢀ3ꢀ(Y´OBu)x(YOH)32–x
Gꢀ1ꢀ(Y´OBu)x(YOH)8–x
x = 96, 64, 32
x = 24, 16
x = 6, 4
R = YOH =
;
R´ = Y´OBu =
Fig. 1. Objects of the study: amphiphilic carbosilane codendrimers with terminal butoxyphenylbenzoate and phenolic groups.
(3) synthesis of the codendrimer with the random disꢀ
tribution of phenolic and mesogenic terminal groups.
The reactive component was synthesized according to
a known procedure10,11,12 (Scheme 1).
It was necessary to protect the initial phenolic group
for carrying out consecutive reactions, especially the
hydrosilylation reaction, which does not occur in the presꢀ
ence of the phenolic group. The acid was esterified with a
higher ωꢀunsaturated alcohol to facilitate mesophase forꢀ
mation, and a hydrodisiloxane fragment with the terminal
functional Si—H group capable of reacting with the “surꢀ
face” groups of dendritic matrices was formed. Then the
synthesized derivative was attached to the terminal allyl
groups of the carbosilane matrices of different generaꢀ
tions, and finally the protecting groups were removed
(Scheme 2).
The codendrimers with the random distribution of the
phenolic and mesogenic groups with different composiꢀ
Scheme 1

Liquidꢀcrystalline amphiphilic codendrimers
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 10, October, 2008
2103
Scheme 2
BuOC6H4COCl
DM is a dendritic matrix
Y =
,
Y´ =
Table 1. Experimental and calculated compositions of the synꢀ
thesized codendrimers
tion were synthesized from the corresponding carbosilane
dendrimers with the terminal phenolic groups of the genꢀ
eral formula Gꢀn(YOH)m by reaction with the stoichioꢀ
metric amount of paraꢀbutoxybenzoyl chloride (see
Scheme 2). The reaction was carried out in anhydrous
THF in the presence of triethylamine, and the target
compounds were isolated by preparative GPC. Random
codendrimer Gꢀ5ꢀY´OBu(75) (Table 1) was synthesized
by hydrosilylation using a mixture of mesogenic and proꢀ
tected silanes taken in the corresponding ratio, followed
by purification from lowꢀmolecularꢀweight admixtures,
deprotection, and repeated purification by GPC. The
Codendrimer
Formula
α* (%)
I
II
Gꢀ1ꢀY´OBu(50)
Gꢀ1ꢀY´OBu(75)
Gꢀ3ꢀY´OBu(50)
Gꢀ3ꢀY´OBu(75)
Gꢀ5ꢀY´OBu(25)
Gꢀ5ꢀY´OBu(50)
Gꢀ5ꢀY´OBu(75)
Gꢀ1ꢀ(Y´OBu)4(YOH)4
Gꢀ1ꢀ(Y´OBu)6(YOH)2
Gꢀ3ꢀ(Y´OBu)16(YOH)16
Gꢀ3ꢀ(Y´OBu)24(YOH)8
Gꢀ5ꢀ(Y´OBu)32(YOH)96
Gꢀ5ꢀ(Y´OBu)64(YOH)64
Gꢀ5ꢀ(Y´OBu)96(YOH)32
50
75
50
75
25
50
75
47
78.5
47
75
24.5
50.5
75
* α is the degree of substitution of R´ for R (see Fig. 1); I is
calculation, and II is experimental.
composition of the synthesized codendrimers was deterꢀ
mined from the 1Н NMR spectra by calculating the ratio
of integral intensities of signals for the protons correꢀ
sponding to the substituted and unsubstituted phenolic
groups (Fig. 2). The experimentally calculated degrees of
substitution were very close to the stoichiometrically speciꢀ
fied values (see Table 1).
The individual character and purity of all synthesized
dendrimers were confirmed by GPC, and the structures
were determined by 1Н NMR spectroscopy.
0.39 (I)
Phase behavior. The phase behavior of the synthesized
codendrimers was studied by differential scanning caloꢀ
rimetry (DSC) (Fig. 3), polarization optical microscopy
(POM), and Xꢀray diffraction analysis. It should be noted
that the phase behavior of the codendrimers of the lower
(first, third) and fifth generations differed substantially.
The phase behavior of the codendrimers of the first and
third generations was the same as regards the number and
character of the phases, and only the enthalpies and temꢀ
0.38 (II)
0.40 (II)
1, 3
80
5
2
4 6
75
70
65
δ
Fig. 2. Fragment of the 1H NMR spectrum of codendrimer
Gꢀ3ꢀY´OBu(50).

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Leshchiner et al.
I•10–5 (arb. units)
10.0
a
8.0
6.0
4.0
2.0
b
d
c
b
a
–50
0
50
50
T/°C
1
2
Fig. 3. DSC curves for codendrimers Gꢀ1ꢀY´OBu(75) (а) and
Gꢀ3ꢀY´OBu(75) (b).
0.1
0.2
0.3
0.4
0.5
0.6
0.7 Q/Å–1
Fig. 4. Smallꢀangle Xꢀray scattering patterns for codendrimer
Gꢀ3ꢀY´OBu(75) at 20 (a), 25 (b), 35 (c), and 40 °C (d).
peratures of phase transitions were different (Table 2).
The DSC curves for codendrimers Gꢀ1ꢀY´OBu(75) and
Gꢀ3ꢀY´OBu(75) (see Fig. 3) exhibit two endothermic tranꢀ
sitions corresponding to the consecutive melting of two
lowꢀtemperature crystalline phases in the temperature
interval from 0 to 25 °C. The comparison of the phase
behavior of the codendrimers with that of the homodenꢀ
drimer bearing the butoxyphenylbenzoate mesogenic
groups13 suggests that the second transition corresponds
to melting of the butoxybenzoate domains, because the
temperatures and heats of transitions of the homoꢀ and
codendrimers are close (see Table 2). The codendrimer
differs from the homodendrimer only in the presence of
some number of peripheral phenolic groups, and the first
of the melting transitions (near 10 °C) is absent in the
DSC curve of the homodendrimer. Therefore, the first
transition can be ascribed to the melting of the phenolic
domains. At temperatures above 25 °C the smectic A phase
(SmA) is observed in the codendrimers, which is conꢀ
firmed by the characteristic fanꢀlike structure seen with a
polarization microscope. However, the interval of the
existence of the LC phase for the first generation is someꢀ
what narrower than that for the third generation, which
was also observed for the homodendrimers as the generaꢀ
tion number decreased.13
The study of the phase behavior of codendrimers
Gꢀ1ꢀY´OBu(50) and Gꢀ3ꢀY´OBu(50) showed that a deꢀ
crease in the number of mesogenic groups in the molecule
resulted in the gradual degeneration of the phase transiꢀ
tions. The region of existence of the crystalline and LC
phases of codendrimer Gꢀ1ꢀY´OBu(50) shifts to lower
temperatures and the enthalpies of melting do not exceed
1 J g–1 (see Table 2). It is known that the enthalpies
of transitions decrease with an increase in the number of
generation of the LC dendrimers13—15 and, hence, no sigꢀ
nificant transitions were detected for the codendrimer of
a higher generation (Gꢀ3ꢀY´OBu(50)). In addition, the
low temperatures of phase existence do not allow one to
study the textures with a polarization optical microscope.
The Xꢀray studies were carried out to confirm that the
codendrimers formed the smectic mesophase (Fig. 4).
The smallꢀangle diffraction patterns of nonoriented
codendrimer Gꢀ3ꢀY´OBu(75) exhibit the peaks correꢀ
sponding to the first and second reflection orders from
the smectic layers at Q1 = 0.127 Å–1 and Q2 = 0.253 Å–1
(peaks 1 and 2). The calculated interplanar spacing for
this codendrimer at room temperature is 50 Å. Based on
these data and calculated lengths of the lateral groups
(Y´OBu = 29 Å, YOH = 19 Å, see Fig. 1), one can
propose the molecular packing of the codendrimer in
the SmA phase presented in Fig. 5. The presence of the
Table 2. Temperatures and enthalpies of the phase transitions of
the codendrimers based on the data from POM, DSC, and Xꢀray
diffraction analysis
Codendrimer
Phase transitions, T/°С
(E/J g–1
)
Gꢀ1ꢀY´OBu(100)*
Gꢀ1ꢀY´OBu(75)
K 35.3 (16.5) SmC 101.6 (11.3) I
К1 24.0 (2.8) K2 27.6 (11.2)
SmA 55.0 (5.2) I
Gꢀ1ꢀY´OBu(50)
Gꢀ3ꢀY´OBu(100)*
Gꢀ3ꢀY´OBu(75)
K6 (0.8) SmА 14.2 (0.9) I
К 20.0 (8.2) SmC 108.3 (7.7) I
К1 10.1 (4.7) K2 25.7 (8.9)
SmA 64.1 (4.9) I
Gꢀ5ꢀY´OBu(100)*
К 22.7 (5.8) Colrec 90
Colhd 124.3 (6.3) I
К 30 Col 95 I
К 30 Col 85 I
К 30 Col 59 I
Gꢀ5ꢀY´OBu(75)
Gꢀ5ꢀY´OBu(50)
Gꢀ5ꢀY´OBu(25)
Note. K is the crystalline phase, SmC is the smectic C mesophase,
Colrec is the orthogonal columnar mesophase, Colhd is the hexꢀ
agonal columnar mesophase, and I is the isotropic melt. The
enthalpies of transition (E) are given in parentheses.
* Data for the phenylbenzoate homodendrimers.13

Liquidꢀcrystalline amphiphilic codendrimers
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 10, October, 2008
2105
T/ °C
140
Dendritic matrix
120
100
80
60
40
20
1
2
3
0
25
50
75
100 c (mol.%)
Fig. 6. Dependences of the temperatures of transitions from
the LC phase to the isotropic state on the composition of the
codendrimers: 1, Gꢀ5; 2, Gꢀ3; 3, Gꢀ1 (c is relative concentration
of phenolic groups).
smectic phase for codendrimer Gꢀ1ꢀY´OBu(75), whose
Xꢀray pattern contains two reflections at Q1 = 0.140 Å–1
and Q2 = 0.280 Å–1, is confirmed analogously.
The substantial change in the phase behavior is
observed for the codendrimers of the fifth generation.
According to the DSC and POM data, codendrimers
Gꢀ5ꢀY´OBu(25), Gꢀ5ꢀY´OBu(50), and Gꢀ5ꢀY´OBu(75)
presumably form the columnar phase. To determine the
character of the structures formed, we intend to perform
further detailed Xꢀray studies of oriented samples of the
dendrimers.
Dendritic matrix
Let us consider the thermal properties of the phases of
the codendrimers synthesized. As can be seen from Fig. 6
presenting the temperatures of transitions from the LC
phase to the isotropic state, the stability of the LC phase
increases with an increase in the generation number (i.e.,
molecular weight), which is consistent with published data
for homodendrimers.13 The same trend of the transition
temperatures is observed with an increase in the number
of mesogenic groups in the codendrimer. The increase in
the overall number of mesogenic groups leads to a broader
interval of existence of both the smectic (first and third
generations) and columnar (fifth generation) mesophases.
Studies of the Langmuir and Langmuir—Blodgett films.
First let us consider the behavior of the synthesized
amphiphilic statistical codendrimers in monolayers at the
water—air interface, and then we will consider their beꢀ
havior in monoꢀ and polylayers on a silicon support.
It should be noted that stable films formed for all
compositions and all generations of the codendrimers
under study. However, distinctions in the behavior of the
dendrimers of different generations, viz., different hysterꢀ
esis effects, in the compression—decompression process
Dendritic matrix
Fig. 5. Scheme of the proposed packing of LC codendrimer
Gꢀ3ꢀY´OBu(75) in the smectic A mesophase.

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Leshchiner et al.
Ps/mN•m–1
17
16
15
14
13
5
12
11
10
9
4
8
7
6
3
5
4
3
2
1
2
1
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 S/Å–1
0
Fig. 7. Surface pressure—surface area isotherm for codenrimer Gꢀ3ꢀY´OBu(75) at 25 °С; S is the surface area per molecule.
should be emphasized. They indicate the different nature
of the processes that occur at the interface with an inꢀ
crease in the rigidity of the matrix core.
a
Let us consider the behavior of the lowerꢀgeneration
codendrimers using the Gꢀ3ꢀY´OBu(75) codendrimer as
an example. The compression isotherm of the codendrimer
Gꢀ3ꢀY´OBu(75) film in the coordinates surface pressure—
surface area is shown in Fig. 7. Five regions (1–5) are
distinctly seen on the curve. The first region corresponds
to the “twoꢀdimensional gas”: the dendrimer molecules
are remote from each other and, probably, they lie flat on
the interface with no interaction between them. Thereꢀ
fore, a decrease in the film surface area does not increase
the surface pressure. The second region corresponds to
the “twoꢀdimensional liquid,” where the dendrimer molꢀ
ecules still lie flat, but the interaction between them
increases the surface pressure upon compression of the
film (elastic deformation). The “phase transition” occurs,
most likely, in the third region: the shape of the dendrimer
changes: its molecules gradually acquire the vertical oriꢀ
entation. In this case, the hydrophilic phenolic groups are
immersed into the subphase (water), and the hydrophobic
phenyl benzoate groups remain on the surface. In the
fourth region, the surface pressure increases sharply with
a small decrease in the film surface area, which suggests
the formation of a “twoꢀdimensional solid” and the end of
orientation of the surface groups of the dendritic molecule.
Finally, the film collapses in the fifth region. The approxiꢀ
b
Fig. 8. The Brewster angle microscopic image of the film of
codendrimer Gꢀ3ꢀY´OBu(75) under surface pressures of 4 (a)
and 6 mN m–1 (b). Lighter areas correspond to the vertical
orientation of the dendrimer molecules.
mation of the isotherm in the fourth region to the zero value
of the surface pressure allows one to calculate the surface
area occupied by one molecule in the densest packing of

Liquidꢀcrystalline amphiphilic codendrimers
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 10, October, 2008
2107
Ps/mN m–1
30
this transition is jumpwise, the molecules are rapidly oriꢀ
ented, and cavities of the unfilled surface are formed upon
the rearrangement.
a
25
20
The behavior of the codendrimers of the fifth generaꢀ
tion was virtually the same, but differed basically from
that of the codendrimers of the lower generations. This
distinction is well observed when the hysteresis in the
compression—decompression curves is considered (Fig. 9).
As can be seen from the data presented (see Fig. 9, a), the
decompression curve for codendrimer Gꢀ5ꢀY´OBu(25)
passes along the same route as the compression isotherm
passes and demonstrates only small hysteresis. It can be
assumed that no rearrangement of the molecules occurs
during compression in this case. At the same time,
codendrimer Gꢀ3ꢀY´OBu(75) exhibits considerable hysꢀ
teresis related to the rearrangement of the molecules from
the vertically oriented state back to the “flat” conformaꢀ
tion (see Fig. 9, b).
The monolayer formation by the fifth generation
codendrimers suggests that no rearrangement of the hydroꢀ
phobic and hydrophilic groups occurs within the molꢀ
ecule. The poor deformability of the carbosilane core of
the fifth generation codendrimer and steric hindrance on
the surface of the molecule do not allow the terminal
groups to move freely in space, which results only in the
gradual compaction of molecules in the monolayer and a
smooth growth of the curve up to the film collapse. In this
case, the molecules behave as “elastic balls” (Fig. 10).
The prepared films were transferred by the vertical
dipping method onto the solid support (a silicon plate),
thicknesses of 2, 10, 14, and 24 layers were obtained. The
films were transferred under a constant pressure correꢀ
sponding to the densest packing of the dendritic molꢀ
ecules in the layer. It was shown that the coefficient of
transfer of the substance to the support is inversely proꢀ
portional to the number of transferred layers and varies
from 85% for the bilayer film to 60% for the 24ꢀlayer film.
The structure of the films obtained on the support was
studied by the grazing incidence Xꢀray diffraction method.
The diffraction patterns were primarily recorded at the
grazing incidence angle varied in such a way that the Q
vector was always perpendicular to the support surface
and the reflection (record) angle remained unchanged.
The Q value relates to the incidence angle θ and waveꢀ
length λ as follows: Q = 4πsinθ/λ. The formation of lamelꢀ
lar structures was observed only for the codendrimers
1
15
2
10
5
0
6000 S/Å–1
1000
2000
3000
4000
5000
Ps/mN m–1
b
12
10
8
1
6
4
2
2
0
500
1000
1500 2000 2500 3000
S/Å–1
Fig. 9. Hysteresis during compression/decompression of the monoꢀ
layer of codendrimers Gꢀ5ꢀY´OBu(25) (a) and Gꢀ3ꢀY´OBu(75) (b):
1, compression; 2, decompression.
dendrimers in the film. For codendrimer Gꢀ3ꢀY´OBu(75)
this value is 470 Å2 per molecule, which corresponds to
the theoretical calculations (one mesogenic group occuꢀ
pies a surface area of 20 Å2, and the number of hydrophoꢀ
bic groups in a molecule is 24, i.e., the surface area occuꢀ
pied by a molecule should be 480 Å2).
This behavior of the monolayer was confirmed using
the Brewster angle microscopy (Fig. 8). Rather homogeꢀ
neous film experiences a sharp change in the structure
upon the formation of a new phase, during which the
dendrimer molecules are oriented vertically. As can be
seen from Fig. 8, on going from region 2 (the dendrimer
molecules lie flat) to region 3 (the molecules transit to the
vertical position), light islands corresponding to the vertiꢀ
cally oriented molecules are formed. It is noteworthy that
1 mN m–1
5 mN m–1
20 mN m–1
Fig. 10. Scheme of molecular packing of the fifth generation codendrimers in the monolayer with an increase in the surface pressure.

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Leshchiner et al.
a
b
I (arb. units)
I (arb. units)
8000
200
150
100
50
6000
4000
2000
0
Q/Å–1
–2
0
2
4
θ/rad
0.1
0.2
0.3
0.4
Fig. 11. Diffraction patterns of the 14ꢀlayer film of dendrimer Gꢀ3ꢀY´OBu(75) at the fixed (a) and variable Xꢀray radiation incident
angles (b).
with the 75% substitution of the phenolic groups for the
butoxybenzoate groups (Fig. 11, a). Further the measureꢀ
ments were carried out at a fixed incidence angle to deterꢀ
mine the direction of layer ordering, and then the inciꢀ
dence angle was varied (see Fig. 11, b). The distinct Bragg
peak (1.73°) indicates that the layers formed are parallel
to the support.
The interlayer spacings calculated from the diffraction
patterns for dendrimers Gꢀ1ꢀY´OBu(75) and Gꢀ3ꢀY´OBu(75)
was equal to 47 and 51 Å, respectively, which are someꢀ
what larger than the interlayer distances in the SmA
mesophase for these codendrimers in block.
Experimental
Physicochemical methods of investigation. The 1Н NMR
spectra were recorded on a Bruker WРꢀ250 instrument. Analyꢀ
tical and preparative GPC were carried out on a Knauer
instrument on the Phenomenex column (19Ѕ300 mm) packed
with Ultrastyrogel 1000 Å. The eluent was tetrahydrofuran, and
a Waters Rꢀ410 refractometer and a Knauer UV spectrometer
were used as detectors. The heats of phase transitions were
determined by differential scanning calorimetry using a Mettler
ТАꢀ4000 system. The scanning rate was 10 deg min–1. Optical
studies of the textures were carried out and the temperatures of
phase transitions were determined in crossed polaroids of a
LOMO Rꢀ112 optical polarization microscope equipped with a
heating stage with a Mettler FРꢀ800 microprocessor heating rate
regulator. The Xꢀray diffraction studies of the samples in block
were carried out on a specially designed diffractometer using the
CuKα radiation. The Ni film was used for the radiation
monochromatization, and the scattered radiation was measured
using a twoꢀdimensional detector connected with a computer
for data analysis and collection. The sample—detector distance
was 800 mm.
Thin Langmuir—Blodgett films were studied using a NIMA
Langmuir trough (model 601S) and a NIMA PS4 surface pressure
sensor. The NIMA software was used for the calculation of the
isotherm parameters and transfer coefficients. The films were
studied at the air—water interface, and ultrapure water was used
as the subphase. Water was purified on a Purite Neptune ionꢀ
exchange system. A solution of a codendrimer in chloroform
with a concentration of 1.00 g L–1 was used for film formation.
The rate of film compression was 30 mm min–1. The films were
transferred onto the solid support (silicon plates) by the vertical
dipping method.
The diffraction patterns of other codendrimers exhibit
no reflections, because these codendrimers form, most
likely, structures ordered in the support plane (first genꢀ
eration) or columnar phases (fifth generation).
Thus, we synthesized for the first time the carbosilane
codendrimers with the random distribution of the termiꢀ
nal hydrophilic and hydrophobic groups. The study of
the phase behavior of the codendrimers synthesized
showed that an increase in the generation number of the
codendrimers, regardless of their composition, resulted in
an increase in the isotropization temperatures and qualiꢀ
tative transition from the lamellar to columnar mesoꢀ
phases, whereas a decrease in the overall number of
mesogenic groups in a codendrimer molecule led to the
narrowing of the intervals of liquidꢀcrystalline phase
existence, a decrease in the clearing point, and degeneraꢀ
tion of the phase transitions. The codendrimers syntheꢀ
sized form stable films at the water—air interface and on
the solid support. An increase in the generation number
of the codendrimers changes the mechanism of monoꢀ
layer formation. The data obtained make it possible to
consider the carbosilane codendrimers as promising
materials for the modification of various surfaces.
The films were deposited layer by layer, the surface
pressure was maintained corresponding to the maximum
compressed state of the film (for example in case of
Gꢀ3ꢀY´OBu(75) equal to 0.015 N m–1), and the rate of support
dipping was 14 mm min–1. The thicknesses of the films were
2, 10, 14, and 24 layers.

Liquidꢀcrystalline amphiphilic codendrimers
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 10, October, 2008
2109
The structures of the deposited films were studied by grazing
incidence angle Xꢀray diffraction on an XPERT PRO diffractoꢀ
Dendrimer Gꢀ5ꢀY´OBu(25). The synthesis was carried out
similarly to the procedure for the preparation of compound
Gꢀ3ꢀY´OBu(75) from compound Gꢀ5ꢀ(10ꢀYOH)128 (0.200 g,
0.00292 mmol) and Py (24 mg, 0.280 mmol), which were
dissolved in anhydrous THF (10 mL), and paraꢀbutoxybenzoyl
chloride (63 mg, 0.280 mmol) was added. The product was purified
by preparative GPC. The yield of the chromatographically pure
dendrimer was 138 mg (64%). 1Н NMR (THFꢀd8, 250 MHz), δ:
–0.08 (s, 372 Н); 0.03 (s, 1536 Н); 0.4—0.7 (m, 1264 Н);
1.2—1.4 (m, 2296 Н); 1.67—1.77 (m, 256 Н); 4.05 (t, 64 Н);
4.30 (m, 256 Н); 6.85 (d, 192 Н); 6.95 (d, 64 Н); 7.27 (d, 64 Н);
7.89 (d, 192 Н); 8.06 (d, 64 Н); 8.11 (d, 64 Н).
meter. The range of accessible Q values was 0.07—2.1 Å–1
.
Synthesis of codendrimers. The dendrimers with the phenolic
periphery were synthesized according to a procedure known for
the dendrimers of the first10 and third generations.11,12
1
The Н NMR spectra were similar for all dendrimers (the
only difference being the number of protons) and the assignment
of the signals can be presented as follows, δ: –0.08 (s, Si—CH3
matrix); 0.03 (s, Si—O—Si—CH3); 0.4—0.7 (m, Si—CH2);
1.2—1.4 (m, CH3 of the Bu group); 1.67—1.77 (m, CH2
spacers); 4.05 (t, OCH2 of the Bu group); 4.30 (m, OCH2
of the spacer); 6.85 (d, CH, YOH); 6.95 (d, CH, Y´OBu); 7.27
(d, CH2, YO); 7.89 (d, CH, YOH); 8.06 (d, CH, Y´OBu); 8.11
(d, CH, YO).
Dendrimer Gꢀ3ꢀY´OBu(75). paraꢀButoxybenzoyl chloride
(0.44 mmol, Sigma—Aldrich) was added to a solution of
compound Gꢀ3ꢀ(YOH)32 (0.0178 mmol) (see Scheme 2) and
Et3N (0.44 mmol) in anhydrous THF (10 mL). The reaction
mixture was stirred without cooling for 48 h, then the precipitate
was filtered off, the filtrate was diluted with diethyl ether and
three times washed with water. The organic layer was concenꢀ
trated in vacuo to dryness. The chromatographically pure
dendrimer was isolated by GPC in 58% yield. 1Н NMR (CDCl3,
250 MHz), δ: –0.08 (s, 84 Н); 0.03 (s, 384 Н); 0.4—0.7 (m, 304
Н); 1.2—1.4 (m, 312 Н); 1.67—1.77 (m, 64 Н); 4.05 (t, 48 Н);
4.30 (m, 64 Н); 6.85 (d, 16 Н); 6.95 (d, 48 Н); 7.27 (d, 48 Н);
7.89 (d, 16 Н); 8.06 (d, 48 Н); 8.11 (d, 48 Н).
Dendrimer Gꢀ3ꢀArOBu(50). The synthesis was carried out
similarly to the procedure of the synthesis of compound Gꢀ3ꢀ
ArOBu(75) from Gꢀ3ꢀ(YOH)32 (0.240 g, 0.0142 mmol), Py
(18 mg, 0.228 mmol), and paraꢀbutoxybenzoyl chloride (48 mg,
0.228 mmol). The final purification of the product from
admixtures was carried out by preparative GPC. The yield of the
chromatographically pure dendrimer was 158 mg (56%). 1Н NMR
(CDCl3, 250 MHz), δ: –0.08 (s, 84 Н); 0.03 (s, 384 Н); 0.4—0.7
(m, 304 Н); 1.2—1.4 (m, 568 Н); 1.67—1.77 (m, 64 Н); 4.05
(t, 32 Н); 4.30 (m, 64 Н); 6.85 (d, 32 Н); 6.95 (d, 32 Н); 7.27 (d,
32 Н); 7.89 (d, 32 Н); 8.06 (d, 32 Н); 8.11 (d, 32 Н).
Dendrimer Gꢀ1ꢀY´OBu(75). The synthesis was carried out
similarly to the procedure for the preparation of compound Gꢀ
3ꢀY´OBu(75) from compound Gꢀ1ꢀ(YOH)8 (0.263 g, 0.066
mmol), Py (31.2 mg, 0.396 mmol), and paraꢀbutoxybenzoyl
chloride (84 mg, 0.396 mmol). The product was purified from
admixtures by preparative GPC. The yield of the chromatoꢀ
graphically pure dendrimer was 131 mg (39%). 1Н NMR
(CDCl3, 250 MHz), δ: –0.09 (s, 12 Н); 0.012 (s, 96 Н); 0.55 (m,
64 Н); 1.2—1.4 (m, 136 Н); 1.73 (m, 16 Н); 4.05 (t, 12 Н); 4.27
(m, 16 Н); 6.85 (d, 4 Н); 6.95 (d, 12 Н); 7.27 (d, 12 Н); 7.89 (d,
4 Н); 8.06 (d, 12 Н); 8.11 (d, 12 Н).
Dendrimer Gꢀ5ꢀY´OBu(50). The synthesis was carried out
similarly to the procedure for the preparation of compound Gꢀ
3ꢀY´OBu(75) from compound Gꢀ5ꢀ(YOH)128 (0.130 g, 0.00190
mmol) and Et3N (49.5 mg, 0.490 mmol), which were dissolved
in anhydrous THF (10 mL), and paraꢀbutoxybenzoyl chloride
(24 mg, 0.490 mmol) was added. The product was finally purified
from admixtures by preparative GPC. The yield of the chroꢀ
1
matographically pure dendrimer was 111 mg (74%). Н NMR
(THFꢀd8, 250 MHz), δ: –0.08 (s, 372 Н); 0.03 (s, 1536 Н);
0.4—0.7 (m, 1264 Н); 1.2—1.4 (m, 2296 Н); 1.67—1.77 (m, 256
Н); 4.05 (t, 128 Н); 4.30 (m, 256 Н); 6.85 (d, 128 Н); 6.95 (d,
128 Н); 7.27 (d, 128 Н); 7.89 (d, 128 Н); 8.06 (d, 128 Н); 8.11
(d, 128 Н).
Dendrimer Gꢀ5ꢀY´OBu(75). The reaction mixture conꢀ
sisting of the dendritic carbosilane matrix Gꢀ5ꢀ(CH=CH2)128
(0.100 g, 6.31•10–6 mol), 10ꢀ(1,1,3,3ꢀtetramethyldisiloxanyl)ꢀ
decyl 4ꢀ[(methoxycarbonyl)oxy]benzoate (0.15 g, 0.30•10–3 mol),
4ꢀ{[11ꢀ(1,1,3,3ꢀtetramethyldisiloxanyl)undecyl]oxy}phenyl
4ꢀbutoxybenzoate (0.58 g, 0.91•10–3 mol), a 3% solution (10 μL)
of a Pt complex with divinyltetramethyldisiloxane in xylene
(PCꢀ072), and anhydrous toluene (10 mL) was magnetically
stirred in a closed vessel under argon at 35 °С (in an oil bath) for
72 h. After the cessation of the reaction, the reaction mixture
was passed through silica gel to deactivate the catalyst using
THF as the eluent. Then a 25% aqueous solution of ammonia
(10 mL) was added dropwise on cooling to a solution of the
synthesized compound in an ethanol—THF (1 : 1) system (10 mL).
The reaction mixture was stirred without cooling for 2 h and
then poured into water, and the pH value was brought to 8 with
acetic acid. The resulting suspension was extracted with diethyl
ether three times. The ethereal fraction was washed with water
three times and dried with anhydrous sodium sulfate. The obtained
solution was concentrated in vacuo to dryness. The product was
purified from highꢀmolecularꢀweight admixtures by preparative
GPC. The yield of the chromatographically pure dendrimer was
0.260 g (73%). 1Н NMR (THFꢀd8, 250 MHz), δ: –0.08 (s, 372 Н);
0.03 (s, 1536 Н); 0.4—0.7 (m, 1264 Н); 1.2—1.4 (m, 2296 Н);
1.67—1.77 (m, 256 Н); 4.05 (t, 192 Н); 4.30 (m, 256 Н); 6.85
(d, 64 Н); 6.95 (d, 192 Н); 7.27 (d, 192 Н); 7.89 (d, 64 Н); 8.06
(d, 192 Н); 8.11 (d, 192 Н).
Dendrimer Gꢀ1ꢀY´OBu(50). The synthesis was carried
out similarly to the procedure for the preparation of comꢀ
pound Gꢀ3ꢀY´OBu(75) from compound Gꢀ1ꢀ(YOH)8 (0.100 g,
0.025 mmol), Py (8.1 mg, 0.103 mmol), and paraꢀbutoxybenzoyl
chloride (22 mg, 0.103 mmol). The product was purified from
admixtures by preparative GPC. The yield of the chromatoꢀ
graphically pure dendrimer was 131 mg (39%). 1Н NMR (CDCl3,
250 MHz), δ: –0.09 (s, 12 Н); 0.012 (s, 96 Н); 0.55 (m, 64 Н);
1.2—1.4 (m, 136 Н); 1.73 (m, 16 Н); 4.05 (t, 8 Н); 4.27 (m, 16 Н);
6.85 (d, 8 Н); 6.95 (d, 8 Н); 7.27 (d, 8 Н); 7.89 (d, 8 Н); 8.06 (d,
8 Н); 8.11 (d, 8 Н).
The authors are grateful to A. M. Muzafarov and
E. A. Rebrov (Institute of Synthetic Polymeric Materials,
Russian Academy of Sciences) for the carbosilane denꢀ
drite matrices with terminal allyl groups kindly presented
for the synthesis, as well as to the coworkers of the Instiꢀ
tute of Synthetic Polymeric Materials (Russian Academy
of Sciences) for NMR studies.

2110
Russ.Chem.Bull., Int.Ed., Vol. 57, No. 10, October, 2008
Leshchiner et al.
8. J.ꢀM. Rueff, J. Barbera, B. Donnio, D. Guillon, M. Marcos,
J.ꢀL. Serrano, Macromolecules, 2003, 36, 8368.
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R. Sijbesma, E. W. Meijer, D. Reinhoudt, Langmuir, 2002,
18, 674.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 07ꢀ03ꢀ01089),
European Cooperation in Science and Technology (COST
Program, Chemistry, Grant D35, WG13), and the Counꢀ
cil on Grants at the President of the Russian Federation
(Program for State Support of Leading Scientific Schools
of the Russian Federation, Grant NShꢀ5899.2006.3).
10. N. Boiko, X. Zhu, A. Bobrovsky, V. Shibaev, Chem. Mater.,
2001, 13, 1447.
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R. M. Richardson, Zhidkie kristally i ikh prakticheskoe
ispol´zovanie [Liquid Crystals and Their Application], Izd.
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Received June 14, 2007;
in revised form March 20, 2008