Synthesis and properties of carbosilane dendrimers with perfluorohexyl groups in the outer layer of the molecular structure

Article abstract of DOI:10.1007/s11172-018-2237-x

Branched perfluorohydrosiloxane with CF₃CF₂CF₂C(CF₃)₂(CH₂)₃ groups at the silicon atom was synthesized by a sequence of chemical reactions. The resulting compound was used as a modifying agent for carbosilane dendrimers of the 3rd and 6th generations. Dendrimers with perfluorohexyl terminal groups in surface layer are characterized by a complex of physicochemical methods. It is demonstrated that due to the branching of perfluoroalkyl terminal groups, obtained carbosilane dendrimers are soluble in organic and inorganic media. Differences in the solubility of small and large dendrimers are caused by the formation of the outer fluoride shell of different densities.

Full text of DOI:10.1007/s11172-018-2237-x

1440
Russian Chemical Bulletin, International Edition, Vol. 67, No. 8, pp. 1440—1444, August, 2018
Synthesis and properties of carbosilane dendrimers
with perfluorohexyl groups in the outer layer of the molecular structure
a
b
a
b
a
N. A. Sheremetyeva, O. A. Serenko, E. A. Tatarinova, M. I. Buzin, F. V. Drozdov,
b,c
b,c
a,b
I. V. Elmanovich, M. O. Gallyamov, and A. M. Muzafarov
aN. S. Enikolopov Institute of Synthetic Polymeric Materials, Russian Academy of Sciences,
7
0 ul. Profsoyuznaya, 117393 Moscow, Russian Federation.
Fax: +7 (495) 334 88 47
b
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5085. E-mail: aziz @ispm.ru
c
Faculty of Physics, M. V. Lomonosov Moscow State University,
Build. 2, 1 Leninskie Gory, 119991 Moscow, Russian Federation.
Fax: +7 (495) 932 8820
Branched perfluorohydrosiloxane with CF CF CF C(CF ) (CH ) groups at the silicon
3
2
2
3 2
2 3
atom was synthesized by a sequence of chemical reactions. The resulting compound was used
as a modifying agent for carbosilane dendrimers of the 3rd and 6th generations. Dendrimers
with perfluorohexyl terminal groups in surface layer are characterized by a complex of physico-
chemical methods. It is demonstrated that due to the branching of perfluoroalkyl terminal
groups, obtained carbosilane dendrimers are soluble in organic and inorganic media. Differences
in the solubility of small and large dendrimers are caused by the formation of the outer fluoride
shell of different densities.
Key words: dendrimer, perfluoroalkyl terminal groups, solubility.
Dendrimers is an unique class of polymers that differ
makes it difficult to study their structure and properties,
but also hinders their potential practical application, for
example, as highly effective surface active nanoscale macro-
from other polymeric macromolecules by regular branched
structure and monodisperse nature.1 High density of
branching forces the molecules of the dendritic architec-
ture to adopt three-dimensional globular conformations,
which affects their characteristics. The composition of the
terminal groups of dendrimers has a determining effect on
such physical properties as solubility, glass transition
temperature, packing density of monolayers, ability to
form self-ordered structures, etc.
,2
7
molecule particles. In addition, the solubility of high gen-
eration dendrimers with perfluorinated terminal groups is one
of the conditions for their use for encapsulating of catalysts
8
,9
and chemical reagents in a supercritical carbon dioxide.
We assume that replacing the linear perfluoroalkyl
terminal groups of carbosilane dendrimers by branched
groups with the same number of fluorine atoms will create
a "barrier" for the formation of an ordered interdendritic layer
or lead to the formation of a layer with a less dense struc-
ture. This can promote the solubility of dendrimers of both
low and high generations, at least in fluorinated solvents.
The purpose of this work is to synthesize and study the
properties of carbosilane dendrimers with branched fluoro-
silicon-organic groups in the surface layer of the molecular
structure. A hydrosilylation method using a modifying
agent with a fluorocarbon branched-chain substituent based
on hexafluoropropylene dimers was chosen to produce them.
The introduction of fluorine atoms into the surface
layer of the dendrimer molecular structure promotes an
increase in their hydrophobicity, a change in the friction
coefficient, glass transition temperature, and thermal
3
stability. Most of the work in the field of fluorine-con-
taining carbosilane dendrimers involves the study of ob-
jects containing linear perfluoroalkyl substituents С F
6
13
in the surface layer.4 These first and second genera-
tion dendrimers are highly soluble in perfluorohexane.
However, starting from third generation, they lose their
,5
6
solubility. According to the authors, the reason for this
effect is the formation of an ordered layer of terminal
linear perfluoroalkyl groups, which are rigid rods.
The insolubility of high-generation carbosilane den-
drimers with perfluorinated terminal groups not only
Results and Discussion
A modifying agent, a fluorosilicon compound hav-
ing a branched fluorocarbon substituent С(СF ) —
3
2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1440—1444, August, 2018.
1066-5285/18/6708-1440 © 2018 Springer Science+Business Media, Inc.

Soluble polyfluorinated carbosilane dendrimer
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
1441
Scheme 1
(
(
СF ) —CF was prepared at the first stage of the work
Scheme1).
We used known data on the synthesis of fluorine-
The fluorine-containing carbosilane dendrimer G-4.5F
is a colorless viscous liquid highly soluble in various organic
solvents, such as THF, hexane, diethyl ether, hexafluoro-
benzene, and freons. Dendrimer G-7.5F is a transparent
colorless resinous substance soluble in fluorine-containing
solvents, for example in hexafluorobenzene and fluoroxy-
lol. The composition and structure of fluorine-containing
carbosilane dendrimers are proved by elemental analysis
2
2
3
containing alkylsilanes and siloxanes10 in the preparation
of hydrosiloxane with a perfluorocarbon substituent (com-
pound 3). The synthesis consisted of three subsequent
reactions. The reaction of the original fluorocarbon re-
agent, perfluoro-2-methylpent-2-ene, with allyl bromide in
the presence of cesium fluoride was carried out according to
a known procedure.11 The product, 5,5,6,6,7,7,7-hepta-
fluoro-4,4-bis(trifluoromethyl)hept-1-ene (1), was iso-
lated by distillation at 120 С under atmospheric pressure.
The purity of the main fraction was 98% by GC. The
structure of the obtained product was confirmed by
1
and H NMR spectroscopy.
In view of the specific features associated with the
solubility of the resulting fluorine-containing dendrimers,
the GPC method was not possible for analysis of their
purity. In the case of G-4.5F generation dendrimer, the
analysis was complicated by close refractive indices of
1
20
Н NMR spectroscopy
the system under study (n
= 1.415) and THF eluent
d
2
0
In the next step, the hydrosilylation of polyfluoroalkene
(nd = 1.405). As already noted larger generation den-
drimer (G-7.5F) is soluble only in fluorine-containing
solvents and is insoluble in non-fluorinated organic sol-
vents used as eluent in the GPC method.
1
with chlorodimethylsilane in the presence of Karstedt´s
catalyst was carried out to form the chlorosilyl derivative
(
compound 2) in quantitative yield. The entire reaction
mass was used in the next step of cohydrolysis.
Figure 1 shows the distribution curves for the hydro-
dynamic radii R of the synthesized dendrimers, and Table 1
shows the values of R. Obviously, the R value for the den-
drimer G-7.5F is larger than for the dendrimer of smaller
generation. As it can be seen from Fig. 1, the samples are
Cohydrolysis of compound 2 with chlorodimethyl-
silane was carried out in the presence of pyridine and traces
of water. The resulting hydrosiloxane was isolated by dis-
tillation in vacuo at a temperature of 85 С (35 Torr). The
purity and structure of (5,5,6,6,7,7,7-heptafluoro-4,4-bis
(
trifluoromethyl)heptyl)tetramethylsiloxanehydride (3)
1
was confirmed by GC, Н NMR spectroscopy, and elemen-
tal analysis. The product was a colorless transparent liquid.
Synthesized perfluorohydrosiloxane was used as a mod-
ifying agent for carbosilane dendrimers of the third and
sixth generations with terminal allylic groups. In all cases, the
modification of the outer layer of the molecular structure
of the dendrimers was carried out by hydrosilylation of allyl
groups of macromolecules with an excess of compound 3
in the presence of Karstedt´s catalyst in methyl tert-butyl
ether medium according to the previously described
method.1 The reaction was followed by the disappearance of
f(R)
1.0
1
2
0
.5
2
1
proton signals at a double bond in Н NMR spectra. After
complete conversion of the allyl groups, the products were
separated from the reaction mixture by reprecipitation.
Carbosilane dendrimers of generations 4.5 (G-4.5F) and
0
1
10
100 R/nm
7
.5 (G-7.5F) with branched perfluorohexyl groups in the sur-
Fig. 1. Distribution functions for hydrodynamic radii of den-
drimers G-4.5F (1) and G-7.5F (2).
face layer of the molecular structure were obtained as a result.

1442 Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
Sheremetyeva et al.
Dendrimer G-7.5F
monodisperse and are detected as unassociated objects.
The absence of G-7.5F associates in the hexafluorobenzene
solution is indirectly indicated by the results of viscosi-
metry. The values of the intrinsic viscosity of dendrimers
of two generations are similar (see Table 1).
Thus, the above suggestion that replacing the linear
perfluoroalkyl terminal groups of siloxane dendrimers by
branched groups with the same empirical formula will
promote the solubility of these dendrimers turned out to
be correct. Carbosilane dendrimer G-4.5F with branched
perfluoroalkyl groups is soluble not only in fluorinated
solvents, but also in ordinary organic solvents. Dendrimer
G-7.5F is soluble in fluorine-containing solvents. Differences
in the solubility of the "small" and "large" dendrimers,
given almost complete identity of their chemical composi-
tion, indicate that in the latter case a dense shell of fluoride-
containing fragments is formed. This isolates the inner
sphere of the dendrimer from the solvent. To disorder the
outer layer of the dendrimer molecule, stronger (fluorine-
containing) solvating agent is required.
Table 1. Properties of carbosilane dendrimers G-4.5 and G-7.5
with perfluorinated terminal groups
Characteristics
G-4.5F
G-7.5F
Molecular weight, calculated
Intrinsic viscosity, []/dL g–
Hydrodynamic radius, R/nm
19550
0.035
1.3
158590
0.036
3.6
1
Glass transition temperature, T /С
–76
–75
g
Thermostability, Т5%/С
400/200*
400/210*
The resulting dendrimers are readily soluble in liquid
*
Values of Т5% are given in the numerator under thermal destruc-
2
СО . Figure 2 shows the phase diagrams of G-4.5F—СО2
tion (argon atmosphere), and in the denominator under thermal-
oxidative destruction (air atmosphere).
and G-7.5F—СО systems for the supercritical region of
2
the solvent. Regardless of the generation number of dendri-

Soluble polyfluorinated carbosilane dendrimer
Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
1443
P/atm
Experimental
2
Homogenous area
Perfluoro-2-methylpent-2-ene (98%, CAS 1584-03-8, PiM-
invest, Russia) was used for synthesis.
2
00
60
1
H NMR spectra were registered using a Bruker WP-250SY
(
250.13 MHz) spectrometer, solvent was CDCl with addition of
3
hexafluorobenzene, internal standard was tetramethylsilane.
Investigation of dendrimers by dynamic light scattering was
carried out using an ALV/DLS/SLS-5022F Compact Gonio-
meter System (ALV-GmbH, Germany) with a He—Ne-laser
1
1
(
 = 632.8 nm, power 22 mW). All measurements were carried
1
20
out at scattering angle of 90 at 25 С using hexafluorobenzene
Heterogeneous area
as a solvent.
Glass transition temperature (T ) of samples was determined
g
using differential scanning calorimetry with a DSC-822e thermo-
analyzer (Mettler-Toledo, Swiss) at heating rate of 20 deg min–1
.
4
0
50
60
T/С
A temperature corresponding to the inflection point at the stage
Fig. 2. Phase diagrams for systems G-4.5F—СО2 (1) and
of its devitrification was assumed to be T of the sample.
g
G-7.5F—СО (2).
Thermostability of the samples was evaluated from the results
of thermogravimetric analysis. The studies were conducted using
a Derivatograf_К device (МОМ, Hungary) at heating rate of
2
–
1
mers, they are soluble in supercritical СО , with the phase
10 deg min in air and in argon.
2
diagram for the G-7.5F—СО system shifted to higher
Phase diagrams for dendrimer—СО systems were obtained
2
2
by measuring the cloud points of a solution in a variable-volume
pressures relative to the G-4.5F—СО diagram. Con-
2
1
3
reactor. The device for measuring cloud points was a high-
pressure flow reactor equipped with a piston, one outlet of which
was connected to an optical cell manufactured by SITEC, and
the other output was used for regulation and pressure control.
The initial pressure in the optical cell was 400 atm, while the
sequently, the solubility of dendrimer G-7.5F in super-
critical СО is somewhat lower than solubility of G-4.5F,
2
since at the same temperature, a change in the quality of
the solvent by increasing the pressure is required to convert
the G-7.5F—СО system to a homophase state. Thus, even
2
system for both dendrimers was a homophase. After equilibrium
in supercritical СО , the differences due to changes in the
was established, the pressure was reduced at a rate of 0.5 atm s–1
2
density of the shell are also clearly manifested.
for 30 min. The cloud point was determined visually through the
sapphire windows of the optical cell. The measurements were
carried out at various temperatures, the phase diagram was ob-
tained in the "pressure-temperature" coordinates.
The solubility results of dendrimers with branched
perfluoroalkyl groups suggest that the G-7.5F dendrimer
with a dense outer layer is capable of performing the func-
tion of a nanoscale container.
5
,5,6,6,7,7,7-Heptafluoro-4,4-bis(trifluoromethyl)hept-1-ene
(
1). Perfluoro-2-methylpent-2-ene (98%, 169.9 g, 0.6 mol) was
Table 1 shows thermal characteristics of dendrimers
and the surface properties of films based on them. Accord-
ing to the results of the calorimetric study, the modified
carbosilane dendrimers G-4.5F and G-7.5F are amorph-
ous systems with a low glass transition temperature, which
is independent of the generation number. The limit of
thermal stability of dendrimers for both G-4.5F and
G-7.5F is 400 С in an inert medium and 200 С in an
oxidizing atmosphere.
Thus, we have obtained and characterized with the help
of variety of physicochemical methods dendrimers of two
generations (4.5 and 7.5), containing perfluoroalkyl groups
in the surface layer of the molecular structure and soluble
in organic and inorganic media. The branching of per-
fluoroalkyl terminal groups of carbosilane dendrimers is
an effective tool for controlling the solubility of these
dendrimers, both low and high generations. The proposed
approach to the synthesis of high-generation dendrimers
with fluorine-containing terminal groups, soluble in super-
critical carbon dioxide, expands the prospects for their
use, in particular, in the solution of synthetic problems by
the methods of "green chemistry".
added dropwise in argon atmosphere to the mixture of anhydrous
CsF (86.0 g, 0.6 mol) and freshly distilled diglyme (161.5 g,
1
.0 mol). The reaction mixture was heated to 30 С and allyl
bromide (68.5 g, 0.6 mol) was added at 40 С and intensive stir-
ring. After storing at this temperature for 40 h diethyl ether
(250 mL) was added and the mixture was washed with NaCl
solution to remove the main part of diglyme. After storing of the
reaction mixture over Na SO for 8 h and evaporation of di-
2
4
ethyl ether, the reaction mixture was distilled at atmospheric
pressure into several fractions. Product (88 g, 85% yield) was
1
obtained. The purity was 98% (by GC). Н NMR (CDCl ), :
3
2
.95 (m, 2 Н, CH CH=CH ); 5.24 (m, CH CH=CH ); 5.85
2 2 2 2
(
m, 1 Н, CH CH=CH ).
2 2
Chloro(5,5,6,6,7,7,7-heptafluoro-4,4-bis(trifluoromethyl)-
heptyl)dimethylsilane (2). 5,5,6,6,7,7,7-Heptafluoro-4,4-bis(tri-
fluoromethyl)gept-1-ene (40.06 g, 0.111 mol) (1) was added to
Pt-catalyst РС-072 (Karstedt´s catalyst, 80 μL) in inert atmo-
sphere. Then chlorodimethylsilane (33.22 g, 0.351 mol) was
added dropwise to the mixture. The reaction mixture was stored
for 48 h at 40 С. The signals of СН —СН=СН bond practi-
2
2
1
cally disappeared in Н NMR spectra for this time. Complete
reaction mixture was used in the synthesis of hydrosiloxane 3.
(5,5,6,6,7,7,7-Heptafluoro-4,4-bis(trifluoromethyl)heptyl)-
tetramethylsiloxanehydride (3). The water (2 mL, 0.111 mol) in

1444 Russ. Chem. Bull., Int. Ed., Vol. 67, No. 8, August, 2018
Sheremetyeva et al.
4
00 mL of THF was added dropwise to the mixture of chloro-
5,5,6,6,7,7,7-heptafluoro-4,4-bis(trifluoromethyl)heptyl)di-
methylsilane (50.58 g, 0.111 mol) (2), chlorodimethylsilane
01037 А) and Russian Science Foundation (Project
No. 16-13-10521, synthesis of allyl derivatives of carbo-
silane dendrimers).
(
(
(
84.11 g, 0.889 mol), pyridine (136 g, 1.732 mol), and dried THF
100 mL). Formed precipitate was removed by extraction with
References
diethyl ether. Then 35.23 g of product (72%) was obtained by
distillation in vacuo of water jet pump. B.p. 85 С (35—40 Torr),
2
0
nD = 1.3549. Found (%): C, 31.26; H, 3.78; F, 50.25; Si, 11.04.
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1
Calculated (%): C, 31.58; H, 3.87; F, 49.95; Si, 11.36. Н NMR
(
CDCl ), : 0.18 (m, 12 Н, Si(CH ) ); 0.55 (m, 2 Н, CH CH -
3
3 2
2
2
CH Si); 1.7 (m, 2 Н, CH CH CH Si); 2.09 (m, 2 Н, CH CH -
2
2
2
2
2
2
CH Si); 4.65 (m, 1 Н, SiН).
2
6
1
Carbosilane dendrimer with perfluorohexyl groups Si 32F.
Dendrimer Si2932(All) (1.13 g, 0.3 mmol) in dry tert-butyl
methyl ether (8 mL) was added to Pt-catalyst РС-072 (15 μL) in
inert atmosphere. (5,5,6,6,7,7,7-Heptafluoro-4,4-bis(trifluoro-
methyl)heptyl)tetramethylsiloxanehydride (7.2 g, 0.015 mol) (3)
was added to the reaction mixture under stirring. Reaction mix-
ture was kept for 48 h at 40 С and for 72 h at 20 С. Conversion
1
was 98% according to Н NMR data. An isomerization of ~2%
allyl groups occurred during hydrosilylation. The resulting den-
2
0
drimer was fractionated by reprecipitation, nD = 1.4152. Yield
4
.6 g (78%). Found (%): C, 38.44; H, 5.18; F, 38.54; Si, 13.40.
C624H1020F416O32Si93. Calculated (%): C, 38.33; H, 5.22;
1
F, 40.40; Si, 13.36. Н NMR (CDCl ), : –0.9 (m, 84 Н, SiСН );
3
3
0
.05 (m, 384 Н, Si(СН ) ); 0.55 (m, 304 Н, SiCH ); 1.35
3
2
2
(
m, 120 H, CH ); 1.70 (m, 64 Н, CH CH CН Si); 2.15 (m, 64 Н,
2 2 2 2
CH CH CH Si).
2
2
2
5
09
Carbosilane dendrimer with perfluorohexyl groups Si 256F.
Pt-catalyst РС-072 (13 μL) was added in inert atmosphere to
dendrimer Si2532 (All) (1.085 g, 0.0033 mmol) solution in dry
tert-butyl methyl ether (8 mL). Excess of (5,5,6,6,7,7,7-hepta-
fluoro-4,4-bis(trifluoromethyl)heptyl)tetramethylsiloxanehydr-
ide (6.86 g, 0.014 mol) (3) was added to the reaction mixture
under stirring. Reaction mixture was kept for 48 h at 40 С in
sealed flask. After achieving 88% conversion of allyl groups (ac-
56
1
cording to Н NMR) solution was double concentrated and the
catalyst РС-072 (8 μL) was added. The mixture was kept 48 h at
4
5 С. After achieving of total conversion of allyl groups of dendri-
1
mer ( Н NMR spectra), the product was reprecipated four time
from C F into C H OH. 4.3 g (80%) was obtained. Found (%):
6
6
2
5
C, 38.73; H, 5.48; F, 38.23; Si, 13.48. C5104H8412F3328
Calculated (%): C, 38.65; H, 5.30; F, 39.85; Si, 13.47. Н NMR
O
256Si765
.
1
(
CDCl ), : 0.05 (m, 756 Н, SiСН ); 0.20 (m, 3072 Н, Si(СН ) );
3 3 3 2
.70 (m, 2544 Н, SiCH ); 1.45 (m, 1016 H, CH ); 1.80 (m, 512 Н,
2 2
0
CH CH CН Si); 2.30 (m, 512 Н, CH CH CH Si).
2
2
2
2
2
2
The work was financially supported by the Russian
Foundation for Basic Research (Project No. 17-03-
Received February 19, 2018;
accepted May 23, 2018