Synthesis of a 12-membered cyclic siloxane possessing alkoxysilyl groups as a nanobuilding block and its use for preparation of gas permeable membranes

Article abstract of DOI:10.1039/c7ra09380b

A 12-membered cyclic siloxane possessing alkoxysilyl groups was synthesized as a nanobuilding block for siloxane-based materials by the alkoxysilylation of organometallasiloxane containing a 12-membered ring with Si-Me and Si-O^- groups as the side groups. The cyclic structure was retained not only in the hydrolysis and condensation reactions (sol-gel process) of the alkoxysilyl groups but also in the xerogel and membrane preparation processes. The degree of condensation of the xerogel derived from the 12-membered ring siloxane was higher than that derived from alkoxysilane monomers, indicating that the alkoxysilylated cyclic oligosiloxane is useful for controlling siloxane networks. A membrane composed of the cyclic siloxane was prepared by coating the hydrolyzed solution onto a porous alumina tube for evaluating the gas permeation properties. The membrane showed a molecular sieving effect for H₂/SF₆.

Full text of DOI:10.1039/c7ra09380b

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis of a 12-membered cyclic siloxane
possessing alkoxysilyl groups as a nanobuilding
block and its use for preparation of gas permeable
membranes†
Cite this: RSC Adv., 2017, 7, 48683
a
a
b
a
Masashi Yoshikawa,
Atsushi Shimojima,
Hiroya Shiba, Masakoto Kanezashi,
Hiroaki Wada,
a
b
ac
Toshinori Tsuru
and Kazuyuki Kuroda
*
A 12-membered cyclic siloxane possessing alkoxysilyl groups was synthesized as a nanobuilding block for
siloxane-based materials by the alkoxysilylation of organometallasiloxane containing a 12-membered ring
ꢀ
with Si–Me and Si–O groups as the side groups. The cyclic structure was retained not only in the hydrolysis
and condensation reactions (sol–gel process) of the alkoxysilyl groups but also in the xerogel and
membrane preparation processes. The degree of condensation of the xerogel derived from the 12-
membered ring siloxane was higher than that derived from alkoxysilane monomers, indicating that the
alkoxysilylated cyclic oligosiloxane is useful for controlling siloxane networks. A membrane composed of
the cyclic siloxane was prepared by coating the hydrolyzed solution onto a porous alumina tube for
Received 24th August 2017
Accepted 7th October 2017
DOI: 10.1039/c7ra09380b
rsc.li/rsc-advances
2 6
evaluating the gas permeation properties. The membrane showed a molecular sieving effect for H /SF .
properties similar to cyclic organic compounds such as cyclo-
dextrins and crown ethers. Actually, inclusion compounds
Introduction
6
Siloxane-based porous materials have been used in practical composed of cyclic penta-, hexa-, and hepta-siloxanes and metal
1,2
7–9
applications, such as catalysis, separation, and adsorption,
ions have been reported,
which indicates that the cavity
because of their thermal and chemical stability and high within cyclic siloxanes is accessible to some guest species. The
compatibility with other materials (such as polymers, metals, inner spaces provided by larger cyclic siloxanes are expected to
and metal oxides) for composite formation. The properties of show unique host–guest interactions with various molecular
such materials depend on the structure of the siloxane network; species. In contrast to many reports concerning the use of
therefore, the structural control at a molecular level is organic host compounds (carbon based), the effective utiliza-
important.
The use of nanobuilding blocks with dened oligosiloxane
tion of the cavity of cyclic siloxanes remains largely unexplored.
There have been many reports concerning the synthesis of
structures is quite effective for controlling siloxane networks at cyclic siloxanes with various ring sizes. In this study, we have
3
the molecular level. This pathway provides unique materials chosen a 12-membered cyclic siloxane as a nanobuilding block.
that cannot be obtained from monomeric silicon compounds. The inside diameter of the 12-membered siloxane ring is
Branched, cyclic, and cage-type oligosiloxanes have been roughly estimated to be ca. 0.9 nm when the ring structure is
synthesized and used as nanobuilding blocks for various fully extended and planar,‡ and the ring is larger than that of
4,5
siloxane-based nanomaterials. Among them, cyclic siloxanes a benzene ring. The 12-membered cyclic siloxanes are easily
are expected to act as nanobuilding blocks possessing inclusion obtained as complexes with metal cations by the hydrolysis and
condensation of organotrialkoxysilanes in the presence of alkali
10,11
metal hydroxide and transition metal cations.
Despite the
a
Department of Applied Chemistry, Faculty of Science and Engineering, Waseda attractiveness of cyclic siloxanes, 12-membered cyclic siloxanes
University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan. E-mail: kuroda@ have rarely been used as nanobuilding blocks for the formation
waseda.jp
of siloxane-based materials to the best of our knowledge.
b
Department of Chemical Engineering, Graduate School of Engineering, Hiroshima
University, 1-4-1 Kagami-yama, Higashi-Hiroshima 739-8527, Japan
c
Kagami Memorial Research Institute for Materials Science and Technology, Waseda
University, 2-8-26 Nishiwaseda, Shinjuku-ku, Tokyo, 169-0051, Japan
‡ The 12-membered cyclic siloxane of complex shows a saddle conformation
ꢀ
before silylation because of the interaction among SiO groups and metal
†
Electronic supplementary information (ESI) available. Characterizations of
cations. Aer silylation, the cyclic structure can take an extended and planar
state because such strong interactions to regulate the conguration does not
work. The inside diameter of 12-membered cyclic siloxane is calculated by
using Chem3D.
1
2MR-Me-TES, 12MR-Me-TES-derivedgels, TEOS–MTES-derived gels, and
precursor of 12MR-Me-TES. Experimental apparatus for gas permeation
measurement. See DOI: 10.1039/c7ra09380b
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 48683–48691 | 48683

View Article Online
RSC Advances
Paper
plane switches every three Si–O bonds. The intensity ratio of the
2
9
Si NMR signals ((A + B) : C : D ¼ 12 : 4 : 8) is consistent with
the structure.§ These results strongly suggest that the alkox-
ysilylation of Cu Na (MeSiO ) $x(nBuOH)$yH O proceeds with
4
4
2 12
2
the retention of the 12-membered ring structure, including the
up-and-down arrangement of side groups.
1
The H NMR spectrum of 12MR-Me-TES (Fig. 1b) shows four
signals assigned to ethoxy groups (3.83–3.79 ppm for
–
2 3 2 3
OCH CH , 1.22–1.19 ppm for –OCH CH ) and methyl groups
(0.26 ppm and 0.25 ppm). The intensity ratio of these signals is
in accordance with the calculated ratio. The two different
environments for the methyl carbons are consistent with the
structure, as mentioned above. Regarding the ethoxy groups,
the separation of the signals was too small to be observed
clearly. These H NMR results, together with the C NMR
results (Fig. S1 in the ESI†), also support the formation of 12MR-
Me-TES.
Scheme 1 Synthesis of the cyclic siloxane with alkoxysilyl groups and
the membrane preparation.
1
13
12,13
Shchegolikhina et al.
reported the preparation of layered
The high-resolution electrospray ionization mass spectros-
copy (ESI-MS) spectrum of 12MR-Me-TES shows a peak at m/z ¼
compounds by the solid-phase condensation of 12-membered
cyclic siloxanes possessing both hydroxy and phenyl groups.
Zheng et al. prepared a porous polymer by the hydrosilylation
polymerization of a 12-membered cyclic siloxane possessing
2
879.8320, corresponding to the sodium adduct of 12MR-Me-
TES (calcd. for 2879.8205), conrming that 12MR-Me-TES had
been successfully synthesized. This is the rst report concern-
ing the synthesis of a 12-membered ring siloxane possessing
alkoxysilyl groups that is available as a sol–gel precursor of
siloxane-based materials. This synthetic procedure is applicable
to the alkoxysilylation of metalorganosiloxanes possessing
14
both vinyl and hydrosilyl groups. Zheng et al. also reported
a polymer by thiol–ene polymerization of a 12-membered cyclic
15
siloxane possessing both vinyl and thiol groups. Unfortu-
nately, these reports did not clarify the retention of the 12-
membered cyclic siloxane structure in the products.
19–23
cyclic siloxane structures other than 12-membered rings,
In this study, a 12-membered cyclic siloxane with alkoxysilyl
groups as side groups was synthesized as a new nanobuilding
block by alkoxysilylation of the complex between 12-membered
cyclic siloxane and metal cations (Scheme 1). Hereaer, the
obtained compound is referred to as 12MR-Me-TES (based on
which could result in the variation of bond densities and angles
of the formed siloxane networks.
Hydrolysis and polycondensation of 12MR-Me-TES
12-membered ring molecule possesses Methyl groups and
TriEthoxySilyloxy (TES) groups as side groups). The hydrolysis To investigate the behavior of 12MR-Me-TES in the sol–gel
and polycondensation processes of this compound were process, the hydrolysis and polycondensation of 12MR-Me-TES
studied in detail by NMR spectroscopies to conrm that the in solution was analyzed by liquid-state NMR spectroscopies.
1
3
ring structure was retained aer the reaction. Furthermore, Fig. 2 shows the C NMR spectra of the hydrolyzed solution of
the cyclic siloxane was hydrolyzed and polycondensed onto 12MR-Me-TES. The signal intensity arising from the methylene
a porous alumina tube to prepare composite membranes, and carbon of the TES groups at 59.6 ppm decreased, and the
the membrane gas permeation properties were investigated to intensity of the signal corresponding to the methylene carbon of
discuss the usefulness of the cyclic siloxane as a nanobuilding ethanol (57.7 ppm) increased as the reaction time progressed.
block.
The signals arising from the TES groups almost disappeared
aer 3 h, which indicates the complete hydrolysis of the TES
groups of 12MR-Me-TES. The signal arising from the –SiMe
groups broadened with reaction time. The signal broadening is
Results and discussion
Characterization of 12MR-Me-TES
2
9
also conrmed by the Si NMR data (next paragraph).
29
Fig. 3 shows the Si NMR spectra of the hydrolyzed solution
2
9
Fig. 1a shows the Si NMR spectrum of 12MR-Me-TES. The two of 12MR-Me-TES. Three new signals are observed in the Q
3
T
signals (Fig. 1a, A and B) observed at ꢀ67.43 ppm and region (ꢀ85 ppm to ꢀ93 ppm) aer 1 h, in addition to the
ꢀ
67.45 ppm can be assigned to the Si atoms constituting the 12- original signal arising from the TES groups of 12MR-Me-TES
2
membered ring. No signal of the complex was observed in the T
region (typically ꢀ56.8 ppm to ꢀ58.8 ppm (ref. 16–18)). The two
§
Two TES groups located in the end of the continuous three TES groups (Q unit),
1
Q signals (Fig. 1a, C and D) at ꢀ88.95 ppm and ꢀ89.04 ppm are facing to the same direction against 12-membered ring plane, are set in the cis and
trans positions against both of the adjacent TES groups. The center TES groups are
due to the Si atoms of the TES groups. The two slightly different
3
1
in the cis position against both of the adjacent TES groups. Hence, the signals due
to TES groups are observed at ꢀ88.95 ppm and ꢀ89.04 ppm, and signal intensity
ratio of these signals is 1 : 2. In addition, magnication of the signal due to the Si
atoms (T unit) of 12-membered ring exhibits the presence of the shoulder signal
environments for both T and Q units can be attributed to the
up-and-down arrangement of the side TES groups on the 12-
membered ring siloxane, as shown in Fig. 1a. Please note that
the arrangement of side groups against the 12-membered ring probably due to the conformation.
48684 | RSC Adv., 2017, 7, 48683–48691
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
13
Fig. 2
C NMR spectra of the hydrolyzed solution of 12MR-Me-TES.
(a) 0 h, (b) 1 h, (c) 3 h, and (d) 6 h.
are observed. Aer 3 h and 6 h, all signals had weakened and
broadened. This is caused by the following two factors: (i) the
types of hydrolyzed and condensed molecules become more
diverse with the progress of hydrolysis and condensation, and
(ii) the molecular mobility of the condensed species is
decreased by the increasing molecular weight as intermolecular
condensation progresses or the rigidity of the cyclic siloxane
increases through intramolecular condensation. During the
2
reaction, no T signals arising from the cleavage of the Si–O–Si
2
bonds appeared (the T signal of the Si atom possessing methyl
group is generally observed at ꢀ56 ppm to ꢀ58 ppm), which
suggests that the cyclic structure of 12MR-Me-TES is retained
without rearrangement. Even if the rearrangement occurred too
3
rapidly to observe by NMR spectroscopy, chemical shi of T
29
1
Fig. 1 NMR spectra of 12MR-Me-TES. (a) Si and (b) H.
(
ꢀ88.8 ppm). The new signals at ꢀ86.3 ppm, ꢀ90.7 ppm, and
ꢀ
92.8 ppm can be assigned to –SiOSi(OEt) (OH), –SiOSi(OEt)-
2
17,24
(
OH)(OSi), and –SiOSi(OH) (OSi), respectively,
which indi-
2
cates that the partial hydrolysis and condensation of the TES
groups of 12MR-Me-TES had occurred. Meanwhile, the T
3
29
Fig. 3
Si NMR spectra of the hydrolyzed solution of 12MR-Me-TES.
signals corresponding to the Si atoms of the 12-membered ring (a) 0 h, (b) 1 h, (c) 3 h, and (d) 6 h.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 48683–48691 | 48685

View Article Online
RSC Advances
Paper
silicon in reformed siloxanes bonds would not be shied to
3
downeld by 3 ppm. Regarding to the downeld shi of T
signals, there are a couple of explanations. One probable reason
is cyclization of adjacent TES groups to form four-membered
rings. The other probable reason is the gradual progress of
hydrolysis and condensation of TES groups, and this variation
in the Q units must affect the electronic states of linked
3
neighboring T silicons. Because –SiOH and –SiOSi groups show
a more electron-withdrawing effect than TES group, the signals
3
due to T silicon can be shied to downeld. Therefore, the
downeld shi observed in this study can be explained by the
variations in the electron density during the sol–gel reaction.
These results indicate that the cyclic structure of 12MR-Me-TES
is retained aer the sol–gel reactions, which is important for the
preparation of separation/adsorption media using siloxane
oligomers.
Characterization of the 12MR-Me-TES-derived gels and
tetraethoxysilane–methyltriethoxysilane-derived gels
The stability of the 12-membered ring units in the gels derived
from 12MR-Me-TES was investigated. The hydrolyzed solution
of 12MR-Me-TES was dried to obtain a xerogel (12MR-gel-as).
ꢁ
ꢁ
Subsequently, the obtained gel was heated at 100 C, 200 C, or
3
ꢁ
00 C under an argon atmosphere (12MR-gel-heat100, 12MR-
gel-heat200, and 12MR-gel-heat300, respectively). These
2
9
Fig. 4
Si MAS NMR spectra of 12MR-Me-TES-derived gel. (a) 12MR-
2
9
samples were analyzed by solid-state Si NMR spectroscopy.
2MR-gel-as was obtained by drying the solution containing
gel-as, (b) 12MR-gel-heat100, (c) 12MR-gel-heat200, and (d) 12MR-
gel-heat300.
1
hydrolyzed and partially polycondensed 12MR-Me-TES. Please
note that the reaction conditions were different from those used
ꢀ
3
for the investigation of hydrolysis process described in the 3.0 ꢂ 10 ). Even the reaction time was increased from 1 d to
1
3
previous section. The hydrolysis conditions in this section were 2 d, the ethoxy groups remained ( C CP/MAS NMR: Fig. S4 in
the same conditions as those for the preparation of the 12MR- the ESI†), and the partial cleavage of the 12-membered ring
2
9
Me-TES-derived membrane precursor sol. The larger amount of occurred ( Si MAS NMR: Fig. S5 in the ESI†). To avoid this
solvent (ethanol) in these systems is favorable for the suppres- cleavage, it is important to induce gelation aer 1 d by evapo-
sion of the hydrolytic cleavage of the 12-membered ring. The rating the solvent.
2
9
Si magic angle spinning (MAS) NMR spectrum of 12MR-gel-as
Aer the heat treatment of 12MR-gel-as under an argon
shows T and Q signals (Fig. 4a). Three signals are observed in atmosphere, the polycondensation progress was conrmed by
2
3
4
29
the Q region (Q , Q , and Q ), indicating the progress of
Si MAS NMR and Fourier-transform infrared (FT-IR) spec-
hydrolysis and polycondensation of 12MR-Me-TES; however, troscopies, which demonstrates the reduction in the number of
2
3
the appearance of Q and Q signals indicates these reactions SiOH groups (Fig. 4b–d and S3 in the ESI, respectively†),
had not completed and –SiOEt and –SiOH groups remained. In although some ethoxy groups remained (Fig. S2b–d in the ESI†).
3
3
the T region, only the T signal corresponding to the Si atoms in In the case of 12MR-gel-heat100, only the T signal was
the 12-membered rings was observed, suggesting that the 12- observed, in common with 12MR-gel-as (Fig. 4b), indicating
membered ring structure of 12MR-Me-TES had been retained.
that the 12-membered ring structure of 12MR-gel-as did not
1
3
ꢁ
The signals assigned to ethoxy groups are observed in the
C
deteriorate at 100 C. On the other hand, at higher tempera-
2
29
cross-polarization (CP)/MAS NMR spectrum (Fig. S2a in the tures, small T signals appeared in the Si MAS NMR spectra of
ESI†), which indicates that the hydrolysis of 12MR-Me-TES had both 12MR-gel-heat200 and 12MR-gel-heat300 (Fig. 4c and d,
not completed. As described in the previous section, the respectively). It is likely that the 12-membered rings were
hydrolysis reaction was completed under the conditions for the cleaved by increasing strain arising from the progress of poly-
investigation of hydrolysis and polycondensation process of condensation with heating.
12MR-Me-TES. Such a difference in the degree of hydrolysis can
For comparison, equimolar amounts of tetraethoxysilane
be explained by the difference in the concentrations of the HCl (TEOS) and methyltriethoxysilane (MTES) were co-hydrolyzed
2
9
catalyst. The concentration of HCl in the reaction mixture for and polycondensed to obtain a xerogel. The Si MAS NMR
2
the preparation of the 12MR-Me-TES-derived gel (HCl/(EtOH + analysis conrmed that the signal intensity of the T silicon
ꢀ
5
H
2
O) ¼ 6.3 ꢂ 10 ) is much lower than that for the investigation atom of TEOS–MTES-derived gel (Fig. S6 in the ESI†) is higher
2
of hydrolysis process of 12MR-Me-TES (HCl/(EtOH + H
2
O) ¼ than that of 12MR-Me-TES-derived gel (Fig. 4). The lack of T
48686 | RSC Adv., 2017, 7, 48683–48691
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
silicon atoms in the 12MR-Me-TES-derived gel can be attributed siloxanes with heat treatment. The increase in the permeance
3
to the usage of 12MR-Me-TES having only T silicon atoms as with increasing heating temperature is probably due to the
a precursor under controlled conditions. These results indicate desorption of adsorbed water with heat treatment, which is
26
that the cyclic oligosiloxanes, which are composed of silicon oen observed for sol–gel derived membranes.
atoms with controlled condensation degree, are useful precur-
sors to control the siloxane networks.
The physical adsorption of gas molecules affects the gas
ꢁ
permeance measured at 100 C (Fig. 5), but the effect can be
ꢁ
ignored at 200 C and higher. The gas permeation experiments
ꢁ
at 100 C show that the permeance of 12MR-Me-TES-derived
Gas permeation properties of 12MR-Me-TES-derived
membranes and TEOS–MTES-derived membranes
membranes does not depend on their heating temperature;
therefore, the gas permeance of the 12MR-Me-TES-derived
The gas permeance of the 12MR-Me-TES-derived membranes was
ꢁ
membranes was evaluated at 200 C.
ꢁ
evaluated at 100 C, and the inuence of the heat treatment of the
TEOS–MTES-derived membrane was fabricated by hydrolysis
and co-condensation of TEOS and MTES, and its gas permeance
was also evaluated for comparison. Fig. 6a shows the gas
membranes was investigated. Fig. 5 shows the gas permeances of
ꢁ
ꢁ
the 12MR-Me-TES-derived membranes heated at 100 C, 200 C,
ꢁ
and 300 C as a function of kinetic diameter. There are no
signicant changes in both the shape of these curves and the
selectivity with heating temperature (e.g., H /SF : 550, 700, and
2
6
ꢁ
ꢁ
ꢁ
6
50 for the membranes heated at 100 C, 200 C, and 300 C,
respectively). The selectivity for H
the expected value for Knudsen diffusion (H
2
/SF
6
shows higher values than
/SF Knudsen
2
6
selectivity: 6 (ref. 25)), indicating that the 12MR-Me-TES-derived
membranes show a molecular sieving effect.
The slopes of the gas permeances against the kinetic diam-
eter were almost the same, and the gas permeances were
increased with increasing heat treatment temperature (Fig. 5).
The former result indicates that the average pore diameter of
the membrane does not depend on the heating temperature.
Assuming that gas molecules pass through the inner space of
12-membered ring siloxanes, the slope of gas permeances
against kinetic diameter would decrease with the cleavage of the
1
2-membered ring siloxanes. Actually, the 12-membered ring
ꢁ
siloxanes are slightly cleaved by heat treatments at 200 C and
ꢁ
300 C, as shown in Fig. 4; however, the slopes were almost the
same (Fig. 5). This could indicate that the relative positions of
the Si atoms in the 12-membered ring siloxane of 12MR-Me-TES
were not changed signicantly by the cleavage of the cyclic
Fig. 6 (a) Gas permeance and (b) dimensionless permeance based on
ꢁ
He permeance at 200 C as a function of molecular size. (circle) 12MR-
ꢁ
Me-TES-derived membrane heated at 300 C, (triangle) TEOS–MTES-
C for 12MR-Me-TES-derived derived membrane, and (broken line) calculated dimensionless per-
ꢁ
Fig.
5
Gas permeance at 100
membranes as a function of molecular size. The membranes are meance under Knudsen mechanism based on He (the calculation is
ꢁ
ꢁ
ꢁ
heated at 100 C (circle), 200 C (square), and 300 C (triangle).
based on ref. 25).
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 48683–48691 | 48687

View Article Online
RSC Advances
Paper
permeances of the 12MR-Me-TES-derived membrane and TEOS– toluene (dehydrated >99.5%), and pyridine (dehydrated >99.5%)
MTES-derived membrane as a function of kinetic diameter. Both were purchased from Wako Pure Chemical Industries, Ltd. and
ꢁ
membranes were heated at 300 C aer the coating of sols onto used as received. Chlorotrimethylsilane (>98.0%), tetra-
porous alumina tubes. Fig. 6b shows the dimensionless per- chlorosilane (SiCl4 >98.0%), tetraethoxysilane (TEOS >96.0%),
ꢁ
meances based on the He permeance at 200 C for these triethoxymethylsilane (MTES >98.0%), and zirconium tetrabut-
membranes. Compared with dimensionless permeance under oxide (80% ZrBT in 1-butanol) were purchased from Tokyo
the Knudsen mechanism, both membranes showed low dimen- Chemical Industry Co., Ltd. and used as received. Copper(II)
sionless permeance between N and SF , which indicates that chloride (CuCl >97%) was purchased from Sigma-Aldrich Co.,
2 6 2
both membranes showed a molecular sieving effect. The 12MR- LLC. and used as received. The a-alumina powders were
Me-TES membrane showed approximately the same level of gas purchased from Sumitomo Chemical Co., Ltd. The SiO –ZrO sol
2
2
permeance and pore size distribution with that of TEOS–MTES was obtained by hydrolysis and condensation of tetraethoxysilane
membrane. There are two possible reasons for the similar per- and zirconium tetrabutoxide. The detailed sol preparation
27,28
meances. (i) The exibility of siloxane or (ii) the formation of procedure has been described previously.
smaller cyclic structure than the 12-membered ring among tubes (HU-A01, average pore size: 2.1 mm, outside diameter: 10
2MR-Me-TES during the condensation of 12MR-Me-TES. (i) mm) were kindly supplied by the NIKKATO CORPORATION.
Porous a-alumina
1
The shape of such a large cyclic siloxane easily changes; in fact,
the precursor of the 12MR-Me-TES-derived membrane
Synthesis of Cu
Cu Na (MeSiO
to the literature reported by Shchegolikhina et al. 1-Butanol
80 mL), NaOH (2.01 g, 50.2 mmol), and water (2.72 mL, 150.9
mmol) were mixed in a three-neck ask equipped with a reux
condenser. Aer stirring the mixture for 30 min at room
temperature, a solution of MTES (10 mL, 50.3 mmol) in 20 mL
of 1-butanol was added to the mixture with vigorous stirring.
Then, 7.24 mL of water was added to the mixture, and it was
4
Na
4
(MeSiO
2
)
12$x(nBuOH)$yH
2
O
(
Cu Na (MeSiO ) $x(nBuOH)$yH O) contains a bending 12-
4 4 2 12 2
4
4
2
)
12$x(nBuOH)$yH
2
O was synthesized according
membered ring siloxane. So, the inner space of the 12-membered
cyclic siloxane may be narrowed and/or distorted by the bending
of the ring structure during the sol–gel reaction. (ii) When cyclic
siloxanes smaller than the 12-membered ring are formed
between the intermolecular spaces of 12MR-Me-TES, the gas
permeance is underestimated by the averaging of the 12-
membered rings and the small intermolecular ring structures.
The inclusion of some guest species into the ring before poly-
merization will be effective for the polymerization of extended
29
(
heated to reux. A solution of CuCl
2
(2.24 g, 16.7 mmol) in
60 mL of 1-butanol was added dropwise over ca. 20 min, and the
12-membered ring structures, which is now under investigation.
mixture was reuxed for an additional 30 min. The hot solution
was ltered to remove precipitates, and the ltrate was cooled to
room temperature. The ltrate was evaporated in a rotary
In addition, intermolecular spacing among cyclic oligomers is
quite important and should be further studied, although the
present study suggests that there are no large spaces among the
cyclic oligomers, as judged from the permeance data, which is
promising for future research on the molecular design of nano-
building block approach based on ring-type oligosiloxanes.
ꢁ
evaporator, and then the residue was dried in vacuo at 90 C. A
blue powder (Cu Na (MeSiO ) $x(nBuOH)$yH O) was ob-
4
4
2 12
2
tained. The X-ray diffraction (XRD) pattern of the obtained blue
powder was not consistent with that of Cu Na (MeSiO
x(nBuOH)$yH O reported by Shchegolikhina et al. (Fig. S8 in
the ESI†), probably because of the difference in the number of
solvated molecules (1-butanol and/or H O). To conrm the
4
4
2 12
) -
29
$
2
Conclusions
2
An alkoxysilylated 12-membered ring siloxane was successfully
synthesized as a nanobuilding block for siloxane-based mate-
rials. The cyclic structure of the molecule can be retained during
the sol–gel reaction and membrane preparation processes,
which indicates that the cyclic siloxane is a useful precursor
for siloxane-based materials with controlled structures. A
membrane composed of the cyclic siloxane was fabricated, and
the membrane showed molecular sieving effect for H /SF .
formation of the 12-membered cyclic siloxane structure, the
product was silylated with chlorotrimethylsilane (detailed
1
13
method and characterization are shown in ESI†). The H, C,
2
9
and Si NMR and MS data of the trimethylsilylated compound
29
coincided with those of the reported compound; therefore, we
concluded that the blue powder synthesized here possessed the
12-membered ring siloxane structure.
2
6
These results demonstrate that oligomeric siloxanes with rela-
tively large ring structures are useful nanobuilding blocks for
nanomaterials. Further studies on the control of extended ring ClSi(OEt)
Synthesis of chlorotriethoxysilane (ClSi(OEt)
was synthesized by the alkoxylation of SiCl
structure with precisely controlled arrangements are underway ethanol under nitrogen atmosphere. Tetrachlorosilane
3
)
3
4
with
a
for the creation of functional siloxane-based nanomaterials.
(16.5 mL, 143.7 mmol) was added to a Schlenk ask under a N
atmosphere, and the ask was cooled to 0 C. Dehydrated
2
ꢁ
ethanol (29.3 mL, 501.8 mmol) was added dropwise with stir-
Experimental
Materials
ꢁ
ring at 0 C. Aer the ethanol had been added, the mixture was
ꢁ
stirred at 0 C for 1 h and at room temperature for 4 h. A
1
(
-Butanol (>99.0%), chloroform (>99.0%), deuterated ethanol colorless clear liquid was obtained. In this procedure, an excess
EtOH-d >99.5%), ethanol (dehydrated >99.5%), hydrochloric of ethanol (3.5 eq.) was used to avoid the formation of dieth-
2 2 2
acid (6 mol L HCl aq.), sodium hydroxide (NaOH >97.0%), oxydichlorosilane (Cl Si(OEt) ) because Cl Si(OEt) leads to
6
ꢀ
1
2
48688 | RSC Adv., 2017, 7, 48683–48691
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
intermolecular crosslinking between Cu
4
Na
4
(MeSiO
2
)
12
-
solution was cast on a Petri dish. Then, a colorless transparent
ꢁ
$
x(nBuOH)$yH O at the silylation step. Although tetraethox- xerogel was formed by drying at 100 C for 10 min in air. A white
2
ysilane (TEOS) was also formed with ClSi(OEt) (approximately powder was obtained by scraping the gel from the Petri dish for
3
TEOS : ClSi(OEt) ¼ 1 : 1), the mixture was used for the silyla- analysis (12MR-gel-as). The white powder was heated under an
3
ꢁ
ꢁ
ꢁ
tion without purication because TEOS is much less reactive argon atmosphere at 100 C, 200 C, or 300 C for 1 h (12MR-gel-
than ClSi(OEt)
H, C, and Si NMR spectroscopies.
3
. The formation of ClSi(OEt)
3
was conrmed by heat100, 12MR-gel-heat200, and 12MR-gel-heat300, respectively)
to investigate the possible structural changes of the siloxane
network.
1
13
29
Synthesis of the 12-membered ring siloxane possessing
alkoxysilyl groups (12MR-Me-TES)
Preparation of TEOS–MTES-derived gel
Cu
ClSi(OEt)
dine (17 mL, 210.6 mmol) were added to ClSi(OEt) in a Schlenk 24 h. The molar ratio of TEOS : MTES : H O : HCl was
4
Na
4
2 2
(MeSiO )12$x(nBuOH)$yH O was alkoxysilylated with The mixture of TEOS, MTES, ethanol, water, and 6 M hydro-
3
. Dehydrated toluene (40 mL) and dehydrated pyri- chloric acid was stirred at 1200 rpm at room temperature for
3
2

ask. Then, Cu Na (MeSiO ) $x(nBuOH)$yH O (1.06 g) was 1 : 1 : 70 : 0.4. The EtO : H O molar ratio and mass concentra-
4 4 2 12 2 2
added to the solution, and blue-green colored precipitates were tion of alkoxides (TEOS + MTES) were the same as those for the
formed. The mixture was stirred for 48 h at room temperature aforementioned system of 12MR-Me-TES (EtO : H
O ¼ 10 and
under N atmosphere. Then, an excess of dehydrated pyridine and 1 wt%, respectively). The hydrolyzed solution was cast on a Petri
2
2
dehydrated ethanol were added to the mixture for the ethoxylation dish, and a colorless transparent gel was formed by drying at
ꢁ
of the remaining ClSi(OEt)
a glass lter under N
3
. The precipitates were ltered with 100 C for 10 min in air. A white powder was obtained by
2
atmosphere. Then, the solvent, unreacted scraping from the Petri dish for analysis (TEOS–MTES-gel). The
ꢁ
pyridine, ethanol, and the following two byproducts ((1) TEOS, powder was heated under an argon atmosphere at 100 C,
ꢁ
ꢁ
generated by the ethoxylation of ClSi(OEt) , and (2) hexaethox- 200 C, or 300 C for 1 h (TEOS–MTES-gel-heat100, TEOS–MTES-
3
ydisiloxane, formed by the reaction between ClSi(OEt)3 and gel-heat200, and TEOS–MTES-gel-heat300, respectively).
adsorbed water from Cu Na (MeSiO )12$x(nBuOH)$yH O) were
4 4 2 2
removed in vacuo. A small amount of the precipitate was removed Fabrication of membranes from 12MR-Me-TES or mixed
by syringe ltration. Finally, the alkoxysilylated 12-membered ring TEOS–MTES
siloxane was isolated by gel permeation chromatography (GPC)
using chloroform as an eluent (colorless clear viscous liquid,
a-Alumina particles (a mixture of two types of particles with
average diameters of 0.2 and 1.9 mm) were coated onto the
outside of porous a-alumina tube by using a SiO –ZrO sol as
2 2
1.8902 g, yield: 78%).
1
2MR-Me-TES. dH (500.13 MHz; CDCl ; TMS) 0.25 (s, 24H,
3
a binder. To obtain a smooth surface, the tube was calcined in
SiCH ), 0.26 (s, 12H, SiCH ), 1.21 (t, J ¼ 7.0 Hz, 108H,
ꢁ
3
3
air at 550–600 C for 30 min. These procedures were repeated
OCH
CDCl
2
CH
3
), 3.81 (q, J ¼ 7.0 Hz, 71H, OCH
2
CH
), 58.9 (OCH
), ꢀ88.95,
), ꢀ67.43 to ꢀ67.45 (T , 12Si, O SiMe
overlapping two signals)); HRMS (Electrospray ionization,
3
); d
C
(125.76 MHz;
several times to prevent the formation of pinholes in the nal
membrane. Then, the diluted SiO –ZrO sol (ca. 0.5 wt%) was
3
; TMS) ꢀ2.8 (SiCH
3
), 18.1 (OCH
2
CH
3
2
CH ); dSi
3
2
2
1
(
99.36 MHz; CDCl
3
; TMS) ꢀ89.04 (Q , 8Si, SiOSi(OEt)
3
coated onto the tube to form an intermediate layer (pore size:
1
3
(Q , 4Si, SiOSi(OEt)
3
3
30
ꢁ
2
3
–3 nm). Aer calcination of the tube in air at 550–600 C for
0 min, the 12MR-Me-TES-derived layer was fabricated by
(
+
+
2
2
kV): calcd for C H O Si Na [M + Na] : 2879.8205; found:
84 216 60 24
879.8320 main paragraph text follows directly on here.
coating with the hydrolyzed solution of 12MR-Me-TES, which
was prepared as the same way as 12MR-gel-as. Finally, the tube
ꢁ
was dried and heated at 100 C for 1 h under N
2
atmosphere. A
Hydrolysis and polycondensation of 12MR-Me-TES
2MR-Me-TES was dissolved in a mixture of dehydrated ethanol as the 12MR-Me-TES-derived membrane by using the TEOS–
and deuterated ethanol (40 vol% of EtOH-d ). Then, water and MTES sol instead of the 12MR-Me-TES sol. The TEOS–MTES sol
TEOS–MTES-derived membrane was fabricated in the same way
1
6
6
M hydrochloric acid were added to the solution. The molar was prepared as shown above.
ratio of 12MR-Me-TES : EtOH EtOH-d : H O : HCl was
: 96 : 36 : 0.4. The mixture was analyzed by NMR spectros- Evaluation of single-gas permeation property
+
6
2
1
copies aer 1 h, 3 h, and 6 h of reaction.
The experimental apparatus for a single-gas permeation
measurement is shown in Fig. S9 in the ESI† as a schematic. A
single gas (He, H , CO , N , CH , CF , or SF ) was fed to the
2 2 2 4 4 6
Preparation of 12MR-Me-TES-derived gel
1
2MR-Me-TES was dissolved in dehydrated ethanol. Then, water outside surface (upstream) of a cylindrical membrane at 200
and 6 M hydrochloric acid were added to the solution. The molar kPa, and the downside was kept at atmospheric pressure. At
ratio of 12MR-Me-TES : EtOH : H O : HCl was 1 : 6006 : 360 : 0.4 rst, the values for the single gas permeances were measured at
EtO : H
O ¼ 10), and the concentration of 12MR-Me-TES was 100 C, and then the membrane was heat-treated at 200–300 C
wt%. Please note that the molar ratio among those compounds under a N2 atmosphere. Aer conrming the attainment of
2
ꢁ
ꢁ
(
1
2
is different from that for the investigation of hydrolysis and a steady state at each temperature by measuring the time course
ꢁ
polycondensation process of 12MR-Me-TES. Aer the mixture of N
2
permeance, the temperature was cooled to 100 C and the
had been stirred at 1200 rpm at room temperature for 24 h, the gas permeance was measured. The permeation rate was
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 48683–48691 | 48689

View Article Online
RSC Advances
Paper
measured by a bubble lm meter. The deviation of the perme- University) for his help on separation by GPC and Mr E.
ation data was less than 5%.
Yamamoto, Mr S. Mori, and Ms. S. Uchida (Waseda University)
for their help in the preparation of the TEOS–MTES sol. M. Y. is
thankful to the JX-Waseda Research Fund for Young
Researchers and Japan Chemical Industry Association for
a fellowship (Human Resources fostering Program in Chem-
istry). This work was supported in part by JSPS KAKENHI (Grant-
in-Aid for Scientic Research(B), No. 15H03879).
Characterization
1
13
29
Solution H, C, and Si NMR spectra were recorded on
AVANCE 500 (Bruker) or JNM-ECZ 500 (JEOL) spectrometers
with resonance frequencies of 500.13 MHz, 125.76 MHz, and
99.36 MHz, respectively, at room temperature using 5 mm glass
tubes. Tetramethylsilane (TMS) was used as an internal refer-
ence at 0 ppm. CDCl and ethanol-d were used to obtain lock
3
6
Notes and references
signals. A small amount of Cr(acac) (acac: acetylacetonate) was
3
2
9
13
added as a relaxation agent for Si nuclei. C NMR spectra
were measured with a recycle delay of 2 s. Si NMR spectra were
measured with a 45 pulse and a recycle delay of 10 s. Solid-state
Si MAS NMR spectra were recorded on a JNM-ECX 400 (JEOL)
1
2
3
M. E. Davis, Nature, 2002, 417, 813–821.
2
9
T. Tsuru, J. Sol-Gel Sci. Technol., 2008, 46, 349–361.
C. Sanchez, G. J. d. A. A. Soler-Illia, F. Ribot, T. Lalot,
C. R. Mayer and V. Cabuil, Chem. Mater., 2001, 13, 3061–
ꢁ
2
9
spectrometer with a resonance frequency of 78.7 MHz at room
3083.
ꢁ
temperature with a 45 pulse and a recycle delay of 250 s. The
4
5
A. Shimojima and K. Kuroda, Chem. Rec., 2006, 6, 53–63.
K. Kuroda, A. Shimojima, K. Kawahara, R. Wakabayashi,
Y. Tamura, Y. Asakura and M. Kitahara, Chem. Mater.,
recycle delay was set at ve times as long as longitudinal
relaxation time (T ) to complete the relaxation of all nuclear
1
spins. The samples were placed in 4 mm zirconia tubes and
2
014, 26, 211–220.
J. S. Ritch and T. Chivers, Angew. Chem., Int. Ed., 2007, 46,
610–4613.
A. Decken, F. A. LeBlanc, J. Passmore and X. Wang, Eur.
J. Inorg. Chem., 2006, 4033–4036.
spun at 6 kHz. The chemical shis were externally referenced to
6
7
8
9
1
3
poly(dimethylsilane) at ꢀ33.8 ppm. Solid-state C CP/MAS
NMR spectra were also recorded on a JNM-ECX 400 (JEOL)
spectrometer with a resonance frequency of 99.5 MHz at room
temperature with a recycle delay of 10 s and a contact time of 5
ms. The samples were put in 4 mm silicon nitride tubes and
spun at 10 kHz. The chemical shis were externally referenced
to the methyl groups of hexamethylbenzene at 17.4 ppm. High-
resolution electrospray ionization mass (HRMS) analysis was
conducted by using an Exactive Plus (Thermo Fisher Scientic)
instrument. Low-resolution electrospray ionization mass anal-
ysis was conducted by using a JMS-T100 CS AccuTOF (JEOL)
instrument. Samples were dissolved in ethanol. Gel permeation
chromatography (GPC) was carried out using a LC-9100 with
a recycling preparative HPLC system, a refractive index (RI)
detector (Japan Analytical Industry Co., Ltd.) and two types of
crosslinked polystyrene packed columns (JAIGEL-1H and
JAIGEL-2H; exclusion limits of 1000 and 2000, respectively, and
theoretical plate of 13 000). Chloroform was used as an eluent
4
A. Decken, J. Passmore and X. Wang, Angew. Chem., Int. Ed.,
2006, 45, 2773–2777.
T. S. Cameron, A. Decken, I. Krossing, J. Passmore,
J. M. Rautiainen, X. Wang and X. Zeng, Inorg. Chem., 2013,
52, 3113–3126.
1
1
1
1
0 M. Borsari, G. Gavioli, C. Zucchi, G. P ´a lyi, R. Psaro, R. Ugo,
O. I. Shchegolikhina and A. A. Zhdanov, Inorg. Chim. Acta,
1997, 258, 139–144.
1 Y. A. Molodtsova, Y. A. Pozdnyakova, I. V. Blagodatskikh,
A. S. Peregudov and O. I. Shchegolikhina, Russ. Chem.
Bull., 2003, 52, 2722–2731.
2 S. D. Korkin, M. I. Buzin, E. V. Matukhina, L. N. Zherlitsyna,
N. Auner and O. I. Shchegolikhina, J. Organomet. Chem.,
2003, 686, 313–320.
3 O. I. Shchegolikhina, E. V. Matukhina, A. A. Anisimov,
Y. A. Molodtsova, M. I. Buzin, K. A. Lyssenko and
A. M. Muzafarov, Macroheterocycles, 2016, 9, 11–16.
ꢀ1
with a ow rate of 3.5 mL min . FT-IR spectra were recorded on
a FT/IR-6100 (JASCO) spectrometer at ambient temperature.
The FT-IR spectra were measured using KBr disk technique
under vacuum conditions. Powder XRD patterns were recorded
on a RINT-Ultima III (RIGAKU) diffractometer with Cu Ka
radiation at 40 kV and 40 mA.
1
1
4 J. Han and S. Zheng, Macromolecules, 2008, 41, 4561–4564.
5 Y. Yi, N. Liu, L. Li and S. Zheng, RSC Adv., 2016, 6, 87802–
87807.
16 Y. Sugahara, S. Okada, S. Sato, K. Kuroda and C. Kato, J. Non-
Cryst. Solids, 1994, 167, 21–28.
1
1
7 R. J. Hook, J. Non-Cryst. Solids, 1996, 195, 1–15.
8 D. A. Loy, B. M. Baugher, C. R. Baugher, D. A. Schneider and
K. Rahimian, Chem. Mater., 2000, 12, 3624–3632.
Conflicts of interest
There are no conicts to declare.
1
9 Y. A. Pozdniakova, K. A. Lyssenko, A. A. Korlyukov,
I. V. Blagodatskikh, N. Auner, D. Katsoulis and
O. I. Shchegolikhina, Eur. J. Inorg. Chem., 2004, 1253–1261.
Acknowledgements
The authors greatly appreciate Dr T. Shibue and Mr N. Sugi- 20 V. Pashchenko, B. Brendel, B. Wolf, M. Lang, K. Lyssenko,
mura (Materials Characterization Central Lab., Waseda
University) for solid state NMR and HRMS measurements,
respectively. The authors also thank Mr S. Saito (Waseda
O. Shchegolikhina, Y. Molodtsova, L. Zherlitsyna,
N. Auner, F. Sch u¨ tz, M. Kollar, P. Kopietz and N. Harrison,
Eur. J. Inorg. Chem., 2005, 4617–4625.
48690 | RSC Adv., 2017, 7, 48683–48691
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
21 L. Zherlitsyna, N. Auner, M. Bolte, Y. Pozdniakova, 25 R. J. R. Uhlhorn and A. J. Burggraaf, in Inorganic Membranes
O. Shchegolikhina, K. Lyssenko, V. Pashchenko, B. Wolf,
M. Lang, F. Sch u¨ tz, M. Kollar, F. Sauli and P. Kopietz, Eur.
J. Inorg. Chem., 2007, 4827–4838.
Synthesis, Characteristics and Applications, Springer,
Netherlands, Dordrecht, 1991, pp. 155–176.
26 J. Wang, M. Kanezashi, T. Yoshioka and T. Tsuru, J. Membr.
Sci., 2012, 415–416, 810–815.
2
2 I. V. Blagodatskikh, Y. A. Molodtsova, Y. A. Pozdnyakova,
O. I. Shchegolikhina and A. R. Khokhlov, Colloid J., 2008, 27 W. Puthai, M. Kanezashi, H. Nagasawa and T. Tsuru, Sep.
0, 407–415. Purif. Technol., 2016, 168, 238–247.
3 A. N. Bilyachenko, A. N. Kulakova, M. M. Levitsky, 28 W. Puthai, M. Kanezashi, H. Nagasawa and T. Tsuru,
A. A. Petrov, A. A. Korlyukov, L. S. Shul’pina, J. Membr. Sci., 2017, 524, 700–711.
V. N. Khrustalev, P. V. Dorovatovskii, A. V. Vologzhanina, 29 Y. A. Molodtsova, K. A. Lyssenko, I. V. Blagodatskikh,
7
2
U. S. Tsareva, I. E. Golub, E. S. Gulyaeva, E. S. Shubina and
G. B. Shul'pin, Inorg. Chem., 2017, 56, 4093–4103.
4 J. C. Pouxviel, J. P. Boilot, J. C. Beloeil and J. Y. Lallemand,
J. Non-Cryst. Solids, 1987, 89, 345–360.
E. V. Matukhina, A. S. Peregudov, M. I. Buzin,
V. G. Vasil’ev, D. E. Katsoulis and O. I. Shchegolikhina,
J. Organomet. Chem., 2008, 693, 1797–1807.
2
30 M. Kanezashi, S. Miyauchi, H. Nagasawa, T. Yoshioka and
T. Tsuru, J. Membr. Sci., 2014, 466, 246–252.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 48683–48691 | 48691