Highly gas-permeable silanol-functionalized poly(diphenylacetylene)s: Synthesis, characterization, and gas permeation property

Article abstract of DOI:10.1021/ma201280s

Diphenylacetylenes having a diisopropylphenoxysilyl group [PhOSi(i-Pr) ₂C₆H₄C≡CC₆H₄R; R = H (1a), SiMe₃ (1b)] were synthesized and then polymerized with TaCl₅/n-Bu₄Sn to provide the corresponding poly(diphenylacetylene)s (2a and 2b). These siloxy group-containing polymers afforded tough free-standing membranes by casting from toluene solutions. Treatment of the membranes (2a and 2b) with n-Bu₄N⁺F ^- gave the silanol-functionalized poly(diphenylacetylene)s (3a and 3b). FT-IR spectra of the silanol-functionalized polymers revealed that some their silanol groups were consumed and the polymers were cross-linked via siloxane bond. The oxygen permeability coefficients of membranes of 2a and 2b were 12 and 26 barrers, respectively. The deprotection of these membranes in DMF lowered membrane densities, and consequently their gas permeability significantly increased. The oxygen permeability coefficients of silanol group-containing membranes (3a and 3b) were 210 and 1300 barrers, respectively. These silanol-functionalized poly(diphenylacetylene) membranes were found to exhibit very high gas permeability irrespective of the presence of the polar silanol groups in the polymers. Membrane of 3a showed relatively high CO ₂ permselectivity as well as high CO₂ permeability.

Full text of DOI:10.1021/ma201280s

ARTICLE
pubs.acs.org/Macromolecules
Highly Gas-Permeable Silanol-Functionalized Poly(diphenylacetylene)s:
Synthesis, Characterization, and Gas Permeation Property
Toshikazu Sakaguchi,* Aiko Takeda, and Tamotsu Hashimoto
Department of Materials Science and Engineering, Graduate School of Engineering, University of Fukui, Bunkyo 3-9-1, Fukui 910-8507, Japan
ABSTRACT: Diphenylacetylenes having a diisopropylphenox-
ysilyl group [PhOSi(i-Pr)2C6H4CtCC6H4R; R = H (1a), SiMe3
(1b)] were synthesized and then polymerized with TaCl5/n-Bu4Sn
to provide the corresponding poly(diphenylacetylene)s (2a and
2b). These siloxy group-containing polymers afforded tough
free-standing membranes by casting from toluene solutions.
Treatment of the membranes (2a and 2b) with n-Bu4N+Fꢀ
gave the silanol-functionalized poly(diphenylacetylene)s (3a
and 3b). FT-IR spectra of the silanol-functionalized polymers
revealed that some their silanol groups were consumed and the
polymers were cross-linked via siloxane bond. The oxygen
permeability coefficients of membranes of 2a and 2b were 12 and 26 barrers, respectively. The deprotection of these membranes
in DMF lowered membrane densities, and consequently their gas permeability significantly increased. The oxygen permeability
coefficients of silanol group-containing membranes (3a and 3b) were 210 and 1300 barrers, respectively. These silanol-
functionalized poly(diphenylacetylene) membranes were found to exhibit very high gas permeability irrespective of the presence
of the polar silanol groups in the polymers. Membrane of 3a showed relatively high CO2 permselectivity as well as high CO2
permeability.
’ INTRODUCTION
In the present study, we synthesized novel silanol-functional-
ized poly(diphenylacetylene)s by treating tetrabutyl ammonium
fluoride (TBAF) on the membranes of precursor polymers. It is
known that poly(diphenylacetylene) having polar groups cannot
be obtained by metathesis polymerization with TaCl5 catalysts
because the polar groups deactivate active species for metathesis
polymerization. Therefore, we synthesized diphenylacetylene
possessing protected silanol groups and performed metathesis
polymerization of the monomers (Scheme 1). Deprotection of
the polymers afforded silanol-containing poly(diphenylacetylene)
membranes. The membranes of the silanol-functionalized poly-
(diphenylacetylene)s exhibited high gas permeability.
Polyacetylenes with bulky spherical substituents show extre-
mely high gas permeability. This is because the combination of
their stiff main chain composed of alternating double bonds and
the steric repulsion of the bulky substituents make their mem-
branes sparse.1 Therefore, poly(substituted acetylene)s are pro-
mising materials for gas separation membranes. A large number
of poly(substituted acetylene)s have been synthesized so far, and
the gas permeability of their membranes has been investigated.1ꢀ4
The incorporation of functional groups into poly(substituted
acetylene)s is of great interest in the various fields due to their
potential applications as polymer light-emitting devices, sensors,
enantioselective materials, and separation membranes for speci-
fic gases. With regard to gas permeability, however, the incor-
poration of polar functional groups such as hydroxy groups, sulfonic
acid groups, and amino groups into the poly(diphenylacetylene)s
lead to significant decrease of gas permeability on the polymer
membranes.5ꢀ9 In contrast, poly(substituted acetylene)s bearing
silyl groups [ꢀSiR3] generally exhibit high gas permeability
because high local mobility of silyl groups promote gas diffusion
in polymer matrix.10ꢀ13 Therefore, poly(diphenylacetylene) having
silanol groups [ꢀSi(OH)R2] as a functional group is expected to
become an interesting polar material with high gas permeability.
In addition, polymers carrying silanol groups can be used as a
reactive polymer for polymer reaction. Silanol groups are highly
reactive, and they can undergo hydrolysis and condensation reaction
with other reagents. For instance, they are promising polymers as
organic components to prepare organicꢀinorganic hybrid materials
through solꢀgel method using tetraethoxysilane.14ꢀ17
’ EXPERIMENTAL SECTION
Measurements. The molecular weights and polydispersity ratios of
polymers were estimated by gel permeation chromatography (THF as
eluent, polystyrene calibration) at 40 °C on a Shimadzu LC-10AD
chromatograph equipped with three polystyrene gel columns (Shodex
KF-802.5 ꢁ 1 and A-80 M ꢁ 2) and a Shimadzu RID-6A refractive index
detector. IR spectra were recorded on a Nicolet MAGNA 560 spectro-
meter. NMR spectra were obtained on a Jeol LA-500 spectrometer.
Elemental analyses of monomers were performed at the Microanalytical
Center of Kyoto University.
Gas permeability coefficients of polymer membranes were measured
with a Rikaseiki K-315-N gas permeability apparatus at 25 °C under
Received: June 7, 2011
Revised:
July 29, 2011
Published: August 04, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of Polymers and Preparation of Membranes
Scheme 2. Synthesis of Monomers
1 atm upstream pressure. The permeability coefficient P expressed
dropping funnel, a three-way stopcock, and a magnetic stirring bar, and
then flushed with nitrogen. A solution of 1-phenyl-2-p-bromophenyla-
cetylene (20.4 g, 79.3 mmol) in ether (250 mL) was placed in the flask.
Then 1.6 mol/L n-Butyllithium hexane solution (49.6 mL, 79.3 mmol)
was added dropwise at 0 °C. After addition, the reaction mixture was
stirred for 30 min at the same temperature, and then allowed to warm to
room temperature. The solution of the produced diphenylacetylene
lithium salt was added to a mixture of diisopropyldichlorosilane (14.7 g,
79.3 mmol) and ether (50 mL) dropwise at 0 °C. The reaction
mixture was stirred for 3 days at room temperature. After the ether
was evaporated, the crude product was dissolved in hexane, and
insoluble salt was filtered off. The hexane solution of 1-phenyl-2-(p-
chlorodiisopropylsilyl)phenylacetylene was concentrated at reduced
pressure. This product was used in the following reaction without
further purification.
Phenol (14.9 g, 157 mmol), imidazole (27.0 g, 397 mmol), and DMF
(100 mL) was placed in a three-necked flask equipped with a dropping
funnel, a three-way stopcock, and a magnetic stirring bar. A solution of
1-phenyl-2-(p-chlorodiisopropylsilyl)phenylacetylene in DMF (100 mL)
was added dropwise at 0 °C under nitrogen. The reaction mixture was
stirred overnight at room temperature. After ether addition, the solution
was washed with water. The ethereal solution was dried over anhydrous
sodium sulfate, and then concentrated in vacuo. The crude product was
purified by silica gel column chromatography (eluent: hexane followed
in barrer unit (1 barrer =10ꢀ10 cm3(STP) cm cmꢀ2 sꢀ1 cmHgꢀ1
)
was calculated from the slope of the steady-state line. The D value was
determined by the time lag method using the following equation:
D ¼ l2=6θ
here, l is the membrane thickness and θ is the time lag, which is given by
the intercept of the asymptotic line of time-pressure curve to the time
axis. The S value was calculated by using equation S = P/D.
Materials. Toluene as a polymerization solvent was purified by
distillation over calcium hydride. TaCl5 (Aldrich, 99.999%) as a main
catalyst was used without further purification, while n-Bu4Sn as a
cocatalyst was purified by distillation. Phenylacetylene, p-bromoiodo-
benzene, diisopropyldichlorosilane, phenol, tetrabutylammonium fluor-
ide (n-Bu4N+Fꢀ) and common organic solvents were commercially
obtained and used without further purification. p-Trimethylsilylpheny-
lacetylene was kindly donated by NOF Corporation (Tokyo, Japan).
1-phenyl-2-p-bromophenylacetylene18 and 1-(p-trimethylsilyl)phenyl-
2-p-bromophenylacetylene19 were synthesized referring to the litera-
tures. Monomers were synthesized according to Scheme 2. The synth-
esis procedures and analytical data of monomers are as follows.
Synthesis of 1-Phenyl-2-(p-diisopropylphenoxysilyl)phe-
nylacetylene (1a). A 500 mL three-necked flask was equipped with a
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Scheme 3. Synthesis of Diisopropyl(phenylethynylphenyl)silyl Ether
by a mixture of hexane/chloroform (9/1)) to provide the desired product
(15.9 g, overall yield; 46.8%) as white solid. 1H NMR (CDCl3, ppm):
7.61 (d, J = 8.0 Hz, 2H, Ar), 7.55ꢀ7.53 (m, 4H, Ar), 7.36ꢀ7.33 (m, 3H,
Ar), 7.20 (t, J = 7.9 Hz, 2H, Ar), 6.94 (t, J = 7.4 Hz, 1H, Ar), 6.90 (d, J =
7.8 Hz, 2H, Ar), 1.43 (sept, J = 7.4 Hz, 2H, SiCH), 1.09 (d, J = 7.5 Hz,
6H, CH3), 1.04 (d, J = 7.6 Hz, 6H, CH3). 13C NMR (CDCl3, ppm):
155.6, 134.6, 134.5, 131.6, 130.7, 129.4, 128.3, 124.3, 123.2, 121.3, 119.8,
90.3, 89.4, 17.4, 17.2, 12.7. Anal. Calcd for C26H28OSi: C, 81.2; H, 7.3;
O, 4.2; Si, 7.3. Found: C, 81.0; H, 7.5.
Synthesis of 1-(Trimethylsilyl)phenyl-2-(p-diisopropyl-
phenoxysilyl)phenylacetylene (1b). The monomer 1b was prepared
by the same method as for 1a using p-trimethylsilylphenylacetylene instead
of phenylacetylene. Overall yield 54.9%, colorless liquid. 1H NMR (CDCl3,
ppm):7.61 (d, J = 7.7 Hz, 6H, Ar), 7.55ꢀ7.47 (m, 2H, Ar), 7.20 (t, J = 7.7
Hz, 2H, Ar), 6.93 (t, J = 7.3 Hz, 1H, Ar), 6.90 (d, J = 7.7 Hz, 2H, Ar), 1.43
(sept, J=7.5Hz, 2H, SiCH), 1.08(d, J= 7.4 Hz, 6H, CCH3), 1.04(d, J=7.6
Hz, 6H, CCH3), 0.28 (s, 9H, Si(CH3)3). 13C NMR (CDCl3, ppm): 155.6,
141.2, 134.6, 134.5, 133.2, 130.7, 129.4, 124.4, 123.5, 121.3, 119.8, 90.5,
89.8, 17.4, 17.2, 12.7, ꢀ1.2. Anal. Calcd for C29H36OSi2: C, 76.3; H, 7.9; O,
3.5; Si, 12.3. Found: C, 76.3; H, 8.1.
ether (0.2 g, 6.8%) as white solid. 1H NMR (CDCl3, ppm): 7.65ꢀ7.46
(m, 12H, Ar), 7.40ꢀ7.35 (m, 6H, Ar), 1.37 (sept, J = 7.4 Hz, 4H, SiCH),
1.08 (d, J = 7.5 Hz, 12H, CH3), 1.01 (d, J = 7.6 Hz, 12H, CH3). 13C
NMR (CDCl3, ppm): 136.7, 134.2, 131.6, 130.5, 128.3, 128.2, 123.8,
123.3, 90.0, 89.5, 17.7, 17.5, 13.7. Anal. Calcd for C40H46OSi2: C, 80.2;
H, 7.7; O, 2.7; Si, 9.4. Found: C, 79.6; H, 7.7.
Polymerization. Polymerization was carried out in a glass tube
equipped with a three-way stopcock under dry nitrogen. Unless other-
wise specified, the reaction was carried out at 80 °C for 24 h under the
following conditions: [monomer] = 0.20 M, [TaCl5] = 20 mM, and [n-
Bu4Sn] = 40 mM. A detailed procedure of polymerization is as follows:
The monomer solution was prepared in a glass tube. Another glass tube
was charged with TaCl5, n-Bu4Sn, and toluene; this catalyst solution was
aged at 80 °C for 10 min, and then monomer solution was added to it.
Polymerization was run at 80 °C for 24 h, which was quenched with a
small amount of methanol. The resulting polymer was isolated by
precipitation into a large excess of acetone, and its yield was determined
gravimetrically.
Membrane Fabrication and Decomposition of Siloxy
Groups. Membranes (thickness 30ꢀ80 μm) of polymers (2a and
2b) were fabricated by casting their toluene solutions (concentration
0.2ꢀ0.4 wt %) into Petri dishes. The dish was covered with a glass vessel
to slow solvent evaporation (5ꢀ6 days). After a membrane was formed,
the membrane was peeled off, and it was immersed in methanol for 24 h
and dried to constant weight at room temperature. The decomposition
of siloxy groups in polymer membrane was carried out using a
solution of n-Bu4N+Fꢀ in CH3CN or DMF. A detailed procedure
is as follows: The membrane of 2a (0.085 g, 0.22 mmol repeating
unit) was put into a flask, and then flushed with nitrogen. Another
flask was charged with n-Bu4N+Fꢀ (0.58 g, 2.2 mmol), and then it was
dried under reduced pressure at 45 °C for 48 h. A dried CH3CN
(20 mL) was added into the flask under nitrogen, and then the
n-Bu4N+Fꢀ solution was added to the flask in which the membrane was
placed. The decomposition reaction was carried out at room tempera-
ture for 24 h under nitrogen. Then, the membrane was immersed in a
mixture of methanol/water (9/1) for 6 h followed by in methanol for
24 h. The membrane was dried at room temperature under atmospheric
pressure for 24 h. In the case of 2b, the membrane of 2b (0.097 g,
0.21 mmol repeating unit) and n-Bu4N+Fꢀ (0.55 g, 2.1 mmol) were
used, and the decomposition reaction was carried out at the same
condition as for 2a. However, the reaction time was 72 h because 2b
showed poor reactivity. The decomposition of siloxy groups was
confirmed by the comparison between IR spectra of membranes before
and after the reaction.
Synthesis of Diisopropyl(phenylethynylphenyl)silyl Ether
(Model Compound). Diisopropyl(phenylethynylphenyl)silyl ether
was synthesized according to Scheme 3. The synthesis procedure and
analytical data are as follows.
NaOH (1.0 g, 25 mmol) was put in a flask equipped with a three-way
stopcock. After the flask was flushed with nitrogen, NaOH was dissolved
in methanol (10 mL). 1-Phenyl-2-(p-diisopropylphenoxysilyl)phenyla-
cetylene (1a) (2.6 g, 6.8 mmol) was placed in another flask equipped
with a three-way stopcock and magnetic stirring bar. THF (10 mL) and
the NaOH solution were added to it. The mixture was stirred for 18 h at
room temperature. After ether addition, the solution was washed with
water three times. The ethereal solution was dried over anhydrous
sodium sulfate. After filtration, ether was evaporated, and the crude
product was purified by silica gel column chromatography (eluent:
hexane/chloroform (1/1)) to give 1-phenyl-2-(p-diisopropylhydroxysi-
lyl)phenylacetylene (1.6 g, 77%) as white solid.
A solution of 1-phenyl-2-(p-diisopropylhydroxysilyl)phenylacetylene
(1.5 g, 4.9 mmol) in THF (50 mL) was placed in a flask equipped with a
three-way stopcock and a magnetic stirring bar, and then 1.6 mol/L n-
butyllithium hexane solution (3.1 mL, 4.9 mmol) was added at 0 °C.
After stirring for 10 min, a solution of 1-phenyl-2-(p-chlorodiisopro-
pylsilyl)phenylacetylene (1.6 g, 4.9 mmol) in THF (2.5 mL) was
introduced into the flask at 0 °C. The reaction mixture was stirred for
42 h at room temperature. The mixture was washed with water three
times, dried, and concentrated in vacuo. The crude product was purified
by silica gel column chromatography (eluent: hexane followed by a mixture
of hexane/chloroform (9/1)) to give diisopropyl(phenylethynylphenyl)silyl
Fractional Free Volume (FFV) of Polymer Membranes. The
densities of membranes were determined by hydrostatic weighing using
a Mettler Toledo balance and a density determination kit. In this
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method, a liquid with known density (F0) is needed, and the membrane
density (F) is given by the following equation
was obtained in very low yield (3.9%). When the polymerization
was operated at [M]0 = 0.030 M, the generation of insoluble
polymer was prevented in some degree, and the yield of soluble
polymer reached up to 30%. Monomer 1b, which has trimethyl-
silyl groups, was polymerized at [M]0 = 0.20 M to give a soluble
polymer with high molecular weight in good yield (Mw 931 000,
yield 62%) (run 3). The significant difference of solubility
between 2a and 2b would be attributed to the difference of the
geometric structure in the main chain besides the difference of
substituent. Monomer 1a has a bulky substituent on a phenyl
group adjacent to the triple bond, while monomer 1b has bulky
silyl groups on both of the two phenyl groups. The main chain of
polymer 2a synthesized by the polymerization of monomer 1a
would have high stereoregularity because of the conspicuous
difference of the size of substituent compared to that of polymer
2b synthesized by the polymerization of monomer 1b. The
metathesis polymerization of substituted acetylene produces
the polyacetylene main chain composed of a mixture of cis-form
and trans-form.21 Khotimsky et al. reported that the geometric
structure of the substituted acetylene polymer is defined by a
combination of the size of substituent, kind of transition metal,
polymerization solvent, and temperature.22 The weight-average
molecular weights of all the polymers were very high, and they
were in the range of 763 000 to 1 160 000. The property and
preparation of membrane of 2a were examined using the polymer
sample obtained by the polymerization at lower monomer
concentration (run 2).
F ¼ F0 ꢁ MA=ðMA ꢀ MLÞ
where MA is membrane weight in air and ML is membrane weight in the
auxiliary liquid. An aqueous sodium nitrate was used as the auxiliary
liquid. FFV is calculated by the following equation:
FFV ¼ ðvsp ꢀ v0Þ=vsp≈ðvsp ꢀ 1:3vwÞ=vsp
Here vsp is the polymer specific volume, and v0 is the occupied volume
of the polymer. The occupied volume is typically estimated as 1.3 times
the van der Waals volume (vw), which is calculated using the group
contribution method.20
’ RESULTS AND DISCUSSION
Polymerization. The polymerizations of monomers (1a and 1b)
were carried out using TaCl5/n-Bu4Sn catalyst in toluene at
80 °C. The results of polymerizations are summarized in Table 1.
Polymerization of 1a was performed at the initial monomer
concentrations of 0.20 and 0.030 M to produce the polymers,
which contained insoluble products (runs 1 and 2). Toluene-
insoluble product was filtered off, and toluene-soluble part
was isolated by precipitation into acetone. In the case of the
polymerization at [M]0 = 0.20 M, most part of the formed
polymer was insoluble, and consequently the soluble polymer
Table 1. Polymerizations of Monomers with TaCl5ꢀn-Bu4Sna
Decomposition of Phenoxysilyl Groups of Membranes.
Free-standing membranes of polymers 2a and 2b were prepared
by casting polymers from their toluene solutions. The decom-
position of phenoxysilyl groups of membrane 2a was carried out
by TBAF in CH3CN or DMF at room temperature for 24 h,
which afforded membrane 3a bearing silanol groups. Figure 1
shows the IR spectra of 2a, membranes after the reaction in
CH3CH and DMF, and diisopropyl(phenylethynylphenyl)silyl
c
c
run
monomer
[M]0
yieldb[%]
Mw
Mw/Mn
1
2
3
1a
1a
1b
0.20
0.030
0.20
3.9
30
763 000
1 160 000
931 000
3.34
3.66
2.47
62
a In toluene at 80 °C for 24 h; [TaCl5] = 20 mM, [n-Bu4Sn] = 40 mM.
b Toluene-soluble and acetone-insoluble product. c Measured by GPC.
Figure 1. IR spectra of membranes of 2a (a), after decomposition of phenoxysilyl groups in 2a using CH3CN (b) and DMF (c) as solvent, and model
compound 4 (d).
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Figure 2. IR spectra of membranes of 2b (a), after decomposition of phenoxysilyl groups in 2b using CH3CN (b) and DMF (c) as solvent, and model
compound 4 (d).
ether (model compound). The IR spectrum of of 2a shows the
absorption at 1150 cmꢀ1 assigned to the asymmetric stretching
of SiꢀOꢀC in the phenoxysilyl groups (Figure 1a), while no
absorption at 1150 cmꢀ1 was observed in the spectra after the
phenoxysilyl-decomposition (Figure 1, parts b and c). The
characteristic broad peak at 3400 cmꢀ1 in the membranes after
the phenoxysilyl-decomposition is attributed to the OꢀH
stretching of the silanol groups. These results represent the
completion of the decomposition of phenoxysilyl groups and the
generation of silanol. The absorption at 1050 cmꢀ1 derived from
SiꢀOꢀSi bond appeared after the phenoxysilyl-decomposition
of 2a (Figure 1, parts b and c), which indicates that some silanol
groups would form SiꢀOꢀSi bonds through hydrolysis.
The decomposition of phenoxysilyl groups of membrane 2b
having trimethylsilyl groups was carried out for 72 h under the
same condition as for 2a except reaction time. Figure 2 shows the
IR spectra of 2b, membranes after the reaction in CH3CH and
DMF, and diisopropyl(phenylethynylphenyl)silyl ether (model
compound 4). The phenoxysilyl-decomposition of membrane
2b did not proceed in CH3CN (Figure 2b), whereas the reaction
of membrane 2a was achieved. The decomposition of phenox-
Figure 3. Schematic structure of membrane containing silanol groups
ysilyl groups of 2b was accomplished in DMF, which was
(3a, b): (i) represents the silanol group; (ii) represents the cross-linking.
confirmed by the absence of the absorption at 1150 cmꢀ1 derived
from SiꢀOꢀC and the presence of the absorption at 3400 cmꢀ1
derived from OꢀH in the spectrum (Figure 2c). The absorption
at 1050 cmꢀ1 derived from SiꢀOꢀSi appeared after the
phenoxysilyl-decomposition similarly to the case of 2a. The
results of IR spectra suggest that membranes of 3a and 3b had
silanol groups and cross-linking sites via siloxane bonds. The
presumable structure after decomposition is shown in Figure 3.
The conversion of phenoxysilyl groups in decomposition and
the content of SiꢀOꢀSi bonds within the membranes after the
reaction (3a and 3b) were summarized in Table 2. The content
of SiꢀOꢀSi bonds was calculated from the peak strength at
1050 cmꢀ1 on the basis of the peak at 1380 cmꢀ1 attributed to
SiꢀCꢀH bending. Figure 1d and Figure 2d show the spectrum
of diisopropyl(phenylethynylphenyl)silyl ether, which were used
as model compound containing 100% of SiꢀOꢀSi bonds. The
membranes of 3a obtained by the complete phenoxysilyl-decom-
position in CH3CN and DMF included 20% and 30% of
SiꢀOꢀSi bonds, respectively. The content of SiꢀOꢀSi bonds
in membrane 3b was 20%. The conversion of phenoxysilyl
groups in the decomposition of 2b using CH3CN was 0%, while
that in the reaction of 2a was 100%. The poor reactivity of
membrane 2b in CH3CN would be ascribed to the presence of
electron-donating trimethylsilyl groups, which lower the electro-
philicity at Si atoms of phenoxysilyl groups. The decomposition
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of phenoxysilyl of 2b proceeded completely in DMF, while the
reaction did not occur in CH3CN. This would be accounted for
by swelling of membranes in the reaction solvents. To examine
the membrane-swelling in solvents, the membranes of 2a and 2b
were immersed in CH3CN and DMF at room temperature until
the weights of membranes were constant. After removing the
excess solvent, the weights of swelling membranes were mea-
sured. The degrees of swelling are shown in Table 3. The
increases in weight of membrane 2b after immersion in CH3CN
and DMF were 2.5% and 9.9%, respectively. In other words, the
membrane of 2b swells more effectively in DMF than CH3CN. In
the phenoxysilyl-decomposition using DMF as solvent, the
reagent diffuses into membrane more smoothly. The reactivity
of polymer membrane would be influenced by membrane-
swelling besides activity of reactant.
in any solvents. Polymer 3b, which was synthesized by the
phenoxysilyl-decomposition of polymer 2b containing trimethyl-
silyl groups, did not dissolved completely in any solvents, and it
was partly soluble in Et2O and THF. The poor solubility of
membranes of 3a and 3b would be ascribed to their cross-linked
structures and the combination of hydrophilic silanol groups and
hydrophobic diphenylacetylene moiety.
Gas Permeability. The permeability of the membranes of 2a,
2b, 3a, and 3b to various gases was examined at 25 °C, and the
CO2 diffusion coefficients (D(CO2)) and CO2 solubility coeffi-
cients (S(CO2)) were measured by time lag method (Table 5).
Unfortunately, the time lags to oxygen and nitrogen permeability
measurement were so small that D(O2) and D(N2) could not be
calculated. The fractional free volume (FFV) of the membranes
Solvent Solubility. The solubility of the polymers is summar-
ized in Table 4. The polymers having phenoxysilyl groups
(2a and 2b) completely dissolved in common organic solvents such
as CCl4, toluene, CHCl3, and THF. The phenoxysilyl-decom-
position of polymer 2a produced practically insoluble polymer 3a
Table 2. Conversion of SiꢀOꢀPh and Content of SiꢀOꢀSi
Bonds in Membranes After Decomposition of Phenoxysilyl
Groups
reaction
solvent
% conversion of
SiꢀOꢀPha
% content of
SiꢀOꢀSi bondsa
membrane
3a
3a
3b
3b
CH3CN
DMF
100
100
0
20
30
ꢀ
CH3CN
DMF
a Estimated from IR spectra.
Figure 4. Relationship between P(CO2)/P(N2) and P(CO2) for the
present polymers and other polyacetylenes bearing polar groups.
100
20
Table 3. Swelling of Solvents in Membrane 2a and 2b
liquid sorption, wt %
solvent
2a
2b
CH3CN
DMF
4.8
2.5
9.9
16
Table 4. Solubility of Polymersa
hexane CCl4 toluene Et2O CHCl3 THF CH3OH DMF
2a
2b
3a
3b
ꢀ
ꢀ
ꢀ
ꢀ
+
+
(
(
ꢀ
(
+
+
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
+
+
+
+
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(
Figure 5. Relationship between P(O2)/P(N2) and P(O2) for the
present polymers and other polyacetylenes bearing polar groups.
a Symbols: +, soluble; (, partly soluble; ꢀ, insoluble.
Table 5. Gas Permeation Properties and Densities of Phenoxysilyl Group-Containing and Silanol Group-Containing Polymers
membrane
reaction solvent
P(O2)a
P(N2)a
P(CO2)a
D(CO2)b ꢁ 108
S(CO2)c ꢁ 103
density [g cmꢀ3
]
FFV
2a
3a
3a
2b
3b
ꢀ
12
97
3.9
32
61
610
36
110
17
58
66
13
40
1.12
1.10
1.01
1.09
0.887
0.127
CH3CN
DMF
ꢀ
d
210
26
79
1200
130
180
d
7.8
100
0.124
DMF
1300
770
4300
1100
d
a In the unit of barrer [1 barrer =1 ꢁ 10ꢀ10 cm3(STP) cm cmꢀ2 sꢀ1 cmHgꢀ1]. b In the units of cm2 sꢀ1. c In the units of cm3(STP) cmꢀ3 cmHg. d FFV
value could not be calculated because 3a and 3b had cross-linked structures.
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Figure 6. Structures of polar-group-containing polyacetylenes (PA1ꢀ4).
of 2a and 2b was calculated from the membrane density, and the
data are shown in Table 5. However the FFV of 3a and 3b could
not be calculated because they have cross-linked structures. The
permeability coefficients (P) of 2a to oxygen, nitrogen, and
carbon dioxide were 12, 3.9, and 61 barrers, respectively. The P
values of 2b were about twice as large as those of 2a. The
permeability coefficients of phenoxysilyl group-containing poly-
(diphenylacetylene)s are comparable to bulky silyl group-con-
taining poly(diphenylacetylene)s reported previously.23ꢀ27
The D(CO2) value of 2b was 2.8 times larger than that of 2a,
while the FFVs of 2a and 2b were nearly the same value. FFV
value is one of important factors for permeability of membrane,
but local mobility of substituents also affects gas permeability.
Trimethylsilyl groups in poly(substituted acetylene)s are known
to show high local mobility,12,13 the high local mobility would
enhance gas diffusivity in membrane of 2b.
permeable polymer membranes have less selectivity and vice
versa. Robeson’s upper bound, which was determined in 2008,
represents the experimental limit of the separation performance of
polymer membranes.28 Most materials lie below the upper
bound, and membranes exhibiting good performance for gas
separation were located beside or above the bound. The separa-
tion factors of CO2 against N2 (P(CO2)/P(N2)) in membranes of
3a obtained using CH3CN and DMF were 19 and 15, respec-
tively, which were slightly larger than 16 of membrane of 2a. The
phenoxysilyl-decomposition of membrane of 2a led to about 10
or 20 times increase in the CO2 permeability coefficient without
decrease in CO2/N2 selectivity, indicating improvement in CO2
separation performance. It would be due to that the interaction of
silanol groups with CO2 molecules enhances CO2 solubility in
the polymer membrane. From Figures 4 and 5, it is obvious that
the present polymers exhibit much higher gas permeability than
other polyacetylenes with polar groups.
The phenoxysilyl-decomposition of membrane of 2a in-
creased the gas permeability. The P(O2), P(N2), and P(CO2)
of membrane of 3a obtained by the phenoxysilyl-decomposition
in CH3CN were 97, 32, and 610 barrers, respectively. It was
expected that the polar silanol groups makes the membrane
dense owing to their interaction, but the density of membrane of
3a obtained using CH3CN was comparable to that of 2a. The
decomposition was carried out at a solid state, and partially cross-
linking was formed during the reaction. Therefore, the polymer
chain packing was inhibited even though polar silanol groups
were generated. Membrane of 3a synthesized using DMF as
solvent exhibited high gas permeability compared to 3a obtained
using CH3CN. As shown in Table 2, membranes 3a obtained
using CH3CN and DMF had 20% and 30% of SiꢀOꢀSi bonds,
respectively. The higher degree of cross-linking in membrane of
3a obtained using DMF resulted in lower mobility of polymer
chain and hindering dense packing. The density of membrane of
3a obtained using DMF was 1.01 g/cm3, which was much lower
than that of 3a obtained using CH3CN. Membrane of 3b after the
phenoxysilyl-decomposition of membrane of 2b bearing tri-
methylsilyl groups exhibited the high gas permeability, which
may result from its low density. The P(O2), P(N2), P(CO2), and
density of membrane of 3b were 1300, 770, and 4300 barrers and
0.887 g/cm3, respectively. It is noteworthy that the permeability
of 3b is one of the highest among all the known polymers bearing
polar groups.28
’ CONCLUSIONS
A novel functional polyacetylenes have been developed to
introduce silanol groups into poly(diphenylacetylene)s. Poly-
(diphenylacetylene)s having silanol groups were obtained by
treatment of the precursor polymers having siloxy groups with n-
Bu4N+Fꢀ. Poly(diphenylacetylene) having siloxy groups were
prepared by metathesis polymerization of corresponding diphe-
nylacetylene with TaCl5. Membranes of silanol-functionalized
poly(diphenylacetylene)s exhibited low membrane densities and
very high gas permeability. The oxygen permeability coefficient
of poly(diphenylacetylene) bearing both silanol and trimethylsi-
lyl groups was 1300 barrers, whose value is the largest among all
the substituted acetylene polymers with functional groups.
Moreover, silanol-functional poly(diphenylacetylene)s could be
used as a novel reactive conjugated polymer for organic/inorganic
materials, separation membranes, and light-emitting devices.
’ AUTHOR INFORMATION
Corresponding Author
*Telephone: +81 776 27 9779. Fax: +81 776 27 8767. E-mail:
sakaguchi@matse.u-fukui.ac.jp.
Permselectivity for CO2/N2 and O2/N2. The permeability
coefficients and the separation factors of the present polymer mem-
branes are plotted on a logꢀlog scale (Figures 4 and 5). Figures 4
and 5 contain the data of other polyacetylenes bearing polar
groups such as hydroxy,6 sulfonic acid,8 ethylene glycol,29 and esters30
(PA1ꢀ4), whose structures are shown in Figure 6. Generally, more
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