Synthesis and gas permeation properties of poly(diarylacetylene)s having substituted and twisted biphenyl moieties

Article abstract of DOI:10.1002/pola.23836

Diarylacetylene monomers containing substituted biphenyl (1a-f) and anthryl (1g) groups were synthesized and then polymerized with TaCl₅-n- Bu₄Sn catalyst to produce the corresponding poly(diarylacetylene)s (2a-g). Polymers 2a-f were

Full text of DOI:10.1002/pola.23836

Synthesis and Gas Permeation Properties of Poly(diarylacetylene)s Having
Substituted and Twisted Biphenyl Moieties
YANMING HU,1,2 TOSHIYUKI SHIMIZU,1 KYOHEI HATTORI,1 MASASHI SHIOTSUKI,1 FUMIO SANDA,1 TOSHIO MASUDA1
1Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura Campus, Nishikyo-ku,
Kyoto 615-8510, Japan
2State Key Laboratory of Fine Chemicals, Department of Polymer Science and Engineering, School of Chemical Engineering,
Dalian University of Technology, 158 Zhongshan Road, Dalian 116012, China
Received 22 October 2009; accepted 16 November 2009
DOI: 10.1002/pola.23836
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Diarylacetylene monomers containing substituted
biphenyl (1a–f) and anthryl (1g) groups were synthesized and
then polymerized with TaCl5-n-Bu4Sn catalyst to produce the
corresponding poly(diarylacetylene)s (2a–g). Polymers 2a–f
were soluble in common organic solvents such as cyclohexane,
toluene, and chloroform. According to thermogravimetric analy-
sis, the onset temperatures of weight loss of the polymers were
over 400 ꢀC in air, indicating considerably high thermal stability.
Free-standing membranes 2a and 2c–e were prepared by the so-
lution casting method. Desilylation of Si-containing membrane
2c was carried out with trifluoroacetic acid to afford 3c. All the
polymer membranes, especially those having twisted biphenyl
groups, exhibited high gas permeability; for example, their oxy-
gen permeability (PO ) values ranged from 130 to 1400 barrers.
2
Membrane 2d having two chlorine atoms in the biphenyl group
showed the highest gas permeability (PO ¼ 1400 barrers)
2
C
V
among the present polymers.
2010 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 48: 861–868, 2010
KEYWORDS: gas permeation; membranes; polyacetylenes
INTRODUCTION Substituted polyacetylenes have attracted
much attention among scientists because of a variety of func-
tions, such as optical nonlinearity, photoconductivity, liquid
crystallinity, helicity, and high gas permeability.1–5 As an im-
portant class of separation membrane materials, substituted
polyacetylenes are characterized by high gas permeability
and high vapor/gas permselectivity, which are strikingly dif-
ferent from those of conventional glassy polymers.6–10 The
unique permeation properties of these polymers originate
from their stiff main chain composed of alternating double
bonds, bulky pendant groups, and low cohesive energy struc-
ture. One of them, poly(1-trimethylsilyl-1-propyne) [poly-
(TMSP)] is the most permeable polymeric materials among
all the existing polymers, and many studies have been
reported concerning its permeation properties to date.11–15
Since the discovery of poly(TMSP), considerable effort has
been devoted to the synthesis and study on gas permeation
properties of new substituted polyacetylenes aiming at the
development of novel separation membrane materials.
Poly(diarylacetylene)s have the possibility that a variety of
chemical structures can be accessed by the modification of
the precursor monomers to tailor polymer properties
desired for specific applications. Biphenyl-containing poly-
mers have been extensively studied for applications as liquid
crystalline materials, light-emitting diodes, proton exchange
membranes, and gas separation membranes. Recent exam-
ples of such polymers include polyacetylenes,18 poly(isothia-
naphthene methine),19 poly(ether sulfone)s,20 poly(2,7-carba-
zole)s,21 poly(phenylenevinylene)s,22 and polyimides.23 It is
known that incorporation of biphenyl groups contributes for
improving the thermal stability of the polymers. The bulky
biphenyl group is expected to affect the polymer chain pack-
ing and in turn the gas permeation properties of polymer
membranes. However, only a few biphenyl-based poly(diary-
acetylene)s have been reported so far. Although polymers 2h
and 2i in Chart 1 have been synthesized, they are insoluble
in any solvents.24 Introduction of a very bulky tert-butyldi-
methylsiloxy group onto the biphenyl group of 2h solubilizes
the polymer (2j), but the gas permeability of the polymer is
fairly low (e.g., Po2 73 barrers).25 On the other hand, incor-
poration of moderately bulky and spherical groups, such as
tert-butyl and trimethylsilyl, into poly(diarylacetylene)s has
been recognized to not only improve solubility but also favor
high gas permeability. Thus, we synthesized poly(diarylacety-
lene)s having biphenyl moieties substituted with tert-butyl,
Poly(diarylacetylene) derivatives are another important type
of highly permeable polymers. For instance, poly[1-phenyl-2-
(p-trimethylsilyl)phenylacetylene] [poly(TMSDPA)] exhibits
excellent thermal stability and high gas permeability; its oxy-
gen permeability coefficient (PO ) is as large as 1500 barrers,
2
and the onset temperature of weight loss is 420 ꢀC,16,17
which is clearly higher than that of poly(TMSP) (300 ꢀC).12
Correspondence to: T. Masuda, Department of Environmental and Biological Chemistry, Fukui University of Technology, 3-6-1 Gakuen, Fukui
910-8505, Japan (E-mail: masuda@fukui-ut.ac.jp)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 861–868 (2010) 2010 Wiley Periodicals, Inc.
SYNTHESIS AND PROPERTIES OF POLY(DIARYLACETYLENE)S, HU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Denko Shodex K-805, K-806, and K-807) using CHCl3 as an
eluent at a flow rate of 1.0 mL/min, calibrated with polysty-
rene standard. NMR spectra were recorded on a JEOL EX-
400 spectrometer. Melting points were measured with a
Yanaco micromelting point apparatus. Elemental analysis of
monomers was carried out at the Microanalytical Center of
Kyoto University. Thermogravimetric analysis (TGA) was con-
ducted in air with a Shimadzu TGA-50 thermal analyzer.
Materials
Tantalum(V) chloride (TaCl5, Aldrich) was used without fur-
ther purification. Tetra-n-butyltin (n-Bu4Sn, Wako) was used
after distillation. 4-(Trimethylsilyl)phenylacetylene was
donated by NOF. Phenylacetylene (Aldrich), 4-bromo-40-tert-
butylbiphenyl (TCI), 1-bromo-4-iodobenzene, tert-butyl-3,5-
dimethylbenzene, 1,4-di-tert-butylbenzene, 9-bromoanthra-
cene, trifluoroacetic acid (TFA), and common solvents (Wako
Pure Chemical) were used without further purification,
except toluene, as a polymerization solvent, that was purified
by the standard method. Diphenylacetylene-4-boronic acid
and 4-(trimethylsilyl)diphenylacetylene-40-boronic acid were
prepared according to the literature procedures.26 5-tert-
Butyl-2-iodo-1,3-dimethylbenzene and 2,5-di-tert-butyliodo-
benzene were prepared according to the literature meth-
ods.27 Monomers were synthesized referring to the literature
of Suzuki coupling28,29 and ethynylation reactions30,31
(Scheme 2).
CHART 1 Previous examples of poly(diarylacetylene)s having
biphenyl moieties.
methyl, and chlorine groups, because such polymers are
expected to show good solubility due to the substituents,
excellent thermal stability due to the poly(diarylacetylene)
structure, and high gas permeability due to the more or less
twisted structure of the biphenyl moiety.
In this study, we report the polymerization of diarylacetylene
monomers containing a substituted biphenyl or an anthryl
group (Scheme 1, 1a–g). Free-standing membranes were fab-
ricated from several resultant polymers, and desilylation of
the membrane was accomplished with trifluoroacetic acid.
Then, general properties and gas permeability of the
obtained polymers were examined.
EXPERIMENTAL
General
1-Phenyl-2-(40-tert-butyl-biphenyl-4-yl)acetylene (1a)
A 500-mL three-necked flask was equipped with a reflux
condenser, a three-way stopcock, and a magnetic stirring bar.
After the flask was flushed with nitrogen, 4-bromo-40-tert-
Molecular weights of polymers were estimated by gel perme-
ation chromatography on a Shimadzu PU/SPD-6A/UV-975
chromatograph equipped with polystyrene columns (Showa
SCHEME 1 Synthesis of poly(diarylacetylene)s having biphenyl or anthryl moieties.
862
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ARTICLE
SCHEME 2 Synthesis of diarylacetylene monomers having biphenyl or anthryl moieties.
butylbiphenyl (5.0 g, 17 mmol), bis(triphenylphosphine)pal-
1-Phenyl-2-(40-tert-butyl-20,60-dimethylbiphenyl-4-yl)
acetylene (1b)
ladium dichloride (53 mg, 0.08 mmol), cuprous iodide (88
mg, 0.48 mmol), and triphenylphosphine (80 mg, 0.32
mmol) were placed in the flask and dissolved in triethyl-
amine (150 mL) at room temperature. Then, a solution of
phenylacetylene (2.0 g, 20 mmol) in triethylamine (20 mL)
was added, and the reaction mixture was heated at reflux
temperature for 5 h. Triethylamine in the reaction mixture
was evaporated off, and then diethyl ether (200 mL) was
added to the residual mass. Solvent-insoluble solid was fil-
tered off, and the filtrate was washed with 1 M HCl aq. and
then with water. The ethereal solution was dried over anhy-
drous magnesium sulfate. After evaporating the solvent, the
crude product was purified by silica gel column chromatog-
raphy (eluent: hexane) to give a white solid (3.5 g, 65%).
A 100-mL three-necked flask was equipped with a reflux
condenser, a three-way stopcock, and a magnetic stirring bar.
After the flask was flushed with nitrogen, diphenylacetylene-
4-boronic acid (1.5 g, 6.8 mmol), 4-tert-butyl-2,6-dimethylio-
dobenzene (2.3 g, 8.1 mmol), 1,10-bis(diphenylphosphino)fer-
rocene palladium(II) dichloride [Pd(dppf)Cl2, 49 mg, 0.068
mmol], potassium carbonate (K2CO3, 1.9 g, 14 mmol), tolu-
ene (5 mL), methanol (5 mL), and H2O (5 mL) were placed
ꢀ
in the flask. Then, the reaction mixture was heated at 80 C
for 6 h. After that the solution was extracted with diethyl
ether. The ethereal solution was dried over anhydrous mag-
nesium sulfate. After evaporating the solvent, the crude
product was purified by silica gel column chromatography
(eluent: hexane) to provide the desired product (1.5 g, 65%)
1H NMR (400 MHz, d, CDCl3): 7.59–7.23 (br, 13H, Ar), 1.35
(s, 9H, CCH3). 13C NMR (100 MHz, d, CDCl3): 150.2, 140.3,
136.9, 131.5, 131.1, 127.8, 127.7, 126.3, 126.1, 125.3, 122.8,
121.3, 89.5, 88.9, 34.1, 30.9. Anal. Calcd. for C24H22: C, 92.90;
H, 7.10. Found: C, 92.53; H, 7.13.
ꢀ
as a white solid; mp 158.0–159.0 C.
1H NMR (400 MHz, CDCl3, d): 7.59–7.13 (m, 11H, Ar), 2.05
(s, 6H, CH3), 1.35 (s, 9H, C(CH3)3). 13C NMR (100 MHz,
CDCl3, d): 150.0, 141.5, 138.3, 135.4, 131.6, 131.5, 129.5,
SYNTHESIS AND PROPERTIES OF POLY(DIARYLACETYLENE)S, HU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
128.3, 128.2, 124.4, 123.4, 121.4, 89.4, 89.3, 34.3, 31.4, 21.1.
Anal. Calcd. for C26H26: C, 92.26; H, 7.74. Found: C, 92.44; H,
7.65.
135.0, 133.3, 131.8, 130.7, 129.1, 128.9, 128.5, 125.1, 124.3,
122.4, 91.5, 86.7, 34.7, 31.3. Anal. Calcd. for C24H20Cl2: C,
75.99; H, 5.31. Found: C, 76.11; H, 5.18.
1-(4-Timethylsilylphenyl)-2-(40-tert-butyl-20,60-dimethylbi-
phenyl-4-yl)acetylene (1c)
1-Phenyl-2-(20,50-di-tert-butylbiphenyl-4-yl)acetylene (1e)
A 200-mL three-necked flask was equipped with a reflux
condenser, a three-way stopcock, and a magnetic stirring bar.
After the flask was flushed with nitrogen, diphenylacetylene-
4-boronic acid (3.1 g, 14 mmol), 2,5-di-tert-butyliodobenzene
(4.0 g, 14 mmol), tetrakis(triphenylphosphine)palladium(0)
[Pd(PPh3)4,3.2 g, 3.6 mmol], K2CO3 (4.8 g, 35 mmol), ben-
zene (48 mL), methanol (32 mL), and H2O (10 mL) were
placed in the flask. Then, the reaction mixture was heated at
80 ꢀC for 5 h. After that the solution was extracted with
diethyl ether. The ethereal solution was dried over anhy-
drous magnesium sulfate. After evaporating the solvent, the
crude product was purified by silica gel column chromatog-
raphy (eluent: hexane) to provide the desired product (1.5 g,
This monomer was prepared by the same method as for
monomer 1b using 4-(trimethylsilyl)diphenylacetylene-40-
boronic acid instead of diphenylacetylene-4-boronic acid to
ꢀ
give a white solid; yield 70%, mp 155.5–157.0 C.
1H NMR (400 MHz, CDCl3, d): 7.59–7.13 (m, 10H, Ar), 2.05
(s, 6H, CH3), 1.35 (s, 9H, C(CH3)3), 0.28 (s, 9H, Si(CH3)3). 13C
NMR (100 MHz, CDCl3, d): 150.0, 141.5, 140.0, 138.3, 135.4,
133.2, 131.7, 130.7, 129.5, 124.4, 123.6, 121.4, 89.8, 89.5,
34.3, 31.4, 21.1, ꢁ1.2. Anal. Calcd. for C29H34Si: C, 84.82; H,
8.34. Found: C, 84.53; H, 8.37.
1-Phenyl-2-(2,6-dichloro-40-tert-butylbiphenyl-4-yl)acety-
lene (1d)
ꢀ
30%) as a white solid; mp 174.6–175.6 C.
A 500-mL three-necked flask was equipped with a reflux
condenser, a three-way stopcock, and a magnetic stirring bar.
After the flask was flushed with nitrogen, 4-bromo-2,6-
dichloroaniline (12 g, 50 mmol), bis(triphenylphosphine)pal-
ladium dichloride (351 mg, 0.50 mmol), cuprous iodide (571
mg, 3.0 mmol), and triphenylphosphine (525 mg, 2.0 mmol)
were placed in the flask. Then, triethylamine (300 mL) and
phenylacetylene (6.1 g, 60 mmol) were added, and the reac-
tion mixture was heated at reflux temperature for 7 h. After
that triethylamine in the reaction mixture was evaporated
off, and then diethyl ether (200 mL) was added to the resid-
ual mass. Solvent-insoluble solid was filtered off, and the fil-
trate was washed with 1 M HCl aq. and then with water. The
ethereal solution was dried over anhydrous magnesium sul-
fate. After evaporating the solvent, the crude product was
purified by silica gel column chromatography (eluent: hex-
ane/ethyl acetate ¼ 30/1) to give 1-phenyl-2-(4-amino-3,5-
dichlorophenyl)acetylene as a red solid (6.2 g, 47%).
1H NMR (400 MHz, CDCl3, d): 7.56–6.97 (m, 12H, Ar), 1.30
(s, 9H, C(CH3)3), 1.18 (s, 9H, C(CH3)3). 13C NMR (100 MHz,
CDCl3, d): 147.5, 146.0, 144.6, 140.9, 131.6, 130.4, 130.2,
129.1, 128.3, 126.4, 126.3, 124.2, 123.4, 121.3, 89.4, 89.3,
36.1, 34.1, 32.7, 31.3. Anal. Calcd. for C28H30: C, 91.75; H,
8.25. Found: C, 91.49; H, 8.54.
1-(4-Trimethylsilylphenyl)-2-(20,50-di-tert-butylbiphenyl-4-
yl)acetylene (1f)
This monomer was prepared by the same method as for
monomer 1e using 4-(trimethylsilyl)diphenylacetylene-40-
boronic acid instead of diphenylacetylene-4-boronic acid to
ꢀ
give a white solid; yield 30%, mp 205.0–206.0 C.
1H NMR (400 MHz, CDCl3, d): 7.53–6.97 (m, 10H, Ar), 1.30
(s, 9H, C(CH3)3), 1.18 (s, 9H, C(CH3)3), 0.28 (s, 9H, Si(CH3)3).
13C NMR (100 MHz, CDCl3, d): 147.5, 146.0, 144.6, 141.0,
140.9, 133.2, 130.7, 130.5, 130.2, 129.2, 126.4, 124.2, 123.6,
121.4, 89.8, 89.5, 36.1, 34.1, 32.7, 31.3, ꢁ1.2. Anal. Calcd. for
With reference to the reported method,32 a 1-L three-necked
flask containing 1-phenyl-2-(4-amino-3,5-dichlorophenyl)ace-
tylene (6.2 g, 24 mmol), p-toluenesulfonic acid (14 g, 71
mmol), and acetonitrile (140 mL) was cooled to 10–15 ꢀC.
Then, a solution of NaNO2 (3.3 g, 47 mmol) and KI (9.8 g,
59 mmol) in H2O (15 mL) was added dropwise. To the reac-
tion mixture were added NaHCO3 (1 M; until pH ¼ 9–10)
and Na2S2O3 (2 M, 350 mL). After extracting the organic
compounds with diethyl ether and evaporating the solvent,
the crude product was purified by silica gel column chroma-
tography (eluent: hexane) to give 1-phenyl-2-(3,5-dichloro-4-
iodophenyl)acetylene as a white solid (4.6 g, 52%).
C31H38Si: C, 84.87; H, 8.73. Found: C, 84.42; H, 8.72.
1-(4-Trimethylsilylphenyl)-2-(4-(9-anthryl)phenyl)acety-
lene (1g)
This monomer was prepared by the same method as for
monomer 1b using 4-(trimethylsilyl)diphenylacetylene-40-
boronic acid and 9-bromoanthracene instead of diphenylace-
tylene-4-boronic acid and 4-tert-butyl-2,6-dimethyliodoben-
ꢀ
zene to give a white solid; yield 30%, mp 206.1–207.1 C.
1H NMR (400 MHz, CDCl3, d): 8.49–7.34 (m, 17H, Ar), 0.30
(s, 9H, Si(CH3)3). 13C NMR (100 MHz, CDCl3, d): 141.2, 139.0,
136.2, 133.3, 131.6, 131.4, 131.3, 130.7, 130.0, 128.4, 126.8,
126.6, 125.5, 125.1, 123.5, 122.5, 90.1, 89.7, ꢁ1.2. Anal.
Calcd. for C31H26Si: C, 87.27; H, 6.14. Found: C, 87.43; H,
6.13.
Monomer 1d was prepared by the same method as for
monomer 1b using 4-tert-butylphenylboronic acid and 1-
phenyl-2-(3,5-dichloro-4-iodophenyl)acetylene instead of
diphenylacetylene-4-boronic acid and 4-tert-butyl-2,6-di-
methyliodobenzene to give a white solid (2.1 g, 52%); mp
Polymerization Procedure
Polymerizations were performed using toluene as a solvent
in a Schlenk tube equipped with a three-way stopcock at 80
ꢀC for 24 h under dry nitrogen at the following reagent con-
centrations: [TaCl5] ¼ 20 mM, [n-Bu4Sn] ¼ 40 mM. The
ꢀ
168.0–169.0 C.
1H NMR (400 MHz, CDCl3, d): 7.55–7.18 (m, 11H, Ar), 1.37
(s, 9H, C(CH3)3). 13C NMR (100 MHz, CDCl3, d): 151.1, 139.5,
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ARTICLE
and all the monomers were identified by 1H and 13C NMR
spectroscopies besides elemental analysis.
TABLE 1 Polymerization of Monomers 1a–g by TaCl5-n-Bu4Sn
Catalysta
The polymerization of diarylacetylene monomers 1a–g was
carried out in toluene by using TaCl5-n-Bu4Sn catalyst, whose
results are summarized in Table 1. It is known that TaCl5-n-
Bu4Sn is an effective catalyst for the polymerization of steri-
cally crowded diphenylacetylene derivatives to provide poly-
mers having high molecular weights,1,34 which is essential
for fabrication of free-standing membranes. In this study, the
polymerization of monomer 1a, which possesses the p-tert-
butylbiphenyl group, gave a soluble polymer (2a) in a good
yield (58%), whose weight-average molecular weight (Mw)
was 2.5 ꢂ 106. Monomers 1b–d having ortho methyl or chlo-
rine substituents in addition to p-tert-butyl group on the
biphenyl moiety also provided polymers in high yields
(ꢃ80%), and their Mw values were as high as 4.9 ꢂ 106 and
above. Monomers 1e and 1f with two tert-butyl groups on
the terminal phenyl group of biphenyl afforded polymers
with lower Mw (1.6 ꢂ 106 and 0.9 ꢂ 106, respectively) than
those of 1a–d, which is due to the steric hindrance of the
bulky tert-butyl groups. On the other hand, polymer 2g
obtained from monomer 1g, which has an anthryl substitu-
ent on a phenyl ring, was insoluble in any organic solvents.
Thus, except 1g, all the present monomers having substi-
tuted biphenyl groups successfully polymerized into high-
molecular-weight soluble polymers in good yields.
Polymerb
c
Monomer
[M]0 (M)
Yield (%)
Mw ꢂ 10ꢁ6c
Mw/Mn
1a
1b
1c
1d
1e
1f
0.20
0.20
0.20
0.10
0.20
0.20
0.10
58
83
83
80
74
53
82
2.5
>6.0
>6.0
4.9
1.6
–
–
3.3
3.0
3.1
1.6
0.91
d
d
1g
a
–
–
Polymerization in toluene at 80 ꢀC for 24 h; [TaCl5] ¼ 20 mM, [n-
Bu4Sn] ¼ 40 mM.
b
Methanol-insoluble product.
c
Determined by GPC, eluted with CHCl3 (polystyrenes as standards).
d
Insoluble in any solvents.
formed polymers were isolated by precipitation into a large
amount of methanol and dried to constant weight. The poly-
mer yields were determined by gravimetry.
Membrane Fabrication and Desilylation
The membranes (thickness ca. 80–120 lm) of polymers 2a–f
were fabricated by casting from toluene solution of the poly-
mer (concentration ca. 0.50–1.0 wt %) onto a flat-bottomed
Petri dish. Then, the dish was covered with a glass vessel to
slow solvent evaporation (ca. 4–7 days). Actually, the mem-
brane of 2b was too brittle to be free standing. After a mem-
brane was formed, the membrane was peeled off, and it was
immersed in methanol for 24 h and dried to constant weight
at room temperature for 24 h. With reference to the method
described in the literature,33 the desilylation reaction of
polymer membrane 2c was carried out using trifluoroacetic
acid.
Solubility and Thermal Stability of the Polymers
The solubility of polymer is an essential factor for membrane
fabrication by solution casting. Hence, the solubility of the
formed polymers in various solvents was examined (Table
2). According to our previous study, polymer 2h, which has
just planar groups but no flexible groups, is insoluble in any
organic solvents. In contrast, all the present polymers having
substituted biphenyl groups, 2a–f, dissolved in common non-
polar or low-polarity solvents such as toluene, chloroform,
and THF. In particular, the good solubility of 2a, which has
just the p-tert-butylbiphenyl moiety, means that the p-tert-
butyl group is effective enough to solubilize this type of
polymers. The good solubility due to the incorporation of the
p-tert-butyl group is attributable to two reasons; that is, one
is that the p-tert-butyl group has sufficient surface to inter-
act with a solvent and is locally quite mobile, namely its
Measurement of Gas Permeability
Gas permeability coefficients of polymer membranes were
measured with a Rikaseiki K-315-N gas permeability appara-
tus equipped with a MKS Baratron detector at 25 ꢀC. The
downstream side of the membrane was evacuated to 0.3 Pa,
whereas the upstream side was filled with a gas at about 1
atm (105 Pa), and the increase of pressure in a downstream
receiving vessel was measured. The P-values were calculated
from the slopes of time–pressure curves in the steady state
where Fick’s law held.
TABLE 2 Solubility of Polymers 2a–ga
2a
2b
2c
2d
2e
2f
2g
Hexane
Cyclohexane
Toluene
CHCl3
ꢁ
6
þ
þ
þ
ꢁ
ꢁ
ꢁ
ꢁ
þ
þ
þ
þ
ꢁ
ꢁ
ꢁ
ꢁ
þ
þ
þ
þ
ꢁ
ꢁ
ꢁ
ꢁ
þ
þ
þ
þ
ꢁ
ꢁ
ꢁ
ꢁ
þ
þ
þ
þ
ꢁ
ꢁ
ꢁ
ꢁ
þ
þ
þ
þ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
RESULTS AND DISCUSSION
Polymerization
As described in the Experimental section, diarylacetylene
monomers containing substituted biphenyl (anthryl) groups
were synthesized by applying the Suzuki and Sonogashira
coupling reactions, namely palladium-catalyzed aromatization
and ethynylation and other reactions (see Scheme 2). The
synthetic reactions all proceeded in moderate to good yields,
THF
Methanol
DMF
DMSO
a
Symbols: þ, soluble; 6, partly soluble; ꢁ, insoluble.
SYNTHESIS AND PROPERTIES OF POLY(DIARYLACETYLENE)S, HU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Gas Permeation Properties of the Polymers
The gas permeability coefficients of membranes 2a and 2c–
e, and desilylated membrane 3c to various gases measured
at 25 ꢀC are listed in Table 3. The membrane of 2f was
mechanically too weak to measure the permeability. As seen
from Table 3, 2a, which has just the p-tert-butylbiphenyl
group, showed the lowest gas permeability among the pres-
ent polymers. Thus, the PO value of 2a remained 130 bar-
2
rers. However, this value is still about twice as that of poly-
mer 2j containing flexible siloxy groups (PO ¼ 73 barrers).
2
We have previously reported that the incorporation of flexi-
ble groups in the polymer accompanies a decrease in gas
permeability; for example, the PO value of poly(TMSDPA) is
2
1500 barrers, whereas that of poly[1-phenyl-2-p-(dimethyl-
tert-butylsiloxy)phenylacetylene] is 160 barrers.36
The other present polymer membranes 2c–e and 3c exhib-
ited higher gas permeability than 2a did. The common fea-
ture of the former polymers is the more twisted structure of
the biphenyl moiety due to the presence of ortho substitu-
ents. For instance, the PO of 2c was 760 barrers, which is
2
FIGURE 1 TGA curves of the polymers (in air, heating rate 10
ꢀC/min).
very close to that of poly(dimethylsiloxane) (PO ¼ 780 bar-
2
rers,37 Fig. 2), a typical polymer well known to have the
highest gas permeability among all the rubbery polymers.
methyl groups can easily rotate, and the other reason is that
the introduction of the p-tert-butyl group gives rise to a
large imbalance of the two side groups of the polymers.
With respect to the latter reason, it is noted that poly(diphe-
nylacetylene) and 2i, whose two side groups are the same or
similar in size, are insoluble.10 All the present polymers
were insoluble in highly polar solvents such as methanol,
DMF, and DMSO.
The PO value of 3c obtained by the desilylation of 2c was
2
1100 barrers, which is even higher than that of its precursor
2c and relatively close to that of poly(TMSDPA) (1500 bar-
rers). This increase of gas permeability after desilylation can
be explained by the idea that microvoids rather increase in
number and/or size upon desilylation in the solid state for
such stiff polymers.24 Polymer 2e also displayed fairly high
oxygen permeability (PO ¼ 810 barrers). Among all the
2
biphenyl-containing poly(diarylacetylene)s, polymer 2d
The thermal stability of polymers was examined by TGA
measured in air (Fig. 1). The onset temperatures of weight
loss of all the polymers were above 400 ꢀC, which are simi-
lar to that of thermally stable poly(PTMSDPA) (420 ꢀC)17
and much higher than those of aliphatic disubstituted acety-
exhibited the highest permeability to various gases. Its PO
2
was as high as 1400 barrers, which is about the same as
that of poly(TMSDPA) and very large among all the synthetic
polymers, although smaller than that of poly(TMSP) (PO
10,000 barrers).
ꢃ
2
12
ꢀ
lene polymers such as poly(TMSP) (330 C). The results of
the TGA analysis indicate that the present polymers have
excellent thermal stability, which seems to be due to the
‘‘jacket effect’’ of the bulky aryl groups that protect the dou-
ble bonds in the main chain from air oxidation.35
Based on the above experimental findings, the following dis-
cussions are possible about the gas permeability of the pres-
ent polymers: (i) the twisted biphenyl structure26,38 induced
by methyl, chlorine, or tert-butyl groups at the ortho posi-
tion(s) is favorable for the generation of excess free volume;
Fabrication and Desilylation of Polymer Membranes
Free-standing membranes could be fabricated by casting
polymers 2a and 2c–f from toluene solution, whereas the
membranes of 2b and 2g could not be prepared because of
their brittleness and insolubility, respectively. The formed
membranes were uniform, yellow, and transparent. A mem-
brane of polymer 3c, which has the same structure as that
of 2b, was prepared by desilylation of 2c. The desilylation
reaction was carried out in a trifluoroacetic acid/H2O (9:1
volume ratio) mixture at room temperature for 24 h. The
completion of desilylation could be confirmed by TGA analy-
sis; namely, when Si-containing polymer 2c was heated
above 700 ꢀC, the weight residue composed of SiO2
remained, whereas no residue was detected with the desily-
lated 3c (Fig. 1).
TABLE 3 Gas Permeability Coefficients (P) of Polymer
Membranes
P (Barrera)
Polymer He
H2
O2
N2
CO2
CH4
PO /PN
2 2
2a
2c
3c
2d
2e
a
170
330
130
46
840
120 2.8
990 2.1
660 1,500
760 360 3,300
780 1,900 1,100 520 4,500 1,500 2.1
920 2,400 1,400 740 6,100 2,100 1.9
820 1,800
810 370 3,100
990 2.2
At 25 ꢀC in the units of 1 ꢂ 10ꢁ10 cm3 (STP) cm/(cm2 s cmHg) (¼ 1
barrer).
866
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ARTICLE
barrers among the present polymers, which is about the
same as that of poly(TMSDPA). The results of this study indi-
cate that the incorporation of methyl/chlorine groups in the
biphenyl moieties clearly enhances the gas permeability of
the present polymers.
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