Synthesis and sulfonation of poly(aryl ethers) containing triphenyl methane and tetraphenyl methane moieties from isocynate-masked bisphenols

Article abstract of DOI:10.1021/ma035825i

Wholly aromatic poly(aryl ethers) containing triphenylmethane and tetraphenylmethane moieties were successfully synthesized by aromatic nucleophilic substituting polycondensation from masked bisphenols and decafluorobiphenyl followed by sulfonation with chlorosulfonic acid. The sulfonation took place only at the para positions on the pendant phenyl rings due to the novel biphenol structures designed. For the synthesized polymers, the sulfonation content can be easily controlled and the water-takeup can be conveniently tailored by changing the amount of sulfonation agent. These sulfonated polymers are soluble in polar organic solvents, such as NMP, dimethylacetamide, dimethyl sulfoxide, dimethylformamide, and ethylene glycol monomethyl ether and can be readily cast into tough and smooth films from solutions. The films exhibited very high water absorption ability and superior mechanical strength. These polymers also showed high glass transition temperatures ranging from 176 to 203°C compared with Nafion. The sulfonated polymers can be potentially used as the proton-exchange membranes for fuel cells.

Full text of DOI:10.1021/ma035825i

Macromolecules 2004, 37, 3151-3158
3151
Synthesis and Sulfonation of Poly(aryl ethers) Containing Triphenyl
Methane and Tetraphenyl Methane Moieties from Isocynate-Masked
Bisphenols
L. Wa n g,† Y. Z. Men g,*,‡,§ S. J . Wa n g,‡ X. Y. Sh a n g,† L. Li,§ a n d A. S. Ha y|,
Institute of Energy & Environment Materials, School of Physics & Engineering, Sun Yat-Sen
University, Guangzhou 510275, People’s Republic of China, Guangzhou Institute of Chemistry,
Chinese Academy of Sciences, P.O. Box 1122, Guangzhou 510650, People’s Republic of China,
Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal,
Quebec, Canada H3A 2K6, and School of Mechanical & Production Engineering,
Nanyang Technology University, North Sprine (N3) 639798, Singapore
Received December 4, 2003
ABSTRACT: Wholly aromatic poly(aryl ethers) containing triphenylmethane and tetraphenylmethane
moieties were successfully synthesized by aromatic nucleophilic substituting polycondensation from
masked bisphenols and decafluorobiphenyl followed by sulfonation with chlorosulfonic acid. The sulfonation
took place only at the para positions on the pendant phenyl rings due to the novel biphenol structures
designed. For the synthesized polymers, the sulfonation content can be easily controlled and the water-
takeup can be conveniently tailored by changing the amount of sulfonation agent. These sulfonated
polymers are soluble in polar organic solvents, such as NMP, dimethylacetamide, dimethyl sulfoxide,
dimethylformamide, and ethylene glycol monomethyl ether and can be readily cast into tough and smooth
films from solutions. The films exhibited very high water absorption ability and superior mechanical
strength. These polymers also showed high glass transition temperatures ranging from 176 to 203 °C
compared with Nafion. The sulfonated polymers can be potentially used as the proton-exchange
membranes for fuel cells.
In tr od u ction
partially fluorinated membranes have been disclosed in
the literature. The most successful one is the sulfonated
poly(trifluorostyene) membrane19,20 developed by Bal-
lard Advanced Materials Corp. Some properties of the
membrane are almost the same as those of Nafion117.20,21
Furthermore, the radiation grafting of styrene/divinyl-
benzene mixtures onto the backbone of fluorinated
polymer has been extensively used to fabricate partially
fluorinated polymer membranes.22-24 Amarilla et al.25
have reported a method for the preparation of thin
composite membrane consisting of poly(vinylidene
floride), linear sulfonated polystyrene, and antimonic
acid. A similar polymer membrane synthesized from
sulfonated polystyrene microspheres, poly(vinylpyrroli-
done) and poly(vinylidene fluoride) also has been re-
ported.26 More recently, Miyatake and Hay27,28 have
designed aromatic copolymers containing sulfonated
tetraphenylphenylene (or hexaphenylbiphenylene), flu-
orinated alkane, and perfluorophenylene moieties.
In recent years there has been growing interesting
in the development of a new proton exchange membrane
to meet the requirement of fuel cells. It is generally
accepted that among the many available kinds of proton
conducting polymer electrolytes, poly(perfluoroalkylsul-
fonic acid) (Nafion) is the most preferable from the
standpoint of chemical and thermal stabilities and
physical and proton-conducting properties.1-3 However,
its extremely high cost has limited to a large-scale
practical use of Nafion. Many efforts have been devoted
to developing cheaper proton-conducting polymers. Fluo-
rine-free or partially fluorinated membranes have been
shown to be potential candidates to substitute for the
poly(perfluoroalkylsulfonic acid) membranes, as long as
their mechanical, chemical, and electrochemical proper-
ties are comparable to Nafion. For instance, many
fluorine-free polymers with sulfonic and/or phosphonic
acid groups onto highly stable aromatic polymers have
been reported. These include poly(ether ether ketone)
(PEEK),4-8 polysufone (PSF),9-11 poly(aryl ether sulfone)
(PES),12,13 poly(aryl ether phthalazines),14 and poly-
(phenylene sulfide) (PPS).15,16 Unfortunately, most of
them failed to be used as proton-exchange membranes
with reasonable lifetime, due to a combination of
hydrolytic and oxidative degradation.17,18
Despite a lot of new polymer membrane materials
that have been synthesized, there is still no one candi-
date that is practically applicable for a proton exchange
membrane having equivalent properties with Nafion.
To meet the needs of fuel cell electrolytes, the polymers
should exhibit chemical and electrochemical stability in
the cell-operating environment, such as high resistance
to oxidation, reduction, and hydrolysis. They should also
possess reasonable mechanical strength and stability
during the cell operation. Meanwhile, chemical proper-
ties compatible with the bonding requirements of
the membrane electrode assembly (MEA) have to be
achieved. Finally, the production costs of the polymers
should be compatible with the application of fuel cells.
In previous papers, we have reported the synthesis and
properties of the polyaromatics with hindered and bulky
To improve the durability of a polymer electrolyte
membrane for fuel cells, many research works on
* Corresponding author. Fax: +8620-85232337. E-mail: mengyz@
yahoo.com.
† Chinese Academy of Sciences.
‡ Sun Yat-Sen University.
§ Nanyang Technology University.
| McGill University.
E-mail: allan.hay@mcgill.ca.
10.1021/ma035825i CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/07/2004

3152 Wang et al.
Macromolecules, Vol. 37, No. 9, 2004
Sch em e 1. Syn th eses of Mon om er s 1a -d a n d 2a -d
groups that allowed the position-directed sulfonation.29
These polymers showed high proton conductivity that
could support high currents with minimal resistive
losses and zero electronic conductivity.
SSC-5200) under a protective nitrogen atmosphere (200 mL/
min). The heating rate used was 20 °C/min. Matrix-assisted
laser desorption/ionization time-of-flight mass spectroscopy
(MALDI-TOF-MS) analyses were carried out on a Kratos
KOMPACT MALDI-TOF-MS. The analyte consisted of 1:4:2
(weight) of a sample, lithium bromide, and 1,8,9-trihydroxy-
anthracene (Dithranol) matrix. A sample with about 0.2 µL of
this analyte was spotted on the sample slot and dried at a
temperature of about 50 °C. All spectra were recorded in the
reflection mode. High-performance liquid chromatographic
(HPLC) experiments were performed on a Milton Roy CM4000
multiple-solvent delivery system with a C8 Prime Sphere 4.6
mm × 250 mm column, with chloroform as the eluent, and
with a UV detector at 254 nm. NMR data were recorded at
400 MHz on a Varian 400 Hz NMR instrument and are listed
in parts per million downfield from tetramethylsilane. Melting
points were taken on a XT4A melting point apparatus.
Mon om er Syn th esis. (a ) P r ep a r a tion of Bis(4-h yd r oxy-
p h en yl)p h en ylm eth a n e (1a ). To a 50 mL, three-neck, round-
bottom flask, equipped with a magnetic stirrer and a nitrogen
inlet, containing 2.12 g (20.0 mmol) of benzaldehyde and 5.64
g (60.0 mmol) of phenol in 10 mL of toluene, 3.0 g of 60%
sulfuric acid was added dropwise at 25 °C under nitrogen
atmosphere with stirring (Scheme 1). The mixture was heated
to 60-70 °C and maintained at that temperature for 8 h. Then
the reaction mixture was cooled to room temperature to
precipitate out a red brown solid. The solid was filtered and
washed with water twice and a little toluene once and dried
in a vacuum to yield 3.98 g of red brown solid as crude product
(72.0% yield). It was recrystallized twice from toluene to obtain
1a as a pale brown crystalline solid (m.p. 163-165 °C; 58%
yield).
1H NMR (CDCl3, ppm): δ 2.343 (s, 2H, OH); 5.408 (s, 1H,
CH); 6.716-6.959 (t, 8H, 2C6H4); 7.147-7.171 (m, 5H, C6H5).
MS: m/e 39, 55, 77, 94, 115, 152, 165, 181, 199, 228, 259, 276
(100%, M+).
(b) P r ep a r a tion of Bis(3,5-d im eth yl-4-h yd r oxyp h en yl)-
p h en ylm eth a n e (1b). The preparation of 1b was carried out
using the same procedure as the synthesis of 1a except that
phenol and 2,6-dimethylphenol were used. The crude product
was recrystallized twice from toluene to afford 1b as a pale
brown crystalline solid (m.p. 159-160 °C; 62% yield).
1H NMR (CDCl3, ppm): δ 2.178 (s, 12H, CH3); 3.821 (s, 2H,
OH); 5.292 (s, 1H, CH); 6.709 (s, 5H, C6H5); 7.093-7.284 (m,
4H, 2C6H2). MS: m/e 39, 65, 77, 91, 127, 152, 165, 181, 255,
317 (100%), 332 (M+).
It is well-known that poly(arylene ethers) are very
stable structural materials; however, fuel cells as-
sembled using these materials can only run a relatively
short time due to membrane damage. Presumably, the
damage results from a combination of hydrolytic and
oxidative degradation. The degradation was documented
to take place at the ether bonds in the backbone of
aromatic polymers when there is a sulfonic acid group
on the ortho position to the ether bond. However, the
position-directed sulfonation of polyaromatics seems
very difficult. Therefore, it is important to design and
synthesize without the ortho-position-substituted sul-
fonic acid groups. In this respect, we report in this paper
the synthesis of a series of partially fluorinated poly-
(arylene ethers) and the sulfonation of these polymers
with chlorosulfonic acid. The sulfonation took place only
at the para positions on the pendant phenyl rings due
to the novel bisphenol structures designed. These novel
polymers were very soluble in common organic solvents
and could be readily cast into tough and smooth films.
It is expected that these partially fluorinated polymers
should be more stable for use as membranes in fuel cells.
Exp er im en ta l Section
Ma ter ia ls. All the chemicals used were reagent grade and
purified by the standard methods. 2,6-Dimethylphenol, dichlo-
rodiphenylmethane, and decafluorobiphenyl were obtained
commercially from Aldrich Chemical Co. Dimethyl sulfoxide
(DMSO), N,N-dimethyformamide (DMF), ethylene glycol
monomethyl ether, chloroform, methylene chloride, toluene,
methanol, phenol, and benzaldehyde were obtained from
commercial sources and used as received. N,N′-Dimethylac-
etamide (DMAc) was dried over 4 Å molecular sieves. Toluene
was dried over sodium wire prior to being used. Anhydrous
potassium carbonate was dried at 60 °C for 10 h in a vacuum
oven.
Ch a r a cter iza tion . The glass transition temperatures (Tg’s)
were determined on a Seiko 220 differential scanning calo-
rimetry (DSC) instrument at a heating rate of 20 °C/min under
nitrogen protection. The second scan was immediately initiated
after the sample was cooled to room temperature. Thermal
stability of the polymers from 30 to 600 °C was determined
with a Seiko thermogravimetric analyzer (TGA/DTA; model
(c) P r ep a r a tion of Bis(4-h yd r oxylp h en yl)d ip h en yl-
m eth a n e (1c). To a 50 mL, two-necked flask fitted with a
condenser and a nitrogen inlet, dichlorodiphenylmethane (2.37
g, 10 mmol) and phenol (2.07 g, 22 mmol) were introduced.

Macromolecules, Vol. 37, No. 9, 2004
Synthesis and Sulfonation of Poly(aryl ethers) 3153
The mixture was stirred at room temperature until no gas was
produced and then slowly heated to 150 °C followed by
introducing nitrogen through the system for 20 min. Finally,
the resulting mixture was distilled under reduced pressure for
30 min. Upon cooling to room temperature, the residue in the
flask was subjected to recrystallization from ethanol. Pure 1c
was obtained as a pale yellow solid powder (2.1 g; m.p. 273-
274 °C; 60.0% yield).
in 15 mL of toluene was heated to 120 °C and maintained at
that temperature for 10 h. The mixture was rotavapped to ∼6
mL, and cooled to room temperature. White product powders
were precipitated out from the solution after cooling to room
temperature. The precipitates were filtered, washed twice with
a minimum amount of toluene, and dried under vacuum at
60-70 °C for 24 h. Compound 2d , as pure white powders, was
obtained in good yield (90.48%; m.p. 204-205 °C).
1H NMR (DMSO-d6, ppm): δ 6.656 (d, 4H), 6.868 (d, 4H),
7.067-7.269 (m, 10H, 2C6H5). MALDI-TOF-MS: found, 352.0;
calcd for C25H20O2, 352.4.
1H NMR (CDCI3, ppm): δ 0.96 (t, 6H, 2CH3), 1.59 (m, 4H,
2CH2), 2.11 (s,12H, 4CH3), 3.23 (m, 4H, 2CH2), 5.05 (b, 2H,
2NH), 6.87 (s, 4H, 2C6H2), 7.15-7.24 (m, 10H, 2C6H5).
Syn th esis of P oly(a r ylen e eth er s). (a ) Syn th esis of
P olym er 3a . A typical polymerization procedure is given as
follows. To a 25 mL, three-neck, round-bottom flask equipped
with a magnetic stirrer, a Dean-Stark trap, condenser, and
nitrogen inlet, 2a (0.2777 g, 0.62 mmol), decafluorobiphenyl
(0.2079 g, 0.62 mmol), and potassium carbonate (0.1289 g, 0.93
mmol) in DMAc (2.0 mL) were added. The reaction mixture
was heated to 80-90 °C and kept at that temperature for 8 h.
The reaction mixture was diluted with DMAc (3 mL) when it
became too viscous. After cooling to room temperature, the
solution was poured slowly into methanol (60 mL) containing
a few drops of hydrochloric acid. The polymer was precipitated
out and washed successively with water (20 mL) and methanol
(20 mL). The obtained polymer was redissolved in 30 mL of
chloroform. After depositing for more than 5 h, the solution
was filtered through a thin layer of Celite. The filtrate was
concentrated to 4 mL, and poured slowly into 60 mL of
methanol with stirring. The polymer was precipitated out and
then filtered, washed with methanol, and dried at 120 °C
under vacuum for 24 h. White fibrous polymer 3a was obtained
in a yield of 84.3%.
(d ) P r ep a r a tion of Bis(3,5-d im eth yl-4-h yd r oxyp h en yl)-
d ip h en ylm eth a n e (1d ). Using the same procedure as the
synthesis of 1c, 1d was synthesized from dichlorodiphenyl-
methane (2.37 g, 10 mmol), 2,6-dimethylphenol (2.68 g, 22
mmol), and a catalytic amount of phenol (100 mg). The mixture
was stirred at room temperature until no volatiles were
produced. The reaction mixture was then heated to 50-60 °C
and stirred at that temperature for 4 h. Then the temperature
of the mixture was increased slowly to 150 °C, and nitrogen
flow was allowed to pass through the system for 20 min.
Thereafter, the resulting mixture was distilled under reduced
pressure for 30 min. Upon cooling to room temperature, the
resulting crude product was recrystallized from the mixture
solvent of ethanol with petroleum ether to yield pure yellow
product (2.8 g; m.p. 200-201 °C; 68.6% yield).
1H NMR (DMSO-d6, ppm): δ 2.11 (s, 12H, 4 CH3), 6.76 (s,
4H, 2C6H2), 7.127-7.24 (m, 10H, 2C6H5). MALDI-TOF-MS:
found, 408.1; calcd for C29H28O2, 408.5.
(e) P r epar ation of Bis(4-pr opylcar bam oylph en yl)ph en -
ylm eth a n e (2a ). The synthesis procedure for 2a is as follows.
A solution of 1a (5 mmol), n-propyl isocyanate (3.75 mL), and
triethylamine (1 mL) in 20 mL of toluene was heated to 120
°C and kept at that temperature for 8 h. Upon the completion
of the reaction, the mixture was rotavapped to ∼8 mL using a
rotavapor. White product powders were precipitated out from
the solution after cooling to room temperature. The precipitate
was filtered, washed twice with a minimum amount of toluene,
and dried under vacuum at 60-70 °C for 24h. Compound 2a ,
as pure white powders, was obtained in a good yield (85.0%;
m.p. 127-128 °C).
1H NMR (400 MHz; ppm): δ 6.945 (d, 4H), 7.076 (d, 6H),
7.193-7.240 (m, 1H), 7.285 (m, 2H).
(b) Syn th esis of P olym er 3b. Polymer 3b (Figure 1) was
synthesized from 2b and decafluorobiphenyl using the same
procedure as the synthesis of polymer 3a . White fibrous
polymer 3b was obtained in a yield of 85.0%.
1H NMR (400 MHz; ppm): δ 2.1525 (s, 12H), 6.741 (s, 4H,),
7.073 (d, 2H), 7.260(d, 1H), 7.288 (m, 2H).
(c) Syn th esis of P olym er 3c. A typical polymerization
procedure is as follows. Compound 2c (0.5220 g, 1 mmol),
decafluorobiphenyl (0.3343 g, 1 mmol), and potassium carbon-
ate (0.2087 g, 1.5 mmol) and DMAc (3.50 mL) were introduced
into a 25 mL, three-neck, round-bottom flask equipped with a
magnetic stirrer, a Dean-Stark trap, condenser, and nitrogen
inlet. The reaction mixture was heated to 150-160 °C and
maintained at that temperature for 18 h. The reaction mixture
was diluted with DMAc (5 mL) when it became too viscous.
After cooling to room temperature, the solution was poured
slowly into methanol (60 mL) containing a few drops HCl. The
polymer was precipitated out and washed with methanol. The
obtained polymer was redissolved in 30 mL of chloroform. After
depositing for more than 5 h, the solution was filtered through
a thin layer of Celite. The filtrate was rotavapped to 4 mL
and then poured slowly into 60 mL of methanol with stirring.
The polymer was precipitated out and filtered, followed being
washed with methanol and dried at 120 °C under vacuum for
24 h. White fibrous polymer 3c was obtained in a yield of
85.5%.
1H NMR (CDCI3, ppm): δ 0.95 (t, 6H,2CH3), 1.58 (m, 4H,
2CH2), 3.24 (m, 4H, 2CH2), 4.99 (b,2H,NH), 5.50 (s,1H,CH),
7.02-7.28 (m, 13H).
(f) P r ep a r a tion of Bis(3,5-d im eth yl-4-p r op ylca r ba m -
oylp h en yl)p h en ylm eth a n e (2b). A solution containing 1b
(2 mmol) , n-propyl isocyanate (1.7 mL), and triethylamine (0.5
mL) in 10 mL of toluene was heated to 120 °C and kept at
that temperature for 10 h. After the reaction, the mixture was
concentrated to 5 mL using a rotavapor and cooled to room
temperature. White product powders were precipitated out
from the solution. The precipitates were filtered, washed twice
with a minimum amount of toluene, and dried under vacuum
at 60-70 °C for 24h. Compound 2b, as pure white powders,
was obtained in good yield (73.6%; m.p. 173-174 °C).
1H NMR (CDCI3, ppm): δ 0.96 (t, 6H,2CH3), 1.59 (m, 4H,
2CH2), 2.11 (s,12H,4CH3), 3.24 (m, 4H, 2CH2), 6.76 (b, 4H,
2C6H2), 7.11-7.28 (m, 5H, C6H5).
(g) P r ep a r a t ion of Bis(4-p r op ylca r b a m oylp h en yl)-
d ip h en ylm eth a n e (2c). A solution of 1c (4.0 mmol), n-propyl
isocyanate (3.75 mmol), and triethylamine (1 mL) in 10 mL of
toluene was heated to 120 °C and kept at that temperature
for 8 h. The mixture was concentrated to 5 mL by evaporating
the solvent. White product powders were precipitated out from
the solution after cooling to room temperature. The precipi-
tates were filtered, washed twice with a minimum amount of
toluene, and dried under vacuum at 60-70 °C for 24 h.
Compound 2c, as pure white powders, was obtained in good
yield (82.2%; m.p. 190-191 °C).
1H NMR (400 MHz; ppm): δ 6.907 (d, 4H,), 7.145-7.196
(m, 10H), 7.224-7.260 (m, 4H).
(d ) Syn th esis of P olym er 3d . Polymer 3d (Figure 2) was
synthesized from decafluorobiphenyl and 2d using the same
procedure as the synthesis of polymer 3c. White fibrous
polymer 3d was obtained in good yield (94.8%).
1H NMR (400 MHz; ppm): δ 3.229 (s, 12H), 6.824 (d, 4H),
7.159-7.179 (m, 6H), 7.240-7.255 (m, 4H).
(e) Syn th esis of Cop olym er 3e. Copolymer 3e was
synthesized from the copolymerization decafluorobiphenyl with
2d (0.5 mmol) and 2b (0.5 mmol) using the same procedure
as the synthesis of polymer 3c. White fibrous polymer 3e was
obtained in yield (0.6069 g; 91.4%).
1H NMR (CDCI3, ppm): δ 0.96 (t, 6H, 2CH3), 1.58 (m, 4H,
2CH2), 3.23 (m, 4H, 2CH2), 6.98 (b, 4H, 2C6H2), 7.14-7.24 (m,
14H).
(h ) P r ep a r a tion of Bis(3,5-d im eth yl-4-p r op ylca r ba m -
oylp h en yl)d ip h en ylm eth a n e (2d ). A solution of 1d (3.6
mmol), n-propyl isocyanate (3.1 mL), and triethylamine (1 mL)
1H NMR (400 MHz; ppm): δ 6.947 (d, 4H,), 7.028 (d, 4H),
7.196-7.217 (m,10H), 7.240-7.273 (m, 4H), 7.764 (d, 4H).

3154 Wang et al.
Macromolecules, Vol. 37, No. 9, 2004
F igu r e 1. 1H NMR spectrum for polymer 3b.
F igu r e 2. 1H NMR spectrum for polymer 3d .
Su lfon a tion of P oly(a r ylen e eth er s). A typical procedure
for the sulfonation of polymers is given as follows: To the
solution of 3a (0.25 mmol) in 25 mL of methylene chloride,
2.5 mL of 0.8 M chlorosulfonic acid in methylene chloride was
added dropwise at room temperature over 1 h. The mixture
was stirred vigorously for 6 h until the pale brown products
precipitated out from the solution. The precipitates were
collected and washed with hexane three times and redissolved
in 5 mL of DMSO. To the solution was added 10 mL of 3 wt %
potassium hydroxide aqueous solution. After 6 h reaction, the
mixture was acidified with 100 mL of 5 vol % hydrochloric acid.
The aqueous solution was dialyzed for 2 days. The sulfonated
product 4a was recovered by evaporation of the water. All of
(c) P olym er 4c. 1H NMR (DMSO-d6; ppm): δ 7.103-7.227-
(br, 8H), 7.476(br, 4H), 7.740(2H). FT-IR (KBr): 1036.0 (νSO
H
3
sym), 1228.4 (νSO asym).
H
3
(d ) P olym er 4d (Figure 4). 1H NMR (DMSO-d6; ppm): δ
2.154 (s, 12H, 4CH3), 6.901 (s, 4H), 7.156 (d, 4H), 7.573 (d,
4H). FT-IR (KBr): 1036.0 (νSO sym), 1226.5 (νSO asym).
H
H
3
3
(e) P olym er 4e. 1H NMR (DMSO-d6): δ(ppm) 2.142-2.168
(m, 24H, 8 CH3), 6.966 (s, 8H), 7.132-7.295 (br, 6H), 7.577
(br, 6H). FT-IR (KBr): 1036.5 (νSO sym), 1190.3 (νSO asym).
H
H
3
3
Resu lts a n d Discu ssion
Syn th eses of Bisp h en ols 1. Novel bisphenols 1a ,b
were readily synthesized from benzaldehyde and the
phenols using 75% sulfuric acid as catalyst. The bisphe-
nols tend to be easily oxidized, even though the reactions
were performed under nitrogen atmosphere. A 50%
excess of phenol in stoichiometric ratio was added in
order to afford bisphenols in high yields. The bisphenols
1c,d were synthesized by the reaction of dichlorodiphen-
ylmethane with different phenols. The reaction should
be carried out under nitrogen atmosphere with 10%
1
the products were characterized by both FT-IR and H NMR.
The results of characterization of the sulfonated polymers are
listed as follows.
(a ) P olym er 4a . 1H NMR (DMSO-d6; ppm): δ 7.112-7.230
(br, 7H), 7.614 (m, 4H). FT-IR (KBr): 1035.9 (νSO sym),
H
3
1190.8 (νSO asym).
H
(b) P oly3m er 4b (Figure 3). 1H NMR (DMSO-d6; ppm): δ
2.138(s, 12H, 4CH3), 5.533 (s, 1H), 6.871 (s, 4H,) 7.079 (d, 2H),
7.533 (d, 2H). FT-IR (KBr): 1030.0 (νSO sym), 1211.4 (νSO
H
H
3
3
asym).

Macromolecules, Vol. 37, No. 9, 2004
Synthesis and Sulfonation of Poly(aryl ethers) 3155
F igu r e 3. 1H NMR spectrum for polymer 4b.
F igu r e 4. 1H NMR spectrum for polymer 4d .
excess of phenol used, because the phenols were easily
oxidized and dichlorodiphenylmethane was easily hy-
drolyzed. To get a good yield, the reaction temperature
needed to be slowly raised and carefully controlled.
Syn th eses of th e Ma sk ed Bisp h en ols 2. The
aforesaid and synthesized bisphenols 1 are extremely
unstable and can be easily oxidized during the polym-
erization with decafluorobiphenyl, even though under
the protection of nitrogen atmosphere. The reaction of
isocyanates with alcohols to give N-carbamates has been
widely employed to prepare polyurethanes.29,30 There-
fore, an alternate approach to stabilize bisphenols 1 is
to react isocyanates with 1 to give N-carbamates, which
can be easily purified by recrystallization. Urethanes
usually decompose to alcohols at temperatures above
220 °C to give free isocyanate and alcohol or free amine,
carbon dioxide, and olefin. For phenolic urethanes, the
decomposition begins at temperatures as low as 150
°C.31 So, they can decompose at 150 °C and could be
polymerized with activated dihalo aromatic compounds
to form high molecular polymers. It is preference to
afford purer polymers via this method due to lower
polycondensation temperature used.
The syntheses of N-carbamates are a simple addition
reaction without any byproducts formation, and side
reactions can be minimized under the appropriate
conditions.32 Various catalysts can speed up this reac-
tion, and in this study triethylamine was adapted. To
ensure the completed protection of hydroxyl groups of
bisphenols 1, a large excess of n-propyl isocyanate was
added. After the reaction, the excess n-propyl isocyanate
and solvent (toluene) were easily removed by distillation
under reduced pressure.
Syn th eses a n d P r op er ties of P olym er s 3. Hay et
al.33 have reported that the carbamates of bisphenol A,
which could be rapidly cleaved by K2CO3 to generate

3156 Wang et al.
Macromolecules, Vol. 37, No. 9, 2004
Sch em e 2. Syn th eses of P olym er s 3a -e
Ta ble 1. Molecu la r Weigh ts of P olym er s 3a -e
potassium phenoxide in situ, could be directly polym-
erized with dihalo aromatic compounds in DMAc to form
high molecular weight poly(arylene ethers). Therefore,
the carbamate method is quite useful for the prepara-
tion of poly(arylene ethers), especially when unstable
bis-phenols are involved in the polymerization.
3a
3b
3c
3d
3e
a
ηinh (dL/g)
0.40
0.46
0.43
0.47
0.34
b
Mn
Mw
32 378
83 468
2.58
45 306
97 276
2.15
39 714
70 315
1.77
49 983
319 263
6.39
26 159
70 899
2.71
b
MDIc
In previous work,29 we have synthesized a series of
fluorine-free and wholly aromatic polymers from bisphe-
nols and activated dihalo aromatic compounds, such as
bis(4-fluorophenyl)sulfone, 4,4-difluorobenzophenone, or
1,3(4)-bis(4-fluorophenzoyl)benzene. Since the polymers
showed poorer solubility and precipitated out from the
solution during the polymerization, it is difficult to
obtain very high molecular weight polymers. Using
decafluorobiphenyl, which is more reactive in nucleo-
philic substitution reaction and makes the polymers
more soluble than the above difluoride monomers,
allows the polymerization to take place at lower tem-
peratures (Scheme 2). Moderately high molecular weight
polymers (Mn ) 10 000-15 000) were obtained at 170
°C under a basic condition (K2CO3 in DMAc). However,
since oxidative reaction with a trace amount of oxygen
in the system was inevitable, the polymers obtained
exhibited a slightly dark color. As is well-known, there
are three advantages using masked biphenols.15 They
are that (1) monomers can be purified by simple
recrystallization, (2) no water is generated during
polymerization, and (3) high molecular weight polymers
are readily formed in a short period of time under mild
conditions. Using the propylcarbamoyl-masked biphe-
nol, high molecular weight polymers were synthesized
with molecular weights (Mn) ranging from 26 159 to
49 983 Da that corresponded to inherent viscosities from
0.34 to 0.47 dL/g (Table 1).
a
b
0.5 g/dL in CHCl3 at 25 °C. Determined by GPC using
polystyrenes as standards. c Molecular weight distribution index.
Ta ble 2. Th er m a l P r op er ties for P olym er s 3a -e
3a
3b
3c
3d
3e
Tg (°C)
176.0
195.2
200.9
203.3
190.8
TGA (N2)
T-5% (°C)
T-10% (°C)
336.5
360.1
396.6
424.1
513.2
544.7
438.1
453.9
401.0
424.1
Polymers 3c-e were synthesized at higher temper-
ature than polymers 3a ,b. Presumably, it is because the
steric hindrance of 2c,d is greater that that of 2a ,b, and
the propylcarbamoyl groups in 2c,d are more difficult
to eliminate than that in 2a ,b. Therefore, the in-situ
deprotection and polymerization of 2c,d took place at
higher temperature.
Thermal properties of the synthesized polymers are
listed in Table 2. It can be seen that the polymers
exhibited high glass transition temperatures and excel-
lent thermal stabilities. Tg’s ranged from 176.0 to 203.3
°C, and 5% weight loss temperatures ranged from 340
to 510 °C, respectively.
The incorporation of bulky methyl groups onto the
polymer backbone led to the increase in the Tg’s of the
resulting polymers. Thus, the polymers derived from
methyl-containing bisphenols 1b,d exhibited higher Tg’s
than their counterparts derived from bisphenols 1a ,c.
It is apparent that the tetraphenyl-containing polymers
3c,d exhibited better thermal stability than the triphen-
yl-containing polymers 3a ,b. It is believed that the poor
thermal stability resulted from the presence of methyl
groups on the polymer backbone.
The synthesized polymers are very soluble in common
organic solvents, such as acetone, tetrahydrofuran
(THF), and CHCI3 and could be cast into smooth and
flexible film from solutions. The molecular structures
1
of the polymers were confirmed by H NMR as stated
in the Experimental Section.

Macromolecules, Vol. 37, No. 9, 2004
Synthesis and Sulfonation of Poly(aryl ethers) 3157
Sch em e 3. Su lfon a tion of P olym er 3b
Sch em e 4. Su lfon a tion of P olym er 3d
Sch em e 5. Su lfon a tion of P olym er 3e
Ta ble 3. Elem en ta l An a lyses of 4b,d ,e
Ta ble 4. P r op er ties of Su lfon a ted P olym er s
found
calcd
water-take-up
content,
wt % in 80 °C
(12 h)
Ce
He
Se
Ct
Ht
St
Sr
4b
4d
4e
53.75
45.85
51.41
4.22
4.36
3.85
4.06
6.06
5.07
58.09
54.91
53.15
3.04
2.90
2.80
4.43
7.14
5.60
4.39
7.25
5.24
polymer
EWa
solubility
4b
4d
4e
788
528
631
45.0
75.3
62.7
DMSO, DMAc, DMF, NMP
DMSO, DMAc, DMF, NMP
DMSO, DMAc, DMF, NMP
Syn th eses a n d P r op er ties of Su lfon a ted P oly-
m er s. All the polymers were sulfonated using chloro-
sulfonic acid in methylene chloride. The sulfonation
completed at room temperature in a few hours. Because
of the insolubility of the resulted products, chlorosulfonic
acid must be added as slowly as possible under acutely
stirring. Residual sulfonyl chloride was neutralized with
aqueous potassium hydroxide in DMSO. Upon treat-
ment with hydrochloric acid followed by dialysis, brown-
ish polymers were obtained after evaporating the water.
Based on the FT-IR spectra, strong absorption bands
of sulfonic acid groups were observed at ∼1035 cm-1
(νSO H symmetric) and ∼1220 cm-1 (νSO H asymmetric).
were greater than those from calculation. This behavior
was resulted from the strong water absorption ability
of the sulfonated polymers. To eliminate the effect of
water, the sulfur contents were generally calculated
using the following equation:
sulfur content (Sr) ) CtSe/Ce
where Se and Ce are the sulfur and carbon contents
respectively based on elemental analyses and Ct repre-
sents the theoretical carbon content calculated from the
repeating unit of sulfonated polymer.
3
3
1
In the H NMR spectrum, a peak at 7.20-7.30 ppm for
3b,d ,e disappeared and a new peak was observed at
7.50-7.60 ppm, indicating that the sulfonation occurred
at only the para position of the pendant phenyl rings,
as depicted in Schemes 3-5. For the polymers 3a 3c,
as expected, the sulfonation reaction was confirmed
The solubility and the water-take-up content of
sulfonated polymers 4b,d ,e are summarized in Table
4. All the sulfonated polymers were soluble in polar
solvents such as DMSO, DMAc, DMF, and NMP.
Polymers 4b,d ,e were swelled in water showing good
water affinity. As expected, the water-take-up ability
increased with the decrease of equivalent molecular
weight (EW). Self-supporting, flexible, and transparent
films can be obtained from these sulfonated polymers
by casting from DMSO. Unlike other sulfonated poly-
mers, which completely lose their mechanical strength
1
from the H NMR spectrum to take place on the ortho
position to ether bonds of phenylene groups. Elemental
analyses were further performed to determine the
sulfonation degrees of 4b,d ,e. From Table 3, we can see
that the hydrogen contents from elemental analyses

3158 Wang et al.
Macromolecules, Vol. 37, No. 9, 2004
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the National Science Foundation of China (NSFC) (Key
project, Grant No. 29734120), the China High-Tech
Development 863 Program (Grant No. 2003AA302410),
the Natural Science Foundation of Guangdong Province
(Excellent Team Project, Grant No. 015007), the Canton
Province Science & Technology Bureau (Key Strategic
Project Grant No. A1100402), and Guangzhou Science
& Technology Bureau for financial support of this work.
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