Synthesis of 3,6-dioxa-δ7-4-trifluoromethyl sulfonimide: Bis[(perfluoroalkyl)sulfonyl] superacid monomer and polymer

Article abstract of DOI:10.1016/j.jfluchem.2004.05.009

A new type of ion exchange polymer, bis[(perfluoroalkyl)sulfonyl]imide ionomers (PFSI), were developed by the copolymerization of sodium 3,6-dioxa-Δ⁷-4-trifluoromethyl perfluorooctyl trifluoromethyl sulfonimide with tetrafluoroethylene (TFE) using an aqueous redox initiation system in an emulsion type polymerization. These polymers have been prepared in various equivalent weights and processed into functional membranes. The new ionomers exhibit excellent chemical and thermal stability. The materials have high potential for electrochemical applications especially as solid polymer electrolytes (SPE) in proton exchange membrane (PEM) fuel cells.

Full text of DOI:10.1016/j.jfluchem.2004.05.009

Journal of Fluorine Chemistry 125 (2004) 1231–1240
Synthesis of 3,6-dioxa-D7-4-trifluoromethyl perfluorooctyl
trifluoromethyl sulfonimide: bis[(perfluoroalkyl)sulfonyl]
superacid monomer and polymer
Brian H. Thomas, Gregory Shafer, Jing Ji Ma, Ming-Hu Tu, Darryl D. DesMarteau*
H.L. Hunter Hall Chemistry Laboratory, Chemistry Department, Clemson University, Clemson, SC 29634-1905, USA
Available online 30 July 2004
Abstract
A new type of ion exchange polymer, bis[(perfluoroalkyl)sulfonyl]imide ionomers (PFSI), were developed by the copolymerization of
sodium 3,6-dioxa-D7-4-trifluoromethyl perfluorooctyl trifluoromethyl sulfonimide with tetrafluoroethylene (TFE) using an aqueous redox
initiation system in an emulsion type polymerization. These polymers have been prepared in various equivalent weights and processed into
functional membranes. The new ionomers exhibit excellent chemical and thermal stability. The materials have high potential for
electrochemical applications especially as solid polymer electrolytes (SPE) in proton exchange membrane (PEM) fuel cells.
# 2004 Elsevier B.V. All rights reserved.
Keywords: Perfluorinated ionomers; Solid polymer electrolyte; Sulfonimide; Ion exchange polymer; Proton exchange membrane
1. Introduction
was introduced in the 1960s by E.I. du Pont de Nemours and
Co. and has extraordinary chemical, mechanical, thermal,
and electrochemical properties [10–12]. Dow Chemical Co.
later introduced their version of a PFSA known as XUS [9].
Both Nafion1 and XUS are copolymers of poly(tetrafluor-
oethylene) containing a perfluorosulfonic acid side chain
(Fig. 1). These materials show good performance as thin
membranes in a PEM fuel cell operating below 100 8C.
There is great interest in a PEM fuel cell that could operate
above 120 8C. At these temperatures, many systems issues
would be improved, including reducing CO poisoning of the
platinum catalyst [8]. Carbon monoxide is introduced into
the fuel cell from the hydrogen fuel. Sulfonic acid ionomers
loose hydration above 80 8C and proton conductivity
decreases. At still higher temperatures, sulfonic acids further
dehydrate forming an anhydride (–SO2OSO2–) which leads
to decomposition in molecular acids [13]. In our opinion this
same process may be operative in PFSA polymers. There-
fore, the goal of this research has been a polymer with a
different acid function, capable of operating as a PEM at
higher temperatures without significant decomposition
while maintaining good proton conductivity.
The development of high performance polymers for use as
solid polymer electrolytes (SPE) in proton exchange mem-
brane (PEM) fuel cells has been under intense investigation.
PEM fuel cells offer an environmentally clean energy source
with high efficiency. In a single cell, two platinum electrodes
are separated by a solid polymer electrolyte membrane
which allows the transport of hydrated protons and water.
At the anode, hydrogen fuel dissociates into free electrons
and positive hydrogen ions. The free electrons form the
usable electric current. The protons migrate through the
membrane electrolyte to the cathode where they combine
with reduced oxygen to form water [1]. The polymers
currently being explored as PEMs include sulfonated poly-
styrenes, poly-a,b,b-trifluorostyrenes, polysulfones, par-
tially fluorinated polymers, and perfluorinated polymers
[2–11]. The hydrocarbon polymers often suffer from poor
chemical resistance [8]; therefore, recent work has focused
on the fluorinated or partially fluorinated polymers such as
DuPont’s Nafion1, Dows’ XUS PFSA, and Ballard’s
BAM3G01 [8–11]. Due to its commercial availability,
Nafion1 is one of the polymers of choice for PEM fuel
cells. Nafion1, a perfluorosulfonic acid ionomer (PFSA),
The emphasis of the work was to produce a PEM which
operates at higher temperatures (>110 8C) and that has better
proton conducting properties then the current sulfonic acid
polymers [14]. The polymers which were developed are
known as perfluorosulfonimide ionomers or PFSI (Fig. 1)
* Corresponding author. Tel.: þ1-864-656-4705; fax: þ1-864-656-0627.
E-mail address: fluorin@clemson.edu (D.D. DesMarteau).
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.05.009

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B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
Scheme 1. Synthesis of Nafion1 perfluorocarbon vinyl ether monomer.
Fig. 1. Examples of perfluorinated ionomers.
monomer has not been published. The synthesis of 9
involves a series of steps each forming several products.
The first step (Scheme 1) is the formation of the acyl fluoride
from the fluorinated b-sultone.
and evolved from small molecule work on perfluoroalkyl-
sulfonyl derivatives to form carbon and nitrogen xenon bonds
[15,16]. Beginning in the late 1970s, numerous Brfnsted
nitrogen superacids were synthesized and are known as
bis((perfluoroalkyl)sulfonyl)imides [17]. The parent member
of this family is (CF3SO2)2NH, which has a pKa value of 7.8
in acetic acid (CF3SO2H ¼ 4.7) [18] and was shown in gas
phase acidity measurements to have a much greater acidity
than CF3SO3H and HI [19]. The high acidity associated with
(RfSO2)2NH and the oxygen solubility in perfluorocarbon
compounds led to excellent oxygen reduction kinetics in a
typical phosphoric acid fuel cell when used as an electrolyte
additive and as the bulk electrolyte [14,20]. It was decided to
initiate a program to produce the first perfluorinated PEM
containing the sulfonimide acid function.
Fluorinated b-sultones are formed by the reaction of SO3
with fluoroalkenes [34,35]. In this case, the desired sultone
can be prepared by the reaction of monomeric SO3 with
tetrafluoroethylene to give 1 (Scheme 2) [36,37]. In the
synthesis of the b-sultone, three products are observed. The
major product 1 is formed by the nucleophilic attack of
oxygen on the double bond; the cyclic compounds 2 and 3
may also be produced. Because the b-sultone 1 slowly
isomerizes to the corresponding acyl fluoride, compound
4 is also observed in this reaction in small amounts. The
isomerization of fluorinated b-sultones to their correspond-
ing acyl fluorides is very slow at lower temperatures [38–
40]. Because the isomerized product 4 is desired, triethyla-
mine is added as a catalyst to the reaction. The isomerized
product can also be produced using a fluoride ion catalyst
[41]. The acyl fluoride 4 can be easily separated after
isomerization through distillation.
Herein we report details on the synthesis of the monomer
CF2¼CFOCF2CF(CF3)OCF2CF2SO2N(Na)SO2CF3, 16, its
copolymers with tetrafluoroethylene (TFE), and some phy-
sical properties of these polymers. Electrochemical charac-
terization of these polymers has been reported previously
[21–24], as well as some preliminary reports on their pre-
paration and reports on their properties [14,25–30].
The second step is the coupling of the acyl fluoride with
hexafluoropropylene oxide (HFPO). In this step, fluoride ion
reacts with 4 to form the fluoroalkoxy anion intermediate
which then ring opens HFPO to produce the corresponding
sulfonyl fluoride adducts 7 (Scheme 2). The ratio of the
products formed is dependent on the molar ratio of HFPO to
b-sultone as well as the solvent and fluoride ion source.
When the ratio is controlled at 2:1 (HFPO:b-sultone), the
main product in the reaction is n ¼ 1 with a yield of
approximately 70%. The side products, n ¼ 0 and 2 are
also formed and are difficult to separate by simple distilla-
tion. The purification of the sulfonyl fluoride adducts can be
performed easier after pyrolytic decarboxylation shown in
the third step (Scheme 3).
2. Results and discussion
2.1. Monomer synthesis
The existing perfluorinated sulfonyl fluoride monomers
which are currently used in the production of sulfonic acid
polymers offer an excellent starting material for the produc-
tion of 3,6-dioxa-D7-4-trifluoromethyl perfluorooctyl tri-
fluoromethyl sulfonimide monomer. Previous work has
shown that the reaction of sulfonyl fluorides with silylated
sulfonamides yields the corresponding sulfonamide [17,31–
33]. This reaction offers a viable route to the synthesis of the
perfluorinated sulfonimide monomer 16 in high yield from
9, CF2¼CFOCF2CF(CF3)OCF2CF2SO2F. Since 9 was not
readily available, it had to be synthesized before coupling
with sodium trimethylsilyl trifluoromethyl sulfonamide 13.
Although the synthesis of the 9 is well known from patents,
to the best of our knowledge the laboratory synthesis of this
The reaction of perfluoroacyl fluorides of the type
–CF(CF3)C(O)F with strong bases like Na2CO3 at elevated
Scheme 2. Reaction of tetrafluoroethylene with sulfur trioxide.

B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
1233
Scheme 4. Synthesis of the sodium 3,6-dioxa-D7-4-trifluoromethyl
perfluorooctyl trifluoromethyl sulfonimide.
amide 11 can then be neutralized to 12 with NaOH (aq) and
then silylated using HMDS to give 13. Attempts at direct
reaction of the silylated material 13 with monomer 9
resulted in vinyl attack and formed a complex mixture.
Therefore the vinyl group of monomer 9 must be protected.
Early work focused on protecting the double bond with
chlorine; however, the dehalogenation step was often slug-
gish and difficult. Subsequently, it was found that bromine
protection was superior. The bromine protected sulfonyl
fluoride is coupled with the silylated sulfonimide 13. This
reaction is catalyzed by small amounts of base and can be
slow in the absence of catalyst. On the other hand, larger
amounts of base can lead to attack on the –SO2F group
forming –SO3M salts. The coupled product 14 is then
dehalogenated with activated zinc and acidified to give
the acid form of the monomer 15. Because the polymeriza-
tion is an aqueous emulsion, the acidic monomer 15 is
converted to its salt form using sodium hydroxide.
Scheme 3. Pyrolytic decarboxylation of perfluorosulfonyl fluoride.
temperatures has been shown to be a viable route to the
synthesis of fluorinated vinyl ethers [42,43]. The sulfonyl
fluoride adducts 7 readily undergo these pyrolytic decarbox-
ylation to form the corresponding sulfonyl fluoride vinyl
ether 9 and the cyclic adduct 8 [36]. During pyrolytic
decarboxylation, the carbanion intermediate of the n ¼ 0
adduct will cyclize to form 8. In the n ¼ 1 and 2 adducts, the
carbanion intermediate loses fluoride ion to form the corre-
sponding perfluorovinyl ethers 9. The pyrolysis was per-
formed by passing the acyl fluoride 4 through a heated
column (200–220 8C) packed with dry sodium carbonate.
The conditions must be carefully controlled throughout the
reaction. If the temperature is below 180 8C or if the flow
rate of the acyl fluoride 4 is too fast through the column, then
the anhydride {(FO2SCF2CF2[OCF(CF3)CF2]nOCF(CF3)-
C(O))2O} will be produced. If the temperature is above
220 8C, the corresponding neutralization reaction can occur
in which the acyl fluoride 4 reacts with sodium carbonate to
form the corresponding sodium sulfonate salt. The column
must also be free of active hydrogen compounds (H2O,
RCOOH, NHCO3, etc.) which can undergo hydrogen
abstraction by the carbanion intermediate to the correspond-
ing 2-H alkane. The desired perfluorosulfonyl fluoride
monomer 9 where n ¼ 1 is known as Nafion1 XR resin.
The preparation used to produce the sulfonimide mono-
mer 16 is shown in Scheme 4. Meubdoerffer and Neider-
prum were the first to prepare bis((perfluoroalkyl)-
sulfonyl)imides by reacting a sulfonyl fluoride with its
sodium N-silyl form. In their route, the N-silyl was prepared
by amination of the corresponding sulfonyl fluoride fol-
lowed by neutralization then silyation [31–33]. Instead of
preparing trifluoromethane sulfonamide 11 from the sulfo-
nyl fluoride , the material can be synthesized from trifluor-
methane sulfonic anhydride 10 with ammonia [44,45]. The
2.2. Copolymerization
Tetrafluoroethylene and the perfluorosulfonimide mono-
mer 16 readily undergo a free radical polymerization in an
emulsion system (Scheme 5). The copolymerization of the
perfluorosulfonimide monomer 16 with tetrafluoroethylene
does not behave as a typical emulsion polymerization.
Scheme 5.

1234
B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
Table 1
Typical reaction conditions for the copolymerization of sulfonimide
monomer with TFE in 1 L autoclave
Monomer 16
4.68:4.64
4.6:4.64
6.422:4.57
(reactor:addition) (g)
C7F15CO2NH4 (g)
Na2HPO4ꢁ7H2O
4.64
4.65
4.69
6.51:0.74
6.63:0.74
6.66:0.76
(reactor:addition) (g)
NaH2PO4 (reactor:addition) (g) 3.32:0.36
3.36:0.74
0.6957
3.36:0.39
0.6998
(NH4)2S2O8 (g)
0.6954
0.6374
600:41.4
145–150
212
NaHSO3 (g)
0.6383
0.6395
H2O (reactor:addition) (mL)
Pressure of TFE (psi)
Stirring speed (rpm)
Temperature (8C)
Reaction time (h)
600:41.4
600:41.4
143–150
212
143–151
150
6–8
10–12
5.5
9–11
9.3
5.3
Average TFE drop rate (psi/h) 10.4
9.8
6.21
Fig. 2. Polymerization system.
TFE consumed (g)
PTFE recovered (g)
Polymer weight (g)
IEC (mgH/g)
5.04
4.7
5.09
0.0
10.94
0.84
0.12
1.18
Typical emulsion polymerizations use a hydrophobic mono-
mer with some of the monomer solubilized in the interior of
the micelle [46]. The majority of the monomer will be
dispersed throughout and stabilized by the emulsifying
agent. In the case of the perfluorosulfonimide monomer
16, the monomer can behave as an emulsifying agent with
both a hydrophobic region and a hydrophyllic region. There-
fore, the monomer readily dissolves in the aqueous medium,
contrary to typical emulsion polymerizations.
12.12
0.83
12.93
0.93
EW
1200
1175
1075
viscous at the end of the polymerization at room tempera-
ture. The polymer can be coagulated from the thick latex
emulsion using 70% HCl and produces a white, fibery
polymer when dried. All polymerizations based on con-
sumed TFE had approximately a 50% conversion of the total
perfluorosulfonimide monomer 16 added. The TFE con-
sumed in the reaction was calculated using either the ideal
gas or the Van der Waals equation based on the head space of
the reactor and the total pressure drop of the TFE. By
plotting the consumed TFE versus the time of the polymer-
ization, it was possible to monitor the polymerization pro-
cess and achieve very reproducible results. Table 1 shows
some typical copolymerizations involving monomer 16 with
TFE to produce different equivalent weights or ion exchange
capacities. The polymerizations were reproducible within
experimental error and the ion exchange capacity (IEC) of
the copolymer can be changed by varying either the stirring
rate, the pressure of TFE in the reactor, or the amount of
monomer in the reactor.
The semi-continuous copolymerization of the perfluoro-
sulfonimide monomer 16 with TFE was initiated by
(NH4)2S2O8/NaHSO3/catalytic iron with ammonium per-
fluorooctonate and Na2HPO4/NaH2PO4 as the emulsifier
and pH buffer respectively. The iron/bisulfite/persulfate
initator system was used because at low temperatures the
reaction rate of persulfate-bisulfite initiators with TFE
emulsion copolymerizations is quite slow [47]. Berry
reported that the reaction between persulfate and bisulfite
was found to have a threshold initiation temperature for
tetrafluoroethylene of 35–36 8C, while the bisulfite/iron
initiator had a threshold initiation temperature for TFE of
0–10 8C [48]. The source of iron in our polymerizations was
from the buffer salts as well as the 316 ss autoclave. The
polymerization of the perfluorosulfonimide monomer 16
with TFE employed a semi-batch reactor system as shown
in Fig. 2. Early work used a batch reactor and produced
blocky copolymers due to the changing ratio of the two
monomers during polymerization. The continuous semi-
batch reactor system used a high-pressure metering syringe
pump for the continuous addition of aqueous perfluorosul-
fonimide monomer 16 to the autoclave at a rate close to the
rate of uptake of 16. After the initial charge of TFE to the
reactor, the pressure was maintained at 145–150 psi by
incremental (every few minutes) addition of TFE. This
system allowed the concentration of the two monomers to
remain fairly constant throughout the copolymerization. The
consumed TFE was monitored by pressure drops throughout
the reaction. The polymerization was stopped when the
desired amount of TFE was consumed. Unlike typical
emulsion polymerizations, our emulsions are extremely
2.3. Characterization
Similar to the commercial perfluorosulfonic acid resins,
the perfluorosulfonimide copolymer 17 has excellent ther-
mal stability. The polymer’s typical onset for thermal
decomposition is around 400 8C in the acid form and around
480 8C in the salt form. Fig. 3 shows a thermograph of the
bulk copolymer material at different equivalent weights in
the acid form under a nitrogen atmosphere. The first step in
the weight (%) loss corresponds to the loss of the perfluor-
osulfonimide function. The copolymer has a Tg at ꢀ60 8C.
Fig. 4 shows a typical DSC spectrum of the copolymer
with various equivalent weights. A broad endotherm at
155–200 8C is indicative of coordinated water. The second
endotherm at 320–350 8C occurs at nearly the same

B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
1235
Fig. 3. Thermogram for various equivalent weight sulfonimide polymers
Fig. 5. Cyclic DSC For a sulfonimide polymer in the acid form.
in the acid form IEC: (a) 0.68 mgH/g, (b) 0.84 mgH/g, (c) 0.93 mgH/g.
temperature as the melting temperature of virgin poly(tetra-
fluoroethylene) [49], therefore, this peak is assigned to the
melting (Tm) of PTFE crystallites in the copolymer. The heat
of fusion (DHf) can be calculated for the second endotherm
and is related to the extent of crystallinity in the polymer
[50]. As seen in Fig. 4, as the ion exchange capacity of the
polymer increases, the extent of crystallinity decreases;
which is due to the introduction of more bulky side chains
in the copolymer which reduce the crystalline order and
reduce the crystallization of the macromolecular chains.
Fig. 5 shows a cyclic DSC spectrum of the copolymer after
two heating and cooling cycles. In the second heat there is no
broad endotherm at 155–200 8C associated with the coordi-
nated water. If the sample is opened to the atmosphere for
some time or if water is added to the sample, the endotherm
returns. It is also interesting to note that after initial heating,
the second endotherm related to the PTFE crystallite melting
has also decreased. This is not unusual to see for polymers
which have no thermal history. During the initial polymer-
ization, the crystallites formed vary in size and perfection
and thus, the transition is not sharp [46]. As is common in
Teflon-like polymers, after thermal processing the heat of
fusion for the PTFE crystallite region is lower and is due
mainly to the reorientation of the polymer to its more stable
thermodynamic state. Likewise, in charged ionomers, the
polymer chain reorients through the thermal heating to form
ionic clusters which break up the crystallinity of the polymer
and reduce the endothermic transition [51].
2.4. Membrane and solution formation
Membranes of typical PFSA materials such as Nafion1
and XUS are melt processed in the precursor sulfonyl
fluoride form (–SO2F) and then hydrolyzed to the sulfonic
acid form using caustic followed by acidification [52,53].
In the case of the sulfonimide polymer 17, membranes
cannot be formed from melt processing since the polymer
exhibits no melting point; however, membranes of the
polymer can be prepared by solution-casting. A consider-
able amount of work has been published on preparing PFSA
polymer membranes from solution for use to repair pin
holes in chlor-alkali membranes and as coating materials
for modified electrodes [51–55]. For the PFSA materials,
solution-cast membranes can be formed using a variety of
solvents including DMF, DMSO, and EG. Although mem-
branes were obtained using a variety of solvents, the
preferred solvent for film formation of a PFSI polymer
17 is DMF. The acid form of the polymer is blended with
DMF to form a viscous liquid and this converts the acid
function into the dimethylammonium salt form. The solu-
tion can then be filtered and the solvent removed under a
slight vacuum around 90 8C to obtain what Gebel describes
as a ‘‘compact nearly dried solution’’ [51]. The remaining
clear film is brittle and will readily dissolve in the casting
solvent; which shows that only small reentaglement and
rearrangement of the polymer chains has occurred. The
PFSI solution-cast films also exhibit the same behavior and
were found to exhibit better properties when annealed
between 200 8C and 250 8C [51]. The poor physical proper-
ties of the unannealed cast films has been attributed to the
Fig. 4. DSC for various equivalent weight sulfonimide polymers in the
acid form IEC: (a) 0.50 mgH/g, (b) 0.80 mgH/g, (c) 0.95 mgH/g, (d)
1.14 mgH/g.

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B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
IR of the monomer, are not present in the spectra of the
polymers and is consistent with 19F NMR.
3. Conclusions
Sodium 3,6-dioxa-D7-4-trifluoromethyl perfluorooctyl
trifluoromethyl sulfonimide monomer can be prepared in
high yield and readily copolymerizes with tetrafluoroethy-
lene using an aqueous redox initiation system in an emulsion
type polymerization. These polymers have been prepared in
various equivalent weights and processed into functional
membranes. The polymers have been characterized and
exhibit excellent thermal stability. Investigation of this
polymer and other related ionomers is ongoing.
Fig. 6. 19F NMR of a sulfonimide polymer in the acid form.
supermolecular features of the polymer, i.e. the PTFE
crystallites and the ionic aggregates [54]. When casting,
the polymer chains become immobile and crystallization
cannot occur. Therefore, thermal excitation provides the
necessary mobility which allows the polymer to reorient
and form the PTFE crystallinity and the ionic aggregation
needed to form a high-quality membrane [51,54]. In
Nafion1, it was found that the glass transition temperature
of the ionic-domain was around 150 8C; therefore, below
these temperatures the ionic crystallites cannot form [54].
Thus, annealing of the polymer film becomes essential in
preparing quality membranes of PFSI polymers. The sul-
fonimide polymer 17 membranes that are annealed
between 225 8C and 250 8C discolor due to organic impu-
rities in the film casting process. However, soaking in hot
nitric acid restores a colorless appearance and converts the
polymer to the acid form.
4. Experimental
4.1. General methods
Infrared spectra were obtained on Perkin-Elmer 1600 and
2000 series FTIR spectrometers. A 10 cm gas cell fitted with
KCl or AgCl windows was used for gas samples. Solids were
sampled as Nujol mulls or thin films between AgCl or KCl
windows. 1H and 19F NMR spectra were recorded on a Bruker
AC 200 (1H ꢀ200.33 MHzand19F ꢀ188.31 MHz). 13C NMR
spectra were recorded on a Bruker AC 300 at 75.469 MHz.
NMRspectraweremeasuredusingsolutionsof1–2 mmol/Lin
1
an appropriate deuterated solvent. H chemical shifts were
PFSA polymers and PFSI polymer 17 are insoluble in
all solvents below 200 8C [55]. Therefore, a dissolution
technique was used to place these polymers into solution.
Considerable work has been published on producing solu-
tions of perfluorinated ion containing polymers which
involve a high temperature dissolution process [53–57].
The preferred solvent system for the PFSA materials has
been an alcohol/water blend with the polymer in the salt or
acid form [55,57]. Solutions of PFSI polymer 17 have
been produced from a similar dissolution process in the
sodium salt, potassium salt, tetrabutyl ammonium salt,
and acid forms and are typically 1–5 wt.% polymer [57].
The best solvent system for the PFSI polymer 17 appears
to be a mixture of alcohols with the polymer in the acid
form.
The 19F NMR spectrum (Fig. 6) of the dissolved PFSI
polymer 17 which was prepared by dissolution, is consistent
with the bulk copolymer. The vinyl fluorine atoms (chemical
shifts d ¼ ꢀ112.4, ꢀ120.8, ꢀ135.6 ppm) observed in the
monomer, were not observed in the copolymer. Likewise, a
new broad unresolved resonance at d ¼ ꢀ120.4 ppm is
indicative of aliphatic fluorine atoms associated with the
poly(tetrafluoroethylene) backbone of the copolymer. Reso-
nances for the other fluorine atoms in the structure were
broad and unresolved, but similar in chemical shift to that of
the monomer. The bands characteristic of vinyl ether car-
bon–fluorine and carbon–carbon (1840 cmꢀ1) present in the
referenced to CD3CN, 19F chemical shifts were referenced
to CFCl3, and 13C NMR were referenced to CD3CN, CDCl3,
or d6-acetone. Unless indicated otherwise, samples were a
minimum of 99.5% pure by 19F NMR. Compounds without
hydrogen were checked by 1H NMR for hydrogen-containing
impurities and were found to be free of impurities by the
procedure given. Dry NMR solvents were prepared using an
appropriate drying agent followed by storing over molecular
sieves. Dry NMR samples were prepared in 4 mm tubes
and sealed under vacuum. Positive and negative electron
(EI) and chemical ionization (CI, with CH4(g)) mass spectra
were obtained using a Fision Trio 1000 MS system operating
at 70 eV by direct solid inlet techniques. Thermogravimetric
Analysis and Differerential Scanning Calorimetry were
recorded on a Perkin-Elmer TGA7 and DSC7 respectively.
Melting points were determined using a Mel-Temp apparatus
and a Perkin-Elmer DSC-7.
4.2. Reagents
The starting materials were obtained from commercial
sources and used as received unless otherwise stated. CH3CN
was dried over CaH2 and then distilled off P4O10 before
use. SO3 from Aldrich was melted at 70 8C, then cooled to
room temperature and transferred to a round bottom flask
equipped with a Kontes glass-Teflon valve before use.

B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
1237
4.3. Preparation of FC(O)CF2SO2F (4)
46 g of distillate 2 from the previous reaction and the
distillate was added dropwise to the heated column over a
4 h period. The collected material in the round bottom flask
was distilled to give 22 g (49.3 mmol) of the desired product
(55%). 19F NMR dM ꢀ112 AMX (1F, dd), JMX ¼ 66 Hz,
83 Hz; dX ꢀ135 AMX (1F, dd), JMX ¼ 66, JAX ¼ 86 Hz; db
ꢀ79.7 (2F, m); dc ꢀ145.1 (1F, tm); dd ꢀ80.3 (3F, q-m); de
ꢀ85.1 (2F, m); df ꢀ112.4 (2F, m); dg 45.1 (1F, pent.). IR
(cmꢀ1) 1839 (m); 1467 (s); 1341 (s); 1317 (s); 1286 (s); 1243
(s); 1206 (s); 1164 (s); 989 (s); 819, 802 (doublet, m); 748
(m); 710 (m).
In 300 mL stainless steel cylinder was vacuum transferred
61.0 g (760 mmol) of SO3 and 80.0 g (800 mmol) of C2F4.
(Caution! This is a potentially hazardous reaction.) The
vessel was heated to 40–60 8C for 2 days. The excess
dissolved C2F4 was removed by opening the trap to the
atmosphere while being protected with a CaCl2 drying tube
and allowing the trap to warm to room temperature. The
reaction yielded 120 g of a colorless liquid. The crude
product was added to a 250 mL round bottom flask contain-
ing a magnetic stir bar and equipped with an addition funnel
which contained 2 mL (14.34 mmol) of (CH3CH2)3N. The
triethylamine was added dropwise to the flask and the
colorless liquid changed to red. The reaction was allowed
to proceed for 1 h and FC(O)CF2SO2F was distilled out of
the flask at 29–31 8C to give 106 g (588.7 mmol). 78% yield.
19F NMR (CDCl3) d(SO2F) 45.04 (1F, q) J ¼ 7.33 Hz; d(OF)
24.49 (1F, m); d(CF2) –104.69 (2F, t) J ¼ 7.14 Hz; IR (film)
1881 (s); 1762 (w); 1465 (s); 1445 (s); 1367 (m); 1279 (m);
1232 (s); 1175 (s); 1093 (s); 995 (m); 930 (m); 823 (s); 788
(m); 716 (w); 636 (m); 605 (m); 523 (m).
JAM ¼ 66 Hz; dA ꢀ121 AMX (1F, ddt), JAM ¼ 83 Hz, JAX
¼
4.6. Preparation of CF2aBrCFbBrOCF2cCFd(CF3e)-
OCF2f CF2gSO2Fh
To a two-necked 100 mL round bottom flask equipped
with a reflux condenser, addition funnel, and magnetic stirrer
was added 107 g (239.8 mmol) of CF2¼CFOCF2CF(C-
CF(CF3)OCF2CF2SO2F. To the flask was added 38.4 g
(240.3 mmol) of Br2 dropwise to the flask at 0 8C over
2 h. The resulting mixture was washed with 5% aqueous
solution of NaHSO3 and then with water. The resulting
organic layer was dried with anhydrous Na2SO4 and distilled
to give 130.1 g (214.7 mmol) of bromine protected product
in 90% yield. 19F NMR da ꢀ63.6 (2F, q), db ꢀ71.9 (1F, m),
dc ꢀ84 (2F, AB pattern multiplet), dd ꢀ145.3 (1F, t-m), de
ꢀ79.6 (3F, qm), df ꢀ79.4 (2F, m), dg ꢀ112.4 (2F, m), dh 45.3
(1F, s). IR: 1464 (s); 1304 (s); 1244 (s); 1185 (s); 1138 (s);
1113 (s); 1005, 986,976 (s, triplet); 985, 872 (s, doublet);
823 (s), 795 (s), 767 (s), 741 (s).
4.4. Preparation of FC(O)CF(CF3)OCF2CF(CF3)-
OCF2CF2SO2F (9)
In a 1 L round bottom flask equipped with a Kontes glass-
Teflon valve and magnetic stirrer was placed 15.0 g
(98.7 mmol) of fused CsF and 150 mL of dry tetraglyme.
The flask was evacuated and 120 g (660 mmol) of
FC(O)CF2SO2F was vacuum transferred into the flask
cooled to ꢀ196 8C. The reaction mixture was placed in a
ꢀ15 8C bath for 1 h and then pressurized to 750 Torr with
hexafluoroproplyene oxide. As the reaction proceeded over
an 8 h period and the hexafluoropropylene oxide was used
up, more hexafluoropropylene oxide was added to maintain
a pressure between 400 and 750 Torr. A total of 210 g
(1190 mmol) of hexafluoropropylene oxide was used. The
mixture was fractionally distilled at 80–100 8C and at 110–
135 8C. The first distillate contained only n ¼ 0 product
(28 g) while the second distillate contained 14% n ¼ 0, 66%
n ¼ 1 and 16% n ¼ 2. IR (film) 1881 (s), 1772 (w), 1654 (w),
1469 (s), 1448 (m), 1443 (m), 1376 (m), 1341 (m), 1318 (m),
1266 (s), 1233 (s), 1156 (s), 1103 (s), 1018 (s), 822 (m), 799
(w), 741 (w), 692 (w), 602 (w).
4.7. Preparation of CF3SO2NH2 (11)
Into a specially fabricated addition funnel which could be
evacuated was placed 61.74 g (218.8 mmol) of (CF3SO2)2O.
To a 250 mL two-necked round bottom flask was condensed
115 g (6.7 mol) of anhydrous ammonia. The flask was
removed from the vacuum line and fitted with the addition
funnel containing (CF3SO2)2O, a magnetic stirrer, and a
drying tube to exclude moisture. The reaction mixture was
placed in a ꢀ78 8C bath and the anhydride was added
dropwise over a 2 h period. The excess ammonia was
removed by allowing the reaction to warm to room tem-
perature, leaving a white solid. The product was purified by
sublimation at 80 8C under vacuum to give 28.96 g
(194.3 mmol) of white crystalline product (89% yield).
19F NMR (CD3CN) d(CF3) ꢀ79.4 (3F,s); 1H NMR (CD3CN)
d (NH2) 6.6 (2H,s); IR (solid, KBr pellet) 3379 (s); 3372 (s);
1511 (m); 1348 (s); 1232 (m); 1185 (s); 1155 (m).
4.5. Preparation of CF2AX¼CFMOCF2bCFc(CF3d)-
OCF2eCF2f SO2Fg
A two-necked 100 mL round bottom flask was blanketed
with nitrogen and was equipped with a reflux condenser and
an addition funnel connected to the top of a heated column
(50 cm ꢂ 25 mm). To the column was added 160 g of
Na2CO3 and 160 g of glass beads. The column was pre-
heated at 300 8C for 8 h and then maintained at 210–225 8C
throughout the experiment. To the addition funnel was added
4.8. Preparation of CF3SO2NHNa (12)
In a 100 mL round bottom flask was placed 16.7 g
(112 mmol) of CF3SO2NH2 and 50 mL of deionized water.
The solution was neutralized with 56.17 mL of 1.96 M

1238
B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
NaOH solution until pH 9.2. The water was removed by
vacuum distillation and the product was heated at 1008C
under vacuum for 12 h to dry and to sublime out any excess
CF3SO2NH2. The reaction yielded 18.7 g of the amide
(109 mmol) of a white solid amide. 19F NMR (CD3CN)
ꢀ120.7 AMX (1F, ddt), JAM ¼ 82 Hz, JAX ¼ 82 Hz; dX
ꢀ135.8 AMX (1F, dd), JMX ¼ 56, JAX ¼ 82 Hz; db ꢀ77.4
(2F, m); dc ꢀ143.9 (1F, t/m); dd ꢀ76.5 (3F, qm); de ꢀ83.8
(2F, m); df ꢀ112.9 (2F, m); dg ꢀ79.3 (3F, s). IR (cmꢀ1
)
(liquid film): 3204 (w), 1439 (m), 1318 (m), 1236 (s), 1163
(s) 986 (m), 868 (m), 607 (m).
1
d(CF3) ꢀ79.2 (3F,s); H NMR (CD3CN) d(NH(Na)) 2.57
(1H,s); IR (nujol; AgCl plates) 3344 (m); 3285 (s); 1620 (w);
1291 (s); 1271 (s); 1247 (vs); 1218 (vs); 1178 (vs); 1091 (m);
1068 (m); 998 (m); 759 (vw); 639 (m); 570 (w); 512 (w); 479
(w).
4.12. Preparation of CF2AX¼CFMOCF2bCFc(CF3d)-
OCF2eCF2f SO2NNaSO2CF3g (16)
The acid monomer 5.00 g (8.7 mmol) was dissolved in
50 mL of water. This aqueous solution was neutralized with
0.10 M NaOH solution to a pH of 7.00. The water was
removed slowly under vacuum and the solid which was
obtained was dried at 100 8C under high vacuum for 12 h.
The reaction yielded 5.20 g (8.7 mmol) of the desired pro-
duct. 19F NMR dM ꢀ112.0 AMX (1F, dd), JMX ¼ 66 Hz,
JAM ¼ 56 Hz; dA ꢀ120.5 AMX (1F, ddt), JAM ¼ 82 Hz, JAX
¼ 82 Hz; dX ꢀ135.7 AMX (1F, dd), JMX ¼ 56, JAX ¼ 82 Hz;
db ꢀ77.4 (2F, m); dc ꢀ144.3 (1F, t-m); dd ꢀ77.9 (3F, q-m);
de ꢀ77.6 (2F, m); df ꢀ112.9 (2F, m); dg ꢀ79.6 (3F, s).
4.9. Preparation of CF3SO2NNaSi(CH3)3 (13)
In a 500 mL round bottom flask equiped with a reflux
condenser and a drying tube was placed 37.4 g (218 mmol)
of dry powdered CF3SO2NHNa, 50 mL of dry acetonitile,
and 100 mL (474 mmol) of HN[Si(Me)3]2. The reaction
mixture was refluxed at 110 8C for 12 h. The solvent and
excess HMDS were removed by vacuum distillation and the
remaining solid dried under high vacuum at 100 8C for 4 h to
give 52.4 g (216 mmol) of the silyated product (98% yield).
19F NMR (CD3CN) d(CF3) ꢀ78.6 (3F,s); 1H NMR (CD3CN)
d(Si(CH3)3) 0.02 (6H,s); IR (fluorolube [subtracted]) 2965
(m); 1259 (vs); 1252 (vs); 1232 (vs); 1206 (s); 1184 (m);
1166 (m); 1154 (m); 1114 (m); 1083 (m); 1065 (s); 967 (w);
979 (m); 953 (m); 890 (m); 879 (s); 840 (vs); 760 (m); 714
(m); 692 (m); 670 (w); 626 (s); 615 (m); 598 (m).
4.13. Copolymerization of CF2¼CFOCF2CF(CF3)-
OCF2CF2SO2NNaSO2CF3 (16) with tetrafluoroethylene
Care must be taken in the polymerization. Tetrafluor-
oethylene forms a shock sensitive explosive peroxides with
oxygen. The continuous copolymerization of the perfluor-
osulfonimide monomer with TFE was initiated by
(NH4)2S2O8/NaHSO3 with C7F15COONH4 and Na2HPO4/
NaH2PO4 as the emulsifier and pH buffer. A Parr 1 L 316 ss
autoclave was precleaned with nitric acid, rinsed, and thor-
oughly dried. Approximately 800 mL of distilled water was
degassed overnight using nitrogen and constant stirring. To
prepare the solution for the autoclave, 4.64 g surfactant,
6.51 g Na2HPO4. 7H2O, and 3.32 g NaH2PO4 were dis-
solved into 500 mL of degassed DI water. Once the salts
were dissolved, 4.68 g of monomer 16 was added to the
solution and the solution was cooled to 8 8C while con-
stantly sparging with nitrogen. The addition solution was
prepared by dissolving 0.74 g Na2HPO4. 7H2O, 0.36 g
NaH2PO4, and 4.64 g of monomer in 41.4 mL of degassed
DI water. The initiators were added to the 500 mL solution
approximately 5 min before adding to the fully evacuated
autoclave which had been purged with nitrogen three times.
The addition solution was added to a metering pump
reservoir and was degassed with helium for at least
20 min. The 500 mL solution was sucked into the fully
evacuated autoclave followed by 100 mL of degassed
water. When the reactor was at 10 8C, the TFE was added
to a pressure of 150 psi and the continuous addition pump
was then started. The TFE was added throughout the run to
maintain a TFE pressure between 145 and 150 psi. When
the desired amount of TFE was consumed, the TFE was
vented and the solution filtered through Whatman filter
paper and acidified with 70% HCl. The polymer was then
4.10. Preparation of CF2aBrCFbBrOCF2cCFd(CF3e)-
OCF2f CF2gSO2NNaSO2CF3h (14)
To a well dried flask was added 3.71 g (15.3 mmol) of
CF3SO2NNaSiMe3, 100 mL of dry CH3CN, and 14.00 g
(23.1 mmol) of bromine protected monomer 9. The mixture
was stirred at 808C under dry nitrogen until the reaction was
complete by 19F NMR. After completion, the CH3CN and
excess bromine protected 9 monomer were removed under
vacuum and the residue dried at 80 8C under high vacuum
for 1 day. 19F NMR (CD3CN): ꢀ63.7 (2F), ꢀ71.9 (1F),
ꢀ77.9 (10F), ꢀ115.8 (2F), ꢀ144.8 (1F).
4.11. Preparation of CF2AX¼CFMOCF2bCFc(CF3d)-
OCF2eCF2f SO2NHSO2CF3g (15)
To the bromine protected sulfonimide was added 1.5 g of
activated zinc dust and 100 mL of CH3CN. The mixture was
stirred at room temperature for 1 h and then at 60 8C for 4 h.
The excess zinc was filtered off of the reaction mixture and
the CH3CN was removed under vacuum. The resulting
residue was acidified with 10 mL of water and 10 mL of
37% HCl. The solution was then extracted with ether and the
organic layer washed twice with deionized water. The ether
was evaporated and the remaining liquid distilled to give
7.40 g (12.86 mmol) of the desired monomer in 84% yield.
Bp: 67 8C/0.01 mmHg; 1H NMR (CD3CN): 11.9; 19F NMR
dM ꢀ112.3 AMX (1F, dd), JMX ¼ 66 Hz, JAM ¼ 56 Hz; dA

B.H. Thomas et al. / Journal of Fluorine Chemistry 125 (2004) 1231–1240
1239
[2] S.G. Ehrenberg, T. Serpico, G.E. Wnek, J.N. Rider, U.S. Patent
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rinsed and dried. The reaction yields 10 þ g of polymer
(Scheme 5).
[3] J. Wei, C. Stone, A. Steck, U.S. Patent 5,422,411 (1995).
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M. Bursell, Electrochem. Acta 43 (1998) 1881.
4.14. Formation of membrane
Membranes were cast in either a 50 mL PTFE dish or a
250 mL highly polished stainless steel dish. A typical
membrane was made using 1.54 g of copolymer (IEC
0.83 mgH/g) which was dissolved into 200 mL of DMF,
18 mL of methanol and 10 mL of water. The solution was
heated to ꢃ80 8C for 16 h. After 16 h, the solution was
allowed to cool to room temperature. The polymer mixture
was then briefly blended into a homogenous liquid using a
high-speed ss blender and filtered through the low pass filter
equipped with a nylon cloth. The solution filtered relatively
easy through the filter and no residual polymer was col-
lected. The resulting viscous liquid was degassed under
vacuum in the oven and then poured into the 250 mL ss
dish. The oven was heated to 90 8C under 25 in. Hg and the
majority of the solvent was removed over 1 day. The oven
was then heated to 180 8C under full vacuum for 8 h to
remove any remaining DMF. The membrane was annealed at
250 8C for 4 h. The membrane was then boiled in 70% nitric
acid until the membrane was colorless and then boiled in
repetitive DI water rinses until neutral. The thickness of the
membrane was 3.15 mils with a water uptake of 82%.
[7] A.E. Feiring, S. Rozen, U.S. Patent 5,668,233 (1997).
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4.15. Dissolution of polymer
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1.31 g of copolymer (IEC of 0.83 mgH/g) was placed into
a 75 mL bomb along with ꢃ20 glass beads. The bomb was
evacuated overnight. Then, 17.25 mL deionized water,
27.5 mL of n-propanol, and 23.0 mL of methanol were
sucked into the evacuated reactor. Assuming no ether for-
mation, the end solution should be around 3%. The bomb
was wrapped with heating tape and placed on the shaker. The
reactor was allowed to heat to 260–280 8C for 4 h. The bomb
was allowed to cool to room temperature and the reactor was
opened. The solution was filtered through #4 Whatman filter
paper and the undissolved polymer dried and weighed. The
concentration of the solutions were calculated by taking
0.5 mL aliquots of the solutions and drying them in an oven
at 120 8C overnight. The solution was 2.24 wt.% polymer
with 88% of the starting polymer dissolved.
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Acknowledgements
Financial support for this research was provided by DOE/
EPSCoR, GRI and ARPA.
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