Two New Diazonium Bis(perfluoroalkyl)arylsulfonyl Imide Zwitterionic Monomers from Perfluoro(3-oxa-4-pentene)sulfonyl Fluoride for Proton Exchange Membrane Fuel Cells

Article abstract of DOI:10.1016/j.jfluchem.2017.04.006

Two new bis(perfluoroalkyl)arylsulfonyl imide monomers, which contain the aryl diazonium moiety and intramolecular zwitterionic fragment, have been designed and prepared for the first time from perfluoro(3-oxa-4-pentene)sulfonyl fluoride. As promising monomer candidates for high-performance proton exchange membrane fuel cell electrolytes, these two monomers have furnished perfluorinated electrolytes that include the polymers from perfluorinated sulfonic acid or perfluorinated sulfonimide monomers. The synthesis strategies and NMR analysis are summarized and discussed in details.

Full text of DOI:10.1016/j.jfluchem.2017.04.006

Accepted Manuscript
Title: Two new diazonium bis(Perfluoroalkyl)arylsulfonyl
Imide Zwitterionic Monomers from
Perfluoro(3-oxa-4-pentene)sulfonyl Fluoride for Proton
Exchange Membrane Fuel Cells
Authors: Hua Mei, Faisal Ibrahim
PII:
S0022-1139(17)30018-0
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2017.04.006
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Revised date:
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14-3-2017
24-4-2017
Please cite this article as: Hua Mei, Faisal Ibrahim, Two new diazonium
bis(Perfluoroalkyl)arylsulfonyl Imide Zwitterionic Monomers from Perfluoro(3-oxa-
4-pentene)sulfonyl Fluoride for Proton Exchange Membrane Fuel Cells, Journal of
Fluorine Chemistryhttp://dx.doi.org/10.1016/j.jfluchem.2017.04.006
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Two New Diazonium Bis(Perfluoroalkyl)arylsulfonyl Imide Zwitterionic Monomers from
Perfluoro(3-oxa-4-pentene)sulfonyl Fluoride for Proton Exchange Membrane Fuel Cells
Hua Mei, Faisal Ibrahim
Department of Chemistry, East Tennessee State University, Johnson City, TN 37614, United States
Graphic Abstract
The Structures of Diazonium PFSI Zwitterionic Mononomers from POPF Monomer
Highlights:
 Two new diazonium PFSI zwitterionic monomers from POPF monomer are successfully
synthesized
 The novel fluorinated compounds are the best candidate for further polymerization as
Hyflon Ion membrane
 A preparation method of around 40 % yield is well-established
 Special properties revealed by NMR and detailed analysis of those monomers need
further study
Abstract
Two new bis(perfluoroalkyl)arylsulfonyl imide monomers, which contain the aryl
diazonium moiety and intramolecular zwitterionic fragment, have been designed and prepared
1

for the first time from perfluoro(3-oxa-4-pentene)sulfonyl fluoride. As promising monomer
candidates for high-performance proton exchange membrane fuel cell electrolytes, these two
monomers have furnished perfluorinated electrolytes that include the polymers from
perfluorinated sulfonic acid or perfluorinated sulfonimide monomers. The synthesis strategies
and NMR analysis are summarized and discussed in details.
Key words: POPF, Hyflon Ion, Diazonium Bis(perfluoroalkyl)arylsulfonyl Imide, Nafion
® , PFSI, Fuel Cells.
Introduction
Fluoropolymer materials are well-known in industrial applications, such as electrolyte for
fuel cells and Lithium batteries, because of their remarkable durability.1 Over the last several
decades, the perfluorosulfonic acid (PFSA) polymers are broadly used in proton exchange
membrane (PEM) fuel cells.2 The recently developed thin-film catalyst layer in PEM fuel cells is
fabricated from catalyst ink, consisting of uniformly distributed PFSA ionomers and catalyst.3
Much research has been focused on developing new materials also by adjusting the catalyst
properties, the catalyst support, and electrolyte structures to maximize the three phase contact
regions and thereby leading to the better performance and durability of cells.4
The final target electrode is based on mesocarbon with big surface area decorated with Pt
particles and grafted (perfluoroalkyl)arylsulfonyl imides (PFSI) polymer electrolyte via
diazonium chemistry.5 PFSI polymers, which exhibit greater thermal stability (up to 400 ◦C in
the acid form) as well as better chemical and electrochemical inertness and less susceptibility to
dehydration and oxidative degradation reactions than PFSA polymers,6 are promoted in our
research to replace the traditional PFSA polymers, such as Nafion (EW ~ 1,100 g/mol) (1a) for
PEM fuel cells. In general, the traditional PFSA and PFSI polymers are based on random
copolymers derived from tetrafluoroethylene (TFE) and PFSA/PFSI-based monomers. The base
monomer, TFE constituting the basic structure of modern fluoropolymers and the latter special
PFSA/PFSI-based monomers can add special desired characteristics for PEM fuel cell
requirements.7 The new PFSI polymers, as depicted in Figure 1, are anticipated to be prepared
with the similar procedures as the Nafion/Hyflon Ion membrane, but with bis-sulfonylimide
aromatic perfluorovinyl ether and TFE monomers. In particular, our bis-sulfonylimide aromatic
perfluorovinyl ether monomers contain the diazonium moiety, which can be chemically bound to
carbon electrode before/after polymerization. According to the related research carried by Dow
company and Solvay Solexis, the Hyflon Ion Ionomers and their membranes showed higher
2

conductivity, similar mechanical properties, and a higher ionic glass-transition temperature,
compared to the presently commercially available membranes (Nafion ®).8 Lately, Solvay
Solexis has applied its proprietary fluorovinyl ether process to the production of short chain
PFSA monomers, such as perfluoro(3-oxa-4-pentene)sulfonyl fluoride (POPF) monomer at the
industrial scale. Compare to the process developed by DOW, 9 the whole procedure is shortened
to three steps. 10
In the present work, a facile and efficient protocol was used to prepare two diazonium
bis(Perfluoroalkyl)arylsulfonyl imide (bis-PFSI) zwitterionic monomers, 4-diazonium
perfluoro(3-oxapent-4-ene)benzenesulfonimide I and 4-(trifluoromethyl)-2-diazonium
perfluoro(3-oxapent-4-ene)benzenesulfonimide II from one of short chain PFSA monomers, the
commercially available POPF monomer. The trifluoromethyl (CF3) group was introduced into
the aromatic ring scaffold in order to study the substituent effect on its physical/chemical
proprieties.11
These novel monomers I and II were expected to at least contain three major fragments: aryl
diazonium zwitterion, PFSI pendant, and perfluorovinyl ether as polymerizable unit. With the
shorter perfluoroalkyl chain, the synthesis strategy of these two monomers is still unique (as
explained in the following section), in comparison to the previous reported diazonium PFSI
zwitterionic monomer analogues from the Nafion® monomer.12
Results and discussion
Preparation The initial investigation began with the POPF monomer and aromatic sulfonyl
chlorides and via the 6-step synthesis route to synthesize the target monomers (Scheme 1). To
our delight, the expected monomers were obtained in 35-40% yield, which is slightly higher
when compared to the similar monomers derived from the Nafion® monomer. Notably, the
acetal protected aromatic amine10b,13 offers more effective procedure than nitroaromatics14 in
providing the desired diazonium PFSI zwitterionic monomers with less time and better yields.
The reason is that the acetamide, as a moderate electron donating group, promotes the typical
SN2 reaction, such as ammonolysis and the coupling reaction (Step i and Step iii) and is easier to
be deacetylated later (Step v). Herein, instead of the aromatic nitro starting material, 4-acetamido-
benzenesulfonyl chloride (1a) was employed to prepare Monomer I (Figure 2). But because of its
commercial availability, 2-nitro-4-trifluoromethylbenzenesulfonylchloride was another starting
material for Monomer II (Figure 2).
The PFSA monomers, including Nafion® and POPF monomers, are susceptible to
nucleophilic addition because of the strong electron withdrawing perfluoroalkyl group. The
perfluorovinyl ether double bond therefore needs be protected first and released later as
bromination and debromination (Step ii and Step iv). For substrates bearing electron-deficient
substituents (CF3) on the benzene ring, the coupling (Step iii), the debromination (Step iv), and
reduction (step v) worked well to give the corresponding products with yields around 85%, but
taking a longer time. It is interesting to note that our developed debromination method (Step iv)
was tested under the different conditions. Ultimately, the optimal conditions for the generation of
7a were eventually finalized with the use of 6a (0.17 mmol) sonicated in the presence of NaOH
solution (The pH is around 8) in water-acetone solvent at room temperature for 2 days. To gain
insight into this special method, additional mechanistic studies are under investigation.15
3

(Step i: ammonia : water, the ratio is around 35 : 1, reflux at 100 °C overnight, 80%; or NH3(l), -
50 °C to r.t., 95%; Step ii: Br2, 0 °C to r.t., 66%; Step iii: N, N-diisopropylethylamine, dry
CH3CN, 80 °C, ~85%; Step iv Cs2CO3, acetone, reflux 8h, ~85%; Step va: Conc. H2SO4,
CH3OH, sonication, 6 hr., 93%; Step vb: Iron powder, H2, HCl, dry CH3CN, 80 °C, 77%; Step
vi: HCl, NaNO2, 0 °C, ~73%. )
Due to presence of short perfluoroalkyl chain, the differences compared to Nafion® based
monomers were discovered during the synthesis process. First, the brominated monomer 4 was
obtained with lower isolated yield due to several reasons, such as too much bromine was used
and poor extraction from water during the work up process. Subsequently, it took longer period
for completion of debromination and reduction (Steps iv and vb), the isolated yields for last 4
steps are all higher. It indicates that the overall synthesis scheme was fulfilled for fabricating
various diazonium bis-PFSI zwitterionic monomers from PFSA monomers.
Characterizations
Other than the common characteristics, it is interesting to observe some unique features in
the fluorine and proton NMR spectra during the process to analyze several intermediates. For the
brominated intermediate, such as FSO2CF2CF2OCFBrCF2Br (4), there is an AB type multiplet
around -82 ppm (Figure 3). The similar signals are manifested in the Fluorine NMR of
brominated Nafion® monomer FSO2CF2CF2OCF(CF3)CF2OCFBrCF2Br. The chemical shifts for
–OCF(CF3)CF2(e)- are correspondingly at around -84 ppm (Figure 3). The two diastereotopic
fluorine atoms of –OCF(CF3)CF2(e)- display two AB type multiplets spliting due to the presence
of the nearby stereogenic center fluorine –OCF(c)(CF3)-. For FSO2CF2CF2 OCFBrCF2Br, the
near two fluorine atoms of -CF2(a)CF2O- does not split the fluorine atoms b into a triplet because
the vicinal F–F coupling constant usually decreases as one increases the number of the proximate
electronegative atoms, such as fluorine and oxygen. Yet the AB type multiplet: actually, a double
doublet was still observed for the fluorine atoms b. The fluorine atom-OCF(c)Br- located on the
chiral carbon interferes with the fluorine atoms b. Therefore, the two diastereotopic fluorine
atoms b have different chemical shifts. The geminal (two-bond) coupling constants between
fluorine atoms are relatively large compared to those between hydrogen atoms. According to the
calculation, the two fluorine atoms b has 2JFF =137 Hz. But another AB type splitting is not
exhibited for fluorine atoms d, which is closer than fluorine atoms b. The relative lack of
resolution of fluorine atoms d likely derives from the multiple isotopes of bromine, which will
give rise to broadening of the signals due to isotope effects.16
Another unresolved phenomenon is found in the proton NMR of 2b (Figure 4), 5b, and 6b.
For example in 2b, -CF3 and -NO2 are stronger electron withdrawing groups than –SO2NH2. Due
to the inductive effect, the proton A should be more deshielded than protons B and C. The
deshielding effect of electron withdrawing groups should result in further downfield of proton
resonance chemical shift. The case is not matching the chemical shift of proton A, which is in
between of the chemical shift of protons B and C. All of them are confirmed with their splitting
conditions: the proton A is a singlet and the protons B and C obviously split each other as two
doublets. For 7b, the aromatic amine, the chemical shift of proton A also sits between the
chemical shift of protons B and C. It confirms the less inductive effect of –NH2 compared with –
SO2N(M)SO2Rf group. The most deshielded proton is the proton A in 8b, which is surrounded
+
by –N2 and –CF3 group. The similar results are also discovered in the trifluoromethylated
substituted diazonium PFSI zwitterionic monomer synthesized from Nafion® monomer.
4

However, the unclear reasons for the downfiled movement of proton A in 2b, 5b and 6b need to
be further investigated.
Experimental
General Consideration
The 1H and 19F NMR spectra were measured on a JEOL JNM-ECP 400 MHz FT NMR
spectrometer, using 1-2 mmol/L concentrations of the solutions (unless indicated otherwise). The
chemical shifts were reported in parts per million (ppm) using the high-frequency position
conversion, and the coupling constants were reported as a ‘J’ value in Hz. Tetramethylsilane
(TMS) was used as a reference material for the 1H NMR spectra while the 19F NMR chemical
shifts were referenced against a CFCl3 external standard. The chemical shift of residual H in
CD3CN was 1.97 ppm with respect to TMS. Unless indicated otherwise, samples were a
minimum of 99.5% pure by 19F NMR spectroscopy.
The infrared spectra were documented on the Shimadzu 1R Prestige-21 FTIR spectrometers.
A 50 mg solid sample was spread on the spectrometer crystal as a thin film between the clamp
tip and the opposing base. The IR spectra were scanned from 4000 cm-1 to 450 cm-1 and quoted
in wavenumbers (cm-1) with intensity abbreviations of vs (very strong), s (strong), m (medium),
w (weak), and vw (very weak).
The GC-MS spectra were recorded on Shimadzu GCMS-QP2010 plus GC system
spectrometer. The samples were prepared by dissolving 1 mg of the solid samples in 1 mL of
acetone.
The starting materials N-acetylsulfanilyl chloride and 2-Nitro-4-
(trifluoromethyl)benzenesulfonyl chloride were bought from Sigmaaldrich and POPF monomer
FSO2CF2CF2OCF=CF2 was bought from Synquestlab. 2-Nitro-4-
(trifluoromethyl)benzenesulfonylamide and 4-sulfamonylacetanilide were prepared according to
the reported procedure.25 All other reagents were from commercial sources and were used as
received except where noted.
(Caution: Diazonium salts are energetic materials and the dry salts should be treated with due
caution. We experienced no incidents in this work, but small sample size is recommended in the
absence of further testing.)
FSO2CF2CF2OCFBrCF2Br (4)
In a typical procedure, POPF monomer FSO2CF2CF2OCF=CF2 3 (3.0 g, 10.7 mmol) was
added into a 25 mL round bottom flask containing a stir bar and placed in an ice bath at
0 ºC. The bromine (1.50 mL, 29.3 mmol) was then added slowly using a pressure equalizing
funnel for about 2 hours. Persistence of a reddish color for another 30 mins indicated that there
was excess bromine. The reaction was allowed to continue overnight in the presence of light,
which can encourage a free radical reaction.
The excess bromine was removed by the slow addition of 5 % NaHSO3 until the reddish
color disappeared. The product was separated by extraction with 3×5 mL DI water in a
separatory funnel. The product was dried, using Na2SO4 after it was distilled out around 65 ºC
under dynamic 300mm vacuum. A percent yield of 65.6 % (3.09 g) of the product 4 was
obtained.
5

19F-NMR (CD3CN, ppm): δa -111.4 (2F, m), δb -81.8 (2F, AB pattern multiplet), δc -72.2 (1F,
m), δd -63.8 (2F, m), and δe 46.3 (1F, s).
CH3CONHPhSO2N(M)SO2CF2CF2OCFBrCF2Br (5a)
In a typical procedure, brominated POPF monomer 4 (1.50 g, 3.41 mmol) and the 4-
acetamidobenzenesulfonamide 2a (0.72 g, 3.34 mmol, 1.02:1 ratio) were added into a 100 mL
three-necked round bottom flask equipped with a stir bar and two rubber septa in a dry box. Then
20 mL of dry acetonitrile and 5 mL of dry diisopropyl ethylamine (DIEA) were injected into the
closed flask subsequently in the dry box. The solution was refluxed for 5 days at 90 ° C with
nitrogen gas protection. The disappearance of the –SO2F peak in the 19F NMR spectroscopy
indicated the reaction was completed. All of the remaining volatile compounds were then
removed by rotary evaporator, leaving the crude product as the DIEAH+ salt and the inorganic
impurities. The crude product was then run through column with a 1:1 ratio of acetone to tert-
butyl methyl ether to remove the extra starting material 2a-b. Next, the hydrolysis by-product
was removed by recrystallization with acetone/water. The purified product 5a (1.85 g, 87.5 %)
was obtained after removing the solvent and drying under vacuum for 24 hours.
19F NMR (CD3CN, ppm): δa -116.8 (2F, m), δb -82.5 (2F, AB pattern multiplet), δc -72.0 (1F, m),
δd -64.3 (2F, m).
1H NMR (CD3CN, ppm): δA 2.06 (3H, s), δB 9.37 (1H, s), δC 7.72 (2H, d), and δD 7.61 (2H, d),
JCD = 8 Hz.
IR (νmax, cm-1): 3402.43 (NH), 1662.64 m (C=O), 1176.58 m and 1261.45 s (S=O), 1045.43 v
(CF2).
4-CF3-2-NO2PhSO2N(M)SO2CF2CF2OCFBrCF2Br (5b)
Compound 5b (84.8%) was obtained by a similar procedure as 5a. For 5b, the crude product
was run through column with a 1:1 ratio of acetone to hexane.
6

19F NMR (CD3CN, ppm): δa -116.5 (2F, m), δb -82.0 (2F, AB pattern multiplet), δc -71.7 (1F, m),
δd -64.1 (2F, m), δe -63.2 (3F, s).
1H NMR (CD3CN, ppm): δA 7.93 (1H, s), δB 8.24 (2H, d), δC 7.91 (2H, d), JBC = 8Hz).
IR (νmax, cm-1): 1541 s and 1402 m (NO), 1150 vs (CF2), 1049 vs, 1096 vs and 1319 w (S=O).
p-NH2PhSO2N(M)SO2CF2CF2OCFBrCF2Br (6a)
In a typical procedure, the coupled product 5a (0.20 g, 3.20 mmol) was added into a 25 mL
round bottom flask equipped with a stir bar. Then 4 mL of methanol and 2 mL of concentrated
sulfuric acid (conc. H2SO4) were added to the flask. The resulting solution was measured to be
around pH 1-2, according to the pH paper. The solution was allowed to react under the
sonication for 6 hours. Subsequently, the solution was neutralized with NaOH (10%) solution
and the solvent was removed by rotary evaporator. Next the product was dried under vacuum
overnight. The dried sample was re-dissolved in 5 ml of ethyl acetate, and then transferred into a
60 mL separatory funnel. The organic solution was washed with 3×10 mL of brine water. The
solvent was removed and then dried under vacuum to give the pure product 6a with 84.2% yield.
19F NMR (400 MHz; CD3CN): δa -117.1 (2F, m), δb -84.2 (2F, AB pattern multiplet), δc -71.8
(1F, m), δd -64.2 (2F, m).
1H NMR (400 MHz; CD3CN): δA 7.48 (2H, d), δB 6.56 (2H, d), JAB = 8 Hz, δC 4.57 (2H, s).
IR (νmax, cm-1): 3365 (NH), 1300 m and 1315 s (S=O), 1143 vs (CF2).
p-NH2PhSO2N(M)SO2CF2CF2OCF=CF2 (7a)
7

In a typical procedure, the compound 6a (0.10 g, 0.17 mmol) was added into a 25 mL round
bottom flask equipped with a stir bar. Then 3 mL of acetone and 3 ml of 3.0 M Na2CO3 were
added to it. The pH of the resulting solution was tested to be 8.83 using a PH meter. The solution
was allowed to react under sonication for 2 days. Next the solvent was removed by rotary
evaporator and dried under vacuum overnight. The dried sample was re-dissolved in 5 mL of
ethyl acetate, and then transferred into a 60 mL separatory funnel. The organic solution was
washed with 3×5 mL of brine water. The final product 7a (0.068 g, 92.8 %) was isolated after
removing the remaining solvent and drying under vacuum for 24 hours.
19F NMR (400 MHz; CD3CN): δa -116.9 (2F, m), δb -83.7 (2F, m), δc -115.1 (1F, qm), δd -123.2
(1F, qm), δe -135.3 (1F, qm).
1H NMR (400 MHz; CD3CN): δA 7.48 (2H, d), δB 6.56 (2H, d), JAB = 8Hz, δC 4.55.
IR (νmax, cm-1): 3360 m (NH), 1600 m (C=C), 1260 s (S=O), 1015 vs (CF2).
4-CF3-2-NO2-PhSO2N(M)SO2CF2CF2OCF=CF2 (6b)
In a typical procedure, the coupled product of 5b (0.50 g, 1.73mmol) was added into in a 50
ml round bottom flask equipped with a rubber septum. Then 10 mL of acetone and 12 ml of 3.0
M Cs2CO3 were added to the flask. The pH of the resulting solution was determined to be 10.76
by the pH meter. The solution was refluxed at 90 oC for 8 hours to complete the debromination.
The excess solvent was then removed by rotaary evaporator and the product dried under vacuum
overnight. The dried product was re-dissolved in 5 ml ethyl acetate and then transferred into a 60
ml separatory funnel. The organic portion was extracted and washed with 3 x 5 ml brine water.
The solvent was removed by rotary evaporator and dried under high vacuum overnight, to obtain
the pure product 6b with 86.3 % yield.
19F NMR (400 MHz; CD3CN): δa -116.4 (2F, m), δb -83.3 (2F, m), δc -114.25 (1F, qm), δd -
122.63 (1F, qm), δe -135.1 (1F, qm), δf -63.17 (3F, s).
1H NMR (400 MHz; CD3CN): δA 7.93 (1H, s), δB 8.24 (2H, d), δC 7.91 (2H, d), JBC = 8Hz.
IR (νmax, cm-1): 1551 s and 1368 m (NO), 1125 vs (CF2), 1624 m (C=C), 1076 vs, 1281 vs and
1321 w (S=O).
8

4-CF3-2-NH2-PhSO2N(M)SO2CF2CF2OCF=CF2 (7b)
In a typical procedure, the debrominated product 6b (0.18 g, 3.40 mmol) and iron powder
(1.10 g, 19.6 mmol, 1:5.76 ratio) were added to a 50 ml one-necked round bottom flask
equipped with a stir bar. And then, 10 mL of methanol and 1 mL of 6.0 M HCl were
subsequently added to the round bottom flask. The flask was equipped with a septum, a needle,
and a H2 gas filled balloon. The reaction was run at room temperature in ultrasound sonicator for
2 days. TLC was used to monitor the reaction in 1.5:1 acetone to hexane, which revealed one
spot with an Rf value of 0.07. The excess iron powder was filtered out by vacuum filtration. The
organic portion was extracted out with 3x 10 mL of ethyl acetate from water. The final product
7b (0.13 g, 76.5 %) was obtained after removing the remaining solvent by rotary evaporator and
drying under vacuum for 24 hours.
19F NMR (400 MHz; CD3CN): δa -116.9 (2F, m), δb -83.7 (2F, m), δc -114.6 (1F, qm), δd -123.1
(1F, qm), δe -135.6 (1F, qm), and δF -63.8 (3F, s).
1H NMR (400 MHz; CD3CN): δA 6.96 (1H, s), δB 7.69 (2H, d), δC 6.78 (2H, d), JBC = 8 Hz, δD
5.43 (2H, s).
IR (νmax, cm-1): 3360 m and 1655 s (NH), 1360 m and 1096 vw (S=O), 1254 s and 1050 vs
(CF2).
+
4-N2 PhSO2N-(M)SO2CF2CF2OCF=CF2 (8a)
In a typical procedure, the PFSI substituted aromatic amine 7a (0.10 g, 0.233 mmol), NaNO2
(0.155 g, 2.23 mmol), and 3 ml of 6.0 M HCl were added in a 50 ml round bottom flask
equipped with a stir bar. The solution was stirred for 2 hours in the ice bath and then poured into
ice before vacuum filtration. The final purified product 8a (0.075g, 72.8%) was obtained after
drying under dynamic vacuum line for 12 hours.
9

19F NMR (400 MHz; CD3CN): δa -116.7 (2F, m), δb -83.7 (2F, m), δc -114.7 (1F, qm), δd -123.0
(1F, qm), δe -136.0 (1F, qm).
1H NMR (400 MHz; CD3CN): δA 8.50 (2H, d), δB 8.29 (2H, d), JAB = 8Hz.
IR (νmax/cm-1): 2288 w (N≡N), 1323 s, and 1134 w (S=O), 1090 vs (CF2)
+
4-CF3-2-N2 -PhSO2N-(M)SO2CF2CF2OCF=CF2 8b
Compound 8b (74.4%) was obtained by a similar procedure.
19F NMR (400 MHz; ppm): δa -116.4 (2F, m), δb -83.3 (2F, m), δc -113.6 (1F, qm), δd -122.5
(1F, qm), δe -135.8 (1F, qm), δg -63.6 (3F, s).
1H NMR (400 MHz; CD3CN): δA 8.92 (1H, s), δB 8.53 (1H, d), δC 8.63(1H, d), JBC = 8Hz.
IR (νmax, cm-1): 2301w (N≡N), 1319 s, 1281 w and 1078 vs (S=O), 1125 vs (CF2).
Conclusions
In conclusion, we have herein reported the synthesis and characterization of two new
diazonium PFSI zwitterionic monomers from POPF monomer. Due to the short perfluoroalkyl
chain, these two monomers are the desirable candidates for polymerization and then act as the
high-performance electrolytes for PEM fuel cells. The use of acetamide protected aromatic
amine as the starting material is more efficient with a better yield for the targeted monomers. The
synthesis strategy for such diazonium PFSI zwitterionic monomers from any PFSA monomers is
well established. Moreover, the unusual two AB type multiplets in the fluorine NMR and the
skeptical chemical shift movement in the proton NMR may inspire more investigations towards
the NMR analysis of more complex perfluorinated compounds.
Acknowledgements
For financial support, we gratefully acknowledge the start-up fund from East Tennessee State
University.
10

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Figure 1: The Chemical Structure of Polymers
Figure 2: The Structures of Diazonium PFSI Zwitterionic Monomers
Figure 3: Part of Fluorine NMR of Compound FSO2CF2CF2OCFBrCF2Br (4) and
FSO2CF2CF2OCF(CF3)CF2OCFBrCF2Br.
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Figure 4: Chemical Structure and Part of Proton NMR of Compound 2b
Scheme 1: Overall Synthetic Scheme for Diazonium Bis-PFSI Zwitterionic Monomers.
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