Synthesis and ATRP of novel fluorinated aromatic monomer with pendant sulfonate group

Article abstract of DOI:10.1016/j.jfluchem.2013.02.008

Novel, fluorinated monomer with pendant sulfonate group was synthesized utilizing a two-step derivatization of 2,3,4,5,6-pentafluorostyrene (FS). The first step was a nucleophilic substitution of the fluorine atom in para position by hydroxyl group followed by sulfopropylation. The monomer was polymerized under aqueous ATRP conditions to yield phenyl-fluorinated aromatic homopolymer bearing pendant sulfonates on each repeating unit. Furthermore, this polymer was used as macroinitiator for the ATRP of poly(ethylene glycol) methacrylate. The polymers were characterized by ¹H NMR, SEC and FTIR analyses. Their thermal properties were evaluated by differential scanning calorimetry and thermal gravimetric analyses.

Full text of DOI:10.1016/j.jfluchem.2013.02.008

Journal of Fluorine Chemistry 149 (2013) 30–35
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis and ATRP of novel fluorinated aromatic monomer with pendant
sulfonate group
*
Ivaylo Dimitrov, Katja Jankova, Søren Hvilsted
Danish Polymer Centre, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads, Building 227, Kongens Lyngby 2800, Denmark
A R T I C L E I N F O
A B S T R A C T
Article history:
Novel, fluorinated monomer with pendant sulfonate group was synthesized utilizing a two-step
derivatization of 2,3,4,5,6-pentafluorostyrene (FS). The first step was a nucleophilic substitution of the
fluorine atom in para position by hydroxyl group followed by sulfopropylation. The monomer was
polymerized under aqueous ATRP conditions to yield phenyl-fluorinated aromatic homopolymer
bearing pendant sulfonates on each repeating unit. Furthermore, this polymer was used as
macroinitiator for the ATRP of poly(ethylene glycol) methacrylate. The polymers were characterized
by 1H NMR, SEC and FTIR analyses. Their thermal properties were evaluated by differential scanning
calorimetry and thermal gravimetric analyses.
Received 4 October 2012
Received in revised form 6 February 2013
Accepted 7 February 2013
Available online 17 February 2013
Keywords:
Fluorinated monomer
Synthesis
ß 2013 Elsevier B.V. All rights reserved.
Polyelectrolyte
ATRP
Thermal stability
1. Introduction
can be easily adapted for that of fluoromonomers [19]. Thus,
2,3,4,5,6-pentafluorostyrene (FS) has been polymerized in con-
Polymers with high content of sulfonic acid groups represent a
class of water-soluble polymers and anionic polyelectrolytes [1].
They have attracted much interest in numerous bio-related
applications based on specific acid–base and oppositely charged
ionic interactions with biologically active molecules [2–4]. Sulfonic
acid-based polymer materials have been developed as blood-
compatible coatings [5], cationic drug-delivery systems [6], and
enzyme carriers [7]. Sulfonic acid-containing amphiphilic block
copolymers, on the other hand, are of considerable and increasing
interest, mainly due to their ability to form highly ordered
structures as a result of self-association and their potential
applications as proton conductive membranes [8–10]. The
synthesis of well-defined polymers with sulfonic acid groups
applying various controlled radical polymerization (CRP) methods
has been described in the literature [11–13]. Sulfonic acid-
containing block copolymers were also prepared by controlled
radical polymerization of monomer derivatives with protected
sulfonic acid groups [14,15] or by post-modification [16].
trolled manner by atom transfer radical polymerization (ATRP)
yielding fully phenyl fluorinated polystyrene (PFS) [20]. The
potential of ATRP has been further exploited for the synthesis of
PFS-based linear di-, multiblock- or star-shaped architectures [20–
22]. Furthermore, various 4-substituted-2,3,4,5-tetrafluorostyrene
derivatives were synthesized and successfully polymerized by
ATRP [23,24]. Other CRP methods for the preparation of 4-
substituted FS-based copolymers include nitroxide-mediated
polymerization (NMP) or reversible addition-fragmentation chain
transfer (RAFT) followed by post-modifications [25,26].
Herein, we present the synthesis and controlled polymerization
of novel fluorinated aromatic monomer bearing pendant sulfonate
group. A synthetic strategy based on nucleophilic substitution of
the fluorine atom in para position of FS followed by sulfopropyla-
tion is utilized for the monomer preparation. The controlled
polymerization of the newly synthesized monomer under aqueous
ATRP conditions is demonstrated as well as attempts for block-
copolymer synthesis. Furthermore, the thermal properties of the
sulfonated homopolymer are compared to those of PFS.
Fluorinated polymers have attracted significant attention due
to a series of favorable properties, such as high thermal stability,
hydrophobicity, good chemical resistance, low flammability as
well as their optical and electrical properties [17,18]. Most
fluorinated monomers can be polymerized under radical condi-
tions, and the processes that enable CRP of hydrocarbon monomers
2. Results and discussion
2.1. Synthesis of tetrafluorostyrene alkyl sulfonated monomer
(TFSSNa)
The synthetic procedure is shown on Scheme 1. It involves
modification of FS exploiting the well known fact in organic
synthesis that the labile para-fluorine of the pentafluorophenyl
* Corresponding author. Tel.: +45 4525 2965; fax: +45 4588 2161.
E-mail address: sh@kt.dtu.dk (S. Hvilsted).
0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2013.02.008

I. Dimitrov et al. / Journal of Fluorine Chemistry 149 (2013) 30–35
31
Scheme 1. Synthesis of fluorinated monomer with pendant sulfonate group TFSSNa.
groups can undergo a nucleophilic substitution. Initially, FS was
converted into para-hydroxy-tetrafluorostyrene derivative
(TFSOH). Usually this is done in two steps nucleophilic
corresponding to one oxymethylene and two methylene protons
from the attached sulfopropylate side groups appeared in the
product’s spectrum and their relative intensities compared to
those of the vinyl protons at 6.68, 6.08 and 5.72 suggested
complete functionalization and high purity of the monomer
obtained. The successful sulfopropylation was further confirmed
by FTIR spectroscopy. Characteristic absorption bands for the
asymmetric and symmetric O55S55O stretch of the sulfonate groups
were found at 1183 and 1060 cmꢀ1, respectively in the monomer’s
spectrum.
a
–
substitution of FS by sodium methoxide followed by demethyla-
tion with boron tribromide as described by Pitois et al. [27]. A
drawback of this procedure is the difficult separation of para-
hydroxy substituted tetrafluorostyrene from the unreacted meth-
oxy derivative due to their close boiling temperatures. In our case
we used the more recently reported two step procedure to obtain
para-hydroxy derivative of FS [28]. TFSOH was obtained in one pot
reaction of FS with alkaline tert-BuOH followed by acidification
(Scheme 1). After careful extractions and vacuum distillation the
hydroxy derivative was obtained with 95% purity and 60% yield.
The final step in the monomer preparation was the attachment of
pendant sulfonate groups in para-position of the aromatic ring
through a sulfopropylation. We have previously shown that
fluorinated and non-fluorinated aromatic copolymers can be
2.2. ATRP of TFSSNa
Generally, the controlled polymerization of monomers contain-
ing strong acidic groups under ATRP conditions is hampered due to
the sensitivity of the polymerization-control complex to acidic
media. Recently, Iddon et al. [13] reported an aqueous ATRP of
sodium 4-styrenesulfonate (NaSS) at 20 8C. The water was needed
to dissolve the ionic monomer, while different amounts of
methanol were added to slow down the polymerization rate
and to achieve better control over the process. Due to the aromatic
nature of TFSSO3Na we decided to use similar conditions for the
ATRP of the newly synthesized sulfonated monomer. The ATRP of
TFSSNa was performed in water/methanol = 3:1 (v/v) solvent
mixture at 25 8C and was initiated by 4-(bromomethyl)benzoic
acid (BMBA) in sodium salt form (Scheme 2). After 24 h of
polymerization, followed by dialysis and lyophilization, the
purified product was recovered as white powder in 85% yield.
successfully sulfopropylated by
a nucleophilic ring-opening
reaction of 1,3-propane sultone (PrS) [16,29]. In the current work
we applied this approach to obtain a sulfopropylated tetrafluoro
derivative of styrene. The hydroxy group of TFSOH was activated in
alkaline MeOH and used for the ring-opening of PrS. Regardless of
the availability of four highly hydrophobic fluorine atoms and a
propylate group attached to the aromatic ring, the presence of a
single pendant sulfonate group renders the monomer completely
soluble in water. The overall yield of the monomer was 41%. The
successful and complete sulfopropylation was confirmed by 1H
NMR in D2O (Fig. 1). The resonances at 4.42, 3.14, and 2.22 ppm
Fig. 1. 1H NMR (300 MHz) spectrum of TFSSNa in D2O at 25 8C.

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I. Dimitrov et al. / Journal of Fluorine Chemistry 149 (2013) 30–35
Scheme 2. ATRP of TFSSNa.
The 1H NMR spectrum of PTFSSNa is presented in Fig. 2a. It clearly
shows the peaks at 2.1 and 3.1 ppm attributed to the two
methylene protons from the pendant sulfopropylate groups and
the overlapping backbone protons as well as the peak at 4.3 ppm
attributed solely to the oxymethylene protons next to the aromatic
ring. The molar mass and polydispersity index (PDI) of the polymer
were estimated by aqueous SEC. A typical SEC trace of the
sulfonated polymer is shown in Fig. 2b. It reveals that the polymers
elute as monomodal species with polydispersity indices in 1.3–
1.35 range. The molar masses were estimated versus PNaSS narrow
molar mass standards and were found to be in a good agreement
with the targeted ones. Homopolymers with molar masses ranging
from approx. 10,000 to 30,000 were synthesized.
For the kinetic studies the polymerization was performed in a
mixture of deuterated water and methanol under the same ATRP
conditions over a period of 180 min. At predetermined time
intervals samples were withdrawn and subjected to NMR analyses.
The degree of monomer conversion was estimated from the
relative intensities of the protons at 6.6, 6.0 and 5.7 ppm attributed
to the monomer’s olefinic protons and the oxymethylene protons
from the pendant sulfopropylate groups at 4.3 ppm. The corre-
sponding semilogarithmic plot of monomer conversion versus time
reveals a slight curvature as shown in Fig. 3. This suggests a
deviation from the ideal living character of the process, most likely
due to the non-constant polymer radical concentration during the
polymerization [13,30]. However, the deviation from the linearity
Fig. 2. 1H NMR (300 MHz) spectrum of PTFSSNa in D2O at 25 8C (a) and size exclusion chromatogram of PTFSSNa (Mn = 10 700 Da, Mw/Mn = 1.35) (b).

I. Dimitrov et al. / Journal of Fluorine Chemistry 149 (2013) 30–35
33
Fig. 5. TGA curves for PFS (a) and PTFSSNa (b).
Fig. 3. Semi-logarithmic kinetic plots for the homopolymerization of TFSSNa at
25 8C using the BMBA initiator and CuCl catalyst in 3:1 water/methanol mixture.
(PEGMA) with molar mass of approx. 360 Da was chosen as a
building segment for the second block due to its good solubility in
the water/methanol solvent mixture and the distinct resonances in
1H NMR. The ATRP was performed at 30 8C using the same solvent
mixture and CuCl/bpy catalytic system. The targeted degree of
polymerization (DP) was 60 in order to obtain a clear shift in the SEC
trace of block copolymer. The product was dialyzed to remove the
unreacted PEGMA-monomer and subjected to 1H NMR and SEC
analyses. The 1H NMR spectrum of the product in D2O confirms the
presence of oxyethylene protons from the PEGMA-side groups
(Fig. 4a). The SEC analysisshowsa distinct shifttowardlower elution
volume (higher molar mass) for the block copolymer (Fig. 4b).
However, there is also a leftover of the macroinitiator in the block
copolymer’s SEC-trace indicating an incomplete initiating efficiency
of PTFSSNa. This is most likely due to the incomplete halogen chain-
end functionalization since the macroinitiator used for the block
copolymer synthesis was obtained at 100% monomer conversion.
is much less pronounced and the polymerization rate is much
slower as compared to the ATRP of NaSS performed under similar
conditions by Iddon et al. [13].
2.3. Block copolymerization. Synthesis of PTFSSNa-b-PPEGMA
The synthesized polyionic fluorinated aromatic homopolymers
(PTFSSNa) were used as macroinitiators to test the possibility of
obtaining diblock copolymers. A poly(ethylene glycol) methacrylate
2.4. Thermal properties of PTFSSNa
The thermal properties of the newly synthesized fluorinated
homopolymers with pendant sulfonate groups were evaluated by
their thermal decomposition (Td) and glass transition (Tg) data
measured by TGA and DSC respectively. The sulfonated polymers
exhibit lower thermal stability compared to the fully phenyl-
fluorinated polystyrene (PFS) which is thermally stable up to
390 8C (Fig. 5). The sulfonated polymers start to decompose at
330 8C after an initial loss of water. Moreover, two-step degrada-
tion is observed for PTFSSNa. The first step is attributed to the
degradation of the pendant sulfopropylate groups. The main
weight loss starts above 380 8C, close to the decomposition
temperature of PFS, and is connected with the degradation of the
backbone chain.
The sulfonated aromatic fluoropolymers showed higher glass-
transition temperatures compared to those of PFS. The sulfonated
polymer PTFSSNa with molar mass of 10 700 has a Tg of 134 8C,
whereas the Tg of PFS of comparable molar mass is 94 8C [20]. A
similar increase in the Tg was previously observed by us after the
attachment of pendant sulfonate groups onto a polymer backbone.
The increase was attributed to hydrogen bonding in the sulfonated
polymers which prevails over the plasticizing effect of the short
side alkyl chains [29].
3. Conclusion
A novel aromatic fluorinated monomer with pendant alkyl-
sulfonate group was synthesized and polymerized under aqueous
ATRP conditions. The monomer was prepared in two reaction steps
Fig. 4. 1H NMR (300 MHz) spectrum in D2O at 25 8C of PTFSSNa-b-PPEGMA (a) and
SEC overlay of PTFSSNa-macroinitiator and PTFSSNa-b-PPEGMA (b).

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I. Dimitrov et al. / Journal of Fluorine Chemistry 149 (2013) 30–35
from 2,3,4,5,6-pentafluorostyrene through a nucleophilic substi-
tution of the labile para-fluorine atom by hydroxyl group followed
by sulfopropylation with 1,3-propanesultone. The monomer was
polymerized in controlled manner via ATRP in water/methanol to
yield well-defined fluorinated aromatic homopolymers bearing
pendant sulfonate groups on each repeating unit. The polymers
were characterized by 1H NMR and SEC analyses. Their thermal
properties were investigated by TGA and DSC. A diblock copolymer
was also obtained using the newly synthesized polymer as ATRP-
macroinitiator. The synthesized fluorinated polymers with sulfo-
nate side groups might be used as building blocks for numerous
bio-related applications as well as for polymer electrolytes in fuel
cells.
d6, d, ppm): 11.62 (OH), 6.59 (CH55CH2), 5.60–5.92 (CH55CH2). FTIR
(cmꢀ1): 3400 (OH).
4.4. Synthesis of sodium 3-(2,3,5,6-tetrafluoro-4-
vinylphenoxy)propane-1-sulfonate (TFSSNa)
The hydroxy-functionalized monomer TFSOH (10 g, 0.052 mol)
was dissolved in MeOH (315 mL) followed by the addition of NaOH
(2.28 g, 0.057 mol). The mixture was stirred at room temperature
until the base was completely dissolved. Finally, a solution of PrS
(6.96 g, 0.057 mol) in 1,4-dioxane (26 mL) was added dropwise
and the reaction mixture was stirred for an hour at room
temperature. Then it was refluxed for 24 h. The solvents were
evaporated and the residue was washed with DCM. The product
was recrystallized twice from MeOH/H2O = 2:1 (v/v). Yield: 12.2 g
4. Experimental
(70%). 1H NMR (300 MHz, D2O,
d, ppm): 6.68 (CH55CH2), 6.08–5.68
4.1. Materials
(CH55CH2), 4.42 (O–CH2), 3.14 (CH2–SO3Na), 2.22 (CH2–CH2–CH2).
FTIR (cmꢀ1): 1183 and 1060 (O55S55O).
The chemicals were purchased from Sigma–Aldrich. 2,3,4,5,6-
Pentafluorostyrene (FS, 99%) was passed through an inhibitor-
removing column and distilled under reduced pressure prior to
use. Poly(ethylene glycol) methacrylate (PEGMA, Mn ꢁ 360 Da)
was passed through a column containing neutral aluminum oxide.
Methanol (MeOH, >99%), 1,4-dioxane (DO, >99%), and dichlor-
omethane (DCM, >99.8%) were dried using standard procedures.
1,3-Propane sultone (PrS, 98%), 4-(bromomethyl)benzoic acid
(BMBA, 97%), copper(I) chloride (CuCl, 98%), potassium hydroxide
(KOH, >85%), sodium hydroxide (NaOH, >98%), tertiary butanol
(tert-BuOH, >99.5%), diethyl ether (>99.8%), and 2,20-bipyridyl
(bpy, 99%) were used as received.
4.5. ATRP of TFSSNa – synthesis of homopolymers PTFSSNa
Typically, TFSSNa (1 g, 2.97 mmol) and the initiator BMBA
(21.3 mg, 0.099 mmol) were dissolved in water (4.95 mL). A few
drops of 1 M NaOH were added to the solution in order to adjust
the pH ꢁ 9–10. The alkaline mixture was degassed trice. Separate-
ly, CuCl (9.8 mg, 0.099 mmol) and bpy (30.9 mg, 0.198 mmol) were
dissolved in 1.65 ml of MeOH and the complex solution was
degassed trice. The two solutions were combined via a transfer
needle and the reaction mixture was degassed one more time. The
polymerization was performed at 25 8C for 24 h. The reaction
mixture was dialyzed against distilled water for 4 days (Mw cut-
off = 1200 Da) and the product was recovered through lyophiliza-
4.2. Instrumentation
tion. Yield: 0.85 g (85%). 1H NMR (300 MHz, D2O,
d, ppm): 4.27 (O–
1H NMR spectra were recorded on
a
Bruker 300 MHz
CH2), 3.70–2.65 (CH–CH2 + CH2–SO3Na), 2.63–1.1 (CH2–CH2–
CH2 + CH–CH2). FTIR (cmꢀ1): 1185 and 1045 (O55S55O). Aqueous
SEC (MeOH/H2O = 1:1, v/v): Mn = 10,700 Da, Mw/Mn = 1.35.
The kinetic study was performed in D2O/CD3OD = 3:1 (v/v)
solvent mixture and monomer to initiator ([M]:[I]) ratio = 90
applying the same ATRP conditions. At time intervals, an
appropriate volume of the mixture was withdrawn with a
degassed syringe and subjected to 1H NMR analysis.
instrument. Size exclusion chromatography (SEC) was performed
in MeOH/H2O = 1:1 (v/v) mixture + 50 mM NaCl at a flow rate of
1.0 mL minꢀ1 on a set of PW4000 + PW2500 columns (Tosoh Corp.,
Tokyo, Japan), calibrated versus poly(sodium styrene sulfonate)
narrow molar mass standards; the column temperature was 25 8C
and DRI detector temperature was 37 8C. Infrared spectra were
recorded on a PerkinElmer Spectrum One model 2000 Fourier
transform infrared system with a universal attenuated total
reflection sampling accessory on a ZnSe/diamond composite.
Thermal analyses were carried out on a differential scanning
calorimeter DSC Q1000 (TA Instruments) in a temperature range of
20–250 8C at a heating and cooling rate of 10 8C minꢀ1 under
nitrogen. The glass transition temperatures (Tg) were determined
during the second heating cycle at the inflection point of the
thermal transition. Thermogravimetric analyses (TGA) were
performed on a TGA Q500 instrument measuring the samples’
total weight loss from 25 to 650 8C at a rate of 10 8C minꢀ1 under a
4.6. Synthesis of block copolymer PTFSSNa-b-PPEGMA
The macroinitiator PTFSSNa (0.2 g, 0.019 mmol) and PEGMA
(0.41 g, 1.14 mmol) were dissolved in 2 mL of H2O/MeOH = 3:1 (v/
v) mixture and were degassed trice. Separately, CuCl (18.8 mg,
0.19 mmol) and bpy (59.35 mg, 0.38 mmol) were dissolved in
6.5 mL of H2O/MeOH = 3:1 (v/v) mixture, degassed trice, and
0.65 mL were withdrawn via syringe and added to the monomer
and macroinitiator solution. The combined brown-colored solution
was degassed one more time and the polymerization was started at
30 8C. It was stopped after 3 h by passing air through the reaction
mixture. The green solution was dialyzed against distilled water
and the product was recovered through lyophilization. Yield:
nitrogen flow of 90 mL minꢀ1
.
4.3. Synthesis of 2,3,5,6-tetrafluoro-4-vinylphenol (TFSOH)
The synthesis of TFSOH was performed similar to a previously
reported procedure [28]. Briefly, FS (20 g, 0.1 mol) was added to a
mixture of KOH (30 g, 0.53 mol) in 400 mL of tert-BuOH. The
mixture was refluxed for 2 h, cooled down to room temperature
and diluted with 1200 mL of water. The alcohol was distilled off
and the residue was extracted with diethyl ether (3ꢂ 300 mL). The
aqueous phase was acidified (pH ꢁ 3) with 10 wt.% HCl and was
extracted with diethyl ether (3ꢂ 300 mL). The organic phase was
dried over MgSO4 overnight. The solution was filtered and the
diethyl ether was distilled off. The product was purified through a
vacuum distillation. Yield: 11.5 g (58%). 1H NMR (300 MHz, DMSO-
0.42 g (67%). 1H NMR (300 MHz, D2O,
d, ppm): 4.60–4.00 (O55C–O–
CH2), 3.95–3.4 (O–CH2–CH2–O), 3.30–2.65 (Ar–CH–CH2 + CH2–
SO3Na), 2.63–1.1 (CH2–CH2–CH2 + Ar–CH–CH2 + C–CH2), 1.05–0.6
(C–CH3). FTIR (cmꢀ1): 1185 and 1043 (O55S55O), 1725 (C55O), 3440
(OH).
Acknowledgements
The financial support of this research from the Danish Council
for Strategic Research through contract no. 09-065198 is gratefully

I. Dimitrov et al. / Journal of Fluorine Chemistry 149 (2013) 30–35
35
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