Synthesis of novel fluorinated polymers via cyclodextrin complexes in aqueous solution

Article abstract of DOI:10.1021/ma050065s

Newly synthesized fluorinated monomers 4-(JV-adamantylamino)-2,3,5,6-tetrafluorostyrene (2) and 2,3,4,5,6-pentafluorostyrene (1) were polymerized in water after complexation with randomly methylated β-cyclodextrin (RAMEB) without the use of any surfactant

Full text of DOI:10.1021/ma050065s

5078
Macromolecules 2005, 38, 5078-5082
Synthesis of Novel Fluorinated Polymers via Cyclodextrin Complexes in
Aqueous Solution
Hakan Cinar, Oliver Kretschmann, and Helmut Ritter*
Heinrich-Heine-Universita¨t, Institut fu¨r Organische Chemie und Makromolekulare Chemie,
Lehrstuhl II, Universita¨tsstrasse 1, Geb. 26.33.00, D-40225 Du¨sseldorf, Germany
Received January 12, 2005; Revised Manuscript Received April 6, 2005
ABSTRACT: Newly synthesized fluorinated monomers 4-(N-adamantylamino)-2,3,5,6-tetrafluorostyrene
(2) and 2,3,4,5,6-pentafluorostyrene (1) were polymerized in water after complexation with randomly
methylated â-cyclodextrin (RAMEB) without the use of any surfactants or cosolvents. The complex
stoichiometries of the RAMEB/monomer complexes were investigated by NMR experiments. Kinetic studies
of the homo- and copolymerization with styrene demonstrated a high reactivity of the complexed
fluorinated monomers in aqueous solution. Using a semibatch polymerization technique, the use of RAMEB
induced formation of stable poly(2,3,4,5,6-pentafluorostyrene) latex particles whereas without RAMEB
no spherical particles could be visualized.
Introduction
tion of fluorinated methacrylates in water by the use of
RAMEB.21 In this paper, we report on the first examples
of free radical homopolymerization and copolymeriza-
tion of 2,3,4,5,6-pentafluorostyrene (1) with styrene (3)
and its derivative 4-(N-adamantylamino)-2,3,5,6-tet-
rafluorostyrene (2) in aqueous solution via the host/
guest complexation with RAMEB using water-soluble
initiators.
Fluoropolymers in general are an economically im-
portant class of high performance materials. Some of
their features are high chemical and thermal stability,
outstanding antiadhesive and oil-repellent properties,
low refractive index, and low dielectric constant. They
are industrially used e.g. as coatings, seals, or insula-
tors. Further applications include the use of fluoropoly-
mers in membranes and as lubricants in disk drives and
waveguide devices.1-3
Experimental Section
Materials. 2,3,4,5,6-Pentafluorostyrene (1) (Aldrich) and
styrene (3) (Riedel de Haen) were stored over CaH2 and
vacuum-distilled before use. 1-Adamantylamine (Aldrich),
randomly methylated â-cyclodextrin (RAMEB) (CAVASOL W7
M, technical grade, Wacker), 2,2′-azobis[2-(2-imidazolin-2-yl)-
propane] dihydrochloride (VA44) (Wako Chemicals), 2,2′-
azobis(isobutyronitrile) (AIBN) (Fluka), and potassium per-
oxodisulfate (Fluka) were used as received. All solvents were
distilled before use.
Because of the insolubility of fluorinated polymers in
common solvents, aqueous emulsion polymerization
with added surfactants is a preferred method for
industrial fluoropolymer production. Additionally, po-
lymerization in organic solvent mixtures containing
chlorofluorocarbons or fluorinated surfactants is an
alternative method. Even under these reaction condi-
tions, particularly copolymerization of fluorinated mono-
mers with hydrophilic or lipophilic comonomers often
proves difficulties because of the contrary chemical
nature of the fluorinated monomers. The chemical and
physical characteristics of fluorinated monomers pro-
hibit the homo- and copolymerization in water without
addition of surfactants or cosolvents. This paper reports
about polymerization of fluorinated monomers in aque-
ous phase after complexation with cyclodextrins (CDs).
It is well-known that CDs are able to enclose smaller
molecules to form host/guest complexes.4-7 Water-
insoluble molecules become water-soluble by treatment
with aqueous solutions of CDs without any chemical
modification of the guest molecule. Randomly meth-
ylated â-CD (RAMEB), which is industrially synthesized
on a large scale and readily available, displays a very
high water solubility. This ability qualifies it to transfer
hydrophobic guests into the water phase in a high
concentration.
Measurements. The 1H, 13C, and 19F NMR spectra were
recorded on a Bruker Avance DRX 500 spectrometer (operating
at 500, 125, and 470 MHz, respectively).
Size exclusion chromatography (SEC) was carried out with
a Jasco PU-1580 liquid chromatograph equipped with four PL
gel 5 mm mixed-C columns, a Jasco 830-RI refractive index
detector, and a Perkin-Elmer LC75 UV detector. Measure-
ments were performed in CHCl3 at room temperature with a
flow of 1 mL/min. Monodisperse poly(styrene) standard samples
were used for calibration.
Differential scanning calorimetry measurements were per-
formed on a Mettler DSC-30 instrument in a temperature
range of -40 to 200 °C at a heating rate of 10 °C/min. For
calibration, standard tin, indium, and zinc samples were used.
The Tg values are reported as the average of two or three
measurements using the midpoint method.
Raster electron microscopy (REM) pictures were taken with
a Philips XL-30 ESEM equipped with a LaB6 cathode. The
maximal resolution was 3 nm, and the maximal accelerating
potential was 30 keV.
Dynamic light scattering measurements were performed on
a Malvern HPPS-ET (high performance particle sizer-
extended temperature) instrument equipped with a He-Ne
laser and an Avalanche photodiode detector.
Kinetic measurements were carried out by high-pressure
liquid chromatography (HPLC) using a Biotek Kontron Instru-
ments System 525 equipped with a type 540 diode array
detector and a LiChroCART RP-18 column. For elution,
Our group has investigated the free radical polymer-
ization8 of various RAMEB-complexed monomers under
surfactant-free conditions in aqueous media.9-20 Re-
cently, we demonstrated the homo- and copolymeriza-
* Corresponding author: Fax +492118114788; e-mail H.Ritter@
uni-duesseldorf.de.
10.1021/ma050065s CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/14/2005

Macromolecules, Vol. 38, No. 12, 2005
Novel Fluorinated Polymers 5079
Scheme 1. Synthesis of Monomer 2
mixtures of acetonitril/water were used under isocratic condi-
tions at a flow of 0.5 or 1 mL/min. Obtained data were
evaluated with software Kroma Systems 2000 and plotted with
Origin software.
Synthesis of 4-(N-Adamantylamino)-2,3,5,6-tetrafluo-
rostyrene (2). Monomer 2 was synthesized following a
literature procedure.22 A mixture of 4.00 g (0.02 mol) of
2,3,4,5,6-pentafluorostyrene (1), 3.00 g (0.02 mol) of 1-ada-
mantylamine, 2.76 g (0.02 mol) of anhydrous potassium
carbonate, and 25 mL of DMSO was stirred and heated at 95
°C for 6 h under a nitrogen atmosphere. The mixture was
cooled to room temperature and poured into ice water. The
precipitate was filtered off. After drying under reduced pres-
sure, the solid was dissolved in 500 mL of a diethyl ether/
hexane mixture. After cooling, unreacted 1-adamantylamine
crystallized and could be removed easily by filtration. The
solvent was evaporated to afford pure 2 in 55% yield. 1H NMR
(CDCl3): δ (ppm) 1.87-2.15 (15 H, m, 1-10), 3.12 (1 H, 11),
5.48 (1 H, d, 21a), 5.90 (1 H, d, 21b), 6.53 (1 H, q, 20). 13C
NMR (CDCl3): δ (ppm) 28.58 (3,5,8), 35.06 (4, 9,10), 41.55 (2,
6, 7), 108.52 (15), 120.1 (20), 121.5 (21), 122.7 (12), 139.5 (13,
17), 141.5 (13, 14, 16, 17), 143.1 (13, 17), 145.1 (14, 16). 19F
NMR (CDCl3/CFCl3): δ (ppm) -146.17 (18, 23), -151.53 (19,
22); MS (CI, m/e): 325 (M + H)+. Calcd: C, 66.45%; H, 5.89%;
N, 4.30%. Found: C, 66.15%; H, 6.04%; N, 4.44%.
mmol) of Na2S2O5. Because of the poor solubility of 2, com-
plexation was carried out differently. In the first step monomer
2 was grinded in a mortar to obtain a fine powder. After that
small portions of the powder were added to a 40 wt % aqueous
RAMEB solution and treated in an ultrasonic bath until the
solution became totally clear. This procedure was repeated
until the desired amount of 2 was complexed quantitatively.
Polymerization was carried out as usual.
After polymerization the mixture was treated with a small
amount of trifluoroacetic acid to force decomposition of the
polymer/RAMEB complex 5a. The precipitated polymer 5 was
filtered off, washed twice with methanol, and dried. Yield: 0.44
g (88%).
Poly(2,3,4,5,6-pentafluorostyrene-co-styrene) (6). 0.40
g (2.03 mmol) of 2,3,4,5,6-pentafluorostyrene (1), 0.21 g (2.03
mmol) of styrene (3), 8.00 g (6.01 mmol) of RAMEB, 12.00 g of
water, 0.027 g (0.01 mmol) of K2S2O8, and 0.019 g (0.01 mmol)
of Na2S2O5. Yield: 0.52 g (86%).
General Procedure for Polymerization in Organic
Solvent. The monomers were dissolved in organic solvent
(toluene or benzene), and the solution was flushed with
nitrogen for 20 min. The mixture was heated to 80 °C followed
by addition of the initiator (2.5 mol % AIBN). After a given
time, polymerization reactions were stopped by pouring the
reaction mixture into cold methanol. Precipitated polymers
were filtered off and washed with 50 mL of methanol, dried
at 70 °C, and analyzed by SEC.
Poly(2,3,4,5,6-pentafluorostyrene) (4′). 4.00 g (20.6 mmol)
of 2,3,4,5,6-pentafluorostyrene (1), 25 mL of toluene, 0.070 g
(0.52 mmol) of AIBN. Yield after 4 h: 1.15 g (29%).
Poly(4-(N-adamantylamino)-2,3,5,6-tetrafluorosty-
rene) (5′). 1.00 g (3.08 mmol) of 4-(N-adamantylamino)-
2,3,5,6-tetrafluorostyrene (2), 5 mL of toluene, 0.012 g (0.077
mmol) of AIBN. Yield after 4 h: 0.63 g (63%).
Poly(2,3,4,5,6-pentafluorostyrene-co-styrene) (6′). 2.91
g (15 mmol) of 2,3,4,5,6-pentafluorostyrene (1), 1.56 g (15
mmol) of styrene (3), 25 mL of benzene, and 0.123 g (0.75
mmol) of AIBN. Yield: 2.21 g (50%).
Semibatch Polymerization of Poly(2,3,4,5,6-pentafluo-
rostyrene) (7) by Use of RAMEB. 25 mL of water was
heated to 80 °C followed by addition of 0.50 g (0.38 mmol) of
RAMEB. The solution was flushed with nitrogen for 20 min.
Then 0.025 g (0.093 mmol) of K2S2O8 was added under inert
conditions. 4.19 g (21.59 mmol) of 2,3,4,5,6-pentafluorostyrene
(1) was added dropwise over a period of 2 h under constant
stirring at 350 rpm. After monomer addition the solution was
stirred for 1 h at 80 °C. For REM images a small amount of
the solution was taken and freeze-dried.
General Procedure for the Synthesis of Monomer/
RAMEB Complex 1a, 2a, and 3a. 1 mmol of monomer was
added to a previously prepared 40 wt % aqueous RAMEB stock
solution. The obtained monomer/RAMEB solution was stirred
at room temperature until the solution became absolutely
clear. In the case of 3, 1 equiv of RAMEB was needed to
encapsulate the monomer. In the case of 1 and 2, 2 equiv of
RAMEB was necessary to achieve quantitative complex forma-
tion.
Stoichiometry of the Complexes. The stoichiometry of
the complexes 1a, 2a, and 3a was determined using the
continuous variation method.23 3 mM solutions of monomers
and RAMEB in D2O were mixed in various amounts while
keeping the total concentration fixed. The products of guest
molar fraction and chemical shift differences of the most
significant 1H NMR signals of the guests were plotted against
the molar fraction of the host.
General Procedure for Polymerization in Water by
Using RAMEB. After preparing a 40 wt % aqueous RAMEB
solution, the monomer was added and stirred at room tem-
perature for 24 h followed by degassing with nitrogen for 20
min. The initiator was added, and the solution was stirred at
room temperature for 90 min. After that the reaction mixture
was diluted with water, and the precipitated polymer was
filtered off, washed twice with methanol, and dried under
reduced pressure.
Poly(2,3,4,5,6-pentafluorostyrene) (4). 2.00 g (10.30
mmol) of 2,3,4,5,6-pentafluorostyrene (1), 27.03 g (20.64 mmol)
of RAMEB, 40.55 g of water, 0.070 g (0.26 mmol) of K2S2O8,
and 0.049 g (0.26 mmol) of Na2S2O5. Yield: 1.84 g (92%).
Poly(4-(N-adamantylamino)-2,3,5,6-tetrafluorosty-
rene) (5). 0.50 g (1.54 mmol) of 4-(N-adamantylamino)-2,3,5,6-
tetrafluorostyrene (2), 4.03 g (3.08 mmol) of RAMEB, 6.00 g
of water, 0.010 g (0.038 mmol) of K2S2O8, and 0.007 g (0.038
Semibatch Polymerization of Poly(2,3,4,5,6-pentafluo-
rostyrene) (8) without RAMEB. Polymerization was carried
out under identical conditions but without use of RAMEB.
Results and Discussion
Synthesis of Monomer 2. New fluorinated monomer
2,3,5,6-tetrafluoro-4-(adamantylamino)styrene (2) was
prepared by nucleophilic substitution starting from
2,3,4,5,6-pentafluorostyrene (1) and 1-adamantylamine
in about 55% yield (Scheme 1).
The 1H NMR spectrum of 2 indicates the presence of
vinylic protons (Figure 1). Furthermore, it shows a
strongly deshielded multiplett between 1.61 and 2.41

5080 Cinar et al.
Macromolecules, Vol. 38, No. 12, 2005
Figure 1. 1H NMR spectrum of 2 (500 MHz, CDCl3,) [Ad )
adamantyl].
Figure 3. Job plots by considering the shifts of Hc protons of
1, adamantyl protons (â-position to the amino function) of 2,
and Hc protons of 3 in the presence of RAMEB.
Figure 2. 19F NMR spectrum of 2 (470 MHz, CDCl3/CFCl3).
Scheme 2. Homopolymerization of Free Monomer 1
in Organic Solution (Polymer 4′) and of 1a in Water
(Polymer 4)
ppm, corresponding to the 15 protons of the adamantyl
group. At a chemical shift of 3.25 ppm the proton of the
amino group can be assigned.
Clear evidence for the para-substitution of the ada-
mantylamino group at the phenyl ring in monomer 2 is
obtained from the 19F NMR spectrum depicted in Figure
2. The signals of fluorine atoms imply the symmetrical
para-substitution on the phenyl ring.
The aromatic ring is a good candidate for nucleophilic
substitution due to the presence of electron-withdrawing
fluorine substituents. The regioselective substitution in
the para-position of 1 is a result of the ortho- and para-
directing vinyl group in combination with a steric
hindrance of the competing ortho-position.
Formation of Host/Guest Complexes with
RAMEB. The fluorinated monomers 1, 2, and styrene
(3) were complexed by RAMEB in water. The stoichi-
ometries of the host/guest complexes were determined
by NMR spectroscopy according to the Job method23-25
(Figure 3). It was clearly shown that styrene (3) forms
a defined 1:1 complex while the fluorinated monomers
1 and 2 are encapsulated by two RAMEB molecules. In
the case of monomer 1 this result was not expected since
1 and 3 have the same molecular scaffold and molecular
modeling showed that the fluorinated styrene derivative
1 is only slightly bigger than styrene itself (3).
Homo- and Copolymerization of Monomers. The
RAMEB/monomer complexes 1a and 2a were homopo-
lymerized in water at room temperature using the redox
initiator system K2S2O8/Na2S2O5 (Schemes 2 and 3).
Additionally, copolymerization of 1a with complexed
styrene (3a) was carried out in water (Scheme 4).
To compare our technique with traditional polymer-
ization methods, all polymerizations were also carried
out starting from the free monomers 1, 2, and 3 in
organic solvents (toluene or benzene) at 80 °C using
AIBN as initiator.
In all cases almost quantitative yields of the homo-
and copolymers from complexed monomers were
achieved. Poly(pentafluorostyrene) (4) and polymer 6
could be isolated via simple filtration. Polymer 5a was
completely water-soluble due to the presence of nonco-
valently attached RAMEB. After treatment with tri-
fluoroacetic acid to decompose the RAMEB ring, poly-
mer 5 precipitated after some hours and could be
isolated by filtration (Scheme 3).
In the case of polymerization in organic solvents,
polymers were obtained by pouring the solution into
methanol to precipitate the polymeric material. The
yields of these solution polymerizations were about 40%
after 2 h.
To elucidate the behavior of the new complexes 1a
and 2a, kinetic measurements of homo- and copolymer-
izations in aqueous RAMEB solution were carried out
by determination of monomer concentrations at various
All obtained polymers were characterized by DSC and
SEC, showing molecular weights up to 40 000 g/mol (Mn)
and polydispersities up to 3 (Table 1)

Macromolecules, Vol. 38, No. 12, 2005
Novel Fluorinated Polymers 5081
Scheme 3. Homopolymerization of Free Monomer 2 in Organic Solvent (Polymer 5′) and of 2a in Water Followed
by Treatment with Trifluoroacetic Acid (Polymer 5)
Table 1. Characteristics of Obtained Polymers
polymers
monomoer
solvent
T [°C]
Mn
Mw
PD
Tg
4
4′
5
5′
6
6′
7
8
1a
RAMEB/watera
25
80
25
80
25
80
80
80
5 600
4 500
11 900
12 300
11 400
4 500
11 500
6 800
38 400
38 400
34 200
6 800
2.1
1.5
3.2
3.1
3.0
1.5
2.0
3.2
100
90
1
tolueneb
2a
2
1a, 2a
1, 2
1
1
RAMEB/watera
tolueneb
RAMEB/watera
tolueneb
103
90
104
106
RAMEB/watera
waterc
10 900
38 500
21 400
123 000
a Redox initiator b AIBN. c K2S2O8, semibatch polymerization.
Scheme 4. Copolymerization of 1 with 3 in Toluene
(Polymer 6′) and 1a with 3a in Water (Polymer 6)
Figure 4. Kinetic plots of homopolymerization of RAMEB
complexed 2,3,4,5,6-pentafluorostyrene (1a) and RAMEB com-
plexed 4-(N-adamantylamino)-2,3,5,6-tetrafluorostyrene (2a)
in water (RT, 2.5 mol % redox initiator).
reaction times via HPLC measurements. Resulting
time-conversion plots of the homopolymerization reac-
tions are shown in Figure 4.
ment with RAMEB complexes, as described above. After
30 min, conversions of monomers 1 and 2 were about
25%. This fact indicates a high reactivity of the com-
plexed monomers in water in comparison to classical
polymerization methods. Self-evident, this comparison
can only be qualitative because of the use of different
solvents, initiator systems, and reaction temperatures.
The copolymerization of complexed fluorinated sty-
rene 1a and complexed styrene 3a was carried out in
water in comparison with copolymerization of free
monomers 1 and 3 in toluene (Scheme 4). In both cases
copolymerization parameters had been determined ac-
cording to the method of Kelen and Tu¨do¨s.26 In water
we obtained rA ) 45.5 and rB ) 0.58, where monomer A
In Figure 4 it can be seen that the complexed
fluorinated monomers 1a and 2a are converted to
polymers very fast. In both cases almost 90% yield were
achieved after only 30 min of reaction time. As control
experiment, polymerization of 1 and 2 was carried out
in water under identical conditions but in the absence
of RAMEB. Caused by the very poor solubility of 1 and
2 in aqueous solution at room temperature, no polymer
could be obtained.
Additionally, 1 and 2 were homopolymerized in
toluene at 80 °C. The molar concentration of the
monomer was nearly identical compared to the experi-

5082 Cinar et al.
Macromolecules, Vol. 38, No. 12, 2005
possible in aqueous phase without using RAMEB.
Anyway, in this case conversion was very low (<5%).
REM images of the obtained polymers from the semi-
batch process are shown in Figure 5.
Significant differences in the morphology of the
obtained polymers could be illustrated. Obviously, the
use of RAMEB induces the formation of stable poly-
(2,3,4,5,6-pentafluorostyrene) latex particles with di-
ameters between 1 and 1.5 µm consisting of polymer 7.
Without RAMEB, real spherical particles could not be
visualized.
Conclusions
From the above-described experiments it can be
concluded that the CD complexation is a versatile
method for the preparation of novel fluorinated poly-
mers in water. It was demonstrated that the non-
covalently attached CD rings may keep a polymer in
aqueous solution. This supramolecular structure could
be partially destroyed by use of a strong acid, leading
to formation of uncomplexed polymer that precipitated
immediately. By the way, the CD ring has a strong
influence on copolymerization parameters compared to
the uncomplexed monomers. Finally, the CD opens a
possibility to polymerize in a semibatch process very
effectively while polymer beads are formed.
References and Notes
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Figure 5. REM images of poly(2,3,4,5,6-pentafluorostyrene),
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ally to water without RAMEB. The high reaction tem-
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monomer 1 in water. Thus, polymerization of 1 was also
MA050065S