The effect of fluorine substituents on the polymerization mechanism of 2-methylene-1,3-dioxolane and properties of the polymer products

Article abstract of DOI:10.1016/j.jfluchem.2006.12.005

Perfluoro-2-methylene-1,3-dioxolane (III) was synthesized and polymerized with an initiator, perfluoro dibenzoyl peroxide, and a white solid product III-P was quantitatively isolated. The polymer was insoluble in organic solvents including fluorinated solvents such as Fluorinert FC 75 and hexafluorobenzene, but dissolved in hexafluorobenzene by heating at around 140 °C in a sealed ampoule. The X-ray measurement showed that III-P was semi-crystalline and melted at 230 °C. The IR spectrum of III-P indicated that the polymer obtained did not show carbonyl peak and it was the vinyl addition product. When the solid product was heated above the melting temperature and pressed under 100-200 kg/cm², we obtained an amorphous and flexible film, which is transparent from the UV region to the near IR region. The glass transition temperature was 110 °C and refractive indexes were 1.3443, 1.3434 and 1.3373 at 633, 839 and 1544 nm, respectively. The film did not degrade in concentrated sulfuric acid and aqueous sodium hydroxide solutions even heated at 80-90 °C for 2 days. The film was thermally stable and began to decompose at 300 °C under air atmosphere.

Full text of DOI:10.1016/j.jfluchem.2006.12.005

Journal of Fluorine Chemistry 128 (2007) 202–206
www.elsevier.com/locate/fluor
The effect of fluorine substituents on the polymerization mechanism
of 2-methylene-1,3-dioxolane and properties of the polymer products
a
b
ˇ a
Y. Okamoto a, , F. Mikes , Y. Yang , Y. Koike
*
a Polytechnic University, Polymer Research Institute, 6 MetroTech Center, Brooklyn, NY 11201, USA
b Keio University, Photonic Polymer Project, K2 Town Campus, Kawasaki 212 0054, Japan
Received 27 October 2006; received in revised form 2 December 2006; accepted 7 December 2006
Available online 15 December 2006
Abstract
Perfluoro-2-methylene-1,3-dioxolane (III) was synthesized and polymerized with an initiator, perfluoro dibenzoyl peroxide, and a white solid
product III-P was quantitatively isolated. The polymer was insoluble in organic solvents including fluorinated solvents such as Fluorinert FC 75
and hexafluorobenzene, but dissolved in hexafluorobenzene by heating at around 140 8C in a sealed ampoule. The X-ray measurement showed that
III-P was semi-crystalline and melted at 230 8C. The IR spectrum of III-P indicated that the polymer obtained did not show carbonyl peak and it
was the vinyl addition product. When the solid product was heated above the melting temperature and pressed under 100–200 kg/cm2, we obtained
an amorphous and flexible film, which is transparent from the UV region to the near IR region. The glass transition temperature was 110 8C and
refractive indexes were 1.3443, 1.3434 and 1.3373 at 633, 839 and 1544 nm, respectively. The film did not degrade in concentrated sulfuric acid
and aqueous sodium hydroxide solutions even heated at 80–90 8C for 2 days. The film was thermally stable and began to decompose at 300 8C
under air atmosphere.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Free radical polymerization; Perfluoro 2-methylene-1,3-dioxolane; Amorphous; Thermally and chemically stable polymer
1. Introduction
The III was also readily polymerized with a radical initiator
to yield vinyl addition polymer without the ring opening
isomerization (Fig. 1). We described the effect of fluorine
substituents of the dioxolane compound on the free radical
polymerization mechanism and properties of polymers.
The polymerization of 2-methylene-1,3-dioxolane (I) and
their various substituted derivatives has been widely investi-
gated by Bailey [1,2], Klemm [3,4] and their coworkers. The
free radical initiator attacks the carbon–carbon double bond at
the tail position and the resulting free radical can undergo vinyl
addition polymerization or ring opening as shown in Scheme 1.
The ring opening isomerization and the vinyl addition step are
competitive reactions; the polymerization of I by a free radical
initiator produced a considerable amount of the ring opening
product. However, substitution with fluorine atoms for the two
hydrogen atoms on the methylene of I, 2-difluoromethylene-
1,3-dioxolane (II) was found to readily polymerize by a free
radical initiator without the ring opening isomerization [5]. In
this paper, we report the preparation of perfluoro-2-methylene-
1,3-dioxolane (III) that substitutes all hydrogen atoms of I with
fluorine atoms.
2. Experimental
2.1. Materials
All chemicals were purchased from Aldrich Chemical Co. or
SynQuest Chemical Co. All reagents were used without further
purification. Perfluoro dibenzoyl peroxide was prepared
according to published procedure [6]. The crude initiator
was recrystallized from petroleum ether (bp 40–60 8C), and
purified initiator has a melting point of 76–78 8C; its half-life at
68 8C is 10 h [7].
2.2. Instrumentation
19F, 1H and 13C NMR spectra were obtained on Bruker AC-
300 spectrometer in CDCl3 containing 0.03% (v/v) TMS as an
* Corresponding author. Tel.: +1 718 260 3638; fax: +1 718 260 3508.
E-mail address: yokamoto@poly.edu (Y. Okamoto).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2006.12.005

Y. Okamoto et al. / Journal of Fluorine Chemistry 128 (2007) 202–206
203
Scheme 1. Free-radical polymerization mechanism of the dioxolanes with or without ring opening.
internal reference. The IR spectra were measured on a Perkin-
Elmer 1600 series FTIR. GC–MS measurements were
conducted using a 5970 series by Hewlett-Packard Co. The
refractive indexes of the polymer were measured using a
Merticon model 2010 prism coupler made by Metricon Corp.
Thermal properties were determined using a TA Instruments
Inc. DSC 2920 differential scanning calorimeter and a Hi-Res
Modulated TGA 2950 thermogravimetric analyzer. Wide angle
X-ray experiments were performed by using a Rigaku RINT
2500 V diffractometer with graphite monochromatized Cu Ka1
radiation. The intensities were recorded on a square image plate
of a size of about 130 cm2. The measurements were carried out
for unoriented samples at room temperature.
mixture was washed with saturated aqueous solution of sodium
bicarbonate, with water and dried using anhydrous magnesium
sulfate. After removing benzene using Vigreux column, pure
dioxolane ester was obtained by fractional distillation in 32%
1
yield. Bp 85–87 8C, H NMR (d ppm, DMSO-d6): 4.07 (d, –
CH2–CH2–, 4H), 3.77 (s, –COOCH3, 3H), 1.60 (s, –CH3, 3H).
The yield of 3a was found to be low, thus we have alternatively
prepared 3b.
The ester 3b was prepared by the condensation of 1 (372 g,
6 mol) with 2-oxopropyl acetate (2b) (696 g, 6 mol) and work
up of the reaction mixture was carried out analogously to
aforementioned procedure. 3b was obtained in yield 68%.
1
Bp 97–98 8C/17 Torr, H NMR (d ppm, CDCl3): 4.27 (s, –
CH2–, 2H), 4.00 (d, –CH2–CH2–, 4H), 2.08 (s, –COCH3, 3H),
1.40 (s, –CH3, 3H).
2.3. Monomer preparation
Since the fluorination and following work up of 3a and 3b
produce the same carboxylic compound, we have carried out
the fluorination of the mixture of 3a and 3b. Fluorination of the
mixture of 3a (959 g, 6.57 mol) and 3b (1488 g, 9.30 mol) was
carried out in a fluorinated solvent using F2/N2 mixture as
described before [8,9]. The fluorinated product was neutralized
by aqueous solution of potassium hydroxide.
2.3.1. Preparation of perfluoro-2-methylene-1,3-dioxolane
(III)
Methyl 2-methyl-1,3-dioxolane-2-carboxylate (3a) was
prepared by condensation of ethylene glycol (1) (372 g,
6 mol) with methyl pyruvate (2a) (612 g, 6 mol) in the presence
of p-toluenesulfonic acid (40 g, 0.23 mol) in benzene (1200 ml)
(Scheme 2).
Pure acid 5 was obtained by fractional distillation (25%
yield). Bp 96–98 8C/97 Torr, 1H NMR (d ppm, DMSO-d6): 9.60
(–COOH); 19F NMR (d ppm, DMSO-d6): ꢀ81.41 (3F, –CF3),
ꢀ81.73, ꢀ82.18, ꢀ82.66, ꢀ83.10 (4F, –CF2–CF2–).
The purity of the acid 5 produced was confirmed by acid–
base potentiometric titration. The weight per equivalent was
257.2 g (formula weight of the acid is 258.06 g/mol).
Pure potassium salt of 4,4,5,5-tetrafluoro-2-trifluoromethyl-
1,3-dioxolane-2-carboxylic acid (40) was prepared by neutra-
lization of aqueous solution of acid 5 with aqueous potassium
hydroxide solution and dried.
Water produced was distilled out as azeotropic mixture with
benzene using Dean–Stark adapter. The remaining reaction
Monomer III was prepared by thermal decomposition of salt
40. Potassium salt 40 starts to decompose according to TGA at
Fig. 1. Chemical structures of dioxolane compounds investigated.

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Y. Okamoto et al. / Journal of Fluorine Chemistry 128 (2007) 202–206
Scheme 2. Synthetic route for III.
200 8C. Decomposition was carried out using procedure
described previously [9,10].
continuously for 40 h. The solid product was isolated, washed
with chloroform and dried (9.0 g). Polymer III-P was not
soluble in any organic solvents including hexafluorobenzene
and FC-75 at 60–80 8C. However, the polymer is soluble at
140–150 8C in hexafluorobenzene in a sealed ampoule. IR
spectra of III-P showed that there were no carbonyl peaks at
around 1750–1800 cmꢀ1. The polymer produced was semi-
crystalline and melted at 230 8C.
The III was purified by fractional distillation having bp
21.5 8C under atmospheric pressure. Structure of III obtained
was confirmed by 19F and 13C NMR spectroscopy.
19F NMR (in CDCl3): ꢀ89.04, ꢀ89.05, ꢀ89.06 (–CF2–CF2–,
4F), ꢀ127.65, ꢀ127.66, ꢀ127.67, ꢀ127.68 ( CF2, 2F).
1
13C NMR (in CDCl3): 142.67 (tp, JCF = 272.42 Hz,
2
4
5JCF = 2.30 Hz, CF2 ), 131.27 (tm, JCF = 46.55 Hz, JCF
=
3.45 Hz), 122.93, 122.91, 122.48, 122.45, 121.98, 119.31,
119.29, 118.80, 118.32, 115.65, 115.63, 115.18, 115.14, 114.72,
114.70, 114.69 (–CF2–CF2–).
3. Results and discussion
When the non-fluorinated monomer I was polymerized by a
free radical initiator, AIBN at 60 8C, the ring opening product
was produced as much as 50%, which indicates that the rates of
the ring opening isomerization and propagation of the vinyl
addition polymerization were almost the same [1,2]. However,
Zhu and Pittman reported that when I was polymerized by an
activated carbon supported sulfuric acid (a cationic polymer-
ization), the vinyl addition product was obtained quantitatively
[11]. The solid product was found to be insoluble in common
solvents and had a substantial degree of crystallinity. They
suggested that the polymer produced was a linear structure and
the chains could pack tightly giving a high cohesive energy
density. We have previously found the difluoro polymer (II-P)
obtained by the free radical initiator, AIBN, was insoluble in
common organic solvents such as DMSO, THF, chloroform and
toluene, but was soluble in fluorinated solvents such as
hexafluoro 2-propanol, trifluoroacetic acid (TFA) or mixed
solvent of chloroform and TFA [5]. IR and NMR spectra of II-P
indicated that the polymer obtained was mainly the vinyl
addition product. The powder X-ray diffraction pattern
indicated that polymer was semi-crystalline and its melting
point was 355 8C, which was higher than that of Teflon1
(329 8C). The glass transition of II-P was 125 8C and thermal
decomposition began at 427 8C under nitrogen and at around
414 8C under an air atmosphere. The polymer did not degrade
2.4. Polymerization
Monomer III was polymerized in bulk or in hexafluor-
obenzene solution using a free radical initiator perfluoro
dibenzoyl peroxide, because 2,20-azobisisobutyronitrile
(AIBN) is not soluble in III. Polymerization of III was carried
out in most cases in glass ampoules.
2.4.1. Bulk polymerization
Glass ampoules were charged with mixture of monomer III
and initiator and sealed after repeating of three times cycle
freeze–pump–thaw. In a typical polymerization experiment, the
mixture of monomer III (10 g) and perfluoro dibenzoyl
peroxide (30 mg) in a sealed glass ampoule was heated at
60 8C for 48 h. Polymer was washed with chloroform and after
drying the solid under vacuum at 40 8C, 9.2 g of solid material
was obtained.
2.4.2. Polymerization in hexafluorobenzene
The hexafluorobenzene solution (30 ml) of III (10 g) and
perfluoro dibenzoyl peroxide (30 mg) were degassed, sealed in
glass ampoule and heated at 60 8C. After several hours, a solid
product started to precipitate and the solution was heated

Y. Okamoto et al. / Journal of Fluorine Chemistry 128 (2007) 202–206
205
in 20% aqueous sulfuric acid and 30% aqueous sodium
hydroxide solutions at 60 8C over 2 days.
The III was found to be readily polymerized in bulk or in
hexafluorobenzene using perfluoro dibenzoyl peroxide as an
initiator at 60–80 8C. The white solid product was quantita-
tively isolated. The polymer III-P did not dissolve in any
organic solvents, including fluorinated solvents at 60–80 8C,
but was soluble in hexafluorobenzene by heating around 140–
150 8C in a sealed ampoule. IR spectrum of III-P showed that
there were no carbonyl peaks. As we have described for II-P
[5], the monomer II yielded the vinyl addition product. The X-
ray measurement showed that III-P was semi-crystalline
(Fig. 2A) and melted at 230 8C. When the solid product was
heated above the melting point (250 8C) and pressed under
100–200 kg/cm2, it became an amorphous flexible film
(Fig. 2B) and consequently transparent from the UV to the
near IR regions. The glass transition temperature was 110 8C
(Fig. 3). We have measured the refractive indexes of the
polymer at various wavelengths and were found to be 1.3443,
1.3434 and 1.3373 at 633, 839 and 1544 nm, respectively.
These wavelengths are commonly used in telecommunication.
Fig. 3. Differential scanning calorimetry (DSC) trace of III-P: (A) III-P as
obtained (first scan), (B) the second DSC scan of the III-P sample after heating
to 300 8C and (C) the third DSC scan of the sample B.
The refractive indexes of III-P are similar to the values of
Cytop1 which is transparent amorphous perfluoro polymer.
The films were not degraded in concentrated sulfuric acid
and aqueous sodium hydroxide solutions even when heated at
80–90 8C for 2 days. The polymer obtained was thermally
stable and began to decompose at around 300 8C under an air
atmosphere (Fig. 4).
We argue that when fluorine atoms are present on the outer
positions of the methylene of I, the vinylidene group is then
polarized. Therefore, the vinyl addition in the polymerization
may be more favorable for II and III in comparison with the
hydrocarbon analogue I. The transition state in the polymer-
izations of II and III involves a relatively electrophilic radical
species and a relatively nucleophilic double bond. Conse-
quently, the propagation reaction through vinyl addition is
appreciably faster than the isomerization and results in a
polymer without a ring opening product [12].
The polymers II-P and III-P have a substantial degree of
crystallinity anda similar linear polymer structure as thepolymer
Fig. 2. (A) X-ray data of III-P as obtained and (B) X-ray data of III-P after
heating and compress molding at 250 8C.
Fig. 4. Thermogravimetric analyses (TGA) trace of III-P sample under an air
atmosphere.

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Y. Okamoto et al. / Journal of Fluorine Chemistry 128 (2007) 202–206
[2] W.J. Bailey, in: J.E. McGrath (Ed.), Ring Opening Polymerization, ACS
Symposium Series 286, American Chemical Society, Washington, DC,
1985, p. 47.
product obtained by a cationic polymerization of I. Therefore,
the polymer chains can pack tightly, giving a high cohesive
energy density. II-P was heated over the melting point, but
remained crystalline upon cooling. However, III-P has a
considerably lower melting point (230 8C) in comparison with
II-P (355 8C) and when it was heated over 230 8C, the
crystallinitydisappearedandanamorphousproductwasisolated.
This phenomenon is currently being investigated further.
[3] Th. Schulze, J. Letsch, E. Klemm, J. Polym. Sci., Part A: Polym. Chem. 34
(1996) 81–87.
[4] E. Klemm, Th. Schulze, Acta Polym. (1999) 1–19.
[5] W. Liu, Y. Guo, Y. Koike, Y. Okamoto, Macromolecules 37 (2004) 254–
255.
[6] L. Belf, M. Buxton, G. Fuller, J. Chem. Soc. (London) (1965) 3372–
3380.
[7] N. Sugiyma, European Patent 0,950,672.
[8] R.J. Lagow, T.R. Bierchenk, T.J. Juhlke, H. Kawa, in: G.A. Olah, R.D.
Chambers, G.K.S. Prakash (Eds.), Synthetic Fluorine Chemistry, Willey,
New York, 1992 (Chapter 5).
Acknowledgement
This work was supported in part by the Japan Science and
Technology Corporation through a Grant from ERATO-Sorst
Photonic Polymer.
ˇ
[9] F. Mikes, Y. Yang, I. Teraoka, T. Ishigure, Y. Koike, Y. Okamoto,
Macromolecules 38 (2005) 4237–4245.
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[10] Y. Yang, F. Mikes, L. Yang, W. Liu, Y. Koike, Y. Okamoto, J. Fluorine
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[12] W. Liu, F. Mikes, Y. Guo, Y. Koike, Y. Okamoto, J. Polym. Sci., Part A:
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