Synthesis and polymerization of a novel perfluorinated monomer

Article abstract of DOI:10.1016/j.jfluchem.2007.08.009

Perfluoro(5-methylene-2,2-dimethyl-1,3-dioxolane) (1) was synthesized by utilizing a direct fluorination reaction. Compound 1 was an entirely novel monomer with difluoromethylene at position 5 on the dioxolane ring as an unprecedented polymerization site. It successfully polymerized with tetrafluoroethylene to afford copolymers, which had T_g values in the range of 60-90 °C. The content of monomer 1 in the obtained polymers was less than 20 mol%, which seemed insufficient for giving various unique properties to polymers. However, each polymer was expected to be a superior material because of their advanced thermal stability. Comparison with copolymers of 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole and tetrafluoroethylene is also discussed.

Full text of DOI:10.1016/j.jfluchem.2007.08.009

Journal of Fluorine Chemistry 128 (2007) 1131–1136
www.elsevier.com/locate/fluor
Synthesis and polymerization of a novel perfluorinated monomer
*
Eisuke Murotani , Susumu Saito, Masanori Sawaguchi, Hiromasa Yamamoto,
Youji Nakajima, Tatsuya Miyajima, Takashi Okazoe
Research Center, Asahi Glass Co., Ltd., 1150 Hazawa-cho, Kanagawa-ku, Yokohama, 221-8755 Japan
Received 30 March 2007; received in revised form 6 August 2007; accepted 6 August 2007
Available online 17 August 2007
Abstract
Perfluoro(5-methylene-2,2-dimethyl-1,3-dioxolane) (1) was synthesized by utilizing a direct fluorination reaction. Compound 1 was an entirely
novel monomer with difluoromethylene at position 5 on the dioxolane ring as an unprecedented polymerization site. It successfully polymerized
with tetrafluoroethylene to afford copolymers, which had Tg values in the range of 60–90 8C. The content of monomer 1 in the obtained polymers
was less than 20 mol%, which seemed insufficient for giving various unique properties to polymers. However, each polymer was expected to be a
superior material because of their advanced thermal stability. Comparison with copolymers of 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole
and tetrafluoroethylene is also discussed.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Perfluorinated monomer; Dioxolane; Fluorination; Thermal stability
1. Introduction
[7–11]. From the perspective of applicability for synthesizing
desired perfluorinated compounds, the methodology would
be superior to other perfluorination reactions. Substantially,
most of the desired fluorine-containing compounds could be
obtained by construction of the backbone structure in the
hydrocarbon component at will, followed by perfluorination
with elemental fluorine. Taking the superiority into considera-
tion, compounds having a novel polymerization site would
probably become available and would be candidates for new
materials with superior properties.
Perfluorinated polymers are known as specialty chemicals for
many applications because of their unique properties, e.g.
enhanced chemical and thermal stability, or optical and electrical
properties [1]. In particular, perfluorodioxolane- or perfluor-
odioxole-based amorphous polymers, like the copolymers of
2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (PDD) and
tetrafluoroethylene (TFE) well known as Teflon1 AF by
DuPont, have received great attention in the development of
advanced optical, electrical and chemical materials. Thus,
several perfluorinated monomers with a cyclic structure have
been synthesized, and polymerization of them has also been
reported [1–6]. Althoughtherehave beenvariousexamples ofthe
synthesis of such monomers, it should be noted that species of
polymerization site are still limited, and in many cases
compounds with good reactivity have a structure based on only
perfluoro(2-difluoromethylene-1,3-dioxolane) or perfluoro(4,5-
difluoro-1,3-dioxole).
Herein, we report the synthesis and polymerization with
TFE of perfluorinated compound 1, which has a difluoro-
methylene structure at position 5 on the dioxolane ring as an
unprecedented polymerization site. In addition, the thermal
properties of the obtained polymers are also described.
2. Results and discussion
2.1. Synthesis of perfluoro[5-methylene-2,2-dimethyl-1,3-
dioxolane]
Recently, our group has developed new and innovative
methodology for the synthesis of various perfluorinated
compounds via a direct fluorination reaction (Scheme 1)
The perfluorinated monomer 1 (Fig. 1) was successfully
synthesized from acyl fluoride 2, which was obtained by our
direct fluorination process, as shown in Scheme 2.
The first step of this synthesis is esterification of 5-
hydroxyethyl-2,2-dimethyl-1,3-dioxolane (6) with perfluoroacyl
* Corresponding author. Tel.: +81 45 374 7533; fax: +81 45 374 8858.
E-mail address: eisuke-murotani@agc.co.jp (E. Murotani).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.08.009

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Scheme 3. Isomerization of compound 1 with a fluoride ion.
determined by 19F NMR was 86%. Though no decomposition
was observed, compounds having residual C–H bonds,
especially a tertiary one, remained as main byproducts.
Without any purification, thermal elimination reaction of the
ester was carried out with potassium fluoride as a catalyst. A
suspension of the ester and KF powder was heated at around
100 8C to give the desired perfluoroacyl fluoride 2 and the
starting acyl fluoride 5 by decomposition of the ester bond.
Compound 2 was purified by distillation. The separated acyl
fluoride 5 could be recycled for the esterification step, as shown
in Scheme 2.
Scheme 1. New methodology for producing desired perfluorinated compounds.
Compound 2 was directly converted to the target monomer 1
by pyrolysis. The acyl fluoride 2 was fed on glass beads at over
320 8C, and gas from the outlet of the reactor was condensed in
a trap cooled with liquid nitrogen. Analytical data of NMR, GC
and GC–MS obviously indicated that compound 1 was the main
component in the obtained liquid. It was purified by distillation
up to 99% in GC analysis. Peaks assigned to difluoromethylene
at position 5 of compound 1 were separately observed at À92.5
and À107.0 ppm in the 19F NMR spectrum. In addition, other
peaks corresponding to trifluoromethyl groups and –OCF2–
appeared at À81.4 and À69.3 ppm respectively. The above
NMR spectrum data satisfactorily meet to determine the
exomethylene cyclic structure of compound 1.
Fig. 1. Compound 1.
fluoride 5 in the presence of sodium fluoride as an HF scavenger.
It was simply carried out by dropwise addition of acyl fluoride 5
to alcohol 6 to give partially fluorinated ester 4 with a good yield.
Removal of HF generated during the esterification reaction was
essential because of the acid-labile 1,3-dioxolane ring. Shortage
of sodium fluoride led to production of undefined complex by-
products that might be caused by ring opening reaction of 1,3-
dioxolane.
After distillation, the obtained ester was fluorinated with
elemental fluorine diluted with nitrogen in the same manner as
described in the literature [7–10]. In the case of using 20 vol%
fluorine/nitrogen gas, the yield of the perfluorinated ester 3
According to 19F NMR spectrum, one of the byproducts is
estimated to be compound 7, which is an isomer of compound
1. It was probably produced by isomerization of compound 1
itself with a fluoride ion (Scheme 3). The discriminative peak
Scheme 2. Synthesis of compound 1.

E. Murotani et al. / Journal of Fluorine Chemistry 128 (2007) 1131–1136
1133
Scheme 4. Proposed side-reaction during pyrolysis.
Table 1
Results of copolymerization
a
No.
T [8C]
1 in feed [mol%]
1 in polymer [mol%]
Initiator [wt%]
Yield [%]
Mn Â104
2.0
1.8
4.3
Mw Â104
2.9
2.3
6.0
Tg [8C]
Td [8C]
1
2
3
80
80
48.8
74.0
71.6
6.6
15.0
19.0
0.3b
0.2b
0.2c
4.4
0.7
1.2
63.8
71.8
90.0
403.9
392.0
389.9
100
a
b
c
Temperature in the case of a weight loss of 10% under nitrogen.
(C6F5COO)2.
(CF3)3COOC(CF3)3.
assigned to CF was observed at À132.6 ppm, and peaks of
three trifluoromethyl groups were detected at À66.4 and
À82.4 ppm at an integral intensity ratio of 1:2.
NMR. There was a tendency for a higher molecular weight and
content of monomer 1 to be obtained in the case of a
polymerization at a higher temperature. However, compound 1
unfortunately failed to homopolymerize, in contrast to the case
of PDD [1,13,14]. Furthermore, both the yield of polymer and
content of monomer 1 in the polymer were not high, which
In addition, 2,3,3-trifluoroacryloyl fluoride estimated from
the data of 19F NMR and GC–MS was condensed in the cooled
trap. Furthermore, hexafluoroacetone (HFA) was also detected
when GC analysis of the outlet gas was directly carried out.
Thermal decomposition of the dioxolane ring, as illustrated in
Scheme 4, might cause their generation. Path (a) illustrated in
Scheme 4 leads to formation of the desired compound 1 via
elimination of a fluoride ion. However, path (b) results in
cleavage of the C–O bond, followed by fragmentation to HFA
and 2,3,3-trifluoroacryloyl fluoride. The reaction of the
carbanion intermediate 8 can competitively proceed by these
two pathways.
Scheme 5. Copolymerization of compound 1 and TFE.
Regarding the decomposition of the dioxolane ring, Hung
has reported similar phenomena during synthesis of PDD [12].
The estimated cleavage of the C–O bond of dioxolane supports
the possibility of Scheme 4, even though the position of the
anion of each intermediate was different. In the case of PDD, a
rearrangement reaction to an isomeric epoxide was also
observed. The somewhat analogous structure of monomer 1
suggests a similar reaction. Although no evidence has been
obtained, such a kind of reaction might have occurred.
2.2. Copolymerization of novel monomer 1 and TFE
Compound 1 successfully underwent copolymerization with
TFE leading to the formation of a novel polymer when initiated
by perfluorobenzoyl peroxide (PFBPO) or perfluoro(tert-butyl
peroxide) (Scheme 5).
Polymers with different contents of monomer 1 from 6% to
about 20% were obtained as a white powder (Table 1). The
compositions of each polymer was analyzed by molten state
Fig. 2. Copolymerization curve of monomer 1/TFE (circles) and PDD/TFE
(squares) [1,13,14].

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E. Murotani et al. / Journal of Fluorine Chemistry 128 (2007) 1131–1136
Scheme 6. Polymerization reaction of compound 1 and TFE.
Scheme 7. Difference in polymerization reaction between PDD and 2,2,4-tris (trifluoromethyl)-5-fluoro-1,3-dioxole [15].
indicated that compound 1 has relatively low reactivity. The
copolymerization curve compared with that of PDD as
illustrated in Fig. 2 obviously supported the above result.
We estimated that the reactivity might be markedly influenced
by a steric effect. When a radical is generated at position 5
during polymerization, the bulky dioxolane ring will prevent
the radical from approaching the next monomer (Scheme 6).
This conclusion appears reasonable if we consider the
difference in polymerization reaction rate between PDD and
2,2,4-tris (trifluoromethyl)-5-fluoro-1,3-dioxole [15]. Hung
reported that the failure of copolymerization of the latter
monomer with TFE would be due to steric bulkiness (Scheme 7).
In contrast, perfluoro-4-methoxy-1,3-dioxole monomer, which
has a substitution group at position 4 as well, nevertheless
showed a good reactivity [6]. It is expected that the methoxy
group could easily rotate around an ethereal oxygen to reduce
steric hindrance.
exhibited a clear glass transition and their Tg values were found
to be around 60–90 8C. As shown in Fig. 3, introduction of
monomer 1 is likely to contribute to an increase of Tg. The
increase might be attributable to the fixed and bulky ring
structure of the dioxolane unit, giving less conformational
flexibility to the polymer. Compared with the copolymer of
PDD/TFE with a similar range of monomer content, the Tg
value of the obtained copolymer was slightly higher. This might
be due to the flexibility of each polymer whose dioxolane rings
differently occupy the surrounding space and interact with
polymer chains. Currently, a polymer with less than 20 mol% of
monomer 1 has only been obtained, but higher molecular
content of monomer 1 could still be of great interest in the field
of amorphous fluoropolymers.
A transparent film was successfully obtained by pressing
the polymer at 150 8C. However, it was difficult to manage
the film and measure the refractive index because of its
brittleness, which easily resulted in cracks in the film. In the
case of a much higher molecular weight polymer, the film
might be more flexible and easier to handle. Regarding
thermal stability, on the other hand, these polymers showed
good properties, as shown in Table 1. Especially, TGA showed
a weight loss of 10% around 400 8C, which is close to that of
Teflon1 AF [1].
The Tg values of the new copolymers were determined by
DSC during second heating at a heating rate of 10 8C/min. They
3. Conclusion
In summary, an entirely novel perfluorinated monomer 1
was successfully synthesized by utilizing the direct fluorination
process. It copolymerized with TFE to give highly thermally
stable copolymers. The obtained copolymers had Tg values of
around 60–90 8C, which tended to increase with higher content
of monomer 1. Although monomer content and polymer yield
were not high, the new copolymer exhibited superior thermal
properties, indicating an open door to valuable potential
applications.
Fig. 3. Dependence of Tg value on each copolymer composition; monomer 1/
TFE (circles) and PDD/TFE (squares) [1,13,14].

E. Murotani et al. / Journal of Fluorine Chemistry 128 (2007) 1131–1136
1135
4. Experimental
4.1. General
1H NMR (internal TMS) and 19F NMR (internal CFCl3)
were obtained with a JEOL AL300 spectrometer. High-
resolution mass spectra were obtained with JEOL SX-102A
coupled to HP-5890 with a 60 m capillary column J&W DB-1
or DB 1301. DSC was obtained with a TA Instruments DSC
Q100. TGA was obtained with a TA Instruments TGA Q500.
Elemental fluorine is a highly toxic and corrosive gas, which
may cause explosion when it meets organic compounds in the
vapor phases, so extreme care must be taken when handling it.
Both the liquid and vapor of hydrogen fluoride (bp 19.5 8C)
evolved during the reaction are also highly corrosive and cause
severe contact burns, so care must be taken! Prior to use, all
hydrocarbon grease must be removed and the apparatus must be
gradually passivated with elemental fluorine. Although the use
of 1,1,2-trichrolotrifluoroethane (R113) is regulated, we have
given experimental examples with it for convenience, because
it is still much more cheaply available than compound 5 for
use as a solvent. Care must be taken to avoid its emission to
the environment. Compound 6 was purchased from Daicel
Chemical Industries, Ltd. (Japan). Other commercially avail-
able materials were used without purification.
Fig. 4. Compound 4.
While feeding 20 vol% fluorine gas at the same flow rate, a
solution of compound 4 (72.0 g, 0.115 mol) in R113 (720 g)
was introduced over a period of 20.6 h. After the introduction of
all the solution, 20 vol% fluorine gas was supplied at the same
flow rate for 1 h. Then, nitrogen gas was fed for 2 h to remove
fluorine gas and volatile compounds from the autoclave to give
a solution of the crude perfluorinated product. The structure of
the obtained compound 3 was determined by 19F NMR (93%
yield).
Compound 3: 19F NMR (282.7 MHz, CDCl3): d À76.4 to
À76.9 (1F of l), À79.1 to À81.6 (2F of c and l, 3F of e, m and n),
À82.0 to À82.3 (8F, a, f and h), À84.1 to À85.1 (1F of c),
À85.6 to À87.5 (2F, i), À120.1 (1F, k), À122.2 to À123.3 (1F of
j), À128.1 to À129.7 (1F of j), À130.2 (2F, b), À132.2 (1F, g),
À145.5 (1F, d) (Fig. 5).
After evaporation of solvent and volatile compounds, crude
perfluorinated ester 3 (93.0 g, 0.108 mol) was charged into a
flask with 0.93 g (0.016 mol) of potassium fluoride powder. The
dispersion was heated at 110 8C and vigorously stirred for 4 h in
an oil bath with a reflux condenser at the top of the flask.
Distillation of the crude solution provided compound 2 (82 8C/
101.3 kPa, 54% yield) and starting acyl fluoride 5. The structure
of compound 2 was confirmed by 19F NMR and GC–MS.
Compound 2: 19F NMR (282.7 MHz, CDCl3): d + 24.1 (1F of
i), À76.6 to À77.1 (1F of l), À80.6 to À81.2 (1F of l, 6F of m and
n), À115.7 to À116.8 (1Fof j), À118.2 (1F, k), À118.5 to À119.6
(1F of j); High-resolution mass spectrum (EI+) 290.9712
([MÀCF3]+, calculated for C6F9O3: 290.9704) (Fig. 6).
4.2. Synthesis of perfluoro (5-methylene-2,2-dimethyl-1,3-
dioxiolane) (1)
To a stirred mixture of 103.2 g (0.705 mol) of 5-
hydroxyethyl-2,2-demethyl-1,3-dioxolane (6) and 59.3 g
(1.411 mol) of sodium fluoride in 1600 g of R-225 (mixture
of CF3CF2CHCl2 and CClF2CF2CHClF) at 0–5 8C was added
dropwise a solution of 421.7 g (0.846 mol) of acyl fluoride 5
over a period of 3 h. After completion of addition, stirring was
continued at room temperature for 20 h. The crude mixture
was filtered, and the liquid was washed once with saturated
NaHCO3 aqueous solution and twice with water, followed by
drying over magnesium sulfate. After filtration, the liquid was
purified by distillation in vacuo (83 8C/1.06 kPa), and ester 4
was obtained (294.5 g, 0.471 mol, 67% yield). The GC purity
was 97%.
Compound 4: 1H NMR (300.4 MHz, CDCl3): d 1.34 (s, 3H,
m or n), 1.41 (s, 3H, m or n), 1.97 (dt, 3J = 6.6 Hz, 6.9 Hz, 2H,
j), 3.59 (dd, 3J = 6.6 Hz, 2J = 7.8 Hz, 1H of l), 4.09 (dd,
3J = 6.0 Hz, 2J = 7.8 Hz, 1H of l), 4.17 (m, 1H, k), 4.53 (m, 2H,
i); 19F NMR (282.7 MHz, CDCl3): d À79.0 to À80.5 (1F of c
and 3F of e), À81.8 to À82.7 (8F, a, f and h), À84.5 to À85.5
(1F of c), À130.1 (2F, b), À132.0 (1F, g), À145.6 (1F, d)
(Fig. 4).
Fig. 5. Compound 3.
Into a 3000 ml autoclave made of nickel, R113 (1700 g) was
charged and stirred at 25 8C. At the outlet of the autoclave, a
packed layer of sodium fluoride pellets and a cooler maintained
at À10 8C were installed in series. Further, a liquid-returning
line was installed to return any condensed liquid from the
cooler to the autoclave. After supplying nitrogen gas for 1 h,
20 vol% F2/N2 was fed for more 1 h at a flow rate of 16.7 L/h.
Fig. 6. Compound 2.

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E. Murotani et al. / Journal of Fluorine Chemistry 128 (2007) 1131–1136
Unreacted TFE gas was purged, and into the crude solution was
poured CH3CCl2F to precipitate a produced polymer. Filtrated
polymer was dried at 80 8C in vacuo to give a white powder.
Monomer content of the obtained polymers was determined by
molten state NMR. The temperature of the glass transition point
and the temperature of weight loss of 10% were determined by
DSC and TGA, respectively.
Fig. 7. Compound 1.
References
[1] P.R. Resnick, W.H. Buck, in: J. Schirs (Ed.), Modern Fluoropolymers,
John Wiley and Sons, 1997.
Compound 2 (19.0 g, 0.053 mol) was gradually fed on glass
beads maintained at 320 8C using a syringe pump at a feed rate
of 9.7 mL/h. Nitrogen gas was introduced into an inlet of the
reactor at a flow rate of 5.0 L/h. The gas from an outlet of the
reactor was condensed into a trap cooled by liquid nitrogen.
The obtained crude liquid was purified by distillation to give
5.7 g (0.019 mol, 37% yield) of the desired monomer 1 with GC
purity of 99% (57 8C/101.3 kPa). HFA and 2,3,3-trifluoroa-
cryloyl fluoride were also detected by NMR and GC as side
products. Their yields were not determined.
Compound 1: 19F NMR (282.7 MHz, CDCl3): d À69.3 (2F,
l), À81.4 (6F, m and n), À92.5 (1F of k), À107.0 (1F of k); high-
resolution mass spectrum (EI+) 293.9690 ([M]+, calculated for
C6F10O2: 293.9739) (Fig. 7).
[2] S. Selman, E.N. Squire, US Patent 3,308,107 (1967).
[3] References are cited therein
(a) Y. Yang, F. Mikes, L. Yang, W. Liu, Y. Koike, Y. Okamoto, J. Fluorine.
Chem. 127 (2006) 277–281;
(b) Y. Yang, F. Mikes, L. Yang, W. Liu, Y. Koike, Y. Okamoto, J. Polym.
Sci., Part A: Polym. Chem. 44 (2006) 1613–1618.
[4] N. Sugiyama, WO2005085303 (2005).
[5] T. Okazoe, A. Watakabe, M. Ito, K. Watanabe, T. Kashiwagi, S.-Z. Wang,
WO2003037885 (2003).
[6] References are cited therein
(a) A. Russo, W. Navarrini, J. Fluorine Chem. 125 (2004) 73–78;
(b) W. Navarrini, V. Tortelli, A. Russo, S. Corti, J. Fluorine Chem. 95
(1999) 27–39.
[7] T. Okazoe, K. Watanabe, M. Itoh, D. Shirakawa, H. Murofushi, S.
Tatematsu, Adv. Synth. Catal. 343 (2001) 215–219.
[8] T. Okazoe, K. Watanabe, M. Itoh, D. Shirakawa, S. Tatematsu, J. Fluorine
Chem. 112 (2001) 109–116.
[9] T. Okazoe, E. Murotani, K. Watanabe, M. Itoh, D. Shirakawa, K.
Kawahara, I. Kaneko, S. Tatematsu, J. Fluorine Chem. 125 (2004)
1695–1701.
4.3. Copolymerization of compound 1 and TFE
Compound 1, CF2ClCF2CHClF as a solvent and an initiator
(PFBPO or (CF3)3COOC(CF3)3) at 0.2–0.3 wt% were charged
into an autoclave. The autoclave was cooled by liquid nitrogen,
followed by evacuation and warming to room temperature.
The freezing and warming procedure was repeated twice to
substantially degas the reactor. After the degassing operation,
TFE gas was introduced into the reactor at 80 8C and the
mixture was stirred for 5 h, maintaining the temperature.
[10] T. Okazoe, K. Watanabe, M. Itoh, D. Shirakawa, K. Kawahara, S.
Tatematsu, J. Fluorine Chem. 126 (2005) 521–527.
[11] G. Standford, J. Fluorine Chem. 128 (2007) 90–104.
[12] M.-H. Hung, W.B. Farnham, J. Chin. Chem. Soc. 40 (1993) 563–569.
[13] C.D. Wood, U. Michel, J.P. Rolland, J.M. DeSimone, J. Fluorine Chem.
125 (2004) 1671–1676.
[14] U. Michel, P. Resnick, B. Kipp, J.M. DeSimone, Macromolecules 36
(2003) 7107–7113.
[15] M.-H. Hung, Macromolecules 26 (1993) 5829–5834.