A novel perfluoromonomer: Perfluoro-2,3-dihydro-1,4-benzodioxin

Article abstract of DOI:10.1016/j.jfluchem.2003.08.003

A novel perfluoromonomer, perfluoro-2,3-dihydro-1,4-benzodioxin (FDB), was synthesized. The homopolymerization and copolymerizations of FDB were investigated. The structure and physical properties of those polymers were characterized.

Full text of DOI:10.1016/j.jfluchem.2003.08.003

Journal of Fluorine Chemistry 124 (2003) 183–188
A novel perfluoromonomer: perfluoro-2,3-dihydro-1,4-benzodioxin
Weihong Liua,1, Yasuhiro Koikeb,c, Yoshi Okamotoa,*
aSix Metrotech Center, Polymer Research Institute, Polytechnic University, Brooklyn, NY 11201, USA
bFaculty of Science and Technology, Keio University, Yokohama 223-8522, Japan
cERATO, Koike Photonics Polymer Project, K2 Town Campus 144-8 Ogura, Saiwai-ku, Kawasaki 212-0054, Japan
Received 4 June 2003; received in revised form 6 August 2003; accepted 7 August 2003
Abstract
A novel perfluoromonomer, perfluoro-2,3-dihydro-1,4-benzodioxin (FDB), was synthesized. The homopolymerization and copolymer-
izations of FDB were investigated. The structure and physical properties of those polymers were characterized.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Perfluoromonomer; Fluorinated polymer; Radical polymerization; Perfluoro-2,3-dihydro-1,4-benzodioxin
1. Introduction
polymerized to yield a high polymer [7]. This encourages us
to synthesize a novel perfluoromonomer, perfluoro-2,3-
dihydro-1,4-benzodioxin (FDB), to investigate on its poly-
merization reactivity. Hence, the homopolymerization and
copolymerizations were studied using styrene (St) as a
comonomer. The polymer structure was characterized by
1H, 19F, 13C NMR and FTIR spectroscopy. The physical
properties of the polymers were also characterized. This
monomer may be applied to enhance the copolymer proper-
ties as a comonomer. The copolymerization of FDB with St
produces polymers though the homopolymerization only
affords oligomers.
Fluorinated polymers have become of increasing interest
in the development of advanced materials having high
thermal and oxidative stabilities, chemical resistance, super-
ior electrical insulating ability and superior optical proper-
ties [1,2]. Unlike their hydrocarbon analogues, most
fluorinated vinyl monomers such as perfluorostyrene, per-
fluoroacrylic esters and other trifluorovinyl compounds are
scarcely polymerized under normal free radical conditions
except tetrafluoroethylene and chlorotrifluoroethylene [1,3].
Therefore, designing and synthesizing new perfluoromono-
mers is still a main topic in fluorine and polymer chemistry.
Until now, only few classes of perfluoromonomers could be
radically homopolymerized under normal conditions. Typi-
cal examples are perfluoro-dioxoles [2,4], perfluoro-dihy-
drodioxins [5,6] and perfluoro-dienes [2]. Their common
characteristic is that their polymer structure contains rings.
The monomers containing a ring exhibited unusual reactiv-
ity probably due to the presence of ring strain. With those
monomers, amorphous perfluoropolymers were developed
to exhibit extraordinary properties [2]. Regarding the class
of monomers of perfluoro-dihydrodioxins, the polymeriza-
tion reactivity was extensively investigated by Krespan
and Dixon [5,6]. Recently, a partially fluorinated monomer,
2,3-difluoro-1,4-benzodioxin has been reported to be homo-
2. Experimental
2.1. Materials
Styrene (Aldrich) and perfluorobenzene (SynQuest Fluoro-
chemical Lab. Inc.) were distilled before use. Chlorine
gas, SbF3, SbCl5 and other reagents were commercially
obtained from Aldrich and used as received. 2,20-Azobisiso-
butyronitrile (AIBN) was purified by recrystallization from
methanol.
2.2. Monomer synthesis
2.2.1. Synthesis of 2,2,3,3-tetrahydro-5,6,7,8-tetrafluoro-
1,4-benzodioxin (a)
* Corresponding author. Fax: þ1-718-260-3508.
E-mail addresses: whliu888@hotmail.com (W. Liu), yokamoto@poly.edu
(Y. Okamoto).
1 Tel.: þ1-718-260-3965; fax: þ1-718-260-3125.
This compound was prepared from hexafluorobenzene
and ethylene glycol according to a literature method [8]. The
0022-1139/$ – see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2003.08.003

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W. Liu et al. / Journal of Fluorine Chemistry 124 (2003) 183–188
F
F
F
F
F
OCH2CH2OH
F
F
F
F
F
O
O
F
F
F
F
HOCH2CH2OH
NaOH
K2CO3
DMF
F
(a)
F
F
F
F
F
Cl
F
F
O
O
F
F
O
F
F
F
Cl2
hv
SbF3/SbCl5
55oC
Cl
Cl
Cl
Zn
O
DMF
O
O
F
Cl
Cl
F
F
F
(d)
(c)
FDB
(b)
Scheme 1. Monomer synthesis.
procedure is described in Scheme 1. Yield, 40%. mp: 79–
1
crude product was distilled to give 13.0 g (56%) of FDB.
bp: 65–67 8C (30.0 mmHg). 1H NMR (CDCl3) d (ppm): no
proton. 19F NMR (CDCl3) d (ppm): À140.51 (s, 2F, CF¼);
À159.28 (s, 2F on aromatic ring); À161.25 (s, 2F on
aromatic ring). GC/MS: m/e 242 (Mþ) with expected frag-
mentation pattern.
80 8C. H NMR (CDCl3) d (ppm): 4.36 (s, 4H). 19F NMR
(CDCl3) d (ppm): À165.04 (s, 2F on aromatic ring);
À169.74 (s, 2F on aromatic ring).
2.2.2. Synthesis of 2,2,3,3-tetrachloro-5,6,7,8-tetrafluoro-
1,4-benzodioxin (b)
2,2,3,3-Tetrahydro-5,6,7,8-tetrafluoro-1,4-benzodioxin (a)
was photochlorinated under a GE Sun-Lamp at about 120 8C
with chlorine gas. The reaction was monitored by proton
NMR and stopped when the proton peaks disappeared on the
NMR spectrum. The product (b) was purified by distillation.
Yield, 82%. bp: 62–64 8C (0.50 mmHg) 1H NMR (CDCl3) d
(ppm): none. 19F NMR (CDCl3) d (ppm): À159.27 (s, 2F on
aromatic ring); À160.73 (s, 2F on aromatic ring). GC/MS:
m/e 346 (Mþ) with expected fragmentation pattern.
2.3. Polymerization
2.3.1. Homopolymerization
Polymerization was carried out under an argon atmo-
sphere in a glass tube equipped with a three-way stopcock.
FDB (1.5 g, 6.2 mmol) and perfluorobenzoyl peroxide
(F-BNO) (19 mg, 0.045 mmol) were charged in the glass
tube, which was then degassed and refilled with argon in
three vacuum freeze-thaw cycles. The tube was sealed and
heated at 80 8C for 24 h. The product was precipitated into
methanol, isolated with a centrifuge and dried under vacuum
at 50 8C.
2.2.3. Synthesis of 2,3-difluoro-2,3-dichloro-5,6,7,8-
tetrafluoro-1,4-benzodioxin (c)
A suspension of 11.9 g (66.0 mmol) of SbF3 in 11.5 g
(33.0 mmol) of 2,2,3,3-tetrachloro-5,6,7,8-tetrafluoro-1,4-
benzodioxin was stirred at 55 8C for 10 h with addition of
0.4 ml SbCl5. The volatile product transferred under vacuum
was washed with a saturated aqueous NaHCO3 solution,
and purified by distillation. Yield, 85%. bp: 40–42 8C
(2.0 mmHg). The product is a mixture of stereoisomers.
1H NMR (CDCl3) d (ppm): none. 19F NMR (CDCl3) d
(ppm): À78.52 (s, CFClO of major isomer); –81.66 (s,
CFClO of minor isomer); À159.02 (s, 2F on aromatic ring);
À160.52 (s, 2F on aromatic ring). GC/MS: m/e 312 (Mþ)
with expected fragmentation pattern.
2.3.2. Copolymerization
Similar to the homopolymerization, FDB, St and AIBN
were charged in the glass tube, which was then degassed and
refilled with argon in three vacuum freeze-thaw cycles. The
tube was sealed and heated at 60 8C. The products were
precipitated in methanol, isolated with a centrifuge and dried
under vacuum at 50 8C.
2.4. Measurements
1
The H, 19F and 13C NMR spectra were obtained using
a Bruker ACF 300 spectrometer (300 MHz for 1H and
282 MHz for 19F and 75 MHz for 13C measurement). FTIR
spectra were obtained with a Perkin-Elmer FTIR-1600
spectrometer. GC–mass analysis was accomplished on HP
5890 Gas Chromatograph and HP 5970B Mass Spectro-
graph. Size exclusion chromatographic (SEC) analysis was
accomplished on a system with a Waters 510 pump in line
with TSK gel HMXL and H5000 columns and dual detectors
of a Waters 440UV absorbance detector and a Waters R401
differential refractometer, in which chloroform was eluted
2.2.4. Synthesis of FDB (d)
A mixture of 30.0 g (0.096 mol) of 2,3-difluoro-2,3-
dichloro-5,6,7,8-tetrafluoro-1,4-benzodioxin (c), 100 ml of
dry DMF, 12.0 g (0.18 mol) of zinc dust, and 1.0 ml of
1,2-dibromoethane was stirred at 120 8C for 10 h under
argon atmosphere. The mixture was then poured into a large
amount of water. The aqueous layer was extracted with
diethyl ether. The combined organic layer was washed with
water and dried over Na2SO4. After removal of ether, the

W. Liu et al. / Journal of Fluorine Chemistry 124 (2003) 183–188
185
with a flow rate of 1.0 ml/min at 30 8C. The molecular
weight of the polymers was calibrated with standard PS.
The differential scanning calorimetry (DSC) measurement
was performed on a DSC 2920 module in conjunction
with the TA Instrument 5100 system at a heating rate of
10 8C/min under a nitrogen atmosphere. The midpoint of the
heat capacity transition was taken as glass transition tem-
perature (Tg). The refractive index of the film was obtained
with a Metricon Model 2010 prism coupler.
À160.32 (s, 2F on aromatic ring). GC/MS: m/e 280 (Mþ)
with expected fragmentation pattern].
The last step in the synthesis of monomer was dehalo-
genation of 2,3-difluoro-2,3-dichloro-5,6,7,8-tetrafluoro-
1,4-benzodioxin (c) with activated zinc in DMF. The method
adopted here is similar to that for the preparation of other
perfluoro-dihydrodioxins [5].
3.2. Homopolymerization
The homopolymerization of FDB was carried out using
perfluoro-benzyl peroxide as an initiator at 80 8C. Contrary
to the result of 2,3-difluoro-1,4-benzodioxin which gave
high polymers [7], the homopolymerization of FDB afforded
only an oligomer based on SEC analysis as shown in Table 1.
The degree of polymerization (DP) was estimated to be 10.
Attempts to homopolymerize this monomer via emulsion
polymerization techniques using sodium dodecylbenzene-
sulfonate as an emulsifier and ammonium persulfate as an
initiator failed. The low polymerization reactivity may be
mainly related to the steric effects of the ortho-fluoro
substituents of the perfluorinated monomer. Krespan and
Dixon have reported that perfluoro-2,3-dihydro-2,3-
dimethyl-1,4-dioxinand2,3-dichloro-5,6-difluoro-1,4-dioxin
gave oligomers, whereas perfluoro-2,3-dihydro-1,4-dioxin
and perfluoro-2-methyl-2,3-dihydro-1,4-dioxin gave high
polymers under similar polymerization conditions [5,6].
They explained this as follows: the initial step of the poly-
merization, i.e. the addition of carbon-based free radicals
to the 2,3-dihydro-1,4-dioxin monomer, is a favourable
reaction; the rate of propagation, i.e. the addition of the
resulting radical to another monomer, appeared to be gov-
erned by steric constraints. The polymerization reactivity is
low for those monomers containing a bulky group attached
to the ring.
3. Results and discussion
3.1. Monomer synthesis
Monomer was synthesized according to Scheme 1. All the
melting point and the boiling points reported here are
uncorrected. In the step of fluorination with SbF3, we noted
that temperature affects the reactions. The reaction kept at
55 8C for 10 h afforded the main products with two chlorines
replaced by fluorine. The reactions at 80 and 130 8C were
found three chlorines and all chlorines to be replaced,
respectively (Scheme 2). A perfluoro-compound, per-
fluoro-2,2,3,3-tetrahydro-1,4-benzodioxin (f), was easily
obtained with a high yield at elevated temperature, which
was confirmed by 19F NMR and GC/MS analysis [yield,
65%. bp: 113–115 8C. 19F NMR (CDCl3) d (ppm): À92.64
(s, 4F, –OCF2CF2O–); À158.82 (s, 2F on aromatic ring);
F
F
O
O
F
F
80oC
F
F
F
F
Cl
Cl
Cl
F
O
O
F
F
F
F
(e)
(f)
The 19F NMR of the oligomer was shown in Fig. 1A. The
peak from À154.0 to À166.0 ppm was assigned to the
fluorines on the side group of aromatic ring and the per-
fluorobenzoyl group at the end. The broad peak from À108.0
to À144.0 ppm was assigned to the main-chain fluorines.
FTIR spectrum of the oligomer was shown in Fig. 2A.
The bands at 1492, 1516 and 1531 cmÀ1 were assigned to
130oC
Cl
Cl
O
O
(reflux) F
F
F
(b)
F
F
F
Scheme 2. Fluorination with SbF3 at elevated temperatures.
Table 1
Radical homopolymerization and copolymerization of FDBa
Mn ꢀ 10À4 d
Mw/Mn
Tg (8C)
d
Run
Feed ratio,
St/FDB
Temperature
Time
(h)
Yield
(%)b
Copolymer
compositionc,
(8C)
(mol/mol)
St/FDB (mol/mol)
1
2
3
4
0/1
1/1
4/1
1/0
80
60
60
60
24
48
48
24
24
57
63
94
0/100
75/25
89/11
0.25
0.90
1.28
2.30
1.68
1.62
2.16
2.79
–
137
109, 134
103
100/0
a Conditions: bulk, [initiator] ¼ 2.0 mol% to vinyl groups; initiator: run 1, F-BNO; runs 2–4, AIBN.
b Methanol-insoluble part.
c Determined by 13C NMR.
d Determined by SEC with PS standard.

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W. Liu et al. / Journal of Fluorine Chemistry 124 (2003) 183–188
Fig. 1. 19F NMR spectra of the oligomer of FDB (run 1 in Table 1) (A) and the copolymer of St and FDB (run 2 in Table 1) (B).
the skeletal C¼C stretching of the fluorinated aromatic ring.
The bands at 1025, 1132, and 1170 cmÀ1 were assigned to
CF stretching. No obvious band was found in the range of
1700–1800 cmÀ1, indicating that ring opening did not occur
during the homopolymerization.
It was noted that the copolymerization in bulk also pro-
ceeded readily at 60 8C. A gel-like product was obtained
during polymerization. After dissolving it in chloroform and
precipitating it in a large amount of methanol, a white solid
product was obtained. The molecular weight and yield of the
copolymers are lower than those of the homopolymer of St
as shown in Table 1. This may occur because the FDB has a
favourable reception for the growing St species and the new
formed FDB radical species has a lower growing ability
compared with St radical species.
The copolymer structure was characterized by 19F, 1H and
13C and FTIR spectroscopy. As shown in Fig. 1B, the 19F
spectrum of copolymer of FDB and St is quite different from
that of homopolymer. The peak at about –164.0 ppm was
split into two peaks which was ascribed to the fluorines on
the side group. The peaks from 108.0 to 138.0 ppm ascribed
3.3. Copolymerization with St
It has been reported that the copolymerizations of per-
fluoro-2-methyl-2,3-dihydro-1,4-dioxin with tetrafluor-
oethylene, ethylene and vinyl acetate proceeded readily at
25–55 8C [6]. The easy incorporation of 5–20 wt.% of
perfluoro-2-methyl-2,3-dihydro-1,4-dioxin into the solid
copolymers was ascribed to the receptivity to attack by a
spectrum of radical types [6]. Here we performed the
copolymerization of FDB with St using AIBN as an initiator.
Fig. 2. FTIR spectra of the oligomer of FDB (run 1 in Table 1) (A) and the copolymer of St and FDB (run 2 in Table 1) (B).

W. Liu et al. / Journal of Fluorine Chemistry 124 (2003) 183–188
187
Fig. 3. 1H NMR spectra of the copolymer of St and FDB (run 2 in Table 1) (A) and the homopolymer of St (run 4 in Table 1) (B).
to the fluorines in the main-chain appear a sharp peak at
À118.0 ppm. This may suggest that the product has a
copolymer structure.
be due to the St units adjacent to the FDB unit. The fluorina-
ted units have an electronic drawing power and make the
adjacent proton chemical shift downfield in NMR spectrum.
In order to calculate the copolymer composition, the 13C
NMR spectrum was recorded in chloroform-d at 50 8C and
the central peak of chloroform (77.0 ppm) was used as an
internal reference. As shown in Fig. 4, by comparison the
NMR spectra of the copolymer and the homopolymer of St,
the peaks at 32–47 ppm were assigned to the main-chain
carbon in the St units, whereas the peaks at 104–112 ppm
were assigned to the main-chain carbon in the FDB units. By
comparing the peak area of the peaks at 104–112 ppm and
32–47 ppm, we can easily obtain the copolymer composi-
tions which are given in Table 1. Due to the copolymeriza-
tion, the NMR spectrum in the range of the main-chain
carbon of the St units obviously changed. The 13C NMR
spectra further illustrates that the product is a real copoly-
mer, not a mixture of the two homopolymers.
FTIR spectrum of the copolymer was shown in Fig. 2B.
The presence of the aromatic ring ¼C–H stretching at 3027
and 3060 cmÀ1 and the aliphatic CH and CH2 stretching
bands at 2843 and 2924 cmÀ1 illustrates that the copolymer
contains St unit. The skeletal C¼C stretching vibrations of
the aromatic ring in the St unit and FDB unit overlapped in
the range of 1450–1610 cmÀ1. The typical CF stretching
vibration at 1027 cmÀ1 was also observed in the copolymer.
The absence of carbonyl absorption in the range of 1700–
1800 cmÀ1 indicated that ring opening did not occur during
the copolymerization.
1
Furthermore, the H NMR spectra of the copolymer and
PS are also quite different from each other. As shown in Fig. 3,
the main-chain proton peak becomes broader compared with
PS. The two obvious peaks at 2.2 and 2.5 ppm observed may
Fig. 4. 13C NMR spectra of the copolymer of St and FDB (run 2 in Table 1) (A) and the homopolymer of St (run 4 in Table 1) (B).

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W. Liu et al. / Journal of Fluorine Chemistry 124 (2003) 183–188
4. Conclusion
A novel perfluoromonomer, perfluoro-2,3-dihydro-1,4-
benzodioxin, was synthesized. The polymerization reactiv-
ity of this monomer is quite low and only an oligomer was
obtained via homopolymerization. The copolymerization of
FDB with styrene was readily performed using a radical
initiator to afford a copolymer with a higher glass transition
temperature. This monomer may be applied to enhance the
copolymer properties through the copolymerization as a
comonomer.
Fig. 5. DSC curves of the homopolymer of St (a), the copolymers of St
and FDB (run 2 in Table 1) (b) and (run 3 in Table 1) (c).
Acknowledgements
3.4. Physical properties
Glass transition temperature is an important physical
property to evaluate an amorphous polymer. Fig. 5 shows
the DSC curves of polystyrene and copolymers. The copo-
lymer of FDB and St (St=FDB ¼ 75=25 mol/mol; run 2 in
Table 1) was determined to have a Tg of 137 8C, whereas the
homopolymer of St obtained at 60 8C (run 4 in Table 1)
exhibits a Tg at 103 8C. Thus, the Tg of the copolymer was
improved 34 8C by incorporation of 25 mol% of FDB. In the
case of using a large amount of St, the copolymer (run 3 in
Table 1) exhibits two obvious glass transitions at 109 and
134 8C. The first glass transition is close to that of the
homopolymer of St, and the second glass transition is close
to that of the copolymer with 25 mol% of FDB (run 2 in
Table 1). This may suggest that there is a large fraction of
polystyrene block in the copolymer produced.
This work was supported in part by the Japan Science and
Technology Corporation through the Grant for ERATO-
Photonic Polymer.
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