Synthesis and radical polymerization of perfluoro-2-methylene-1,3- dioxolanes

Article abstract of DOI:10.1021/ma050753b

A new efficient synthetic route was developed for perfluorinated 2-methylene-1,3-dioxolane monomers via a direct fluorination of the hydrocarbon precursors prepared from methyl pyruvate and diols. Perfluoro-2-methylene-4,5- dimethyl-1,3-dioxolane (PMDD) and perfluoro-3-methylene-2,4-dioxabicyclo-[4.3.0] nonane (PMDN) were thus synthesized via this new method, among which PMDN is first reported. The radical polymerizations of those monomers were performed under various conditions. The kinetic results indicated that polymerization rate of PMDD is higher than that of PMDN. Oxygen did not affect the polymerization yield but strongly affected the polymer structure. The polymerization in the presence of oxygen produced a polymer containing unstable units. Hydrogen-containing solvents result in a lower molecular weight polymer. 2,2′-Azobis(isobutyronitrile) cannot initiate the polymerization in a perfluoro solvent or in bulk. Also, photopolymerizations of those monomers were performed in the presence of carbon tetrabromide or carbon tetrachloride, and the mechanism is discussed. The polymer of PMDD has a glass transition temperature at 155 °C, and the polymer of PMDN has a glass transition temperature at 161 °C. These polymers with high glass transition temperature, low refractive index, low material dispersion, and extraordinary optical transmission from the deep ultraviolet to near-infrared regions may be used as optical fibers, pellicles, or antireflective coating materials.

Full text of DOI:10.1021/ma050753b

9466
Macromolecules 2005, 38, 9466-9473
Synthesis and Radical Polymerization of
Perfluoro-2-methylene-1,3-dioxolanes
,†
‡
†
Weihong Liu,* Yasuhiro Koike, and Yoshi Okamoto
Polymer Research Institute, Polytechnic University, 6 Metrotech Center, Brooklyn, New York 11201,
and Faculty of Science and Technology, Keio University, Yokohama 223-8522, and ERATO, Koike
Photonics Polymer Project, K2 Town Campus 144-8 Ogura, Saiwai-ku Kawasaki 212-0054, Japan
Received April 11, 2005; Revised Manuscript Received September 12, 2005
ABSTRACT: A new efficient synthetic route was developed for perfluorinated 2-methylene-1,3-dioxolane
monomers via a direct fluorination of the hydrocarbon precursors prepared from methyl pyruvate and
diols. Perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane (PMDD) and perfluoro-3-methylene-2,4-dioxabicyclo-
[4.3.0]nonane (PMDN) were thus synthesized via this new method, among which PMDN is first reported.
The radical polymerizations of those monomers were performed under various conditions. The kinetic
results indicated that polymerization rate of PMDD is higher than that of PMDN. Oxygen did not affect
the polymerization yield but strongly affected the polymer structure. The polymerization in the presence
of oxygen produced a polymer containing unstable units. Hydrogen-containing solvents result in a lower
molecular weight polymer. 2,2′-Azobis(isobutyronitrile) cannot initiate the polymerization in a perfluoro
solvent or in bulk. Also, photopolymerizations of those monomers were performed in the presence of carbon
tetrabromide or carbon tetrachloride, and the mechanism is discussed. The polymer of PMDD has a glass
transition temperature at 155 °C, and the polymer of PMDN has a glass transition temperature at 161
°
C. These polymers with high glass transition temperature, low refractive index, low material dispersion,
and extraordinary optical transmission from the deep ultraviolet to near-infrared regions may be used
as optical fibers, pellicles, or antireflective coating materials.
Introduction
have been developed by Asahi Glass for producing
amorphous perfluoropolymers since 1989.2 Regarding
the class of perfluoro-2-methylene-1,3-dioxolanes, only
two monomers were reported. The first example in the
class is perfluoro-2-methylene-4-methyl-1,3-dioxolane
,3,6
Fluorinated polymers have become of increasing
interest in the development of advanced materials
having superior thermal and chemical stability, excel-
lent electrical insulating ability, and unique optical
(
PMMD), which was developed by DuPont in 1967 via
1
-3
properties.
Especially, perfluorinated polymer has
perfluoropyruvyl fluoride prepared from hexafluoropro-
been applied in graded-index polymer optical fibers (GI
POF) for short-medium haul data communication in
order to obtain excellent low attenuation loss in the
near-infrared region and high bandwidth due to the
performance of the perfluorinated polymer compared to
the poly(methyl methacrylate) (PMMA)-based plastic
7
pylene epoxide. Using a similar method, perfluoro-2-
methylene-4,5-dimethyl-1,3-dioxolane (PMDD) was de-
8
veloped by Asahi Glass in 1993. The methods for their
preparations were complicated and costly. Recently,
PMMD was prepared from partially fluorinated ester
9
by liquid-phase direct fluorination. However, this method
4
optical fiber. Currently, an interfacial gel polymeriza-
still requires the use of expensive fluorinated starting
materials: perfluoroacyl fluoride. In this work, we
report a new and efficient method for the preparation
of this class of monomers. The polymerization behavior
of the resulting monomers was investigated. The prop-
erties of the resulting polymers were investigated as
well.
tion is utilized to prepare GI-POF preform. This impor-
tant method requires a radically polymerizable mono-
mer. And also, POF requires that polymeric materials
are amorphous and have relatively higher glass transi-
tion temperature (Tg) for high-temperature working
conditions. Therefore, we are currently searching for a
new perfluorinated monomer which can afford amor-
phous perfluoropolymers with a higher Tg through
radical homo- or copolymerization.
Experimental Section
Materials. 2,3-Butanediol (mixture of stereoisomers, 98%),
Dowex 50WX8-100 ion-exchange resin, and absolute benzene
were purchased from the Aldrich Chemical Co. Methyl pyru-
vate (97%) and 1,2-cyclohexanediol (cis- and trans- mixture,
Compared to a large number of radically polymeriz-
able hydrocarbon monomers, only a few classes of
perfluoromonomers can homopolymerize under normal
conditions via the free radical mechanism. The most
typical example of a perfluoromonomer polymerized via
the free radical mechanism and developed by DuPont
9
8%) were purchased from TCI. Hexafluorobenzene (99%) and
hexafluoro-2-propanol (HFIP) (99%) were purchased from
SynQuest Fluorochemical Laboratory. Fluorinert FC-75 (a
perfluorinated solvent) was obtained from 3M Co. All reagents
were used without further purification. Perfluorobenzoyl
peroxide (F-BPO) was prepared from pentafluorobenzoyl chlo-
5
in 1937 is tetrafluoroethylene. Gradually, perfluoro-2-
methylene-1,3-dioxolanes, perfluorodihydrodioxins, and
10
perfluorodioxoles were also developed by DuPont.2,3 In
ride and hydrogen peroxide according to a published method.
The crude initiator was recrystallized from hexane, and the
purified initiator has a melting point of 76-78 °C; its half-
lives were calculated to be 25.6 and 2.6 h at 60 and 80 °C,
respectively, based on the reported decomposition rate constant
addition, perfluorodienes as a new class of monomer
†
‡
Polytechnic University.
11
Keio University and ERATO.
in benzene. 2,2′-Azobis(isobutyronitrile) (AIBN) (Aldrich,
*
Corresponding author. E-mail: wliu@poly.edu.
98%) was purified by recrystallization from methanol.
1
0.1021/ma050753b CCC: $30.25 © 2005 American Chemical Society
Published on Web 10/14/2005

Macromolecules, Vol. 38, No. 23, 2005
Synthesis and Radical Polymerization of PMMD 9467
dCF ), -129.49 (m, -OCF- of major isomer) and -129.84 (m,
Instrumentation. The H (300 MHz) and 19F (282 MHz)
NMR spectra were obtained on a Bruker ACF 300 spectrom-
eter. NMR spectra for these perfluoropolymers were measured
in hexafluorobenzene with deuterated chloroform as an inter-
nal locking solvent at 50 °C. FTIR spectra were obtained with
a Perkin-Elmer FTIR-1600 spectrometer. GC-MS measure-
ments were conducted using an HP 5890 gas chromatograph
and an HP 5970B mass spectrograph. Elemental analyses were
performed at Complete Analysis Laboratories Inc., Parsippany,
NJ. Viscosities of the solvent and filtered polymer solutions
were measured using a modified Ubbelohde viscometer at 25
1
2
-OCF- of minor isomer) (2F in total, -OCF-). GC-MS: m/e
+
+
+
+
3 2
294 (M ), 275 (M -F), 225 (M -CF ), 200 (M -CF COO:
+
+
+
+
4 8 4 7 3 2 2 2
C F ), 181 (C F ), 150 (CF CFdCF ), 131 (CF dCFCF ),
100 (C F ), 78 (CF dCdO ), 69 (CF ), and 50 (CF ).
2 4 2 3 2
+
+
+
+
Synthesis of Perfluoro-3-methylene-2,4-dioxabicyclo-
4.3.0]nonane (PMDN). Synthesis of Methyl 3-Methyl-2,4-
[
dioxabicyclo[4.3.0]nonane-3-carboxylate. The reaction mix-
ture of the 1,2-cyclohexanediol (232 g, 2.0 mol), methyl
pyruvate (204 g, 2.0 mol), cation-exchange resin (H form) (10
g), and absolute benzene (1 L) was refluxed until the evolution
of water ceased in a flask fitted with a Dean-Stark trap. The
reaction was kept for 3 days. After solvent was removed, the
(
0.05 °C in a thermostated bath. The intrinsic viscosity was
evaluated using the Huggins equation. The differential scan-
ning calorimetry (DSC) measurement was performed on a DSC
residue was distilled to give 232 g (1.16 mol) of product. Yield
2
920 module in conjunction with the TA Instruments 5100
1
5
3
8%; bp 60 °C/0.3 mmHg. H NMR (CDCl
3
) δ (ppm): 1.52 (s,
-), 3.8 (s, 3H, -OCH ), 4.2
: C, 59.98; H, 8.05.
system at a heating rate of 10 °C/min under a nitrogen
atmosphere. The instrument was calibrated using indium and
zinc as calibration standards for the temperature and enthalpy
changes. The midpoint of the heat capacity transition was
H, CH
3
), 1.2-1.9 (m, 8H, -CH
m, 2H, -OCH-). Anal. Calcd for C
2
3
(
8 14 4
H O
Found: C, 59.56; H, 8.11.
Synthesis of Perfluoro-3-methyl-2,4-dioxabicyclo[4.3.0]-
nonane-3-carboxylic Acid. The methyl 3-methyl-2,4-dioxa-
bicyclo[4.3.0]nonane-3-carboxylate (666 g, 3.33 mol) was flu-
orinated with fluorine gas diluted with nitrogen in Fluorinert
FC-75. The fluorination was performed at Exfluor (Round
Rock, TX) as mentioned above. After flushing the system using
nitrogen gas for 1.0 h, fluorine gas diluted to 20% with nitrogen
gas was blown into the reaction mixture at a flow rate of 240.0
L/h at ambient temperature (∼25 °C). The reaction was
performed over about 26 h, and the reaction temperature was
controlled around 25 °C. After the reaction stopped, the
mixture was treated with aqueous KOH solution (5 N, 1300
mL) to form organic and water phases. The water phase was
separated, and the water was removed. The solid was treated
with concentrated HCl (900 mL), and the organic phase was
taken as the glass transition temperature (T
g
). Thermogravi-
metric analysis (TGA) was performed on Hi-Res Modulated
TGA2950 thermogravimetric analyzer under nitrogen at a
heating rate of 10 °C/min. The refractive index of the film was
obtained with a Metricon model 2010 prism coupler. The
transmission spectrum was recorded with a Cary 6000i UV-
vis-NIR spectrophotometer.
Synthesis of PMDD. Synthesis of Methyl 2,4,5-Tri-
methyl-1,3-dioxolane-2-carboxylate. The reaction mixture
of the 2,3-butanediol (180 g, 2.0 mol), methyl pyruvate (204 g,
2.0 mol), cation-exchange resin (H form) (10 g), and absolute
benzene (1 L) was refluxed until the evolution of water ceased
in a flask fitted with a Dean-Stark trap. The reaction was
kept for 2 days. After solvent was removed, the residue was
distilled to give 192 g (1.1 mol) of product. Yield 55%; bp 45
obtained; the acid was obtained by distillation. Yield (1317 g,
1
°
C/1.0 mmHg. H NMR (CDCl
3
) δ (ppm): 1.15 (d, 6H, -CH
), 4.2-4.4 (m, 2H,
8 14 4
H O : C, 55.16; H, 8.10. Found:
3
),
1
3
.14 mol) 94%; bp 78 °C/1.0 mmHg. H NMR (CDCl
3
) δ (ppm):
) δ (ppm): -79.6 (t, 3F,
), -122-131 (m, 10F, -OCF- and -CF -).
Synthesis of Perfluoro-3-methylene-2,4-dioxabicyclo-
4.3.0]nonane. The perfluoro-3-methyl-2,4-dioxabicyclo[4.3.0]-
1
.50 (s, 3H, -CH
OCH-). Anal. Calcd for C
C, 55.04; H, 8.15.
3 3
), 3.80 (s, 3H, OCH
1
9
8
.5 (s, 1H, COOH)). F NMR (CDCl
CF
3
-
-
3
2
Synthesis of Perfluoro-2,4,5-trimethyl-1,3-dioxolane-
-carboxylic Acid. The methyl 2,4,5-trimethyl-1,3-dioxolane-
-carboxylate (500 g, 2.87 mol) was fluorinated with fluorine
[
2
2
nonane-3-carboxylic acid (100 g, 0.24 mol) was converted to
potassium salt by neutralization with aqueous KOH (2 N, 120
mL). The salt was dried at 50 °C under vacuum for 1 day. The
salt was decomposed at 250 °C for 2 h to yield the product
which was collected in a trap cooled to -78 °C. The product
was purified by distillation using a spinning band distillation
apparatus to give 71 g (0.20 mol) of the monomer. Yield 84%;
gas diluted with nitrogen in Fluorinert FC-75. The liquid-
phase fluorination was carried out in cooperation with Exfluor
Research Co. (Round Rock, TX). After flushing the system
using nitrogen gas for 1.0 h, fluorine gas diluted to 20% with
nitrogen gas was blown into the reaction mixture at a flow
rate of 240.0 L/h at ambient temperature (∼25 °C). The
reaction was performed over about 20 h, and the reaction
temperature was controlled around 25 °C. After the reaction
stopped, the mixture was neutralized with aqueous KOH
solution (5 N, 1100 mL). The aqueous phase was separated,
and the water was removed. The solid was treated with an
excess of concentrated HCl (800 mL), and the organic phase
1
19
bp 99 °C. H NMR (CDCl
δ (ppm): -126.84 (t, 2F, dCF
2
130.28, -131.66, -132.67, -133.62 and -134.62 (8F, -CF -
3
) δ (ppm): none. F NMR (CDCl
3
)
2
), -127.98, -128.98, -129.29,
-
in the cyclohexyl group), -138.25 (s, 2F, -OCF-). GC-MS: m/e
+
+
+
+
3
56 (M ), 337 (M -F), 262 (M -CF
2
COO:
C
6
F
4
10 ), 243
+
+
+
+
+
(
C
6
F
9
), 212 (C
dCFCF
5
F
8
), 193 (C
), 100(C
5
F
7
), 162 (C
), 93 (FCtCCF
4
F
6
), 143 (C
F
5
), 131
+
+
+
+
(CF
2
2
2
F
4
2
), 78 (CF
2
dCdO ),
was obtained; the acid was obtained by distillation. Yield (925
+
+
1
3 2
69 (CF ), and 50 (CF ).
g, 2.58 mol) 90%; bp 61 °C/2.5 mmHg. H NMR (CDCl
3
) δ
) δ (ppm):
trans and cis isomers, major/minor: 2.67/1.00 (mol/mol);
79.29 and -79.63 (minor), -79.32 and -79.36 (major) (d, 6F
), -80.81 and -80.93 (minor), -81.11 and -81.14
1
9
(
ppm): 9.4 ppm (s, 1H, COOH). F NMR (CDCl
3
Polymerization. PMDD Polymerization. The PMDD
(1.69 g, 5.75 mmol), F-BPO (13.0 mg, 0.031 mmol), and
hexafluorobenzene (0.5 mL) were charged in the glass tube,
which was then degassed and refilled with argon in three
vacuum-freeze-thaw cycles. The tube was then sealed and
heated at 60 °C for 24 h. The resulting polymer (1.50 g, 88%)
was precipitated from hexafluorobenzene solution into chlo-
roform, isolated using a centrifuge, and dried under vacuum
at 50 °C. The intrinsic viscosity of the sample in hexafluo-
robenzene at 25 °C is 11.0 mL/g. The bulk polymerization was
carried out in a similar way. The solid product was dissolved
in hexafluorobenzene and then was precipitated in chloroform.
The polymerization under air atmosphere was performed in a
glass tube equipped with a three-way stopcock which was
closed without degassing. The photopolymerization was also
performed in the presence of carbon tetrabromide or carbon
tetrachloride. The monomer and additive were charged in a
glass tube, which was also then treated in three vacuum-
freeze-thaw cycles and sealed. The glass tube was irradiated
by UV light at about 365 nm.
-
in total, -CF
3
(
major) (d, 3F in total, -CF
3
), -120.8 (minor), -124.6 and
-
125.6 (major) (m, 2F in total, -OCF-).
Synthesis of Perfluoro-2-methylene-4,5-dimethyl-1,3-
dioxolane. The perfluoro-2,4,5-trimethyl-1,3-dioxolane-2-car-
boxylic acid (100 g, 0.28 mol) was converted to potassium salt
by neutralization with aqueous KOH (2 N, 140 mL). The salt
was dried at 50 °C under vacuum for 1 day. The salt was
decomposed at 250 °C for 2 h to yield the product, which was
collected in a trap cooled to -78 °C. The product was purified
by distillation using a spinning band distillation apparatus to
give 64 g (0.22 mol) of the monomer. Yield 78%; bp 60 °C (lit.
8
1
19
6
3 °C ). H NMR (CDCl
ppm): trans and cis isomers, major/minor: 2.67/1.00 (mol/
mol); -80.35 (s, -CF of major isomer) and -81.09 (s, -CF
of minor isomer) (6F in total, -CF ), -126.61 (t, dCF of major
isomer) and -126.88 (t, dCF of minor isomer) (2F in total,
3 3
) δ (ppm): none. F NMR (CDCl ) δ
(
3
3
3
2
2

9468 Liu et al.
Macromolecules, Vol. 38, No. 23, 2005
Scheme 1. Synthesis of Perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane
Scheme 2. Synthesis of Perfluoro-3-methylene-2,4-dioxabicyclo[4.3.0]nonane
Table 1. Radical Polymerization of Perfluororo-2-methylene-1,3-dioxolanesa
intrinsic
run
monomer
additive
solvent
[M]0
atmosphere
time (h)
yieldb
viscosity (mL/g)c
1
2
3
4
5
6
7
8
9
PMDD
PMDN
PMDD
PMDD
PMDD
PMDD
PMDD
PMDD
PMDD
PMDN
PMDN
PMDN
F-BPO
F-BPO
F-BPO
AIBN
F-BPO
F-BPO
AIBN
F-BPO
AIBN
F-BPO
F-BPO
F-BPO
none
none
C6F6
C6F6
C6F6
5.75
5.00
3.85
3.85
3.85
1.92
1.92
1.92
1.92
3.33
3.33
1.67
Ar
Ar
Ar
Ar
air
Ar
Ar
Ar
Ar
Ar
air
Ar
48
96
24
24
24
24
24
24
24
96
96
24
95
24.4
9.6
74
88
11.0
trace
85
7.5
3.1
4.7
7.8
C6F6/CHCl3 (v/v, 1/1)
87
C6F6/CHCl3 (v/v, 1/1)
13
HFIP
HFIP
C6F6
C6F6
HFIP
89
trace
46
10
11
12
3.4
3.0
2.6
35
20
a
[
Initiator]o ) 0.02 M; temperature: 60 °C; PMDD: perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane; PMDN: perfluoro-3-methylene-
b
c
2
,4-dioxabicyclo[4.3.0]nonane. Precipitated into chloroform. In hexafluorobenzene solution at 25 °C.
PMDN Polymerization. The PMDN (1.78 g, 5.0 mmol),
This means the ring-opening of the dioxolane ring did
F-BPO (13.0 mg, 0.031 mmol), and hexafluorobenzene (0.5 mL)
were charged in the glass tube, which was then degassed and
refilled with argon in three vacuum-freeze-thaw cycles. The
tube was then sealed and heated at 60 °C for 96 h. The
resulting polymer (0.82 g, 46%) was precipitated from hexaflu-
orobenzene solution into chloroform, isolated using a centri-
fuge, and dried under vacuum at 50 °C. The intrinsic viscosity
of the sample in hexafluorobenzene at 25 °C is 3.4 mL/g. Other
polymerizations of PMDN were performed with the methods
similar to PMDD polymerizations.
not occur during fluorination in the perfluorinated
solvent at ambient temperature (∼25 °C). After fluori-
nation aqueous KOH solution was added to hydrolyze
the perfluorinated ester. The potassium salt was ob-
tained from the aqueous phase. The salt can be con-
verted into perfluorinated acid by acidification.
The third step for the synthetic route is the thermal
elimination of the obtained perfluorinated potassium
salt to produce the corresponding monomers. This is a
widely used method to produce perfluorinated vinyl
Results and Discussion
14
monomers in fluorine chemistry. The yield is generally
Monomer Synthesis. As shown in Schemes 1 and
, the first step for the synthetic route is to synthesize
high as we reported here.
2
By using the above protocol, dozens of perfluoromono-
mers could be readily designed and synthesized from
methyl pyruvate and diols. This method was first proved
to be feasible by synthesizing a known monomer,
PMDD, which was already reported to be prepared by
the hydrocarbon dioxolane derivatives. The methyl
pyruvate and diols were used as starting materials since
they are commercially available and quite cheap. A
dilute benzene solution and slightly reduced pressure
were adopted to reduce the side reaction such as
condensation polymerization. Even so, the polymer was
still produced in about 30% yield as a main side product.
Hence, the yield in this step was moderate. Similarly,
the dioxolane derivatives have been prepareed from
8
other method. Then, to broaden the utilization of this
method, we designed a new monomer with a bulky
cyclohexyl group which was expected to enhance the
glass transition temperature of the polymer. As ex-
pected, perfluoro-3-methylene-2,4-dioxabicyclo[4.3.0]-
nonane was successfully synthesized with this method
as reported in the experimental part. In addition, this
method could be applied for the preparation of a new
class of monomer: perfluoro-2-methylene-1,3-dioxanes.
We recently synthesized perfluoro-2-methylene-1,3-di-
oxane by this method after the above two monomer’s
preparation and published as part of work to compare
the polymerization reactivity of dioxolane and dioxane
derivatives.15
1
2
pyruvic acid in a yield about 50%.
The second step for the synthetic route is liquid-phase
direct fluorination developed by Lagow.13 Direct fluori-
nation of a hydrocarbon ester such as octanoyl acetate
has been reported to afford two kinds of perfluorinated
13
acids in a high yield. The dioxolane derivatives bearing
a fluorinated ester have also reported to be fluorinated
9
in good yield. However, the dioxolane derivatives
without fluorinated moiety have not been studied using
the direct fluorination method. The direct fluorination
on the hydrocarbon analogues of dioxolanes in a per-
fluorinated solvent afforded a yield over 90% in all cases.
Polymerization. The radical polymerizations of the
two monomers were performed under various condi-
tions. The results are summarized and listed in Table

Macromolecules, Vol. 38, No. 23, 2005
Synthesis and Radical Polymerization of PMMD 9469
Table 2. Photopolymerization of Perfluoro-2-methylene-1,3-dioxolanesa
intrinsic
run
monomer
additive
solvent
[M]0
temp (°C)
time (h)
yieldb
viscosity (mL/g)c
1
2
3
4
5
6
PMDD
PMDN
PMDD
PMDD
PMDD
PMDN
CBr4
CBr4
none
CBr4
CCl4
CCl4
none
none
none
C6F6
none
none
5.75
5.00
5.75
3.85
5.75
5.00
25
50
25
25
25
50
48
96
24
11
24
48
88
10.8
5.6
74
trace
71
85
78
3.6
13.3
8.0
a
Additive: 0.1 mol % for runs 1, 2, 5, and 6; 2.0 mol % for run 4; PMDD: perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane; PMDN:
perfluoro-3-methylene-2,4-dioxabicyclo[4.3.0]nonane. b Precipitated into chloroform. In hexafluorobenzene solution at 25 °C.
c
1
. The bulk polymerization of PMDD was carried out
oxides, F-BPO produces pentafluorobenzoyloxy radical
as the main primary initiating radical at 60 °C.1
Therefore, the polymers obtained by using F-BPO as an
initiator contain a weakly bonded pentafluorobenzoyl
end group which was easily hydrolyzed by moisture,
resulting in opacity of the polymer rod. To avoid the
pentafluorobenzoyl end group, the photopolymerization
was carried out under various conditions. The bulk
photopolymerization of PMDD performed by UV ir-
radiation at about 365 nm at 25 °C for 24 h in the
presence of carbon tetrabromide or carbon tetrachloride
produced more than 80% of polymer (runs 1 and 5 in
Table 2). However, as a control experiment, the photo-
polymerization in the absence of carbon tetrabromide
or carbon tetrachloride produced only trace of polymer
(run 3 in Table 2). This indicates that the initial radicals
were produced by breaking the C-Br or C-Cl bond.
Solution photopolymerization was performed in hexaflu-
orobenzene in the presence of carbon tetrabromide or
carbon tetrachloride under an argon atmosphere, and
the yield was over 70% after 11 h (run 4 in Table 2).
The resulting polymers are soluble in fluorinated sol-
vents such as hexafluorobenzene and Fluorinert FC-75.
The viscosity was measured in a hexafluorobenzene
solution. It is found that the molecular weight of the
polymer obtained in the presence of carbon tetrabromide
is lower than that in the presence of carbon tetrachloride
(runs 1 and 5 in Table 2). Both molecular weights of
the polymer obtained in the presence of carbon tetra-
bromide and carbon tetrachloride are lower than that
of the polymer obtained by bulk polymerization using
F-BPO as an initiator without additives. It is reasonable
that carbon tetrabromide with a higher chain transfer
constant led to a lower molecular weight during poly-
merization.
The bulk photopolymerization of PMDN was also
performed in the presence of carbon tetrabromide and
carbon tetrachloride (runs 2 and 6 in Table 2). Similarly,
but it required a longer time and a higher polymeriza-
tion temperature to obtain a higher yield. The molecular
weight is also lower when carbon tetrabromide was used
as an additive. The possible mechanism is illustrated
in Scheme 3. The initiation was related to the C-Br or
C-Cl bond breaking upon irradiation. The resultant
radicals attack the active carbon-carbon double bond
at the tail position to produce the initial monomer
radical species. The second step is the initial radical
species attack another monomer to propagate. The
termination step may relate to the chain transfer to the
carbon tetrabromide or carbon tetrachloride. Another
possible termination is the coupling of two growing
radicals.
1,17
using F-BPO as an initiator at 60 °C for 48 h to afford
a transparent resin. Similarly, the bulk polymerization
of PMDN at 60 °C for 96 h also afforded a transparent
resin. After the products were purified by reprecipitation
from hexafluorobenzene into chloroform, the yield is
lower in the case of PMDN.
The solution polymerization was performed in hexaflu-
orobenzene, hexafluoro-2-propanol and a mixed solvent
of hexafluorobenzene and chloroform. The PMDD pro-
duces polymer in a high yield with a fluorinated
initiator, but the polymerization gives only a trace of
polymer at 60 °C for 24 h in fluorinated solvents (runs
4
and 9 in Table 1) with a nonfluorinated initiator,
AIBN. This may be due to the fact that nonfluorinated
radical species are not miscible with the fluorinated
monomer. The fluorinated solvents surround the initial
radicals to form a cage which retards the initiation. To
understand the cage effect, an experiment was per-
formed introducing a part of chloroform into the poly-
merization system. The polymer was thus obtained in
an increased yield of 13% (run 7 in Table 1). This may
suggest that the cage effect by perfluorinated solvents
was loosened in the presence of chloroform. On the other
hand, this may also due to the fact that the AIBN initial
radical abstracts a hydrogen atom from chloroform to
produce a trichloromethyl radical which may directly
attack the fluoromonomer. It is reasonable because this
kind of reaction has been applied in synthesizing CCl3-
terminated vinylidene fluoride telomers for preparation
of block copolymers using atom transfer radical polym-
1
6
erization.
Solution polymerization of PMDD in C6F6/CHCl3 and
HFIP with F-BPO as an initiator also afford the polymer
in a high yield at 60 °C for 24 h (runs 6 and 8 in Table
1
). In the mixed solvent of hexafluorobenzene and
chloroform, it was observed that polymer precipitated
out during polymerization. In HFIP, the resulting
polymer is gellike during polymerization. The intrinsic
viscosities of the obtained polymers in HFIP and C6F6/
CHCl3 are lower than that in hexafluorobenzene. It was
thought that the chain transfer readily occurred by the
growing fluorinated radical species abstracting a proton
from the solvent. This may contribute to make the
molecular weight lower than that in hexafluorobenzene.
Solution polymerizations of PMDN in hexafluoroben-
zene and HFIP afford solid polymers (runs 10 and 12
in Table 1). Similarly, the intrinsic viscosity of the
obtained polymer in HFIP is lower than that in hexaflu-
orobenzene. It was also ascribed to the chain transfer
reaction.
Compared with the experiment runs 3, 5, 10, and 11,
it is interesting to note that the polymerization in the
presence of air also affords polymers in a yield similar
to that in an argon atmosphere. The detailed mecha-
nism is discussed below. Unlike perfluoroalkanoyl per-
The photopolymerizations of the two monomers afford
fluorinated polymers with tribromomethyl or trichlo-
romethyl end groups. Therefore, block copolymers with
nonfluorinated monomers such as styrene and MMA

9470 Liu et al.
Macromolecules, Vol. 38, No. 23, 2005
Scheme 3. Schematic Illustration for
Photopolymerization of
Perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane
Figure 2. 19F NMR spectrum of poly(perfluoro-3-methylene-
2,4-dioxabicyclo[4.3.0]nonane) (run 2 in Table 1).
signal centered at -124.3 ppm is assigned to the
fluorines on the dioxolane ring (-OCF-).
The 19F NMR spectrum of poly(PMDN) obtained
under an argon atmosphere is shown in Figure 2. In
the spectrum, the four peaks centered at -118.8,
-
123.4, -130.8, and -135.6 ppm are assigned to the
fluorines on the perfluorocyclohexane ring (-CF2- and
-
OCF-). The signals between -102.0 and -116.0 ppm
are also assigned to the main-chain fluorines (-CF2-)
for poly(PMDN) according to the assignment for poly-
(PMDD). However, it overlaps with one of the side-chain
peaks. It is noted that the area ratio of the signal
between 102.0 and 127.6 ppm to the signal between
1
27.6 and 138.8 ppm is 2:1.
In addition, FTIR spectra of the obtained fluoropoly-
mers were recorded to check the ring-opening possibility
during radical polymerizations. Two very weak peaks
ascribed to the carbonyl absorption of the end group of
could be synthesized via atom transfer radical poly-
merization. The block copolymerization was carried out
in hexafluorobenzene using CBr3-terminated poly-
-
1
perfluorobenzoic ester at about 1795 cm and the
characteristic fluorinated benzene absorption at 1515
(
PMDD) (run 4 in Table 2) as a macroinitiator and MMA
as a comonomer with CuCl/2,2′-bipyridine system at 100
C. To the best of our knowledge, synthesizing block
-
1
cm are observed for the sample prepared in argon
atmosphere. The results may suggest that ring opening
did not occur during polymerizations. In other words,
the percentage of the ring-opening part in the polymer-
izations of perfluorinated dioxolanes is undetectable
using FTIR and NMR techniques. The hydrocarbon
analogues of 2-methylene-1,3-dioxolanes were reported
to produce a product containing ring-opening units via
free-radical mechanism in most cases.18 However, in the
case of 3-methylene-2,4-dioxabicyclo[4.3.0]nonane, ring-
opening did not occur during its radical polymerization.1
The fluorine in the monomers influences the ring-
opening polymerization. Perfluorinated dioxolanes pro-
duced only vinyl addition polymers as we reported
previously.15 This was ascribed to that the fluorinated
ether bond, -O-CF2-, being quite strong and not
cleaving during free-radical polymerization.
°
copolymers with perfluorinated and hydrogenated parts
is still challenging, though the properties of this kind
of block copolymer are quite interesting. The investiga-
tion on characterizing the copolymers is in progress. The
1
9
F NMR spectra of both polymers were recorded in
hexafluorobenzene using chloroform-d as a locking
solvent at 50 °C. The chemical shift was measured from
1
9
CFCl3 as an internal reference. The F NMR spectrum
of poly(PMDD) obtained under Ar atmosphere is shown
in Figure 1A. In the spectrum, the signal centered at
8b
-
80.5 ppm is assigned to the trifluoromethyl group
-CF3). The signals between -102.0 and -118.0 ppm
are assigned to the main-chain fluorines (-CF2-). The
(
Oxygen Effect on the Polymerization. The radical
polymerization under an air atmosphere was also
performed. The conditions and results of polymerization
are shown in Table 1. It was found that the presence of
air did not affect the polymer yield. The polymerizations
of PMDD at 60 °C in hexafluorobenzene produced 88%
and 85% polymer in the presence of argon and air,
respectively (runs 3 and 5 Table 1). The polymerizations
of PMDN at 60 °C in hexafluorobenzene produced 46%
and 35% polymers under argon and air atmosphere,
respectively (runs 10 and 11 Table 1). This is interesting
because the oxygen generally inhibits the free-radical
polymerization of hydrocarbon vinyl monomers at 60 °C
or lower temperature.19 Oxygen reacts with radical
species to form a relatively unreactive peroxy radical
which reacts with itself or another propagating radical
1
9
Figure 1. F NMR spectra of poly(perfluoro-2-methylene-
4
,5-dimethyl-1,3-dioxolane)s obtained under Ar (run 3 in Table
) (A) and under air atmosphere (run 5 in Table 1) (B).
1

Macromolecules, Vol. 38, No. 23, 2005
Synthesis and Radical Polymerization of PMMD 9471
Scheme 4. Oxygen Effect on the Radical
Polymerization of
Perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane
Figure 3. Thermogram of poly(perfluoro-2-methylene-4,5-
dimethyl-1,3-dioxolane) obtained under air atmosphere (run
5
in Table 1).
part. Thus, the oxygen effect may be schematically
illustrated as shown in Scheme 4. The final product is
a copolymer as shown in Scheme 4. The copolymer
contains unstable units such as ester and/or ortho-acid
ester. TGA proves the presence of unstable units. TGA
of the product was performed under a nitrogen atmo-
sphere using a heating rate of 10 °C/min. A clear two-
step decomposition was observed as shown in Figure 3.
The first step was ascribed to the unstable unit decom-
position. It was found to be thermally unstable at about
133 °C. About 17% of the polymer was lost in this step
between 133 and 300 °C. This is agreement with the
calculated mole content of the ester and/or ortho-acid
ester unit of about 21 mol % by fluorine NMR mentioned
above. Thus, to obtain the thermally stable polymeric
materials, it is necessary that the polymerization is
performed under argon or nitrogen atmospheres and
kept until the polymerization is totally completed.
On the other hand, it was reported that reaction of
the perfluorinated double bond with oxygen is a general
behavior of many fluoro olefins.20 For example, the
(photo)oxidation of tetrafluoroethylene and hexafluoro-
propylene with oxygen produced perfluoropolyethers.2
Perfluorodihydrodioxins slowly react with oxygen to
form epoxides and acyl fluorides at 25 °C.2 That is why
an acid gas was observed after storing the monomers
for a long time under air. Therefore, storing those
monomers should be under argon or nitrogen atmo-
spheres at low temperature.
by coupling and disproportionation reactions to form
peroxides and hydroperoxides. The formed peroxides
and hydroperoxides are inactive at relatively low tem-
peratures. The further initiation may occur at quite
higher temperatures, resulting in the polymer contain-
ing an ether bond on the main chain.
In the case of fluorinated vinyl monomers, oxygen
may also react with the radical species to form perox-
ides. However, the formed perfluorinated peroxide is not
stable at 60 °C and readily produces new radical species
to initiate the radical polymerization again. The per-
fluorinated peroxide has a lower decomposition temper-
ature compared to its analogues. As a model compari-
son, tert-butyl peroxide (half-life t1/2 ) 10 h at 126 °C)
was used as a high-temperature radical initiator at
about 110 °C, while perfluoro-tert-butyl peroxide was
used as a radical initiator at 70 °C. Consequently, the
polymerization under an air atmosphere may lead to a
polymer containing an ether bond on the main chain.
On the other hand, the ring opening may occur through
breaking the C-O bond adjacent to the oxy radical to
form a new radical which continues to initiate the
polymerization, producing a product containing an ester
part.
0b
0c
The structure of the polymer obtained in the presence
of air was found to be different from that obtained under
The reaction of fluorinated monomer with oxygen may
also be responsible for the opacity of the polymer rod.
We observed that a lower conversion of the monomer
in the bulk polymerization led to a faster change in the
opacity of the polymer rod and a deeper opacity upon it
exposure to air. This may be ascribed to the fact that
the unreacted monomer reacts with oxygen and mois-
ture to form heterogeneous materials as mentioned
above.
1
9
argon based on the F NMR analysis. Compared with
1
9
the F NMR spectra of the sample obtained under
argon and under air atmosphere (runs 3 and 5 in Table
1
) (Figure 1), three new signals at about -81.9, -82.5,
and -130.6 ppm appeared in the spectrum of the sample
obtained under an air atmosphere. The fluorines on
trifluoromethyl groups (-CF3) and on the dioxolanes
(-OCF-) may slightly shift to the higher field due to
Kinetic Study on the Bulk Polymerization. The
kinetic studies for the two monomers were performed
in bulk at 50 °C at F-BPO concentration of 0.020 M.
Time-conversion curves of the bulk homopolymeriza-
tion are shown in Figure 4. The rate of polymerization
(Rp) was calculated on the basis of the initial slope of
the first-order plot for the monomer consumption rate.
The rate of polymerization of PMDD was found to be
the dioxolane adjacency to the main chain -OCF2-. The
signals overlapped with the trifluoromethyl groups at
about -82.5 ppm, which was ascribed to the fluorine
on the main chain of -OCF2-. The content of the new
formed -OCF- signal at -130.6 ppm is calculated to
be about 21 mol % based on all -OCF- signals.
Considering ring opening from the adjacent C-O bond,
1
9
-2
-1 -1
the three new signals in the F NMR spectrum could
1.25 × 10 mol L
s , whereas that of PMDN was
-
3
-1 -1
be also assigned as the -CF3 (-81.9 ppm), -OCF2-
found to be 5.0 × 10 mol L
s
at 50 °C. The rate of
(
-82.5 ppm), and -OCF- (-130.6 ppm) in the ester
polymerization of PMDD is 2.5 times faster than that

9472 Liu et al.
Macromolecules, Vol. 38, No. 23, 2005
Figure 7. Transmission spectrum of poly(perfluoro-2-meth-
ylene-4,5-dimethyl-1,3-dioxolane) (thickness: 0.10 mm).
Figure 4. Time-conversion curves for the bulk polymeriza-
tions of PMDD (white squares) and perfluoro-3-methylene-2,4-
dioxabicyclo[4.3.0]nonane (black squares) using perfluoroben-
zoyl peroxide as an initiator at 50 °C.
Figure 5. DSC curves for the poly(perfluoro-2-methylene-4,5-
dimethyl-1,3-dioxolane) (run 3 in Table 1) (A) and poly-
(
perfluoro-3-methylene-2,4-dioxabicyclo[4.3.0]nonane) (run 2
in Table 1) (B).
Figure 8. Refractive indices of poly(perfluoro-2-methylene-
4
,5-dimethyl-1,3-dioxolane) (A) and poly(perfluoro-3-methyl-
ene-2,4-dioxabicyclo[4.3.0]nonane) (B).
The low molecular weight polymer contains higher
content of unstable end groups, which may cause an
unzipped effect on the decomposition of the polymer.
The free-standing film could be obtained from poly-
(
PMDD) by casting. Poly(PMDN) cannot afford a free-
standing film due to its brittleness. Hence, only the
poly(PMDD) film was measured for the optical trans-
mission. The vibration overtone of the stretching bond
led to the absorption losses in POF. As Groh reported,21
the carbon-fluorine (C-F) bond has a lowest absorption
losses among carbon-hydrogen (C-H), carbon-deute-
rium (C-D), and C-F bonds in the near-IR region. As
shown in Figure 7, the transmission spectrum of poly-
(PMDD) in the 200-2000 nm range illustrates the
extraordinary optical transmission from the deep-UV
to near-infrared regions for perfluoro-2-methylene-1,3-
dioxolane polymers. This indicated that fluoropolymer
could afford a low loss contribution in POF. On the other
hand, water is observed to have a strong O-H absorp-
tion for the wavelengths over 700 nm. Generally,
hydrogenated polymers have some water absorption.
Fortunately, fluoropolymers typically have a compara-
tively low water absorption. Therefore, a fluoropolymer
is an ideal material for POF.
Figure 6. Thermograms of poly(perfluoro-2-methylene-4,5-
dimethyl-1,3-dioxolane) (A) (run 3 in Table 1) and poly-
(
perfluoro-3-methylene-2,4-dioxabicyclo[4.3.0]nonane) (B) (run
2
in Table 1).
of PMDN. This was ascribed to the steric effect in the
polymerization of PMDN. The propagation is reasonably
slow considering that a growing radical with steric
hindrance attacks a monomer.
Physical Properties. The glass transition for poly-
PMDD) and poly(PMDN) were determined by DSC at
(
a heating rate of 10 °C/min. Both of them exhibited a
clear glass transition as shown in Figure 5. Glass
transition temperatures were found to be 155 and 161
°
C for the poly(PMDD) and poly(PMDN), respectively.
The refractive indices of the films were measured at
different wavelengths and shown in Figure 8. The
refractive indices are dependent on the wavelength. The
theoretical refractive indices were calculated to be
1.3361 and 1.3164 at the wavelength of 589 nm for poly-
(PMDN) and poly(PMDD), respectively, according to a
reported method.22 They are in good agreement with the
experimental values reported here. The refractive in-
dices for the fluoropolymers are low compared to those
TGAs of poly(PMDD) and poly(PMDN) were per-
formed under a nitrogen atmosphere using a heating
rate of 10 °C/min. The thermograms of poly(PMDD) and
poly(PMDN) are shown in Figure 6. The onsets of
decomposition for poly(PMDD) and poly(PMDN) are 368
and 342 °C, respectively. The lower thermal stability
of the poly(PMDN) may be due to low molecular weight
as observed by the intrinsic viscosity of this polymer.

Macromolecules, Vol. 38, No. 23, 2005
Synthesis and Radical Polymerization of PMMD 9473
2
, and paragraphs 6 and 8 in the Results and Discussion
section have been revised. The correct version was
posted on October 31, 2005.
References and Notes
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(
For plastic optical fiber communications, the band-
width is strongly related to the material dispersion. The
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The material dispersion could be calculated on the basis
of the data in Figure 8 according to a reported method.23
The results are shown in Figure 9 for both polymers
between 600 and 1800 nm. The material dispersions of
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1
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PMDD and PMDN are synthesized in a convenient
way with high yield and low byproducts. Despite their
strong steric hindrance, they could be polymerized in a
simple way via the free radical mechanism.
Polymerizations of PMDD and PMDN in bulk and in
hexafluorobenzene were carried out using perfluoroben-
zoyl peroxide as an initiator. The two monomers also
allows the preparation of new fluoro- and perfluoro(co)-
polymers.
Photopolymerizations of the two monomers in bulk
and in hexafluorobenzene were also carried out in the
presence of carbon tetrabromide or carbon tetrachloride
under irradiation by UV light at about 365 nm. Photo-
polymerzation afforded polymers with a range of intrin-
sic viscosity from 3.6 to 13.3 mL/g. There are also
available interesting fluorotelogens, -telomers, and/or
1144.
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-
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-
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(
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(
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Acknowledgment. This work was supported in part
by the Japan Science and Technology Corporation
through the Grant for ERATO-Photonic Polymer.
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Note Added after ASAP Publication. This article
was released ASAP on October 10, 2005. Table 1, Table
MA050753B