Investigation of homopolymerization rate of perfluoro-4,5-substituted-2- methylene-1,3-dioxolane derivatives and properties of the polymers

Article abstract of DOI:10.1016/j.jfluchem.2005.12.004

Five perfluoro-4,5-substituted-2-methylene-1,3-dioxolane monomers were synthesized. These monomers were found to readily polymerized by a free radical initiator in bulk and/or in solutions. Homopolymerization rates were determined using in situ ¹⁹F NMR measurements and found to be 0.25 to 1.66 × 10^-4 mol L^-1 s^-1 in 1,1,2-trichlorotrifluoroethane at 41°C using the perfluorodibenzoyl peroxide as an initiator. The rates depend on the substituents on the 4 and 5 positions of the dioxolane. The purified polymers were thermally stable (up to 350°C). They show low refractive indexes (1.33-1.36 at 532 nm). They are transparent from UV to near IR region and have high glass transition temperatures (100-170°C).

Full text of DOI:10.1016/j.jfluchem.2005.12.004

Journal of Fluorine Chemistry 127 (2006) 277–281
www.elsevier.com/locate/fluor
Investigation of homopolymerization rate of perfluoro-4,5-substituted-2-
methylene-1,3-dioxolane derivatives and properties of the polymers
a
Yu Yang , Frantisek Mikes , Liang Yang , Weihong Liu ,
a
a
ˇ
ˇ a
Yasuhiro Koike b, Yoshiyuki Okamoto a,
*
a Polymer Research Institute, Polytechnic University, 6 Metrotech Center, Brooklyn, New York 11201, USA
b Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan
Received 26 October 2005; received in revised form 8 December 2005; accepted 12 December 2005
Abstract
Five perfluoro-4,5-substituted-2-methylene-1,3-dioxolane monomers were synthesized. These monomers were found to readily polymerized by a
free radical initiator in bulk and/or in solutions. Homopolymerization rates were determinedusingin situ19F NMR measurementsandfoundto be 0.25
to 1.66 Â 10À4 mol LÀ1 sÀ1 in 1,1,2-trichlorotrifluoroethane at 41 8C using the perfluorodibenzoyl peroxide as an initiator. The rates depend on the
substituents on the 4 and 5 positions of the dioxolane. The purified polymers were thermally stable (up to 350 8C). They show low refractive indexes
(1.33–1.36 at 532 nm). They are transparent from UV to near IR region and have high glass transition temperatures (100–170 8C).
# 2006 Elsevier B.V. All rights reserved.
Keywords: Perfluoro-4,5-substituted-2-methylene-1,3-dioxolane; 19F NMR spectra; Polymerization rate; Polymer properties
1. Introduction
peroxide (FBPO) was prepared according to published
procedure [3]. After recrystallization from petroleum ether
(bp 40–60 8C), the pure initiator has melting point of 76–78 8C
and the half-life is 10 h at 68 8C [4].
Amorphous perfluorinated polymers have many potential
applications as opto-electronic materials due to their low
refractive index as well as chemical and thermal stability [1,2].
We have synthesized various perfluoro-4,5-substituted-2-
methylene-1,3-dioxolane compounds. These monomers are
soluble in fluorinated solvents and readily polymerized in bulk
and in solution by a free radical initiator. The polymerization
process involves vinyl additional mechanism. In order to
investigate the effect of the 4,5-substitutions on the perfluoro-
1,3-doxolane, we have determined the homopolymerization
rate of these dioxolane monomers in fluorinated solvents using
in situ 19F NMR spectroscopy.
2.2. Instrumentation
2.2.1. 1H, 19F and 13C NMR spectra
1H, 19F and 13C NMR spectra were taken using a Bruker
ACF 300 spectrometer (300 MHz for 1H, 75 MHz for 13C
measurement). 19F NMR spectra were observed at frequency of
282 MHz with fluorotrichloromethane as a standard. Unless
otherwise stated, CDCl3 or DMSO-d6 was used for field lock.
2.2.2. FTIR spectra
FTIR spectra were obtained with a Perkin-Elmer FTIR-1600
spectrometer
2. Experimental
2.1. Materials
2.2.3. GC–MS analyses
All chemicals were purchased from Aldrich Chemical Co.
and used without further purification. Perfluorodibenzoyl
GC–MS analyses were performed using an HP 5890 gas
chromatography and an HP 590 B mass spectrograph. A J&W
GC capillary column (30 m  1.4 mm film) with stationary
phase DB-624 and helium as the carrier gas was used for
analysis.
* Corresponding author. Tel.: +1 718 260 3638.
E-mail addresses: yangyu_doc@yahoo.com (Y. Yang),
yokamoto@poly.edu (Y. Okamoto).
0022-1139/$ – see front matter # 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2005.12.004

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Y. Yang et al. / Journal of Fluorine Chemistry 127 (2006) 277–281
2.2.4. Differential scanning calorimetry (DSC)
2.3.1.3. Preparation of ketal. The ketalization reaction was
performed between 1,4-anhydroerythritol and 2-oxopropyl
acetate. 1,4-Anhydroerythritol (448 g, 4.3 mol), 2-oxopropyl
acetate (500 g, 4.3 mol), p-toluene sulphonic acid (30 g) and
1 L of benzene were placed into a 2 L flask equipped with a
Dean-Stark trap. The mixture was refluxed until 78 mL of water
was distilled out. The product was neutralized using 30 g of
sodium carbonate, and then washed with 1 L of water.
Distillation gave 624 g (3.09 mol) of pure product in 71%
yield (bp 130 8C/8 Torr). 1H NMR (in CDCl3) d (ppm): 4.8 (s, –
CH2OCO–, 2H), 4.16, 4.05, 4.01 (s, –CH2–, 4H), 3.5–3.3 (m, –
CH–, 2H), 2.11 (s, –OCCH3, 3H), 1.34, 1.48 (s, –CCH3, 3H).
Anal. calcd. for C9H14O5: C, 53.47; H, 6.93. Found: C, 53.60;
H, 6.82.
A DSC 2920 module with TA Instrument 5100 system was
used for the glass transition temperature (Tg) measurements,
and the samples (7–15 mg) were used for the measurement. The
Tg at heating rate of 10 8C/min was determined as an
endothermic shift in the second heating scan.
2.2.5. Refractive index measurements
The polymer films (0.1–0.2 mm thick) fabricated by casting
their hexafluorobenzene (C6F6) solutions on glass plates were
used to measure the refractive index. A prism coupler
(Metricon, modul 2010) was utilized. The measurement
accuracy was Æ0.0005. The probe wavelengths in the prism
were 532, 632, 839 and 1544 nm.
2.3. Synthesis of perfluoro-4,5-substituted-2-methylene-
1,3-dioxolanes (the chemical structures are shown in
Fig. 1)
2.3.1.4. Fluorination of ketal. The ketal (1000 g, 4.95 mol)
was directly fluorinated in fluorinated solvent using F2/N2 [6,7].
The reaction mixture was then neutralized with cold aqueous
KOH solution, and organic and water phases were separated.
The water in aqueous phase was distilled out under reduced
pressure. A 1295 g (3.46 mol) of potassium salt was obtained in
70% yield after drying at 80 8C under vacuum. 1H NMR (in d6-
DMSO): none; 19F NMR (in d6-DMSO) d (ppm): À82, À80.05
(3F, CF3), À78.57, À79.92, À81.58, À91.32 (4F, –OCF2–),
À129.58, 130.79 (m, 2F, –CFO–).
2.3.1. Preparation of perfluoro-2-methylene-furo [3,4-
d][1,3] dioxolane (A) and its polymer
Monomer A was prepared via the decarboxylation of the
potassium salt, which was synthesized by the route described in
Scheme 1.
2.3.1.1. Preparation of 1,4-anhydroerythritol. cis-1,4-Anhy-
droerythritol was prepared according to the published
procedure [5]. bp 105–107 8C/0.2–0.5 Torr. 1H NMR (in
CDCl3) d (ppm): 4.2 (m, –CH–, 2H), 3.6–4.0 (m, –CH2–,
4H), 3.8 (s, –OH, 2H).
2.3.1.5. Decarboxylation of the potassium salt. The potas-
sium salt (100 g, 0.267 mol) was decomposed at 250 8C under
an argon stream. The product was collected in a trap cooled at
À78 8C. Fractional distillation gave 36.3 g (0.134 mol) of pure
1
monomer (bp 74 8C/760 Torr) in 50% of yield. H NMR (in
CDCl3): none; 19F NMR (in CDCl3) d (ppm): À79.66(dm),
2.3.1.2. Preparation of CH3COCH2OOCCH3. Acetyl chlor-
ide (721 g, 9 mol) was added dropwise at 0 8C to a flask charged
with pyridine (719 g, 9 mol), hydroxyacetone (90% of purity,
741 g, 9 mol) and 2 L of ether. After addition, the reaction
mixture was stirred for 2 h at room temperature. The pyridine
salt was removed by filtration. After the ether was evaporated,
the remained oil was distilled under reduced pressure. Pure
product (971 g) was obtained (bp 80–95 8C/40 Torr) in 93% of
yield. 1H NMR (in CDCl3) d (ppm): 4.65 (s, –CH2–, 2H), 2.15
(s, two –CH3, 6H). Anal. calcd. for C5H8O3: C, 51.72, H, 6.90.
Found: C, 51.50, H, 6.96.
5
CF2, JF–
À90.72 (dm, 4F, –OCF2–), À126 (t, 2F,
3
F = 3.09 Hz), À136.20 (dm, 2F, –CFO–, JF–F = 17.53 Hz);
1
13C NMR (in CDCl3) d (ppm): 118.2 (dddd, –OCF2–, JC–
1
F = 273.11 Hz, JC–F = 239.38 Hz, JC–F = 37.59 Hz, JC–
2
3
2
F = 4.97 Hz), 137.99 (t, C, JC–F = 45.33 Hz), 142.8 (tt,
4
CF2, JC–F = 2.21 Hz, JC–F = 273.11 Hz), 109.50 (dm, –
1
CFO–, JC–F = 274.77 Hz). GC–MS: m/e 272 (M+).
1
2.3.1.6. Free radical polymerization of monomer A in
bulk. A glass tube charged with 2 g of monomer A and
8.8 mg of perfluorodibenzoyl peroxide was sealed after three
freeze-pump-thaw cycles. After polymerization at 60 8C for 1
day, a solid polymer bar was obtained. The polymer was
dissolved in C6F6, and then precipitated into chloroform. The
collected polymer was dried to constant weight (1.8 g) and the
yield was 90%. The intrinsic viscosity of the polymer in C6F6 at
25 8C was 25 mL/g. FTIR: no carbonyl group absorption. 19F
NMR (dissolved in C6F6 and using an insert filled with CDCl3
for field lock) d (ppm): À132 (2F, –CF–), À110 (2F, –CF2– in
the main chain), À80, À95 (4F, –CF2– in the ring). DSC: Tg was
168 8C. TGA: initial decomposition temperature was 355 8C
under nitrogen atmosphere. Refractive indexes were: 1.3572,
1.3548, 1.3515 and 1.3502 at 532, 633, 839 and 1544 nm,
respectively.
Scheme 1. Synthetic route of monomer A.

Y. Yang et al. / Journal of Fluorine Chemistry 127 (2006) 277–281
279
2.3.3.3. Decarboxylation of the potassium salt. The potas-
sium salt (100 g, 0.243 mol) was decomposed at 250 8C under
an argon stream. The product was collected in a trap cooled at
À78 8C. Fraction distillation gave 61 g (0.194 mol) of pure
monomer (bp 67 8C/760 Torr) in 81% yield. 1H NMR (in
CDCl3): none; 19F NMR (in CDCl3) d (ppm): À55.56 (dt, 3F, –
OCF3), À82.54 and À87.40 (2F, –OCF2C), À85.28 (m, 2F, –
OCF2O–),À128.29 (s), À128.74 (s), 129.59 (m), 130.04 (m)
(2F, CF2 ), À130.66 (m, 1F, –OCF–). GC–MS: m/e 310 (M+).
2.3.3.4. Free radical polymerization of monomer C in
bulk. A glass tube charged with 4 g of monomer C and
20 mg of perfluorodibenzoyl peroxide was sealed after three
freeze-pump-thaw cycles. After polymerization at 60 8C for 1
day, a solid polymer bar was obtained. The polymer was
dissolved in C6F6, and then precipitated into chloroform. The
collected polymer was dried to constant weight (3.5 g) and the
yield was 88%. The intrinsic viscosity of the polymer in C6F6 at
25 8C was 28 mL/g. FTIR: no carbonyl group absorption. 19F
NMR (dissolved in C6F6 and using insert filled with CDCl3 for
field lock) d (ppm): À58.32 (3F, –OCF3), À79.40 (2F,
CF3OCF2–), À85.8 (2F, –CF2– in the ring), À109.05 (2F, –
CF2– in the main chain), À121.8 (1F, –CF– in the ring). DSC:
Tg was 101 8C. TGA: initial decomposition temperature was
366 8C under nitrogen atmosphere. Refractive indexes: 1.3328,
1.3301, 1.3264 and 1.3233 at 532, 632, 839 and 1544 nm,
respectively.
Scheme 2. Synthetic route of monomer C.
2.3.2. Preparation of perfluoro-2-methylene-4-methyl-1,3-
dioxolane (B) and its polymers
Monomer B and its polymers were prepared in our
laboratory that was previously reported [8].
2.3.3. Preparation of perfluoro-2-methylene-4-
methoxymethyl-1,3-dioxolane (C) and its polymer
Monomer C was prepared according to the following
synthetic route described in Scheme 2.
2.3.3.1. Preparation of ketal. The mixture of 3-methoxy-1,2-
propane-diol (2 mol, 212 g), methyl pyruvate (2 mol, 204 g)
ion-exchange resin (H form, DOWEX1) (10 g) and benzene
(1 L) was charged into a flask equipped with a Dean-Stark trap
and refluxed until the evolution of water ceased (around 38 mL
water). Fractional distillation gave 209 g of pure methyl 4-
2.3.4. Perfluoro-2-methylene-4,5-dimethyl-1,3-dioxolane
(D) and perfluoro-3-methylene-2,4-dioxabicyclo [4,3,0]
nonan (E)
methoxymethyl-2-methyl-1,3-dioxane-2-carboxylate
(bp
1
80 8C/1 Torr) in 55% yield. H NMR (in CDCl3) d (ppm):
1.60 (d, 3H, –CH2OCH3), 4.2–4.5 (m, 1H, –OCH–), 4.12–4.25
and 3.8–3.9 (m, 2H, –OCH2– in the ring), 3.76 (d, 3H, –
COOCH3), 3.41–3.6 (m, 2H, –OCH2– in the side chain), 3.39
(d, 3H, CCH3). Anal. calcd. for C8H14O5: C, 50.53, H, 7.37.
Found: C, 51.10, H, 7.44.
Monomer D and monomer E were prepared in our laboratory
and previously reported [9]. The ratio of the cis and trans of the
fluorine atoms on the 4 and 5 positions of monomer D was
found to be 2.9:1.
3. Results and discussion
2.3.3.2. Fluorination of ketal. Methyl 4-methoxymethyl-2-
methyl-1,3-dioxane-2-carboxylate (650 g, 3.42 mol) was also
fluorinated in fluorinated solvent using F2/N2. The reaction
mixture was neutralized with cold aqueous KOH solution.
Potassium salt (780 g, 2.56 mol) was obtained in 75% yield. 1H
NMR (in d6-DMSO): none; 19F NMR (in d6-DMSO) d (ppm):
À55.11 (dt, 3F, –OCF3), À76.59 and À81.00 (2F, –OCF2C),
À82, À80.05 (3F, –CCF3), À85.35 (m, 2F, –OCF2O–),À120.67
(dm, 1F, –OCFC–).
The chemical structures and 19F NMR spectra of perfluoro-
4,5-substituted-2-methylene-1,3-dioxolanes investigated are
shown in Figs. 1 and 2.
These monomers are soluble in fluorinated solvents such as
1,2,2-trifluorotrichloroethane (FC-113) and a,a,a-trifluoroto-
luene, while the polymers produced are not soluble in these two
solvents. Though polymers were produced throughout the poly-
merizations, only resonances from monomers were observed in
Fig. 1. Chemical structures of perfluoro-4,5-substituted-2-methylene-1,3-dioxolane derivatives.

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Y. Yang et al. / Journal of Fluorine Chemistry 127 (2006) 277–281
Fig. 4. Monomer concentrations vs. the polymerization time for monomer A.
Initial monomer concentration: 1.8 mol LÀ1, solvent: FC-113, initiator: per-
fluorodibenzoylperoxide, polymerization temperature: 41 8C.
triplet at À73.62 ppm. For a,a,a-trifluorotoluene, a resonance
signal corresponding to –CF3 appears at À65.38 ppm. The
solution of a dioxolane monomer in FC-113 and perfluorodi-
benzoylperoxide as a free radical initiator were placed into a
NMR tube, which contains a sealed ampoule filled with d6-
DMSO as a field locker. After replacing air with argon in the
NMR tube, the tube was sealed and placed into a NMR apparatus
thermostated at 41 8C. The instantaneous monomer concentra-
tion was computed from the ratio of the integral of the peak
for CF2 to the resonance for CFCl2– of FC-113. For each
measurement, 50 scans were accumulated and the resulting data
point was assigned the time corresponding to the time from the
beginning to the polymerization to the end of the measurement.
The polymerization rate, Rp = d[M]/dt for monomers A–E was
measured by varying the concentrations of the monomer and
initiator. As seen from Fig. 4, the polymerization rates were
greatly enhanced with increasing the initiator concentration.
This is a typical trend of a free radical polymerization of
a vinyl monomer [10]. The conversion of monomers A–E
versus polymerization time using the same initiator concentra-
tion were measured and are shown in Fig. 5. The initial poly-
merization rates, Rp for these monomers were summarized in
Table 1.
Fig. 2. The 19F NMR spectra of FC-113 solutions of perfluoro-2-methylene-
4,5-substituted-1,3-dioxolane derivatives.
the 19F spectra, as shown in Fig. 3. Thus, it is possible to follow
the concentration of monomers during the polymerization. Two
fluorine atoms attached to the vinylidene group CF2 for the
dioxolane monomers were utilized to calculate the monomer
concentrationduringthepolymerization. 19F signals correspond-
ing to the CF2 group for the monomers A–E appear in the range
of À120 to À130 ppm and the signal for CFCl2 of FC-113 is a
Fig. 3. 19F NMR spectrum of monomer A at 60% conversion. Initial monomer
concentration: 1.8 mol LÀ1, solvent: FC-113, initiator: perfluorodibenzoylper-
oxide, polymerization temperature: 41 8C.
Fig. 5. Monomer conversion vs. the homopolymerization time in FC-113
initiated by perfluorodibenzoyl peroxide (0.05 mol LÀ1) at 41 8C. The initial
concentrations for all monomers were 1.8 mol LÀ1
.

Y. Yang et al. / Journal of Fluorine Chemistry 127 (2006) 277–281
281
Table 1
Polymerization rates, glass transition temperature and refractive index of monomers A–Ea
Monomer
A
B
C
D
E
Rate Rp (Â104 mol LÀ1 sÀ1
Tg (8C)
Refractive index at 632 nm
)
1.66
168
1.3572
1.56
135
1.3310
1.40
101
1.3328
0.15
165
1.3280
0.25
165
1.3280
a
[Monomer] = 1.8 mol LÀ1, [perfluorodibenzoyl peroxide (initiator)] = 0.05 mol LÀ1, at 41 8C, solvent FC-113.
good thermal stability and their initial decomposition
temperatures were higher than 350 8C under nitrogen atmo-
sphere. Their glass transition temperatures were in the region of
100–170 8C (Table 1). The polymers do not show any melting
endotherm under 350 8C in their DSC traces. This indicates that
these polymers are amorphous. These properties make
perfluoro-4,5-substituted-1,3-dioxolane polymers good candi-
dates as optical and electrical materials.
4. Conclusions
A NMR sampling device was designed and constructed to
follow the homopolymerizations rate of the perfluoro-2-
methylene-1,3-dioxolane derivatives. The NMR sample tube
has an insert filled with d6-DMSO for sample locking. FC-113
or a,a,a-trifluorotoluene solutions of monomers, instead of
pure monomers, were utilized to obtain high quality 19F NMR
spectra. Using this technique, the monomer concentration as a
function of polymerization time could be accurately deter-
mined. As a result, it was possible for us to relate
polymerization rate with monomer structure and initiator
Fig. 6. The dependence of ratio of trans- to cis-isomers on polymerization
conversion for the momomer D.
2-Methylene-1,3-dioxolane monomers with substituents on
the 4 position (B and C) were found to be more reactive than
those disubstituted monomers (D and E) except monomer A. A
decrease in the reactivity of disubstituted monomers may be
due to electron withdrawing property of the perfluoro alkyl
group substituents and also to the steric hindrance in the
polymerization process. However, we could not clarify which
factors are dominant. The high reactivity for the monomer A is
not clear at present, but may be reduce the steric hindrance by
the fused five member ring.
concentration.
Poly(perfluoro-4,5-substituted-2-methylene-
1,3-dioxolane)s obtained are chemically and thermally stable
and transparent from UV to near IR regions. Their glass
transition temperatures are 100–170 8C, and they are com-
pletely amorphous. Thus, these polymers may be useful
materials for opto-electronic devices.
For monomer D, there are cis- and trans-isomers. The ratio
of cis- to trans-isomers with the polymerization progress was
followed by measuring 19F NMR on the vinyl and ring
substituted F atoms, and found to be constant. Thus, the
reactivity of the cis- and trans-isomers was same, as shown in
Fig. 6.
References
[1] M.H. Hung, P.R. Resnick, B.E. Smart, W.H. Buck, in: J.C. Salamone (Ed.),
Polymeric Materials Encyclopedia, CRC Press, 1996, pp. 2466–2476.
[2] B.E. Smart, A.E. Feiring, C.G. Krespan, Z.Y. Yang, M.H. Hung, P.R.
Resnick, W.R. Dolbier Jr., X.X. Rong, Macromol. Symp. 98 (1995) 753–
767.
When these monomers were polymerized in bulk at 60–
80 8C for 24–35 h, the conversions were more than 90%. The
polymer rods obtained were colorless and transparent.
However, when the rods were exposed to air they became
hazy. Thus, these polymers were purified by precipitation of
their C6F6 solutions in chloroform. The purified polymers show
no carbonyl groups in IR spectra indicating that the possible
ring-opening structures formed in bulk polymerization were
removed after purification [8]. The films casted from the C6F6
solution of purified polymer were clear and transparent from
UV to near IR region even when they were kept in air at room
temperature for a long period of time (over 6 months). The
polymers have low refractive indexes (Table 1) and also have
[3] J. Burdon, J.G. Campbell, J.C. Tatlow, J. Chem. Soc. (C) (1969) 822.
[4] L. Belf, M. Buxton, G. Fuller, J. Chem. Soc. (Lond.) (1965) 3372.
[5] N. Sugiyama. European Patent 0,950,672.
[6] T.R. Bierschenk, T. Juhlke, H. Kawa, R.J. Lagow, U.S. Patent 5,093,432
(1992).
[7] 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, Wiley,
New York, 1992 (Chapter 5).
ˇ
[8] F. Mikes, Y. Yang, I. Teraoka, T. Ishigure, Y. Koike, Y. Okamoto,
Macromolecules 38 (2005) 4237–4245.
[9] W. Liu, Y. Koike, Y. Okamoto, Macromolecules 38 (2005) 9446.
[10] G. Odian, Principles of Polymerization, third ed., John Wiley & Sons Inc.,
New York, 1991, p. 216.