Synthesis of poly[1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)propan-2-yl methacrylate]: Thermal and optical properties of the copolymers with methyl methacrylate

Article abstract of DOI:10.1016/j.jfluchem.2007.11.011

Poly[1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)propan-2-yl methacrylate (I)] was synthesized, and the copolymers of the monomer I with various compositions of methyl methacrylate (MMA) were prepared and characterized. The glass transition temperature va

Full text of DOI:10.1016/j.jfluchem.2007.11.011

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Journal of Fluorine Chemistry 129 (2008) 248–252
www.elsevier.com/locate/fluor
Synthesis of poly[1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)propan-2-yl
methacrylate]: Thermal and optical properties of the copolymers with
methyl methacrylate
Dingying Zhou a, Yasuhiro Koike b, Yoshiyuki Okamoto a,
*
a Polymer Research Institute, Polytechnic University, 6 Metrotech Center, Brooklyn, NY 11201, USA
b Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan
Received 30 September 2007; received in revised form 14 November 2007; accepted 20 November 2007
Available online 11 January 2008
Abstract
Poly[1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)propan-2-yl methacrylate (I)] was synthesized, and the copolymers of the monomer I with
various compositions of methyl methacrylate (MMA) were prepared and characterized. The glass transition temperature values obtained for the
copolymers were between 120 and 150 8C. The refractive indices of the copolymers were in the range of 1.4350–1.4872 at 532 nm. They were
thermally stable (up to 297–323 8C), and their water absorptive properties were greatly decreased, compared with pure PMMA.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Co polymerization; Fluorinated methacrylate; Water absorption; Thermal property; Optical property; Dipole–dipole interaction
1. Introduction
ophenyl (IIb), and p-trifluoromethyl perfluorophenyl (IIc)
methacrylates (Fig. 1) were found to be 133, 125, and 135 8C,
respectively. Although these fluorine-substituted phenyl metha-
crylates yield excellent random copolymers with various
compositions of MMA, the Tg-values of the copolymers
produced were in the range of 90–120 8C [6]. Generally, the
Tg-values of alkyl and aryl methacrylates are higher than those of
acrylates [7–10]. The Tg of poly(1,1,1,3,3,3-hexafluoro-2-
(pentafluorophenyl)propan-2-yl acrylate was reported as
118 8C [11]. Accordingly the homopolymer’s Tg of the
methacrylate, having a 1,1,1,3,3,3-hexafluoro-2-(pentafluoro-
phenyl)propan-2-yl group, would be expected to be higher than
118 8C. Therefore, in search of a good candidate for POF
materials, we have synthesized methacrylate I (Fig. 1) and the Tg
of the homopolymer was found to be 146 8C. Consequently, the
thermal and optical properties of the homopolymer of I as well as
the copolymers with various amount of MMA (Scheme 1) have
been investigated.
Poly(methyl methacrylate) (PMMA),
a commercially
available polymer, is produced in large quantities, demonstrates
high light transmittance and provides excellent resistance to
both chemical and weather corrosion [1]. These properties,
coupled with low manufacturing cost and easy processing,
make PMMA a valuable substitute for glass in optical device
applications [2]. However, the major disadvantages of PMMA,
such as its relatively low glass transition temperature (Tg)
(around 100 8C) and high water absorption, limit its utility for
optical electronic applications [3,4]. Since introducing fluorine
atoms can dramatically improve the thermal and optical
properties and water absorption of the polymer, Boutevin’s
group and our group have independently prepared fluorine-
substituted phenyl methacrylates (II) and their polymers [5,6].
Because the refractive indices of MMA and the fluorine-
substituted monomers are in a similar range, copolymers of
these monomers may not have an increased light scattering [6].
The Tg-values of homopolymers of polyfluorinated phenyl
methacrylates (II), such as pentafluorophenyl (IIa), tetrafluor-
2. Results and discussion
Using azobis(isobutyronitrile) (AIBN) as an initiator,
homopolymerization of monomer I and its copolymerization
with MMA were carried out in bulk. Without a chain transfer
* Corresponding author. Tel.: +1 718 260 3638; fax: +1 718 260 3508.
E-mail address: yokamoto@poly.edu (Y. Okamoto).
0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2007.11.011

D. Zhou et al. / Journal of Fluorine Chemistry 129 (2008) 248–252
249
Fig. 1. Structures of fluorinated methacrylates.
Scheme 1. Copolymerization of I with methyl methacrylate.
Table 1
The effect of the chain transfer reagent (n-BuSH) on the Mn and Mw of the
copolymers of I with MMA
Entry
Content of I
in feed (mol%)
n-BuSH
Mn
(ꢀ104)
Mw
(ꢀ104)
(mol%)
1
2
3
4
50
50
80
80
1.0
2.0
1.0
1.9
3.5
1.4
2.6
1.7
10.1
3.2
5.3
4.2
Fig. 2. Composition dependence of glass transition temperature (Tg) of I/MMA
copolymers.
Tg-values of the copolymers were plotted versus the monomer
compositions (Fig. 2), they were found to approximately fit
with the Gordon–Taylor equation
reagent, polymers obtained had too high a molecular weight
and were not soluble in common organic solvents such as
chloroform and THF. Therefore, n-BuSH was used to adjust
the molecular weight of the polymers. As shown in Table 1, the
chain transfer reagent, n-BuSH, effectively controls the
molecular weights of the copolymers of I and MMA. Hence
the high conversion (80–90%) copolymerization reactions of I
and MMA were carried out with 1.0 mol% of n-BuSH at
60–80 8C. These results are summarized in Table 2. The
polymers isolated, referred to as P1–P6, have only one Tg. When
w1Tg1 þ kw2Tg2
Tg ¼
(1)
w1 þ kw2
where w1 and w2 are weight fractions of the two monomeric
units in the copolymer, Tg1 and Tg2 are Tg-values of related
homopolymers, and k is generally considered a real fitting
parameter. Depending on the actual value of k the Tg versus
composition curves deviate from linearity defined by k = 1. For
fitting the data it is convenient to linearize equation (1) as
Table 2
Results of copolymerization reaction of I with MMA
Entrya,b
Content of I in
Polymer
Conv. (%)
Mn (ꢀ104)
Mw (ꢀ104)
Tg (8C)
Feed (wt%)
Polymer (wt%)
1
2
3
4
5
6
17.6
31.3
49.4
78.6
93.1
100
18.3
31.9
50.3
78.0
92.6
100
P1
P2
P3
P4
P5
P6
90
88
90
83
82
80
2.3
2.6
3.3
3.5
2.3
2.4
3.5
4.0
121
123
124
132
140
146
7.8
10.1
4.4
4.6
a
n-BuSH (1% mol) was used as a chain transfer reagent.
b
The reaction was proceeded at 60 8C for 48 h and then heated at 80 8C for 12 h.

250
D. Zhou et al. / Journal of Fluorine Chemistry 129 (2008) 248–252
Table 4
follows
The refractive indices and on-set decomposition temperatures of the copoly-
mers
kðTg2 ꢁ TgÞW2
a,b
Td (8C)
Tg ꢁ Tg1
¼
(2)
Polymer
nl (nm)
W1
532
633
839
A plot of Tg ꢁ Tg1 versus (Tg2 ꢁ Tg)W2/W1 yields k via
linear regression [12,13]. In this case, when we set Tg1 and Tg2
as Tg-values of homopolymers of MMA and monomer I,
respectively, the result was k = 0.27.
P1
P2
P3
P4
P5
P6
297
315
317
319
323
323
1.4827
1.4749
1.4689
1.4483
1.4381
1.4350
1.4788
1.4701
1.4642
1.4440
1.4328
1.4298
1.4743
1.4655
1.4598
1.4393
1.4276
1.4253
In the cases of the copolymerizations of IIa and IIb with
MMA, the Tg-values were found to deviate positively from the
Gordon–Taylor equation (k = 1). Since the fluorine substituted
phenyl group is strongly electron-withdrawing, the ester group
in II is highly polarized. Thus, there is a strong dipole–dipole
interaction between the carbonyl group of MMA unit and the
fluorine substituted phenyl ester group of II unit, resulting in an
enhanced Tg and the positive deviation [6,14].
a
Under N2 atmosphere.
b
The Td of PMMA is 300 8C.
I also has a highly fluorinated ester group. However, the two
trifluoromethyl groups on the methylene are much bulkier than
those of IIa and IIb. This bulkier ester group inhibits the
interaction between MMA and I unit, causing Tg to fit with the
Gordon–Taylor equation (k = 1).
In order to calculate reactivity ratios of the monomers, the
copolymerization reactions of I with various amounts of MMA
were stopped at 16.8–34.7% monomer conversion. The
reactivity ratios were found to be r1 = 0.53 ꢂ 0.01 and
r2 = 0.95 ꢂ 0.04 for I and MMA, respectively. These data
are summarized in Table 3.
The reactivity of I was lower than that of MMA. This may be
due to the steric hindrance and the electro-withdrawing
property of the 1,1,1,3,3,3-hexafluoro-2-(pentafluorophenyl)-
propan-2-yl group. The reactivity ratios indicate that both of the
monomers have good copolymerization properties and yield
random copolymers.
Fig. 3. The influence of the weight percent of the fluorinated monomer I on the
refractive indices of the polymers.
The water absorption of the copolymer was greatly
decreased as compared to PMMA. An example of typical data
was shown in Fig. 5.
The refractive indices of the copolymers of I with MMA
were measured at 532, 633 and 839 nm. The data are cited in
Table 4. Compared to the refractive index of pure PMMA,
which is 1.4953, the refractive index of the homopolymer (P6)
of I is lower: 1.4350, both at 532 nm. The refractive indices of
the copolymers exhibited a linear relationship with those of the
monomer compositions as shown in Fig. 3.
Generally, flexibility is a very important character of plastic
optical fiber (POF) materials. It was found that when the
All the copolymers obtained exhibited good thermal
stability. The on-set decomposition temperatures of the
copolymers are summarized in Table 4, and the TGA curves
are shown in Fig. 4.
Table 3
Low conversion copolymerization reactions of I and MMA
Entrya Content of I in
Feed (wt%) Polymer (wt%)
Time (h) Conv. (%) Tg (8C)
1
2
3
4
5
17.6
31.3
49.4
78.6
93.1
23.2
35.4
55.9
79.4
90.4
1.0
3.0
4.0
5.6
16.8
32.9
34.7
21.5
31.4
129
129
128
131
141
18
Fig. 4. The TGA curves of the polymers: (a) for P5; (b) for P3; (c) for
homopolymer P6.
a
All the reactions were carried at 60 8C.

D. Zhou et al. / Journal of Fluorine Chemistry 129 (2008) 248–252
251
combined, washed with water and brine, and then dried over
MgSO4. Fractional distillation gave 110 g of colorless oil, bp
158–160 8C, yield 88%. 1H NMR (CDCl3): 4.08 (s, br., 1H); 19
F
NMR (CDCl3): 76.45 (m, 6F), 133.05 (s, br., 1F), 137.91 (w, br.,
1F), 149.18 (m, 1F), 160.27 (m, 2F); MS (EI, 70 eV): m/z
(%) = 334 (4.10) [M]+, 265 (11.08), 195 (100), 167 (18.98), 117
(14.18), 69 (16.81).
3.2.2. Preparation of the monomer I
An ether (15 mL) solution of methacryloyl chloride (5.22 g,
50 mmol) was added dropwise into a mixture of 1,1,1,3,3,3-
hexafluoro-2-(pentafluorophenyl)propan-2-ol
(16.7 g,
50 mmol), triethyl amine (5.5 g, 54 mmol) and ether (45 mL)
at 0 8C, under N2 atmosphere. The resulting mixture was stirred
at 0–25 8C for 6 h. Then the reaction was stopped. A white
precipitate was filtered and washed with a small amount of
ether. The combined ether solution was washed with 5%
hydrochloric acid, 3% sodium bicarbonate, water, brine, and
then dried over MgSO4. After removing the ether with a rotary
evaporator, the residue was distilled under vacuum to give a
colorless oil at 79 8C/2 mmHg, yield 80%. IR (KBr): n 1772
Fig. 5. The water absorptions of PMMA (&) and copolymer P2 (*) at 60 8C,
under 90% relative humidity (film, 30 mm ꢀ 20 mm ꢀ 2 mm).
amount of I increased to above 40 wt% the copolymers became
a little brittle, while at below 40 wt% the films were flexible.
This property combined with all the other properties mentioned
above, indicate that copolymers with the percentages of
monomer I lower than 40 wt% may be good candidates for POF
materials.
1
(C O); H NMR (CDCl3): 2.02 (s, 3H), 5.85 (s, 1H), 6.32 (s,
1H); 19F NMR (CDCl3): 76.05 (t, J = 14.1 Hz, 6F), 133.28 (s,
br., 1F), 140.34 (s, br., 1F), 148.84 (tt, J = 20.6 Hz, J = 5.1 Hz,
1F), 160.02 (m, 2F); 13C NMR (CDCl3): 18.3, 81.1, 103.5,
121.0, 133.2, 134.1, 138.4, 142.8, 145.8, 163.2; CIMS (M, %):
403 (M + 1, 100), 333 (25).
3. Experimental
3.1. General
3.3. Polymerization
MMA, methacryloyl chloride, triethylamine, diethyl ether,
chloroform and AIBN were purchased from Aldrich. Chlor-
opentafluorobenzene, hexafluoroacetone were bought from
SynQuest Co. Diethyl ether was distilled from sodium wire
containing benzophenone, and the free radical initiator AIBN
was purified by recrystallization from methanol. Monomers
were purified with the traditional method. All the other
AIBN was employed as an initiator. n-BuSH was used as a
chain transfer reagent. Polymerization reactions were carried
out in bulk.
3.3.1. Low conversion copolymerization reactions
The monomer mixtures, including known amounts of
comonomers, and initiator (1.0 mol%), were transferred into
a glass polymerization tube. The tube was subjected to repeated
freeze–pump–thaw cycles and sealed under vacuum. The
polymerization reactions were proceeded at 60 8C. After the
reaction mixture was in proper viscosity, the glass tube was
opened and the contents were poured into a large amount of
methanol with vigorous stirring to precipitate the polymer.
After drying under vacuum at 50 8C for 24 h, polymer samples
were reprecipitated from the chloroform solution into
methanol. The purified polymer samples were dried under
vacuum at 50 8C for 48 h.
1
chemicals were used directly without further purification. H
NMR, 13C NMR and 19F NMR spectra were determined on a
Brucker AC 300 spectrometer, at 300.1, 75.5 and 282.4 MHz,
respectively, using CDCl3 as a solvent. Chemical shifts are
reported in d (ppm) from internal TMS (1H and 13C) or from
internal CFCl3 (19F).
3.2. Synthesis of monomer
3.2.1. Preparation of 1,1,1,3,3,3-hexafluoro-2-
(pentafluorophenyl)propan-2-ol
To a 1 L three-necked flask, chloropentafluorobenzene
(75 g, 0.37 mol) and diethyl ether (300 mL) were added under
N2 stream. The system was cooled to ꢁ78 8C, and n-BuLi
(150 mL, 2.5 M, 0.375 mol) was added dropwise during 1 h.
The reaction was subsequently stirred for 2 h. An excess of
hexafluoroacetone (72 g, 0.43 mol) was added over 70 min.
The resulting mixture was stirred for another 3 h, warmed up to
room temperature, and poured into a 2 L beaker which
contained 20 mL of H2SO4 and ice. The water phase was
extracted with ether (3ꢀ 100 mL). The organic layers were
3.3.2. High conversion copolymerization
The monomer mixtures, including known amounts of
comonomers, chain transfer reagent (1.0 mol%) and initiator
(1.0 mol%), were transferred into a glass polymerization tube.
The tube was subjected to repeated freeze–pump–thaw cycles
and sealed under vacuum. Then the polymerization reactions
were proceeded at 60 8C for 48 h, and then at 80 8C for 12 h.
The glass tube was opened and the contents were dissolved in
small amount of chloroform. The chloroform solution were

252
D. Zhou et al. / Journal of Fluorine Chemistry 129 (2008) 248–252
poured into a large amount of methanol with vigorous stirring
to precipitate the polymer. After drying under vacuum at 50 8C
for 24 h, polymer samples were reprecipitated from the
chloroform solution into methanol. The purified polymer
samples were dried under vacuum at 50 8C for 48 h.
the range of 120–125 8C. The refractive indices of these
copolymers ranged from 1.4827 to 1.4689 at 532 nm. These
copolymers were thermally stable (up to 297–323 8C), flexible,
and displayed much less water absorption than PMMA. Thus,
we suggest these copolymers may have various applications in
the field of optical and electric devices.
3.4. Measurements
Acknowledgement
Molecular weights were determined by gel permeation
chromatography (GPC) (Waters 510) using chloroform as the
eluent at a flow rate of 1.0 ml/min. The molecular weight
calibration curve was obtained using polystyrene standards.
The glass transition temperature (Tg) of polymers was
measured using a DSC 2920 module with the TA Instrument
5100 system, with a scan rate of 10 8C/min. The Tg was taken in
the second heating scan as the midpoint of the heat capacity
transition between the upper and lower points of deviation from
the extrapolated liquid and glass lines. The polymer films (0.1–
0.2 mm thick), fabricated by casting the polymers solutions on
glass plates, were used to measure the refractive index on a
prism coupler (Metricon, model 2010). The measurement
accuracy was ꢂ0.0005. The probe wavelengths in the prism
were 532, 633 and 839 nm. A humidity oven having circulating
air and maintaining 90 ꢂ 3% humidity at 60 ꢂ 2 8C was used
to measure water absorption, and the sample sizes were
30 mm ꢀ 20 mm ꢀ 2 mm films.
This work was supported in part by the Japan Science and
Technology Corporation through a Grant from ERATO-Sorst
Photonic Polymer.
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