A novel copolymer of methyl methacrylate with N-pentafluorophenyl maleimide: High glass transition temperature and highly transparent polymer

Article abstract of DOI:10.1016/j.polymer.2011.05.032

N-pentafluorophenyl maleimide (PFPMI) was synthesized. The homo and copolymers of PFPMI with methyl methacrylate (MMA) were prepared. The monomer reactivity ratio, r₁ (PFPMI) and r₂ (MMA) were 0.389 and 1.06 respectively. Q and e values for PFPMI were calculated as 1.00 and 1.30. The refractive indexes of poly(PFPMI) and PMMA were found to be similar; 1.4989 and 1.4953 at 532 nm, respectively. The copolymers exhibited no light scattering, and the film was very transparent. The glass transition temperatures of the PFPMI-co-MMA were in the range of 140 °C-180 °C with the PFPMI content from 18.8 to 65 mol% and the copolymers obtained have high thermal stability (～370 °C). The water absorption of PFPMI-co-MMA was greatly reduced as compared with that of pure PMMA.

Full text of DOI:10.1016/j.polymer.2011.05.032

Polymer 52 (2011) 3560e3564
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
A novel copolymer of methyl methacrylate with N-pentafluorophenyl maleimide:
High glass transition temperature and highly transparent polymer
Liping Lou , Yasuhiro Koike c, Yoshiyuki Okamoto a
a
b
,
,b,
*
a
Polymer Research Institute, Polytechnic Institute of NYU, 6 MetroTech Center, Brooklyn, NY 11201, USA
Koike Photonics Polymer Project ERATO-SORST, Japan Science and Technology Agency, Kawasaki 212-0032, Japan
Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 April 2011
Received in revised form
N-pentafluorophenyl maleimide (PFPMI) was synthesized. The homo and copolymers of PFPMI with
methyl methacrylate (MMA) were prepared. The monomer reactivity ratio, r (PFPMI) and r (MMA)
1 2
were 0.389 and 1.06 respectively. Q and e values for PFPMI were calculated as 1.00 and 1.30. The
refractive indexes of poly(PFPMI) and PMMA were found to be similar; 1.4989 and 1.4953 at 532 nm,
respectively. The copolymers exhibited no light scattering, and the film was very transparent. The glass
16 May 2011
Accepted 21 May 2011
Available online 27 May 2011
ꢀ
ꢀ
transition temperatures of the PFPMI-co-MMA were in the range of 140 Ce180 C with the PFPMI
ꢀ
content from 18.8 to 65 mol% and the copolymers obtained have high thermal stability (w370 C). The
Keywords:
N-pentafluorophenyl maleimide
Copolymers
water absorption of PFPMI-co-MMA was greatly reduced as compared with that of pure PMMA.
Ó 2011 Published by Elsevier Ltd.
Thermal and optical properties
1. Introduction
high transparency [9]. Among these fluorinated polymers, the
refractive index of poly(pentafluorophenyl methacrylate) (PPFPMA)
Poly(methyl methacrylate) (PMMA) is
a
mass-produced,
is similar to that of PMMA. In general, copolymers tend to have
extremely high scattering losses due to the large heterogenous
structure and the corresponding heterogencity of refractive index.
However, in the copolymer of PFPMA and MMA, both homopoly-
mers possess almost the same refractive indexes and the possibility
of light scattering is minimized [10,11]. Thus, we have recently
prepared various copolymers of MMA and PFPMA, the copolymer
obtained exhibited the following unique properties; the glass tran-
sition temperatures of the copolymers were slightly higher than
those of homopolymers of MMA and PFPMA. The water absorption
decreased as compared with PMMA. The transmittances of the
copolymers were slightly better than that of PMMA. Therefore, we
had successfully prepared a gradient index optical fiber using MMA
and PFPMA copolymer as the core material, which showed the
attenuation of 172e185 dB/km at the emission wavelengths of
a high-speed source (670e680 nm), which satisfies the required
attenuation for the optical home network systems [12].
commercially available polymer that demonstrates high light
transmittance and provides excellent resistance to both chemical
and weather corrosion [1,2]. These properties make MMA a valu-
able substitute for glass in optical device applications [3]. Despite
these advantages, PMMA is of limited use for optical electronics
because of its relatively low glass transition temperature (T
g
; ca.
ꢀ
1
00 C), and high water absorption [4,5]. To increase T
g
of PMMA,
investigators have explored its copolymerization with rigid or
bulky monomers, and with monomers that can form hydrogen
bonds through the carbonyl group of methyl methacrylate (MMA)
[
6,7]. Unfortunately, both types of modifications tend to reduce the
transparency or humidity resistance of the copolymers obtained.
In the visible and near-IR spectrum regions, the intrinsic light
losses of hydrocarbon are dominated by combinations of CeH
overtone stretching and deformation vibrations. When hydrogen
atoms of CeH bonds are replaced by fluorine atoms, there is
a decrease in the band vibration energy, and thus the absorption
band is minimized [8]. Bontevin et al. prepared several fluorine
substituted methacrylate monomers, and their polymers exhibited
Maleimide and its derivatives are well known to be polymerized
to give thermally stable polymers and the copolymerization with
various vinyl monomers has been examined to improve the
thermal properties of the polymers. N-alkyl and aryl maleimides
had been copolymerized with MMA and the resulted copolymers
showed high glass transition temperatures and thermal stability
*
Corresponding author. Polymer Research Institute, Polytechnic Institute of NYU,
MetroTech Center, Brooklyn, NY 11201, USA.
E-mail address: yokamoto@poly.edu (Y. Okamoto).
[13e19]. However, these copolymers exhibited some coloration.
6
0
Fluorine substituted phenyl maleimides were reported to be
032-3861/$ e see front matter Ó 2011 Published by Elsevier Ltd.
doi:10.1016/j.polymer.2011.05.032

L. Lou et al. / Polymer 52 (2011) 3560e3564
3561
*
*
temperature. The reaction mixture was refluxed for 72 h. After the
reaction completed,130 ml 1,4-dioxane was removed by distillation
and equal amount of xylene was added, and continuously refluxing
for 3 h, and then 2/3 of the solvent was removed by distillation. The
reaction mixture was cooled to room temperature, and the resulting
precipitate was collected by a filtration. The powder obtained was
dissolved in 250 ml acetic acid in a 500 ml three-necked flask, stir-
ring and nitrogen bubbling continued for 30 min, and then refluxed
n
O
O
o
N
AIBN, 60 C
O
O
N
Benzene
F5
F5
PFPMI
2
for 15 h under N . The resultant solutionwas poured into ice water to
isolate the product. Recrystallization using EtOH/Hexane (1:4) gave
ꢀ
white pure product, yield 45%. mp. 100e101 C [21].
1
H NMR (CDCl
3
, 300 MHz):
d
¼ 6.99 (s, 2H).
*
n
O
O
o
m
O
N
AIBN, 60 C
+
MMA
O
2.3. Homo and copolymerizations of PMI and PFPMI with MMA
O
O
N
1,4-dioxane
F5
The PFPMI monomer was reported to be unable to radically
homopolymerize in polar solvent, such as THF and 1,4-dioxane [21]
To prepare the poly(PFPMI), we chose benzene as the solvent [23].
F5
PFPMI
ꢀ
The homopolymerization was carried out at 60 C in benzene for
Scheme 1. Homo and copolymerization of PFPMI with MMA.
72 h using AIBN as the initiator. Copolymerization of PMI and PFPMI
with MMA were carried out in 1,4-dioxane solutions and also in
bulk with AIBN as the initiator. Monomer solutions and initiator
were transferred into a glass tube and subjected to three freeze-
pump-thaw cycles, which were followed by sealing under
vacuum. For the determination of the copolymerization parame-
ters, the polymerization reactions were stopped at low conversion
(under 20%). The copolymers were purified by repeated precipita-
tion from THF solution into a large amount of methanol. For the
homopolymerized and its homopolymers were thermally stable
[20,21]. We have synthesized N-pentafluorophenyl maleimide
(
PFPMI) and the homopolymer. The refractive index of poly(PFPMI)
was found to be almost the same as that of PMMA; these were
.4989 and 1.4953 for PFPMI and PMMA at 532 nm, respectively.
Thus these copolymers of PFPMI and MMA were expected to
exhibit no detective light scattering and high T , transparency and
1
g
ꢀ
thermal stability. In this paper, we report the preparation of the
homo and various copolymers of PFPMI with MMA (Scheme 1) and
the physical properties of these copolymers. We also have prepared
the copolymer of nonfluorinated N-phenylmaleimde (PMI) with
MMA, and the physical properties of the both copolymers are
compared.
bulk copolymerization, after polymerizing at 60e80 C for 24 h, the
polymer produced was purified by the precipitation from THF
solution to a large amount of methanol. The polymer collected was
ꢀ
dried under vacuum oven at 60 C for 48 h. The monomer
conversions were in the range of 85e90%.
2.4. Characterization
2
. Experimental
1H NMR and 19F NMR spectra were determined on a Brucker AC
00 spectrometer, at 300.1 and 282.4 MHz, respectively, using
2.1. Materials
3
CDCl
3
as a solvent. Chemical shifts are reported in d (ppm) from
1
13
19
MMA, styrene, maleic anhydride, AIBN, N-phenylmaleimide
PMI) and solvents were purchased from Aldrich. Pentafluoroani-
line was purchased from SynQuest Laboratories, Inc.
internal TMS ( H and C NMR) or from internal CFCl
3
( F). The IR
(
spectra were measured on a PerkineElmer 1600 series FTIR. The
refractive indexes of the polymer were measured using a Metricon
model 2010 prism coupler. The measurement accuracy was
ꢁ0.0005. The probe wavelengths in the prism were 532, 633, and
2
.2. Synthesis of N-pentafluorophenyl maleimide (PFPMI)
839 nm. Molecular weights were determined by gel permeation
The preparations of PFPMI were modified from the synthesis of
N-phenylmaleimide (PMI) [21,22].
chromatography (GPC) (Waters 510) using THF as the eluent at
a flow rate of 1.0 mL/min. The molecular calibration curves were
obtained using polystyrene standards. The glass transition
In a 500 ml three-necked flask provided with a stirrer, a reflux
condenser and a dropping funnel were placed 26.8 g (0.273 mol) of
maleic anhydride and 140 ml of 1,4-dioxane. The 1,4-dioxane solu-
tion (90 ml) of 2,3,4,5,6-pentafluoroaniline (50.0 g, 0.273 mol) was
added to the flask using a dropping funnel during 1 h at ambient
g
temperature (T ) of polymers was measured using a DSC 2920
module with the TA Instrument 5100 system, with a scan rate of
ꢀ
10 C/min. The T
g
was taken in the second heating scan as the
midpoint of the heat capacity transition between the upper and
Table 1
a
Copolymerization of PFPMI with MMA in 1,4-dioxane.
Mnc ꢂ104
PDIc
T
g
( C)
ꢀ
T
( C)
ꢀ
d
Refractive index
Sample
Mole fraction of PFPMI
Conv. (%)
Feed mol%
Copolymer mol%b
532 nm
633 nm
839 nm
PFPMI-co-MMA-1
PFPMI-co-MMA-2
PFPMI-co-MMA-3
PFPMI-co-MMA-4
20
40
60
80
18.8
37.0
45.0
64.5
15.5
16.9
14.0
17.3
4.11
4.00
2.99
1.91
1.95
1.87
1.90
1.96
142
145
158
180
365
367
370
372
1.4965
1.4975
1.4980
1.4980
1.4910
1.4915
1.4915
1.4915
1.4860
1.4860
1.4860
1.4865
a
ꢀ
All the copolymerizations were carried out in 1,4-dioxane, 60 C, using AIBN as initiator.
Calculated by 1H NMR.
Determined by GPC, THF as eluent.
b
c

3562
L. Lou et al. / Polymer 52 (2011) 3560e3564
190
180
170
160
150
140
130
120
110
100
0
20
40
60
80
Content of PFPMI in PFPMI-co-MMA (wt %)
g
Fig. 2. Composition dependence of T of PFPMI-co-MMA.
Fig. 1. 1H NMR spectra of PFPMI-co-MMA with 18.8 (A), 37.0 (B), 45.0 (C) and 64.5 mol
(D) of PFPMI.
%
PFPMI-co-MMA (Fig. 1). Resonance signals arise from the methoxy
and methyl groups in side chains and methylene protons in
lower points of deviation from the extrapolated liquid and glass
lines. The transmittance of polymer films was measured with
a UVevis spectrometer (Lambda 800, PerkineElmer, Inc.) at
copolymer main chain of MMA were observed at
d
¼ 3.43e3.87,
0.7e1.31, and 1.7e2.5, respectively. Meanwhile, the resonance
a scanning rate of 100 nm/min. The film thickness was 540 mm. The
signals around 2.6e3.1 ppm are due to methine group of PFPMI in
the copolymers. In addition, the signal of the methoxy group of
MMA firstly splits into two peaks and then shifts to downfield
when the content of PFPMI in copolymers increases from 18.8 to
water absorption of the copolymer was determined by measuring
the weight change of the specimen immersing in distilled water at
ꢀ
3
6
0 C. The specimens were 30 ꢂ 15 ꢂ 2 mm .
6
4.5 mol%, which may be due to the interaction between the
3
. Results and discussion
electron deficient pentafluorophenyl group of PFPMI and carbonyl
group of MMA in the solution [24].
3
.1. Copolymerizations of PMI and PFPMI with MMA in solution
Since PMI and PFPMI are limited solubility in MMA, the copo-
The monomer reactivity ratios were calculated using Fineman-
Ross method [25]. Value of r
and 1.06, respectively. The Q and e values for PFPMI were also
calculated using the AlfreyePrice equation [26]. The Q and e
values for MMA were taken from the literature [27]. The results
were found to be 1.00 (Q ) and 1.30 (e ), respectively. The Q and e
1 2
(PFPMI) and r (MMA) are 0.389
lymerization of PMI and PFPMI with MMA were carried out in
2
2
ꢀ
1,4-dioxane solution using AIBN as the free radical initiator at 60 C.
The mole fractions of the PFPMI monomer in feed were varied from
1
1
0
.2e0.8. The polymerizations were stopped at low conversion by
values of N-phenylmaleimide were reported to be 1.29 and 1.54,
respectively. The lower Q value for PFPMI as comparing with that of
PMI is due to the electron-withdrawing property of penta-
fluorophenyl group.
In order to compare the physical properties of the copolymers of
PFPMI with MMA and the copolymers of nonfluorinated PMI with
MMA, we investigated on the copolymers of PMI with MMA in the
same procedure as PFPMI-co-MMA. The copolymerizations were
also stopped at low conversion (under 20%). The typical results of
copolymerization are summarized in Table 2. It is found that the
number average molecular weights of PMI-co-MMA obtained are
higher and their polydispersities are broader than those of
pouring the reaction mixture into a large amount of methanol. The
polymers were precipitated and dried under vacuum at 60 C. The
films of the copolymers were obtained by casting the chloroform
solution on glass plates. The films were very clear and transparent.
The typical results of the copolymers obtained are summarized
in Table 1. Since the reactivity of PFPMI is lower than that of MMA
ꢀ
(
see later discussion), the number average molecular weights of the
copolymers decreased with increasing the amount of PFPMI added.
The mole fractions of comonomers in copolymers produced were
calculated by integrating the characteristic proton resonance
1
signals of PFPMI and MMA repeat units in H NMR spectra of
Table 2
a
Copolymerization of PMI with MMA in 1,4-dioxane.
c
4
PDIc
ꢀ
ꢀ
d
Sample
Mole Fraction of PMI
Conv. (%)
Mn ꢂ10
T
g
( C)
T
( C)
Refractive index
Feed mol%
Copolymer mol%b
532 nm
633 nm
839 nm
PMI-co-MMA-1
PMI-co-MMA-2
PMI-co-MMA-3
PMI-co-MMA-4
20
40
60
80
19.7
27.0
38.4
52.6
12.5
14.2
13.9
15.8
7.55
8.31
8.64
5.67
2.58
2.7
2.84
3.05
146
152
158
172
360
365
369
382
1.5165
1.5390
1.5520
1.5680
1.5105
1.5320
1.5440
1.5600
1.5045
1.5250
1.5365
1.5510
a
ꢀ
All the copolymerizations were carried out in 1,4-dioxane, 60 C, using AIBN as initiator.
Calculated by 1H NMR.
Determined by GPC, THF as eluent.
b
c

L. Lou et al. / Polymer 52 (2011) 3560e3564
3563
3
5
6
8
32 nm
33 nm
39 nm
1
1
1
1
1
1
1
.58
.56
.54
.52
.50
.48
.46
PMI-co-MMA
PMMA
2
PFPMI-co-MMA
PFPMI-co-PMMA
1
0
1
0
15
20
25
30
35
40
45
50
55
60
65
70
0
20
40
60
80
100
120
140
160
180
200
Content of PMI and PFPMI (mol%) in the copolymers
Time (hr)
Fig. 3. Refractive indexes of PMI- and PFPMI-co-MMA.
Fig. 4. Water absorption of pure PMMA and PFPMI-co-MMA with 9.8 mol% of PFPMI in
copolymer.
PFPMI-co-MMA, which may due to the higher reactivity of PMI as
compared with that of PFPMI.
3.3. Physical properties of the copolymers prepared in bulk
3.2. Thermal and optical properties of PFPMI-co-MMA
In order to investigate the physical properties of PFPMI-co-MMA
Both of the PFPMI and PMI based copolymers exhibited a single
glass transition temperature (T ) and their values are cited in
g
polymer for the application in the optical devices, we prepared
copolymers in bulk using AIBN as radical initiator. The copolymers
obtained were purified by reprecipitation from the THF solution to
Tables 1 and 2. The glass transition temperatures (Tg) of the
copolymers are found to increase with the increasing amount of
PFPMI in the copolymers. When the copolymer contains 65 mol% of
ꢀ
a large amount of methanol, and dried under vacuum oven at 60 C.
The physical properties of PFPMI-co-MMA are summarized in
Table 3. It is found that the conversions of copolymerization are
generally over 80%, and the number average weights of copolymers
are higher than those produced in 1,4-dioxane solution. The
thermal properties of PFPMI-co-MMA are effectively improved by
inducing PFPMI monomer as compared with that of PMMA. For
ꢀ
PFPMI, the T
relationship between the T
g
value of the copolymer increases up to 180 C, and the
and the polymer composition fits the
g
GordoneTaylor equation (Fig. 2). This indicates that there is no
significant interaction between the pentafluorophenyl groups and
the carbonyl groups in the copolymers in the solid state.
The refractive index of the PFPMI homopolymer was found to be
similar to that of PMMA. The similar refractive indexes of the two
units in the copolymers minimized the possibility of light scat-
tering. Fig. 3 plotted the refractive indexes of both of the copoly-
mers of PFPMI and PMI with MMA at different wavelengths: 532,
instance, the glass transition temperature of PFPMI-co-MMA con-
ꢀ
taining 5 mol% of PFPMI in the copolymer increases up to 133
C
ꢀ
(w105 C for PMMA), and the thermal decomposition temperature
ꢀ
to 350 C, which indicates that this copolymer is much more stable
than pure PMMA [28].
6
33, 839 nm. Since the refractive index of poly(PMI) is much higher
Among the unique properties of fluorinated polymers, low
water absorption is a typical one. It is well known that PMMA has
a tendency to absorb water, however, when MMA was copoly-
merized with PFPMI, the absorption was found to be greatly
decreased. A typical water absorption tendency of the copolymer of
PFPMI-co-MMA is shown in Fig. 4. It shows that the copolymer
containing as little as 10 mol% of PFPMI in the copolymer, the water
absorption is greatly decreased as compared with pure PMMA
(0.75% vs. 2%). The decreasing water absorption could be due to the
highly hydrophobic nature of the fluorinated aromatic rings.
Transmission loss was also studied by measuring the trans-
mittance. As shown in Fig. 5, the transmittance (w90%) of
than that of PMMA (1.64 vs. 1.49), the refractive indexes of PMI-co-
MMA increase linearly with increasing the amount of PMI in the
copolymers, since the refractive indexes of PFPMI and PMMA are
similar, the refractive indexes of the copolymers remained nearly
constant as shown in Fig. 3.
Thermal stability of the copolymers was determined by ther-
mogravimetric analysis in nitrogen atmosphere. The results are also
summarized in Tables 1 and 2. It can been seen that even low mole
fractions of PFPMI (18.8 mol%) and PMI (19.7 mol%) were sufficient to
increasethe decompositiontemperature of the copolymers, whichare
muchhigherthanthedecompositiontemperatureofpurePMMA [28].
Table 3
a
Bulk copolymerization of PFPMI with MMA.
Mnc ꢂ104
PDIc
T
g
( C)
ꢀ
T
( C)
ꢀ
d
Refractive index
Sample
Mole fraction of PFPMI
Conv. (%)
Feed mol%
Copolymer mol%b
532 nm
633 nm
839 nm
PFPMI-co-MMAꢃ5
PFPMI-co-MMAe6
PFPMI-co-MMAe7
PFPMI-co-MMAe8
5.0
10.0
15.0
20.0
4.0
9.8
13.4
18.8
85.5
88.2
89.3
83.8
6.75
7.00
5.82
6.25
2.07
1.97
2.23
2.10.
133
139
142
148
350
353
362
365
1.4965
1.4965
1.4970
1.4970
1.4910
1.4910
1.4910
1.4910
1.4855
1.4855
1.4860
1.4860
a
ꢀ
All the copolymerizations were carried out in bulk, 60 C, using AIBN as initiator.
Calculated by 1H NMR.
Determined by GPC, THF as eluent.
b
c

3564
L. Lou et al. / Polymer 52 (2011) 3560e3564
100
Acknowledgments
This research is supported by the Japan Society for the Promo-
tion of Science (JSPS) through its “Funding Program for World-
Leading Innovative R&D on Science and Technology (FIRST
Program)."
80
60
40
20
0
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Chap. II.
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