Molecular design of diene monomers containing an ester functional group for the synthesis of poly(diene sulfone)s by radical alternating copolymerization with sulfur dioxide

Article abstract of DOI:10.1002/pola.27528

Functional poly(diene sulfone)s are prepared by the radical alternating copolymerization of 1,3-diene monomers containing an ester substituent with sulfur dioxide. Methyl 3,5-hexadienoate (MH) and methyl 5,7-octadienoate (MO) with both an alkylene spacer and a terminal diene structure are suitable to produce a high-molecular-weight copolymer in a high yield, while the copolymerization of 5,7-nonadienoic acid, ethyl 2,4-pentadienoate, and ethyl 4-methyl-2,4-pentadienoate including either an alkylene spacer or a terminal diene structure lead to unsuccessful results. The ¹³C NMR chemical shift values of MH and MO suggest a high electron density at their reacting α-carbon for exhibiting a high copolymerization reactivity. Fluorene-containing diene monomers, 9-fluorenyl 3,5-hexadienoate (FH) and 9-fluorenyl 5,7-octadienoate (FO), are also prepared and copolymerized with sulfur dioxide. The thermal and optical properties of the poly(diene sulfone)s containing the methyl and fluorenyl ester substituents in the side chain are investigated.

Full text of DOI:10.1002/pola.27528

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Molecular Design of Diene Monomers Containing an Ester Functional
Group for the Synthesis of Poly(diene sulfone)s by Radical Alternating
Copolymerization with Sulfur Dioxide
1
2
1
Akikazu Matsumoto, Sungi Lee, Haruyuki Okamura
1
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-Cho, Naka-Ku,
Sakai-Shi, Osaka 599–8531, Japan
2
Department of Applied Chemistry and Bioengineering, Graduate School of Engineering, Osaka City University,
3-3-138 Sugimoto, Sumiyoshi-Ku, Osaka 558–8585, Japan
Correspondence to: A. Matsumoto (E-mail: matsumoto@chem.osakafu-u.ac.jp)
Received 1 December 2014; accepted 8 January 2015; published online 00 Month 2015
DOI: 10.1002/pola.27528
ABSTRACT: Functional poly(diene sulfone)s are prepared by the
radical alternating copolymerization of 1,3-diene monomers con-
taining an ester substituent with sulfur dioxide. Methyl 3,5-hexa-
dienoate (MH) and methyl 5,7-octadienoate (MO) with both an
alkylene spacer and a terminal diene structure are suitable to pro-
duce a high-molecular-weight copolymer in a high yield, while
the copolymerization of 5,7-nonadienoic acid, ethyl 2,4-pentadie-
noate, and ethyl 4-methyl-2,4-pentadienoate including either an
alkylene spacer or a terminal diene structure lead to unsuccessful
ing a high copolymerization reactivity. Fluorene-containing diene
monomers, 9-fluorenyl 3,5-hexadienoate (FH) and 9-fluorenyl 5,7-
octadienoate (FO), are also prepared and copolymerized with sul-
fur dioxide. The thermal and optical properties of the poly(diene
sulfone)s containing the methyl and fluorenyl ester substituents
in the side chain are investigated. V
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3
results. The C NMR chemical shift values of MH and MO sug-
KEYWORDS: alternating copolymer; high performance polymers;
gest a high electron density at their reacting a-carbon for exhibit-
radical polymerization; refractive index; transparency
INTRODUCTION Recent optoelectronic applications have
demanded high-performance polymers with excellent thermal
stability as well as optical, electronic, and other physical proper-
the first trial test resulted in the production of the corresponding
poly(diene sulfone) in only a low yield. In this study, therefore,
functional diene monomers shown in Figure 1 were newly syn-
1–6
ties.
Aromatic polysulfones are synthesized by condensation
thesized and copolymerized with SO . As a result, we revealed
2
polymerization and used as the engineering plastics for the
mechanical and electric parts of machines, separation mem-
branes, and also optical materials, such as lenses and films, due
that methyl 3,5-hexadienoate (MH) and methyl 5,7-octadienoate
(MO) with both an alkylene spacer and a terminal diene struc-
ture were suitable to produce a high-molecular-weight copoly-
mer in a high yield, while the copolymerization of 5,7-
nonadienoic acid (NA), ethyl 2,4-pentadienoate (EP), and ethyl 4-
methyl-2,4-pentadienoate (EMP) including either an alkylene
spacer or a terminal diene structure led to unsuccessful results.
The thermal and optical properties of poly(diene sulfone)s con-
taining the methyl and fluorenyl ester substituents in the side
chain were investigated.
7
to their excellent thermal and mechanical properties. In con-
8,9
10–13
trast, poly(olefin sulfone)s and poly(diene sulfone)s
are
synthesized by the radical alternating copolymerization of olefin
and diene monomers with sulfur dioxide (SO ) and they are used
2
as the degradable polymers, such as resist materials for electron-
beam and X-ray radiation lithography. The resulting poly(diene
sulfone)s are also expected to be used as optical materials due to
their high transparency, good film processability, and excellent
EXPERIMENTAL
11–13
thermal stability after hydrogenation.
We started on the
investigation of the copolymerization of diene monomers con-
General Procedures
taining an ester moiety with SO because the introduction of a
The NMR spectra were recorded in CDCl
AV300N and AV600 and JEOL JNM-A400 spectrometers. The
number-average molecular weight (M ), weight-average
molecular weight (M ), and polydispersity (M /M ) were
3
using Bruker
2
functional group in the side chain of poly(diene sulfone)s can
modify the physical properties of the copolymers. The copoly-
merization using commercially available methyl sorbate (MS) as
n
w
w
n
Additional Supporting Information may be found in the online version of this article.
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tonaldehyde (98%), acrolein (90%), d-valerolactone (98%),
pyridinium chlorochromate (PCC, 98%), allyltriphenylphos-
phonium bromide (98%), 9-fluorenol, and tetraethyl orthoti-
tanate were purchased from Tokyo Chemical Industry Co.,
Ltd., Tokyo, and used as received. Anhydrous dimethyl sulf-
oxide (DMSO) and n-butyllithium (1.6 mol/L in n-hexane)
were purchased from Kanto Chemical Co., Inc., Tokyo, and
used as received. Methacrolein (95%), tert-butylhydroperox-
ide (tBuOOH), and hexamethylphosphoramide were pur-
chased from Sigma-Aldrich Japan Co., Tokyo, and used as
received. The solvents were distilled before use. Sulfur diox-
ide was purchased from Sumitomo Seika Chemicals Co., Ltd.,
ꢀ
and distilled and collected at 2196 C using liquid nitrogen.
The synthetic procedures of the diene monomers used in
this study are described below. The spectral data are shown
in Supporting Information.
FIGURE 1 Chemical structures of 1,3-diene monomers used in
this study. MS, EP, EMP, MH, and FH were used as the pure
(
(
E)-isomer. HD, NA, MO, and FO were used as the mixture of
E)- and (Z)-isomers. All the monomers are shown as the iso-
Synthesis of 5,7-Nonadienoic Acid (NA)
mers with an (E)-configuration for simplification. See the
experimental section and Table 1 for the detailed isomeric
structures.
Sodium hydride (1.10 g, 0.046 mol) was slowly added with
vigorous stirring to anhydrous DMSO (40 mL) maintained at
75 C, then the (4-carboxybutyl)triphenylphosphonium bro-
ꢀ
mide (13.3 g, 0.030 mol) in anhydrous DMSO (60 mL) was
ꢀ
determined by size exclusion chromatography (SEC) in tetra-
hydrofuran (THF) or chloroform using a Tosoh 8020 series
and calibration with standard polystyrenes. The thermogravi-
metric and differential thermal analyses (TG/DTA) were car-
dropwise added at 25 C (Scheme 1). After stirring for 20
min, crotonaldehyde (2.1 g, 0.030 mol) in anhydrous DMSO
(5 mL) was dropwise added. After further stirring for 2.5 h
at room temperature, the mixture was poured into diethyl
ether. The pH of the solution was kept at 3.0 using aq.
sodium hydrogen sulfate (2.0 mol/L) and then the oil phase
was extracted with diethyl ether, and dried over anhydrous
sodium sulfate. The crude product was purified by silica gel
chromatography using diethyl ether and ethyl acetate (6/5
ried out using a Seiko TG/DTA 6200 in a nitrogen stream
ꢀ
(
200 mL/min) at the heating rate of 10 C/min in the tem-
ꢀ
perature range of 302500 C. The onset temperature of
decomposition was evaluated as the 5% weight-loss temper-
ature (T ) in the TG analysis. The maximum temperature of
d5
ꢀ
decomposition (Tmax) was determined using the derivatives
of the TG curves. Differential scanning calorimetry (DSC)
was carried out using a Seiko DSC-6200 in a nitrogen stream
volume ratio) and distilled under reduced pressure (140 C/
0.5 mmHg). Yield: 13.8%; colorless liquid.
ꢀ
at the heating rate of 10 C/min to determine the glass tran-
Synthesis of Ethyl 2,4-Pentadienoate (EP) and Ethyl
4-Methyl-2,4-pentadienoate (EMP)
sition temperature (T ). The UV-Vis spectra were recorded
g
using a JASCO V-550 spectrophotometer. The polymer films
were prepared by casting of the 5 wt % chloroform solution
and drying at 20 C overnight, then further dried under
EP and EMP were synthesized by the following reaction pro-
1
4
cedures. For the synthesis of EP, acrolein (0.56 g, 0.010
mol) and DMAP (0.092 g, 0. 75 mmol) were added to mono-
methyl malonate (1.98 g, 0.015 mol) in pyridine (5 mL), and
ꢀ
reduced pressure at room temperature. The refractive indi-
ꢀ
ces (n , n , and n ) were measured at the wavelengths of
the mixture was stirred at 50260 C for 24 h (Scheme 2).
F
D
C
486, 589, and 656 nm, respectively, using an Abbe-type
Atago DR-M2 refractometer with a zinc dichloride aqueous
saturated solution and a halogen lamp. The average value of
five measurements was typically recorded. The Abbe number
(
m ) was calculated as follows: m 5 (n 2 1)/(n 2 n ).
D D D F C
Materials
Commercially available methyl sorbate (MS, Tokyo Chemical
Industry Co., Ltd., Tokyo) and monoethyl malonate (90%,
Sigma-Aldrich Japan Co., Tokyo) were distilled under reduced
pressure before use. Diisopropylamine was purchased from
Wako Pure Chemicals Co., Ltd., Osaka, and distilled before
use.
(4-Carboxybutyl)triphenylphosphonium
bromide,
sodium hydride, 4-dimethylaminopyridine (DMAP), and pyri-
dine were purchased from Wako Pure Chemicals Co., Ltd.,
Osaka, and used as received. 2,4-Hexadiene (HD, >95%), cro-
SCHEME 1 Synthesis of 5,7-nonadienoic acid (NA).
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SCHEME 2 Synthesis of ethyl 2,4-pentadienoate (EP) and ethyl
-methyl-2,4-pentadienoate (EMP).
4
1
5
SCHEME 4 Synthesis of methyl 5-hydroxypentanoate. Syn-
The mixture was then poured into water (20 mL) and the
product was extracted with diethyl ether (10 mL, three
times). The solution was washed with 15% aq. hydrochloric
acid (15 mL, three times) and saturated aq. sodium bicar-
bonate, then dried over anhydrous sodium sulfate. The EP as
the product was isolated by distillation under reduced pres-
1
6
thesis of methyl 5-oxopentanoate. Synthesis of methyl 5,7-
17
octadienoate (MO).
Synthesis of Methyl 5-Oxopentanoate
To pyridinium chlorochromate (PCC, 6.1 g, 28 mmol) and dis-
tilled dichloromethane (11 mL), methyl 5-hydroxypentanoate
ꢀ
sure (30 C/1.0 mmHg). EMP was similarly synthesized
using methacyrolein.
(
2.5 g, 19 mmol) in dichloromethane (11 mL) was dropwise
16
S4
added at room temperature with vigorous stirring (Scheme 4).
Synthesis of Methyl 3,5-Hexadienoate (MH)
To fresh diisopropylamine (2.45 g, 24 mmol) and distilled
The filtrate was concentrated and passed through a silica gel
column to isolate the methyl 5-oxopentanoate as a liquid.
THF (40 mL) in a degassed Schlenk flask, n-BuLi in n-hexane
ꢀ
1
(
1.6 mol/L, 15 mL, 24 mmol) was slowly added at 278 C
Yield: 44%. H NMR (300 MHz, CDCl d, ppm): 9.78 (s, CH CHO,
3
2
(
ꢀ
Scheme 3). The temperature of the solution was raised to 0
C for 15 min, cooled to 278 C, then several drops of HMPT
1
2
H), 3.68 (s, OCH , 3H), 2.5722.52 (t, CH C(@O)O, 2H),
3
2
ꢀ
.3922.36 (t, CH CHO, 2H), 1.9821.94 (m, CH CH CH , 2H).
2
2
2
2
were added and stirred for 30 min. To this solution, MS
ꢀ
(
2.53 g, 20 mmol) was slowly added over 2 h at 278 C, and
Synthesis of Methyl 5,7-Octadienoate (MO)
further stirred for 1 h. The mixture was poured into aq. acetic
acid cooled at 0 C, the product extracted with n-hexane,
washed with water, then distilled under reduced pressure.
To allyltriphenylphosphonium bromide (5.0 g, 13mmol) in
diethyl ether (70 mL), n-BuLi in n-hexane (1.6 mol/L,
ꢀ
ꢀ
8.2 mL, 13 mmol) was slowly added at 025 C, and further
1
7
S4
stirred for 1 h (Scheme 4).
-oxopentanoate (1.54 g, 11.8 mmol) in diethyl ether
15 mL) was dropwise added, and stirred for 1 h at room
To this solution, methyl
Synthesis of Methyl 5-Hydroxypentanoate
To d-valerolactone (4.03 g, 40 mmol) and methanol (6 mL) in a
flask equipped with a condenser, concentrated sulfonic acid
5
(
temperature. The mixture was washed with water and the
product was extracted with diethyl ether. MO was purified
by silica gel column chromatography and distillation under
reduced pressure. The MO was obtained as the mixture of
the (5E,7E) and (5Z,7E)-isomers, (5E,7E)/(5Z,7E) 5 4/3.
(
0.07 mL, 1.31 mmol) was dropwise added with stirring at
1
5
room temperature (Scheme 4). After reflux for 10 h, sodium
hydrogen carbonate (0.04 g) was added at 0 C. Silica gel chro-
S4
ꢀ
matography provided methyl 5-hydroxypentanoate as a color-
less liquid.
1
Yield: 55%. H NMR (300 MHz, CDCl3 d, ppm): 3.68
(
s, OCH3, 3H), 3.6723.62 (t, CH OH, 2H), 2.3922.34
2
(
t, CH C(@O)O, 2H), 1.7521.57 (m, CH CH , 4H).
2
2
2
SCHEME 5 Synthesis of 9-fluorenyl 3,5-hexadienoate (FH) and
SCHEME 3 Synthesis of methyl 3,5-hexadienoate (MH).
9-fluorenyl 5,7-octadienoate (FO).
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3
TABLE 1 Results of Copolymerization of Diene Monomers with Sulfur Dioxide and C NMR Chemical Shifts for the Diene
a
Moieties
[
Diene]
Copolymer
Yield (%)
1
3
4
3
C NMR Chemical Shift in CDCl (ppm, 10 vol %)
Diene Monomer
MS
(mol/L)
M
n
/10
M /M
w n
Isomer
2E,4E
5E,7E
a
b
c
d
b
b
2
2
1.0
2.5
139.4
129.8
127.5
125.6
124.4
117.2
115.4
117.5
117.3
115.5
117.6
129.7
126.7
131.4
134.9
140.7
136.4
137.1
132.1
136.4
137.1
132.1
145.1
129.8
131.5
134.9
147.1
134.5
132.0
130.4
134.8
132.1
130.5
118.5
127.8
130.1
122.4
118.9
125.6
133.9
131.3
125.4
133.8
131.2
c
d
d
NA
0.13
1.4
5Z,7E
e
d
d
d
d
EP
Bulk
0.3
5.8
0.29
0.94
2.3
2.1
3E
e
EMP
MH
Bulk
3E
e
Bulk
25.5
61.6
4.7
b
2.2
b
5E,7E
5E,7E
c
e
MO
Bulk
5Z,7E
FH
0.5
0.3
47.1
77.7
3.5
4.5
2.1
2.2
5E,7E
5E,7E
c
FO
5Z,7E
f
g
FH/HD-3/1
2
2
2
59.1(65.8)
2.4
3.2
4.7
3.1
2.7
2.5
f
g
FH/HD-1/1
79.9(37.7)
f
g
FH/HD-1/3
74.4(21.1)
a
c
d
e
f
Copolymerization conditions: [SO
2
] 5 5 mol/L, [tBuOOH] 5 0.02 mol/L
For the polymerization of a mixture of isomers.
Determined by SEC in tetrahydrofuran.
ꢀ
in toluene at 278 C for 24 h. The copolymer yield was determined on
the basis of the amount of the charged diene monomers. M
values were determined by SEC in chloroform.
Not determined.
n
and M
w
/
[diene]/[SO
2
]/[tBuOOH] 5 100/250/1.
M
n
Molar ratio of FH to HD in the feed.
b
g
Molar fraction of the FH units in the copolymer.
Synthesis of 9-Fluorenyl 3,5-Hexadienoate (FH) and 9-
Fluorenyl 5,7-Octadienoate (FO)
was removed under reduced pressure, the residue was purified
by silica gel chromatography with hexane/ethyl acetate 5 10/1
For the synthesis of FH, to 0.65 g of MH and 3.45 g of 9-
fluorenol in 25 mL of distilled toluene in a 100-mL flask
in volume (R 5 0.6). Pale yellow solid. Yield: 82.0%.
f
Similarly, FO was synthesized from MO (0.5 g) and purified
4
equipped with a condenser, 0.11 g of Ti(OEt) as the catalyst
18
by silica gel chromatography (R 5 0.720.8). The pale yellow
was added and refluxed for 40 h (Scheme 5). After the toluene
f
solid was isolated as the isomeric mixture [(5E,7E)-FO/
(
5Z,7E)-FO 5 4/3]. Yield: 78.3%.
Polymerization
A diene monomer (20 mmol) and tert-butyl hydroperoxide
(
0.04 mL, 0.2 mmol) in toluene (10 mL) were placed in a
glass ampoule. The solution was degassed by the freeze-
thaw technique. This cycle was repeated three times, then
SO (2.0 mL, 50 mmol) was added by vacuum distillation,
2
and finally the ampule was sealed. After polymerization for a
ꢀ
given time at 278 C, the polymerization mixture was
poured into 200 mL of methanol. The polymer was filtered,
washed with methanol, and then dried in vacuo at room tem-
perature. The yield of the polymers was gravimetrically
determined on the basis of the amount of the charged diene
monomers. The soluble poly(diene sulfone)s were purified
by repeated reprecipitation using chloroform or dimethyl
sulfoxide as the solvent and methanol as the precipitant. The
spectral data of the poly(diene sulfone)s are shown in sup-
porting information.
FIGURE 2 Design of diene monomers appropriate for alternat-
ing copolymerization with sulfur dioxide. The values indicate
1
3
the C NMR chemical shifts for the a-carbon of diene moieties.
Color figure can be viewed in the online issue, which is avail-
Hydrogenation
The poly(diene sulfone)s (0.05 g) and p-toluene sulfonyl
hydrazide (15 eq) were stirred in diethylene glycol dimethyl
[
able at wileyonlinelibrary.com.]
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ical due to the introduction of an electron-withdrawing func-
tional group. The other was a low ceiling temperature for
1
3,19
this polymerization.
For example, the ceiling temperature
for the copolymerization of 2,4-hexadiene (HD) and SO was
2
ꢀ
4
2 C for the copolymerization conditions of [HD] 5 2.0 mol/
1
3
L and [SO ] 5 5.0 mol/L. It was previously concluded that
2
the low ceiling temperature of HD during the copolymeriza-
tion with SO2 was due to a small enthalpy change for the
copolymerization. Any side reaction of a polar functional
group may suppress the copolymer formation with a high
molecular weight during the copolymerization, but it was
negligible because the radical polymerization implies toler-
ance to the polar and functional side groups of the mono-
mers and polymers.
1
3
In fact, the C NMR chemical shift was determined to be high
as 139.4 ppm for the a-carbon of the diene moiety of MS,
being much higher than those reported for the hydrocarbon
diene monomers with high copolymerization reactivities
(124–128 ppm for the HDs and 110–117 ppm for the other
monomers, see Supporting Information Table S1). This sug-
gested a low electron density on the reacting carbon of MS,
which was disadvantageous for the addition of an electron-
1
13
3
FIGURE 3 (a) H and (b) C NMR spectra of MH in CDCl . An
asterisk indicates the peak due to the solvent. [Color figure can
be viewed in the online issue, which is available at wileyonlineli-
brary.com.]
ꢀ
ether (5 mL) at 120 C under a nitrogen atmosphere. After
the reaction, the reaction mixture was poured into 200 mL
of methanol. The precipitated polymers were filtered,
washed with methanol, and then dried in vacuo at room tem-
perature. The yield of the recovered polymers was gravimet-
1
rically determined. The conversion was determined by
H
NMR spectroscopy. The conversion was 68–82% during the
reaction for 12 h. The spectral data of the hydrogenated
poly-(diene sulfone)s are shown in Supporting Information.
RESULTS AND DISCUSSION
We investigated the copolymerization reactivity of MS as the
commercially available diene monomer containing an ester
group as the preliminary test. The radical copolymerization
ꢀ
of MS with SO was carried out in toluene at 278 C in the
2
presence of tBuOOH as the oxidative agent of a redox initia-
tor system (functioning with SO2 as the reducing agent)
under conditions similar to those for the copolymerization of
hydrocarbon diene monomers containing no functional group
1
1
reported in previous reports. As a result, a copolymer was
produced in only a low yield (1.0%), as shown in Table 1.
Several reasons were possible for interpreting the low
copolymerization reactivity of MS; one was a decrease in the
electron density on the diene moiety of the MS monomer
and on the carbon of the corresponding propagating MS rad-
1
13
FIGURE 4 (a) H and (b) C NMR spectra of MO in CDCl . An
3
asterisk indicates the peak due to the solvent. [Color figure can
be viewed in the online issue, which is available at wileyonlineli-
brary.com.]
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SCHEME 6 Synthesis of functional poly(diene sulfones) by the
radical alternating copolymerization of diene monomers con-
taining an ester group.
deficient sulfonyl radical during the copolymerization. The lin-
1
3
ear relationship between the C NMR chemical shift values
and the e values of various vinyl monomers was previously
reported and their reactivity during polymerization was dis-
2
0
cussed in the literature. The electron-donating characteristic
of diene monomers is required for the successful process of
1
13
FIGURE 6 (a) H and (b) C NMR spectra of poly(FO-alt-SO
in CDCl . An asterisk indicates the peak due to the solvent.
Color figure can be viewed in the online issue, which is avail-
2
)
3
the radical alternating copolymerization with SO . At the same
2
[
time, steric hindrance between a propagating radical and an
attacking monomer during the cross-propagation reactions
must be avoided in a strategy for the design of diene mono-
mers used for the copolymerization system.
able at wileyonlinelibrary.com.]
the following two approaches for decreasing in the steric
repulsion and increasing in the electron density on a diene
moiety; (i) the introduction of an alkyl spacer between the
dienyl and ester groups, and (ii) a change in the internal
diene structure to the terminal one (Fig. 2). NA with an alkyl
spacer and EP and EMP with a terminal diene moiety were
first synthesized by the reactions shown in Schemes 1 and 2,
respectively. NA was obtained as the mixture of the (5E,7Z)-
and (5E,7E)-isomers due to no regioselectivity of the Wittig
The chemical structures of diene monomers appropriate for
the copolymerization with SO2 was designed according to
2
1
reaction for the synthesis (see Figs. S1 and S2 in Support-
ing Information for the NMR spectra of NA). EP and EMP
were isolated as pure (3E)-isomers in this study (see Figs.
1
4
S3 to S6 in Supporting Information).
1
13
FIGURE 5 (a) H and (b) C NMR spectra of poly(MH-alt-SO
2
)
in CDCl and DMSO-d , respectively. An asterisk indicates the
3
6
peak due to the solvent. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
FIGURE 7 IR spectrum of poly(MO-alt-SO2).
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SCHEME 7 Reaction mechanism for 1,4-regiospecific propagation during the radical alternating copolymerization of diene mono-
mers with sulfur dioxide.
The results of the copolymerization are shown in Table 1.
The H NMR and IR spectra of the products confirmed the
ification of MH and MO with 9-fluorenol in the presence of
the Ti(OEt)4 catalyst (Scheme 5). The fluorene-containing
1
18
formation of the copolymers of the diene monomers with
monomers also provided the corresponding copolymers in a
1
13
SO
2
, as shown in Figures S10 and S11 in Supporting Infor-
high yield, as shown in Table 1. The H and C NMR and IR
spectra of the produced copolymers are shown in Figures 5
to 7 (see also Supporting Information Figs. S12 and S13).
The MO and FO monomers with a trimethylene spacer
resulted in the copolymer production with higher yields
rather than those for the MH and FH with a short methylene
spacer. This was due to the avoidance of steric hindrance by
the long alkyl spacer between the dienyl and ester moieties.
mation. However, the copolymer yield of 0.3–5.8% was still
low, while the chemical shift values were shifted to 124–130
ppm. Therefore, we further modified the diene monomer
structure. Consequently, MH and MO were synthesized
according to design iii, in which both key structures were
introduced as the monomer design. The synthetic pathways
are shown in Schemes 3 and 4. As a result, MH was obtained
as the single (3E)-isomer, and MO as the mixture of the
4
1
13
The M values of the copolymers were 3.5 to 4.7 3 10 , sim-
(
5E,7Z)- and (5E,7E)-isomers. The H and C NMR spectra
of MH and MO are shown in Figures 3 and 4, respectively
see also Supporting Information Fig. S7).
n
ilar to those of the copolymers with HD and other previously
1
1
reported hydrocarbon diene monomers. The NMR and IR
spectra confirmed the formation of the alternating copoly-
mers under highly regioselective control of the diene repeat-
ing structure; i.e., the 1,4-repeating structure was
predominantly produced (Figs. 5–7, see also Supporting
(
The copolymerization of these newly synthesized monomers
provided the alternating copolymers with SO in high yield,
as shown in Scheme 6. The copolymers were produced in
5.5 and 61.6% yield during the copolymerization of MH
2
1
1–13
2
Information).
Scheme 7 shows a reaction mechanism of
and MO with SO2 (Table 1). We further prepared the
fluorene-containing monomers, FH and FO, by the transester-
the radical alternating copolymerization of diene monomers
with SO2 to produce a highly regioselective 1,4-diene
a
TABLE 2 Solubility of Poly(diene sulfone)s with Ester Side Groups
Polymer
TFA
DMSO
CHCl
3
Acetone
THF
DGDE
Poly(MH-alt-SO
2
)
Insoluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Insoluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Soluble
Insoluble
Insoluble
Soluble
Swelling
Soluble
Swelling
Swelling
Soluble
Soluble
Soluble
Insoluble
Insoluble
Swelling
Swelling
Soluble
Soluble
Soluble
Soluble
Soluble
Insoluble
Insoluble
Insoluble
Soluble
Soluble
Soluble
Soluble
Soluble
Swelling
Swelling
Insoluble
Insoluble
Poly(MO-alt-SO
Poly(FH-alt-SO
Poly(FO-alt-SO
2
)
2
)
Insoluble
Insoluble
Insoluble
Insoluble
Soluble
2
)
Poly(FH/HD-alt-SO
Poly(FH/HD-alt-SO
Poly(FH/HD-alt-SO
2
2
2
)266
)238
)221
Poly(HD-alt-SO
2
)
Soluble
b,c
Poly(MP-alt-SO
2
)
Soluble
c,d
Poly(BD-alt-SO
2
)
Insoluble
a
c
TFA: trifluoroacetic acid, DMSO: dimethyl sulfoxide, THF: tetrahydrofu-
ran, DGDE: diethylene glycol dimethyl ether.
Cited from a previous article (ref. 13).
BD: butadiene.
d
b
MP: 3-methyl-1,3-pentadiene.
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TABLE 3 Thermal and Optical Properties of Poly(diene sulfone)s with a Functional Side Group
ꢀ
ꢀ
ꢀ
g
Polymer
T
d5 ( C)
T
d50 ( C)
T
( C)
%T at 400 nm
n
F
n
D
n
C
m
D
Poly(MH-alt-SO
2
)
136
173
213
240
207
159
150
135
256
254
367
383
330
279
252
200
82.0
47.0
95.1
95.9
1.5381
1.5348
1.5300
1.5267
1.5251
1.5205
40
37
Poly(MO-alt-SO
Poly(FH-alt-SO
Poly(FO-alt-SO
2
)
a
a
a
a
a
2
)
131.0
99.0
–
–
–
–
–
2
)
95.0
94.9
95.3
95.5
95.2
1.6256
1.6149
1.5912
1.5745
1.5449
1.6488
1.6107
1.6001
1.5796
1.5635
1.5377
1.6319
1.6015
1.5938
1.5730
1.5584
1.5317
1.6234
25
28
32
35
41
25
b
b
b
Poly(FH/HD-alt-SO
Poly(FH/HD-alt-SO
Poly(FH/HD-alt-SO
2
2
2
)266
)238
)221
129.0
128.0
126.0
a
Poly(HD-alt-SO
2
)
–
Bisphenol A polysulfone
a
b
Not determined.
The number indicates the molar fraction of the FH units in the
copolymer.
1
2,13
repeating structure.
The DFT calculations were previ-
perature, as already described. Especially, the addition of the
ously carried out using the model reactions in order to eluci-
date the highly regiospecific reaction via a free radical
2
allyl radical to SO is slow and the reverse reaction should
be considered. The reversible propagation steps are a key
for controlling the regioselectivity during the alternating
copolymerizations of diene monomers with SO2.
1
2,22
propagation mechanism.
It had been pointed out that
the thermodynamic analysis is useful for estimating the
propagating fashion during the radical alternating copoly-
The copolymers were soluble in dimethyl sulfoxide and
chloroform and the solubility increased by the introduction
of the alkylene spacer and the fluorenyl ester group in
the order of FO > MO ’ FH > MH (Table 2). The T and
d5
merization of a diene monomer with SO , in which the con-
2
tribution of the depropagation is important due to the low
ceiling temperatures. As shown in Scheme 7, the sulfonyl
propagating radical favors a reaction at the a-position of the
diene (i.e., 4-position of a functional diene in the scheme)
due to the formation of an allyl radical and the steric hin-
drance of the substituent X. During the addition of the diene
T
values of the poly(diene sulfone)s containing an ester
d50
ꢀ
ꢀ
side group were 136–240 C and 254–383 C, respectively,
as summarized in Table 3. The copolymers including the
FH and FO with the fluorenyl substituents in the ester
group showed higher decomposition temperatures due to
the nonvolatile property of the large fluorenyl moiety. The
transmittance spectra of the cast films of poly(diene sul-
fone)s containing an ester group in the side chain are
radical to SO , both the 4,1- and 4,3-propagations of the allyl
2
radical should be considered. The enthalpy changes (DH)
value for the former reaction is negative and seems to be
favored, while the latter is positive, but the difference in
these values is quite small. This suggested that the both
reaction pathways have a chance for to occur during the
copolymerization. During these propagation steps, the depro-
pagation effect is not negligible because of a low ceiling tem-
FIGURE 9 Wavelength dependence of the refractive index of (a)
conventional bisphenol A polysulfone, (b) poly(FO-alt-SO
y(FH/HD-alt-SO )266, (d) poly(FH/HD-alt-SO )238, (e) poly(FH/HD-
alt-SO )221, (f) poly(HD-alt-SO ), and (g) poly(methyl methacry-
2
), (c) pol-
2
2
FIGURE 8 Transmittance of UV and visible lights for the
2
2
poly(diene sulfone)s films. (a) poly(MO-alt-SO
2
), (b) poly(FH/
late). The curves were drawn using the following equation with the
2
HD-alt-SO )266, and (c) poly(FO-alt-SO ). Film thickness 20 mm.
2
2
1 k 1
n and D parameters: n 5 n 1 D/k (See also refs. 13 and 25).
8
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TABLE 4 Hydrogenation of Poly(diene sulfone)s with a
were 25–40, being between the values for the conven-
Functional Side Group and Thermal Properties the Obtained
2
tional aromatic polysulfone and the poly(HD-alt-SO ).
a
Hydrogenated Polymers
It was previously reported that the onset temperature of the
thermal decomposition drastically increased by the hydro-
genation of the unsaturated C@C bonds in the copolymer
Time Conversion
T
d5
ꢀ
T
d50
ꢀ
T
g
ꢀ
Precursor Polymer
Poly(MH-alt-SO
(h)
(%)
( C) ( C) ( C)
1
1
chain. A similar increase in the thermal stability after
hydrogenation was observed for the poly(diene sulfone)s
containing an ester substituent in this study. The Td5 and
2
)
6.0
41.3
81.6
92.1
27.5
44.8
68.0
67.5
36.7
67.5
68.4
92.6
60.5
80.4
89.7
223 286
231 292
232 292
215 301
239 308
244 330
248 445
260 428
275 416
236 358
250 364
244 326
235 341
254 342
57
47
46
42
37
1
2.0
8.0
3.0
1
1
1
ꢀ
ꢀ
Td50 values were increased to 231–275 C and 292–445 C,
Poly(MO-alt-SO
2
)
respectively, when the poly(diene sulfone)s were reacted
ꢀ
8
.0
with hydrazine in diethylene glycol dimethyl ether at 120 C.
b
The conversion was over 68% after hydrogenation for 12 h,
being sufficient for changing the onset temperature of
decomposition (Table 4). No change was observed in the
ester moiety during the chemical reduction using hydrazine
as the reducing agent under the present conditions.
2.0
6.0
6.0
2.0
–
Poly(FH-alt-SO
2
)
102
88
Poly(FO-alt-SO
2
)
86
c
c
c
Poly(FH/HD-alt-SO
2
2
2
)266
)238
)221
15.0
98
2
2.0
6.0
2.0
93
CONCLUSIONS
Poly(FH/HD-alt-SO
104
100
93
In this study, we demonstrated that poly(diene sulfone)s
including functional ester substituents in their side chain
were prepared by the radical alternating copolymerization of
the well-designed diene monomers with sulfur dioxide. The
obtained functional poly(diene sulfone)s were soluble in
organic solvents and the transparent and flexible polymer
films were fabricated by casting their solutions. Their refrac-
tive index values and Abbe numbers were dependent on the
structure of the ester groups and the number of alkylene
spacers between the main chain and the ester group. It was
also revealed that the physical and optical properties of the
copolymers were controlled by the copolymer composition
of the ternary copolymerization systems using two different
kinds of diene monomers with sulfur dioxide. These func-
tional polysulfones are expected to be used as the new opti-
cal polymer materials because the controlled radical
polymerization potentially possesses a high number of
advantages for structure-controlled polymer syntheses.
1
Poly(FH/HD-alt-SO
12.0
a
The hydrogenation was carried out using p-toluene sulfonyl hydrazide
15 eq) in diethylene glycol dimethyl ether at 120 C. The conversion
ꢀ
(
1
was determined by H NMR spectroscopy.
b
Not determined.
c
The number indicates the molar fraction of the FH units in the
copolymer.
shown in Figure 8. These copolymers exhibited a high
transmittance over 95% at 400 nm (see %T values in
Table 3). The T values varied in the temperature range of
7–131 C, which decreased with the introduction of a
g
ꢀ
4
longer alkylene spacer and increased with the bulky fluo-
renyl group. The poly(FH-alt-SO ) film was too brittle to
2
evaluate its optical properties. Therefore, we fabricated the
copolymers consisting of ternary repeating units, which
were prepared using FH and HD as the diene monomers
during the copolymerization with SO . The copolymeriza-
2
tion results and the copolymer properties are shown in
Tables 1 to 3. The poly(FH/HD-alt-SO )s with a 21.1 to
ACKNOWLEDGMENTS
2
6
5.8 mol % FH content were produced as high-molecular-
The authors thank Profs. Yoshiki Chujo and Kazuo Tanaka,
Kyoto University, for their help of SEC measurements.
4
weight copolymers (M 5 2.4–4.7 3 10 ) with good solu-
n
bilities. These ternary copolymers included the alternating
repeating structure of the diene and SO2 units. They also
produced transparent and tough films by casting of their
solutions, similar to the other poly(diene sulfone)s. The
wavelength dependence of the refractive indices of the
copolymers is shown in Figure 9. The order of the refrac-
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