Anionic polymerization of 2-phenyl[3]dendralene and 2-(4-methoxyphenyl)[3] dendralene

Article abstract of DOI:10.1021/ma400987h

Anionic polymerization of two phenyl-substituted trienes containing cross-conjugated carbon-carbon double bonds, 2-phenyl[3]dendralene (P3D) and 2-(4-methoxyphenyl)[3]dendralene (MP3D), was carried out in THF under a variety of different conditions. Poly(P3D) of controlled molecular weight with a narrow molecular weight distribution was obtained when the polymerization reaction was carried out at -78 C for 30 min. Broadening of the molecular weight distribution to the higher-molecular-weight side was observed if the polymerization mixture was left to stand for 20 h at -78 C, presumably because of the attack of the propagating chain-end carbanion at the conjugated diene structure in the polymer chain. Similar broadening occurred if the polymerization was performed at a higher temperature. However, under identical conditions, no such a broadening was observed in the polymerization of MP3D. Block copolymers of predictable molecular weights and compositions containing a poly(2-vinylpyridine) segment were obtained by the sequential addition of P3D and/or MP3D to potassium naphthalenide and then 2-vinylpyridine. Only the conjugate addition structure was found in the resulting polymers.

Full text of DOI:10.1021/ma400987h

Article
pubs.acs.org/Macromolecules
Anionic Polymerization of 2‑Phenyl[3]dendralene and 2‑(4-
Methoxyphenyl)[3]dendralene
Katsuhiko Takenaka,* Shuhei Amamoto, Hiroto Kishi, Hiroki Takeshita, Masamitsu Miya,
and Tomoo Shiomi
Department of Materials Science and Technology, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka, Niigata
940-2188, Japan
ABSTRACT: Anionic polymerization of two phenyl-substi-
tuted trienes containing cross-conjugated carbon−carbon
double bonds, 2-phenyl[3]dendralene (P3D) and 2-(4-
methoxyphenyl)[3]dendralene (MP3D), was carried out in
THF under a variety of different conditions. Poly(P3D) of
controlled molecular weight with a narrow molecular weight
distribution was obtained when the polymerization reaction
was carried out at −78 °C for 30 min. Broadening of the
molecular weight distribution to the higher-molecular-weight
side was observed if the polymerization mixture was left to stand for 20 h at −78 °C, presumably because of the attack of the
propagating chain-end carbanion at the conjugated diene structure in the polymer chain. Similar broadening occurred if the
polymerization was performed at a higher temperature. However, under identical conditions, no such a broadening was observed
in the polymerization of MP3D. Block copolymers of predictable molecular weights and compositions containing a poly(2-
vinylpyridine) segment were obtained by the sequential addition of P3D and/or MP3D to potassium naphthalenide and then 2-
vinylpyridine. Only the conjugate addition structure was found in the resulting polymers.
INTRODUCTION
contains multiple 2- or 2,3-disubstituted 1,3-dienyl frames,
providing the potential for it to be used as a substrate for a
■
Hydrocarbons containing multiple conjugated carbon−carbon
double bonds can be classified into four groups on the basis of
their structural differences. Chart 1 shows examples of
4
−6
diene-transmissive Diels−Alder reaction.
Because the
reactivity in the Diels−Alder reaction strongly depends on
the electron density and the conformation of the dienyl frame, a
variety of substituted dendralenes have been synthesized via the
Chart 1. Examples of Fundamental Hydrocarbon Families
Having Oligoalkene Structures
7
thermal decomposition of certain precursors. Recently, a new
route to synthesizing dendralenes, involving the cross-coupling
reaction of 1,3-butadien-2-yl magnesium chloride with an
8
appropriate alkenyl halide, was reported. Because this route
does not include the thermal decomposition of the precursors,
dendralenes of various chain lengths with a range of
substituents can be obtained in high yield.
The first and smallest dendralene, [3]dendralene, was
9
synthesized in 1955. Since then, a variety of [n]dendralenes
up to [8]dendralene have been systematically synthesized. The
effect of the number of double bonds in the [n]dendralene
molecules on their stability has been evaluated, with larger
dendralenes appearing more stable and those containing an odd
number of carbon−carbon double bonds being less stable than
those with an even number. However, the behavior of these
molecules in addition polymerization reactions has not been
reported thus far.
fundamental hydrocarbon families of oligoalkene structures,
where each family differs in the type of atom connectivity
10
(
unbranched or branched, cyclic or acyclic). The unbranched
acyclic and cyclic systems, namely, linear polyenes and
annulenes, respectively, have a single conjugated chain of
double bonds. In contrast, the branched acyclics (dendralenes)
and cyclics (radialenes) have multiple conjugated systems,
where one carbon−carbon double bond belongs to two
1
,3-Butadiene, the simplest conjugated dienyl monomer, can
be considered to be [2]dendralene and can be polymerized by
1
−3
conjugation systems.
Received: May 13, 2013
Revised: August 10, 2013
Published: September 6, 2013
Among these oligoalkenes, dendralene has been attracting
much attention for its unique chemical reactivity. This molecule
©
2013 American Chemical Society
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free-radical, anionic and coordination polymerization to give a
rubbery material, even though no cross-conjugated double
bond is present in the monomer molecule. Because the
chemical reactivity of the conjugated carbon−carbon double
bond in the monomer and that of the nonconjugated double
bond in the resulting polymer are very different, it is easy to
obtain polydienes without cross-linking. However, if the
dendralene polymerization proceeds via a conjugate addition
mode, as shown in Scheme 1, then the newly formed
P3D and MP3D and discuss the microstructure of the resulting
polymers.
EXPERIMENTAL SECTION
■
Materials. 2-Chloro-1,3-butadiene (chloroprene) was kindly
donated by Denki Kagaku Kogyo Co. Ltd., Japan as a 50% toluene
solution. Prior to use, it was twice purified by fractional distillation
under reduced pressure. P3D and MP3D were prepared according to
8
the reported procedure. Bromine, p-bromoanisole, [1,3-bis-
(
(
diphenylphosphino)propane]dichloronickel(II), and [1,2-bis-
diphenylphosphino)ethane]dichloronickel(II) were used as received.
Scheme 1. Transmission of the Carbon−Carbon Double
Bond to Form a New Conjugated Dienyl Structure by the
Conjugated Addition of [3]Dendralene
α-Bromostyrene was prepared from styrene by the addition of
bromine in CCl , followed by dehydrobromination using KOH/
4
methanol at 25 °C. 1,3-Butadien-2-yl magnesium chloride was
prepared according to a previously reported procedure using
chloroprene and ordinary magnesium turnings with continuous
17
activation of the magnesium surface with 1,2-dibromoethane.
Anionic Polymerization. The synthesized monomers were
purified by distillation under high-vacuum conditions in the presence
of phenylmagnesium bromide. The purified monomers were diluted
with THF and then sealed in ampules with breakable seals. All anionic
polymerizations were carried out under high vacuum using the well-
1
8
known break-seal method. First, the THF solution of initiator was
introduced into the reactor and cooled to −78 °C. After the addition
of the monomer solution to the reactor in one portion at this
temperature, the reactor was put in an aimed constant-temperature
bath and allowed to stand still for a designed time. Finally, degassed
ethanol was added to terminate the polymerization. In the case of
block copolymerization, a small portion of the polymerization mixture
was transferred to the separated part of the reactor prior to the
addition on the second monomer.
conjugated carbon−carbon double bond in the polymer chain
may have similar reactivity to the one in the monomer and
could therefore be susceptible to attack of the propagating
chain end during polymerization. As a result, it is important to
select the polymerization conditions carefully in order to
prevent such a side reaction. For this purpose, in this work, we
chose the method of anionic polymerization, to be carried out
at low temperature.
Materials Characterization. The 1H and 13C NMR spectra were
recorded in CDCl using a JEOL JNM-AL-400 spectrometer. The
3
1
13
solvent peak was used as the reference. One dimensional H and
C
spectra were obtained with 32 768 data points, 15 and 220 ppm
spectral widths, 45 and 30° pulse widths, and 7 and 5 s repetition
times, respectively. A 2D H−H COSY spectrum was obtained with
1024 row data points and 256 column data points with zero filling.
GC−MS data were obtained using a Shimadzu QP-2010plus with
electron impact (EI) ionization. A size-exclusion chromatogram (SEC)
was obtained at 40 °C using a TOSOH HLC-8220 instrument
equipped with three polystyrene gel columns [TOSOH TSKgel
G4000HHR, G3000HHR, and G2000HHR (7.8 mm × 30 cm)] and UV
(254 nm) and refractive index (RI) detectors. THF was used as the
carrier solvent at a flow rate of 1 mL/min. The absolute molecular
weights of the polymers were determined using a Viscotek model 270
instrument connected to an SEC.
In a previous paper, we reported on the anionic polymer-
ization behavior of various functionalized 1,3-butadiene
1
1−14
derivatives.
Because the anionic polymerization of
conjugated 1,3-dienes proceeds smoothly in polar solvents at
low temperature, this mechanism was speculated to be useful
for the polymerization of dendralenes. Another strategy for
controlling the polymerization of dendrarene is to introduce a
substituent at a certain position. Although it is known that the
nucleophilicity of active chain-end species derived from 2-
15
16
phenyl-1,3-butadiene and 2,3-diphenyl-1,3-butadiene was
too weak to initiate the polymerization of styrene, anionic
polymerization of these monomers proceeds in a living manner
to give polymers of predictable molecular weights and narrow
molecular weight distributions. This indicates that the aromatic
substituent on the C2 carbon of the 1,3-butadienyl skeleton can
change the nucleophilicity of active chain-end species through
conjugation. Because one of the conjugation systems in 2-
phenyl[3]dendralene (P3D) can be regarded as 2-phenyl-3-
vinyl-substituted 1,3-butadiene and the other one can be
regarded as 2-(1-phenylethenyl)-1,3-butadiene, active chain-
end species derived from P3D should have lower nucleophlicity
compared to that of ordinary 1,3-dienes, making it possible to
distinguish the conjugated double bond in the monomer from
the one in the polymer chain. Therefore, 2-aromatic-
substituted[3]dendralene would be suitable for studying the
anionic addition polymerization behavior of dendralenes.
Among 2-substituted[3]dendralene, we chose P3D and 2-(4-
methoxyphenyl)[3]dendralene (MP3D) as the first monomer
to polymerize by anionic initiator because the synthesis
RESULTS AND DISCUSSION
■
Anionic Polymerization of P3D. The anionic polymer-
ization of P3D was carried out in THF using potassium
naphthalenide as an initiator. Upon addition of P3D, the
characteristic green color of the initiator turned immediately to
deep red. This color remained unchanged until the end of the
polymerization and disappeared instantaneously on the
addition of ethanol. No gel was formed during the polymer-
ization, and the polymer was precipitated by pouring the
solution into a large excess of ethanol. It was purified by
reprecipitation from THF to ethanol an additional two times
and finally freeze-dried from benzene. Table 1 summarizes the
results of the anionic polymerization of P3D under various
conditions. When the reaction was performed at −78 °C, the
polymerization was not complete in 1 h, whereas in the time
frame of 1−10 h, no residual monomer was detected by GC. In
all cases, polymers of predictable molecular weights based on
the monomer to initiator ratios were obtained with narrow
molecular weight distributions, indicating that the olefinic
8
methodology of these monomers is well established. In this
article, we report the first example of anionic polymerization of
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Table 1. Anionic Polymerization of P3D under Various
Conditions
conditions. The color of the system was almost identical to the
case of P3D. A soluble polymer was obtained by pouring the
solution into a large excess of ethanol. Table 2 summarizes the
results of the anionic polymerization of MP3D under various
conditions. SEC chromatograms of poly(MP3D) thus obtained
are shown in Figure 2. When the reaction was performed at
M , kg/mol
n
K-
P3D, Naph,
mmol mmol temp, °C time, h conv, % calcd
SEC M /Mn
w
−
78 °C, the rate of polymerization was found to be slightly
6.61
4.43
6.90
5.54
3.60
6.80
6.61
5.73
0.23
0.18
0.41
0.29
0.21
0.12
0.25
0.32
−78 10 min
−78 0.5
60 5.4
85 6.7
100 5.3
5.3
6.4
4.7
5.9
5.4
15.6
8.1
8.6
1.08
1.05
1.05
1.07
1.06
1.13
1.11
multi
slower than that of P3D and was not complete in 1 h. If the
polymerization was performed for more than 2 h, then
poly(MP3D) of a predictable molecular weight based on the
monomer to initiator ratio was obtained with a narrow
molecular weight distribution. It should be noted that no
broadening of the molecular weight distribution was observed,
even after 30 h at this temperature. As we discuss in a later
section, the electron-donating character of the methoxy group
on the phenyl ring increased the electron density of the
conjugated double bond in the polymer chain, preventing the
nucleophilic attack of the carbanion at the double bond. It is
interesting that polymer of relatively narrow molecular weight
distributions was also obtained if polymerization was carried
out at −40 or 0 °C for 30 min. However, broadening of the
molecular weight was observed if polymerization was
performed at 0 °C for 5 h, indicating that the above-mentioned
electronic effect was not strong enough to suppress the side
reaction completely.
−78
−78
1
5
100
6
−78 10
−78 20
−40 0.5
100 5.4
100 17.7
100 8.4
100 5.6
a
0
10 min
a
Multimodal distribution.
carbon−carbon double bonds in the polymer chain did not
react with the propagating chain end under these conditions.
However, if the polymerization mixture was left to stand for any
length of time after complete consumption of the monomer
had occurred, then broadening of the molecular weight
distributions toward the higher-molecular-weight side was
observed. Figure 1 shows the SEC results for poly(P3D)
prepared under different polymerization conditions. As will be
discussed in a later section, the polymerization of P3D
proceeded via conjugate addition, forming a conjugated dienyl
structure in the polymer chain. Nucleophilic addition of the
propagating carbanion to this dienyl structure is therefore likely
to be responsible for the broadening of the molecular weight
distribution, as shown in Scheme 2. Similar broadening was
observed when the polymerization was performed at −40 °C,
although the polymerization was complete within 0.5 h. If the
polymerization was carried out at 0 °C, then a polymer of
multimodal molecular weight distribution was obtained
quantitatively, without the formation of a gel. Because the
estimated molecular weight corresponding to the sharp peak on
the lower-molecular-weight side was close to the value
calculated on the basis of the monomer to initiator ratio,
nucleophilic addition of the chain-end carbanion to the double
bond in the polymer chain may have occurred after the
complete consumption of the monomer.
Block Copolymerization. As mentioned above, P3D and
MP3D showed some differences in the rate of polymerization.
The methoxy group on the phenyl ring may increase the
reactivity of the active chain-end species owing to its electron-
donating character; however, in addition, it decreased the
electrophilicity of the carbon−carbon double bond in the
polymer chain. To investigate the reactivity of the chain-end
carbanion, block copolymerization of P3D and MP3D with
styrene and/or 2-vinylpyridine as a second monomer was
performed. Polymerization of the second monomer was carried
out at −78 °C for 2−3 h for 2-vinylpyridine and for 3−18 h for
styrene. Table 3 and Figure 3 summarize the results of block
copolymerizations. When 2-vinylpyridine was used as the
second monomer, a block copolymer of predictable molecular
weight with a narrow molecular weight distribution was
obtained. The SEC peaks moved to the higher-molecular-
weight side, with no residual homo poly(P3D) and (MP3D)
peaks evident. This clearly indicates that the active chain-end
carbanions derived from P3D and MP3D had strong enough
nucleophilicity to initiate the polymerization of 2-vinylpyridine
to form block copolymers. However, a polymer of bimodal
distribution was obtained when styrene, a less-reactive
monomer toward the carbanion, was used as the second
monomer. A mixture of homo poly(P3D) and block copolymer
composed of a high-molecular-weight polystyrene segment and
Anionic Polymerization of MP3D. If the nucleophilic
attack of the chain-end carbanion on the carbon−carbon
double bonds in the polymer was responsible for the
broadening of the molecular weight distribution, it was
speculated that this could be suppressed by changing the
reactivity of both the carbanion and the double bonds. For this
purpose, MP3D, a P3D derivative with an electron-donating
methoxy group, was synthesized and polymerized under similar
Figure 1. SEC chromatograms of poly(P3D) prepared under different polymerization conditions. (a) 0 °C, 10 min, (b) −40 °C, 30 min, (c) −78
C, 1 h, and (d) −78 °C, 20 h. ▼ in plot a indicates the calculated molecular weight based on the monomer to initiator ratio.
°
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Scheme 2. Nucleophilic Addition of a Propagating Carbanion to the Dienyl Structure in the Polymer Chain Causing the
Broadening of the Molecular Weight Distribution
Table 2. Anionic Polymerization of MP3D under Various Conditions
M , kg/mol
n
MP3D, mmol
K-Naph, mmol
temp, °C
time, h
conv, %
calcd
SEC
M /M
w
n
3
3
2
3
2
2
3
2
2
2
2
.14
.04
.96
.58
.96
.75
.16
.75
.61
.55
.65
0.26
0.24
0.24
0.10
0.18
0.21
0.23
0.23
0.15
0.19
0.26
−78
−78
−78
−78
−78
−78
−78
−78
−40
0
10 min
0.5
1
40
75
2.73
4.06
3.95
12.80
6.06
4.80
5.12
4.45
6.35
5.00
3.80
2.41
3.96
4.05
12.10
5.64
4.68
4.71
4.62
6.82
4.75
13.53
1.19
1.07
1.08
1.05
1.04
1.05
1.05
1.05
1.05
1.21
5.61
85
2
100
85
5
10
15
30
0.5
0.5
5
100
100
100
100
100
100
0
initiate the anionic polymerization of styrene, it can be
concluded that the nucleophilicities of the propagating chain
ends derived from P3D and MP3D were much lower than
those of ordinary 1,3-dienes.
Microstructure of the Resulting Polymers. When diene
polymerization is studied, control and analysis of the
microstructure of the resulting polymer are of great importance
because the physical properties of the polymer strongly depend
on the microstructure. Because the [3]dendralene derivatives
used in this study contained two cross-conjugated dienyl
frames, it was extremely interesting to analyze which double
bonds participated in the polymerization. Therefore, the
microstructures of the resulting polymers were analyzed by
1
13
H and C NMR spectroscopy.
In principle, three vinyl addition structures and two
conjugate addition structures can be formed in the polymer-
ization of P3D and MP3D, as shown in Scheme 3. Among
these, only the 5,6 structure has an aliphatic methyne carbon in
the polymer chain. In addition, an aliphatic quaternary carbon
should be present only in the other two vinyl structures (1,2-
Figure 2. SEC chromatograms of poly(MP3D) prepared under
different polymerization conditions. (a) 0 °C, 30 min, (b) 0 °C, 5 h,
13
and 3,4-). Therefore, C NMR analysis can be employed to
(
c) −40 °C, 30 min, (d) −78 °C, 2 h, and (e) −78 °C, 30 h.
determine easily if the vinyl structures are present in the
synthesized polymers. Figure 4 shows the 13C NMR spectrum
of poly(MP3D) prepared at −78 °C. In the aliphatic carbon
region, only three signals were observed at 55, 33−34, and 25−
28 ppm. Though each of the signals appeared as a multiplet, the
mode of monomer addition such as the 4,1 and 4,6 addition,
geometries of the monomer units, E and Z, and their
distribution might have caused the signal splitting. By
comparing the ordinary complete proton-decoupled spectrum
to the DEPT135 spectrum, the signal around 55 ppm could be
assigned to the methoxy carbon on the phenyl ring, with the
others due to methylene carbons. Importantly, no signals
attributable to methyne and quaternary carbons were observed
in this region, within the detectable limit, indicating that no or
very little vinyl addition structure was incorporated into
a poly(P3D) segment was obtained in 3 h. In the case of
MP3D, the rate of initiation was so slow that only a slight
broadening of the SEC peak to the higher-molecular-weight
side was observed in 3 h, and the conversion was very low. It
was necessary to carry out the polymerization for 18 h to
achieve the complete consumption of styrene. This could be
explained by the lower nucleophilicity of the carbanion derived
from MP3D compared to that from P3D. This is also in
accordance with the results of the homopolymerization
discussed above, where the nucleophilic attack of the
propagating carbanion at the carbon−carbon double bond in
the polymer chain was less likely to occur in the polymerization
of MP3D. Because it is well known that an ordinary carbanion
derived from 1,3-dienes such as 1,3-butadiene and isoprene can
1
poly(MP3D). This was further confirmed using H NMR
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Table 3. Anionic Block Copolymerization of P3D and MP3D Using Styrene (St) and 2-Vinylpyridine (2-VP) as a Second
Monomer at −78 °C
M , kg/mol
n
initiator
K-Naph
monomer
time, h
conv, %
calcd
obsd
M /M
w
n
P3D
5
3
100
92
6.3
7.0
1.06
+
2−
a
2K (P3D)n
St
21.3
332.8(7.6)
bimodal
K-Naph
P3D
2
2
100
80
11.7
32.6
12.8
32.6
1.07
1.14
+
2−
2K (P3D)n
2-VP
K-Naph
MP3D
6
3
100
34
7.2
7.2
7.6
1.08
1.12
+
2−
2−
2−
2K (MP3D)n
St
19.7
K-Naph
MP3D
21
18
100
100
5.4
7.2
1.07
+
a
2
K (MP3D)n
St
21.7
395.0 (7.6)
bimodal
K-Naph
MP3D
3
2
100
84
6.4
5.2
1.19
1.13
+
2
K (MP3D)n
2-VP
16.6
15.5
a
Molecular weight corresponding to the SEC peak on the higher-molecular-weight side. The value in parentheses corresponds to the peak on the
lower-moleculer-weight side.
Figure 3. SEC chromatograms of block copolymers (−) and original homopolymer (---). (a) P3D anion + styrene, (b) MP3D anion + styrene, (c)
P3D anion + 2-vinylpyridine, and (d) MP3D anion + 2-vinylpyridine.
Scheme 3. Possible Microstructures
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Figure 4. 13C NMR: (a) ordinary complete decoupling and (b) DEPT135 spectra of poly(MP3D) prepared at −78 °C.
1
Figure 5. H NMR spectrum of poly(MP3D) prepared at −78 °C.
1
analysis. Figure 5 shows the H NMR spectrum of poly-
(
carbon double bonds and a methoxy proton were observed at
1.8−2.5 and 3.7 ppm, respectively. Aromatic proton signals
were observed at 6.6−7.2 ppm. The relative integrated
MP3D) prepared at −78 °C. In the aliphatic proton region,
signals attributable to methylene protons adjacent to carbon−
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Figure 6. COSY spectrum of poly(MP3D) prepared at −78 °C.
Scheme 4. Expected Structure of the Propagating Carbanion
intensities of these signals, 3.9(C−CH ):3(OCH ):4.0-
signals were observed at 111.5 ppm in the 13C NMR spectrum
shown in Figure 4, we could not assign these signals because
their chemical shifts were too close to analyze. The micro-
structure of poly(P3D) was analyzed similarly, and almost
equal proportions of the 4,6 and 1,4 structures were found.
Though the microstructure of the polymers was determined
to be a mixture of 1,4 and 4,6 structures, the mode of monomer
addition was not clear. Each monomer used in this study had
three methylene carbons, C1, C4, and C6, that could be
attacked by the propagating chain-end carbanion, as shown in
Scheme 4. However, because there was no evidence of vinyl
components such as 1,2 or 5,6 structures, it is likely that the
propagating carbanion attacked at C4 on the monomer to form
4,1 and 4,6 anions, resulting in the formation of the above-
mentioned microstructures. The 13C NMR chemical shifts of
the monomers shown in Figure 7 are in agreement with this. In
general, the chemical shift of an olefinic carbon is mainly
affected by the electron density of the double bond. The lower
the electron density, the larger the chemical shift. As can be
2
3
(
arom), were close to the ratio based on the premise that
only the conjugate addition structure was incorporated. In
addition, the fractional number of olefinic proton signals at 5.2
and 6.1 ppm indicated that two or more structures were
included in the polymer chain. Figure 6 shows the COSY
spectrum of poly(MP3D). The olefinic proton signals at 5.2
and 6.1 ppm exhibited cross peaks with the aliphatic proton
signal at 2 ppm and the olefinic proton signal at 4.9 ppm,
respectively. This indicated that the signal at 5.2 ppm is due to
the olefinic methyne proton in the 4,6 structure, with that at 6.1
ppm attributable to the pendant vinyl methyne proton in the
1,4 structure. From the relative integrated intensities of these
signals, the 4,6 structure was observed to predominate slightly
in poly(MP3D). No apparent change in the microstructure was
observed when changing the polymerization temperature. In
the 1,4 and 4,6 structures, two types of methylene carbons, C6
and C1, respectively, should be present in the side group as
shown in Scheme 3. Although multiple olefinic methylene
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13) Takenaka, K.; Akagawa, Y.; Miya, M.; Takeshita, H.; Shiomi, T.
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14) Takenaka, K.; Nakashima, D.; Miya, M.; Takeshita, H.; Shiomi,
T. e-J. Soft Mater. 2013, in press.
15) Tsuji, Y.; Suzuki, T.; Watanabe, Y.; Takegami, Y. Macromolecules
981, 14, 1194−1196.
16) Hirao, A.; Sakano, Y.; Takenaka, K.; Nakahama, S. Macro-
molecules 1998, 31, 9141−9145.
17) (a) Sultanov, N. T.; Mekhtiev, S. D.; Efendieva, T. G.;
(
(
(
Figure 7. 13C NMR chemical shifts of the dienyl skeleton in the
monomer.
(
1
(
seen from Figure 7, the C4 methylene carbon resonates at the
lowest field, indicating that the carbon is most susceptible to
the nucleophilic attack of the carbanion to form a resonance
hybrid consisting of 4,3, 4,1, and 4,6 anions. Among these
anions, the 4,3 anion should be the most stable because of
hybridization; in addition, it is a sterically hindered tertiary
anion, making propagation difficult. Thus, only the 4,1 and 4,6
anions participate in propagation, resulting in the formation of
the observed 1,4 and 4,6 structures in the polymer.
(
Kodzhaeva, Sh. Ya.; Alieva, M. A.; Balakishieva, M. M.; Mamedov, F.
A. USSR Patent 280,476, 1970. See also Chem. Abstr., 1971, 74,
142040. (b) Nunomoto, S.; Yamashita, Y. J. Org. Chem. 1979, 44,
4788−4791.
(18) Uhrig, D.; Mays, J. W. J. Polym. Sci., Part A: Polym. Chem. 2005,
4
3, 6179−6222.
CONCLUSIONS
■
Anionic polymerization of P3D and MP3D was carried out in
THF with a potassium counterion. Poly(P3D) of a narrow
molecular weight distribution was obtained if the polymer-
ization was carried out at −78 °C and terminated after an
appropriate polymerization time. Broadening of the molecular
weight distribution was observed if the polymerization mixture
was left to stand for a period of time after complete
consumption of the monomer had occurred. In the case of
poly(MP3D), such broadening did not occur if the reaction was
carried out at −78 °C. The nucleophilicities of the carbanions
derived from these monomers were too low to initiate the
polymerization of styrene but high enough to initiate the
polymerization of 2-vinylpyridine. Microstructural analysis of
the resulting polymers by NMR revealed that they were
mixtures of 1,4 and 4,6 structures, and no vinyl addition was
observed in the polymer chain.
AUTHOR INFORMATION
Corresponding Author
E-mail: ktakenak@vos.nagaokaut.ac.jp.
■
*
Notes
The authors declare no competing financial interest.
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