Living anionic polymerization of 4-(α-alkylvinyl)styrene derivatives

Article abstract of DOI:10.1007/s00706-006-0493-1

The anionic polymerization of four bis-functionalized styrene derivatives with α-alkylvinyl groups have been carried out in THF at -78°C with the initiator prepared from oligo(α-methylstyryl)lithium and potassium tert-butoxide. The four monomers herein us

Full text of DOI:10.1007/s00706-006-0493-1

Monatshefte f€ur Chemie 137, 855–867 (2006)
DOI 10.1007/s00706-006-0493-1
Living Anionic Polymerization
of 4-(a-Alkylvinyl)styrene Derivatives
Akira Hirao1;ꢀ, Takahiro Imai1, Kenji Watanabe1,
Mayumi Hayashi2, and Kenji Sugiyama1
1
Polymeric and Organic Materials Department, Tokyo Institute of Technology (TIT),
Ohokayama, Meguro-ku, Tokyo, Japan
2
Petrochemicals Research Laboratory, Sumitomo Chemical Co., Ltd., 2-1, Kitasode,
Sodegaura-city, Chiba Prefecture, Japan
Received July 1, 2005; accepted January 23, 2006
Published online July 6, 2006 # Springer-Verlag 2006
Summary. The anionic polymerization of four bis-functionalized styrene derivatives with ꢀ-alkylvinyl
groups have been carried out in THF at ꢁ78ꢂC with the initiator prepared from oligo(ꢀ-methylstyryl)-
lithium and potassium tert-butoxide. The four monomers herein used are 4-isopropenylstyrene (4),
3-isopropenylstyrene (5), 2-isopropenylstyrene (6), and 4-(ꢀ-isopropylvinyl)styrene (7). It was found
that under such polymerization conditions, the vinyl groups of both 4 and 7 are selectively polymerized
and the isopropenyl and ꢀ-isopropylvinyl groups remain completely intact to afford stable living
anionic polymers. As expected, the resulting polymers possessed precisely controlled chain lengths
and narrow molecular weight distributions. More importantly, they also possessed the pendant iso-
propenyl and ꢀ-isopropylvinyl group in each monomer unit possible for further modification. On the
other hand, the anionic polymerization of either 5 or 6 proceeded more or less along with the unwanted
side reactions leading to chain-branching, followed by cross-linking. The positional effect of isopro-
penyl group on the polymerization and the cause of possible side reactions were discussed.
Keywords. Anions; Alkenes; Block copolymerization; Carbanions; Controlled molecular weight.
Introduction
It is known that gelling occurs immediately in the anionic polymerization of 1,4-
divinylbenzene (1) or its isomers of representative bis-functionalized monomers,
resulting in the formation of highly cross-linked materials insoluble in all solvents
[1–5]. On the other hand, treatment of 1,3-diisopropenylbenzene (2) or 1,4-diiso-
propenylbenzene (3) with an anionic initiator leads to a soluble polymer with a
pendant isopropenyl group at up to 50% or even higher conversions [6–8]. In
practice, the polymerization proceeded homogeneously and the resulting polymers
ꢀ
Corresponding author. E-mail: ahirao@polymer.titech.ac.jp

856
A. Hirao et al.
Scheme 1
were essentially linear polymers with relatively narrow molecular weight distribu-
tions, their Mw=Mn values being less than 1.3. Thus, diisopropenylbenzenes appear
to be different from divinylbenzenes in the anionic polymerization behavior. This
may possibly be because the reactivity of isopropenyl group becomes lower than
that of vinyl group presumably due to electron donating ability and steric bulkiness
of the ꢀ-methyl group, although the propagating chain-end anions derived from
diisopropenylbenzenes seem more reactive than those derived from divinyl-
benzenes by the same electronic effect. However, the occurrence of branching,
followed by cross-linking was not avoidable at the final stage of the polymerization
of diisopropenylbenzenes.
Herein, the question has been raised how the anionic polymerization of a
bis-functionalized monomer substituted with both vinyl and isopropenyl groups
proceeds. We speculated that if this monomer was treated with an anionic
initiator, the vinyl group would be predominantly polymerized and the isopro-
penyl group would remain as such, since the vinyl group is more reactive
than the isopropenyl group and the generated styryl-type anion similar to the
1-derived anion seems less reactive than the 3-derived ꢀ-methylstyryl-type
anion as mentioned above. It is therefore expected that a new living polystyrene
functionalized with a pendant isopropenyl group can be produced as illustrated
in Scheme 1.
In this study, we report on the anionic polymerization of a series of bis-func-
tionalized monomers substituted with both vinyl and isopropenyl groups in order to
examine the possibility of living anionic polymerization. These monomers herein
examined are 4-isopropenylstyrene (4) and its meta- and ortho-isomers, 3-isopro-
penylstyrene (5) and 2-isopropenylstyrene (6), and one more similar styrene deri-
vative, 4-(ꢀ-isopropylvinyl)styrene (7), as shown below (Formulae).
monomers

Living Anionic Polymerization
857
Needless to say, the practical significance of this polymerization lies in the fact
that the pendant C¼C bonds activated by phenyl groups are available for further
modification. This is a part of our program to study the living anionic polymeriza-
tion of a series of functionalized styrene derivatives [9–12].
Results and Discussion
Anionic Polymerization of 4
The anionic polymerization of 4 was first carried out in THF at ꢁ78ꢂC with sec-
BuLi as an initiator. Under such conditions, the polymerization of 4 was very rapid
and complete within 5 min. No gelling occurred at all and a soluble polymer was
quantitatively obtained. The addition of the first aliquot of 4 to sec-BuLi turns
instantaneously to reddish violet in color, indicating the generation of the anion
derived from 4. This color disappeared immediately by quenching with degassed
methanol. The polymer was precipitated in methanol and purified by reprecipita-
tion twice from THF to methanol and freeze-drying.
1
The H NMR spectrum of the resulting polymer showed that the vinyl group
had completely reacted and the signals for the isopropenyl group remained in more
than 95%. This indicates that the vinyl group is predominantly polymerized under
the conditions employed here. However, the SEC profile exhibits a multimodal
distribution broadening from 103 to 105 in the molecular weight as shown in
Fig. 1.
The sharp single peak (A) (Mn SEC ¼ 9.2 kg=mol, Mw=Mn ¼ 1.06) corresponds
nearly to the molecular weight (Mn ¼ 8.5 kg=mol) assuming that 4 polymerizes in a
living manner. On the basis of these analytical results, we can explain what hap-
pens in the anionic polymerization of 4 as follows: At first, 4 undergoes living
Fig. 1. SEC curve of poly(4) obtained with sec-BuLi

858
A. Hirao et al.
polymerization, followed by the attacking of the propagating chain-end anion grad-
ually on the pendant isopropenyl group in another polymer chain, thus leading to
chain-branching. A similar result was obtained by the anionic polymerization in
THF at ꢁ78ꢂC with oligo(ꢀ-methylstyryl)lithium as an initiator.
In contrast to such results, the treatment of oligo(ꢀ-methylstyryl)lithium with
potassium tert-butoxide (tBuOK) can be very effective to suppress the unwanted
side reactions leading to the chain-branching. With this treatment, the counter
cation of the initiator was changed from Liþ to Kþ by shifting the equilibrium.
The initiator was prepared by the addition of a 5-fold excess of tBuOK to oligo(ꢀ-
methylstyryl)lithium, followed by allowing the mixture to stand for additional
Table 1. Anionic polymerization of 4 in THF at ꢁ78ꢂC for 5–10 mina
Initiator typeb, mmol
4 mmol
Mn (kg=mol)
c
calcd
obsdc
Mw=Mn
sec-BuLi, 0.0751
4.41
3.79
14.5
6.25
7.33
8.42
5.50
2.88
8.46
9.44
20.7
9.33
27.5
61.4
17.7
10.7
14.9
1.44
1.45
1.02
1.03
1.02
1.02
1.03
1.06
sec-BuLi=ꢀ-MeSt, 0.0578
sec-BuLi=ꢀ-MeSt=tBuOK, 0.105
sec-BuLi=ꢀ-MeSt=tBuOK, 0.104
sec-BuLi=ꢀ-MeSt=tBuOK, 0.0402
sec-BuLi=ꢀ-MeSt=tBuOK, 0.0200
Cumyl-K, 0.0447
12.1
21.3 (20.4)d
9.24
25.9
61.4
19.8
K-Naph, 0.0774
16.3
a
b
t
Yields of polymer were quantitative in all cases; ꢀ-MeSt: ꢀ-methylstyrene, BuOK: potassium
tert-butoxide, Cumyl-K: cumyl potassium, K-Naph: potassium naphthalenide; c determined by SEC
d
relative to polystyrene; end-group analysis by H NMR (see Ref. [13])
1
Fig. 2. SEC curve of poly(4) obtained with sec-BuLi=ꢀ-MeSt=tBuOK

Living Anionic Polymerization
859
10 min. Then, 4 was added to polymerize in THF at ꢁ78ꢂC for 5 min. The color
was immediately changed from orange red to the characteristic reddish violet and
remained unchanged until the quenching with degassed methanol. The polymer
was obtained quantitatively. The results are summarized in Table 1.
As shown in Fig. 2, the resulting polymer exhibits a sharp monomodal SEC
distribution, the Mw=Mn value being 1.02. No higher molecular weight shoulder
was present. The Mn value measured by SEC is in good agreement with the calcu-
lated value from the ratio of [4] to [initiator]. The Mn value determined by the end-
1
group analysis with H NMR also agreed well with that calculated [13].
1
The H NMR spectra of 4 and the resulting polymer show that the signals at
6.75, 5.79, and 5.28 ppm (signals (a), (b), and (d) in Fig. 3) corresponding to the
vinyl protons completely disappear, while those at 5.43 and 5.12 ppm (signals (c)
and (e) in Fig. 3) assignable to the isopropenyl vinylene protons remain in expected
intensities (see Fig. 3).
Fig. 3. 1H NMR spectra of 4 (A) and poly(4) (B)

860
A. Hirao et al.
Likewise, the 13C NMR analysis also indicates the same conclusion. Thus
obviously, all analytical results confirm that the vinyl group of 4 is selectively
polymerized in a living manner and the pendant isopropenyl group remained com-
pletely intact during and after the conclusion of the polymerization. Thus, the
living anionic polymerization of 4 is achieved by using the initiator system pre-
t
pared from BuOK and oligo(ꢀ-methylstyryl)lithium. In order to further evaluate
the usefulness of the initiator system in the polymerization of 4, three more sets of
the polymerization of 4 were carried out at different monomer to initiator ratios
under the same conditions. As was seen in Table 1, the difference between pre-
dicted and observed molecular weights is less than 10% in each of all instances.
Their molecular weight distributions were found to be extremely narrow, the
Mw=Mn values being less than 1.03. These results again confirm the living nature
of the selective anionic polymerization of 4. The success of the living anionic
polymerization of 4 is undoubtedly resulted from the combination of the less
reactive isopropenyl group and the styryl-type anion stabilized via resonance of
the para-substituted isopropenyl group.
The effectiveness of the initiator bearing Kþ as a counter cation was also dem-
onstrated by the successful results of the living anionic polymerization of 4 with
either cumylpotassium or potassium naphthalenide as shown in Table 1. This can
be explained that the chain-end carbanion with Kþ as a counter cation is more
stable than that with Liþ which is dissociated from the carbanion due to strong
coordination by a few THF molecules. Thus the anion attack on the pendant iso-
propenyl group was prevented.
One of the most advantageous features of the living polymerization is to be able
to synthesize the block copolymers with precisely controlled structures. The synthe-
sis of two kinds of block copolymers was carried out by a two-step sequential
monomer addition, styrene followed by 4 and vice-versa with the initiator prepared
t
from BuOK and oligo(ꢀ-methylstyryl)lithium. The first and second polymeriza-
tion times were 5 min and 5 min, respectively. Yields of the polymers were quan-
titative in both cases. The results are summarized in Table 2.
Figure 4 shows SEC profiles of the polymers obtained at the first- and second-
stages of the block copolymerization where styrene and 4 were added in this order.
One can see that the peak (A) of the first-stage polymer disappears completely and
moves toward higher molecular weight after the addition of 4. The molecular
weight distribution of the second-stage polymer remains narrow. Agreement
between the Mn value as well as the composition observed and those calculated
Table 2. Block copolymerization of 4 and styrene in THF at ꢁ78ꢂCa
Initiatorb
1st monomer
2nd monomer
Mn (kg=mol)
mmol
type, mmol
type, mmol
d
calcd
obsdc
Mw=Mn
0.103
0.103
Styrene, 5.25
4, 6.95
15.6
21.4
16.2
21.6
1.04
1.17
4, 11.9
Styrene, 6.48
a
Yields of polymer were quantitative in all cases; b sec-BuLi=ꢀ-MeSt=tBuOK; c determined by SEC
1
d
and H NMR; determined by SEC

Living Anionic Polymerization
861
Fig. 4. SEC curves of polystyrene-block-poly(4) (A) and base polystyrene (B)
is quite satisfactory in the second-stage polymer. Thus, the block copolymerization
of styrene followed by 4 proceeded as desired to afford the expected AB diblock
copolymer of polystyrene-block-poly(4). The success of this block copolymeri-
zation further confirms the living nature of the polymerization of 4 under the
employed conditions.
On the other hand, the block copolymerization by reversing the sequence of
monomer addition, namely 4 followed by styrene, was not completely successful
under the same conditions. As can be seen in Fig. 5, the formation of a small higher
molecular weight shoulder is observed in addition to the main sharp peak corre-
Fig. 5. SEC curves of poly(4)-block-polystyrene (A) and base poly(4) (B)

862
A. Hirao et al.
sponding to the expected BA diblock copolymer. Since a styrene-derived anion
generated at the second-stage polymerization seems more reactive than the
4-derived anion stabilized by the resonance effect via the para-substituted isopro-
penyl group, the styrene-derived anion may react gradually with the pendant iso-
propenyl group. Thus, the addition order of the two monomers is important in the
block copolymerization, although the styrene-derived anion can initiate the poly-
merization of 4 and vice-versa.
Anionic Polymerization of 5 and 6
In order to elucidate the positional effect of isopropenyl group on the polymeriza-
tion, the meta- and ortho-isomers, 5 and 6, were newly synthesized and polymer-
ized under the same conditions. The anionic polymerization of 5 was similarly
t
carried out in THF at ꢁ78ꢂC with the initiator prepared from BuOK and
oligo(ꢀ-methylstyryl)lithium. Upon addition of 5 to the initiator, an immediate
color change for orange red to dark red occurred. The polymerization of 5 was
also rapid and complete within 5 min. A soluble polymer was obtained quantita-
tively. The 1H NMR analysis of the resulting polymer indicated that the vinyl group
of 5 was selectively polymerized. However, a certain amount of higher molecular
weight fraction is formed as can be seen in the SEC profile (Fig. 6(A)). By termi-
Fig. 6. SEC curves of poly(5) terminated after 5 min (A) and 1 min (B)

Living Anionic Polymerization
863
Scheme 2
nating the polymerization after 1 min, a polymer with a narrow monomodal SEC
distribution was obtained in 82% yield (see Fig. 6(B)). The Mn value of this poly-
mer measured by SEC is in good agreement with that calculated. Accordingly, it
may be concluded that the anionic polymerization of 5 proceeds in a living manner,
followed by the reaction of the living chain-end anion gradually with the pendant
isopropenyl group in another polymer chain.
In the anionic polymerization of 6 under the same conditions, turbidity
appeared immediately following the addition of 6, and the precipitate was found
within a few second to cause gelation. After 5 min polymerization time, the gel-like
insoluble polymer was obtained in 43% yield. By extending the reaction time to
3 h, the insoluble polymer was quantitatively obtained.
As mentioned above, the 4-derived anion is stabilized by the resonance via the
para-substituted isopropenyl group. On the other hand, the same resonance effect
can not be expected for the 5-derived anion whose isopropenyl group is placed at
the meta-position. Accordingly, the 5-derived anion is more reactive than the
4-derived anion and thereby reacted with the pendant isopropenyl group in the
polymer to a certain extent under the same conditions. The 6-derived anion,
similar to the 4-derived anion, can be stabilized by the resonance via the
ortho-placed isopropenyl group. However, gelling occurred in this polymeriza-
tion. Therefore, we speculate that the 6-derived anion once generated reacts
intramolecularly with the ortho-isopropenyl group to generate a more reactive
ꢀ-methylstyrene-derived anion, followed by attack of the anion on the pendant
isopropenyl group, as illustrated in Scheme 2. Thus, the influence of substitution
position of the isopropenyl group is of significance on the anionic polymerization
behavior. The para-substitution of isopropenyl group is essential to achieve the
living anionic polymerization.
Anionic Polymerization of 7
As mentioned in the preceding section, the living anionic polymerization of 4 was
successfully demonstrated. It was however observed that the propagating chain-end
anion reacted gradually with the pendant isopropenyl group and a small high
molecular weight shoulder was produced by allowing the polymerization mixture
to stand for additional 20 min under the same conditions. Accordingly, the 4-
derived chain-end anion was not completely stable toward the isopropenyl group
in THF even at ꢁ78ꢂC. In order to suppress such unwanted side reactions, we have
synthesized a new styrene derivative 7 in which ꢀ-methyl group of the isopropenyl
group is replaced by a more sterically bulky isopropyl group.

864
A. Hirao et al.
Table 3. Anionic polymerization of 7 in THF at ꢁ78ꢂCa
Initiatorb mmol
7 mmol
time min
Mn (kg=mol)
d
calcd
obsdc
Mw=Mn
0.0681
0.0508
0.0916
5.29
6.98
3.58
5
10
60
11.7
20.6
7.19
12.9
25.2
7.53
1.03
1.08
1.04
a
Yields of polymer were almost quantitative; b sec-BuLi=ꢀ-MeSt=tBuOK; c determined by RALLS;
determined by SEC
d
The anionic polymerization of 7 was carried out with the initiator from tBuOK
and oligo(ꢀ-methylstyryl)lithium in THF at ꢁ78ꢂC for 5 min. As expected, the
selective living anionic polymerization of 7 was achieved without problem. The
1H NMR analysis of the resulting polymer showed that all the vinyl groups reacted
and the ꢀ-isopropylvinyl group remained completely intact. In order to examine
the stability of the living polymer, the polymerization times were extended to
10 min and 60 min, respectively. Any higher molecular weight shoulder was not
observed in the polymer obtained after 10 min or even after 60 min, indicating that
the living anionic polymer derived from 7 is much more stable than that derived
from 4. As can be seen in Table 3, a comparison of the calculated and observed Mn
values shows good agreement in each instance. These polymers all possessed sharp
monomodal SEC distributions. The replacement of methyl group by isopropyl one
is thus very effective.
Conclusions
The anionic polymerization of four bis-functionalized styrene derivatives 4–7 was
investigated under the conditions in THF at ꢁ78ꢂC mainly with use of the initiator
t
prepared from oligo(ꢀ-methylstyryl)lithium and BuOK. These monomers herein
used were 4-isopropenylstyrene (4), 3-isopropenylstyrene (5), 2-isopropenylstyrene
(6), and 4-(ꢀ-isopropylvinyl)styrene (7). Under such conditions, both 4 and 7
underwent living polymerization where their vinyl groups were selectively poly-
merized and the isopropenyl and ꢀ-isopropylvinyl groups remained completely
intact. The resulting polymers possessed precisely controlled chain lengths and
narrow molecular weight distributions (Mw=Mn<1.08) as well as the pendant iso-
propenyl and ꢀ-isopropylvinyl groups in all monomer units possible for further
modification. In contrast to the successful living polymerization of 4 and 7, the
polymerization of 5 and 6 proceeded more or less along with the unwanted side
reactions, resulting in the formation of polymers with chain-branching or insoluble
cross-linked polymers. The positional effect of the isopropenyl group is thus cru-
cial to achieve the living anionic polymerization and the para-substitution is essen-
tial for this purpose.
It was also found that the replacement of the ꢀ-methyl group of 4 by a sterically
bulkier isopropyl group is effective to stabilize the living anionic polymer derived.
In fact, the living polymer derived from 7 was stable and no side reactions occurred
at all in THF at ꢁ78ꢂC even after 1 h. In forthcoming study, the anionic polymeri-

Living Anionic Polymerization
865
zation of a series of structural similar bis-functionalized monomers will be reported
in the very near future.
Experimental
Materials
All chemicals (>98%) were purchased from Aldrich, Japan, and used as received unless otherwise
stated. 4-Chlorostyrene (>99%, Hokko Chemical Industry Co., Ltd.) was distilled over CaH2 under
reduced pressure. Acetone was distilled over K2CO3 under nitrogen. Isobutyric anhydride was distilled
over CaH2 under reduced pressure. Both 2- and 3-bromostyrenes were prepared by the Wittig reaction
of the corresponding bromobenzaldehyde with methylenetriphenylphosphorane. The resulting styrenes
were distilled over CaH2 under reduced pressures. THF was refluxed over Na wire, distilled over
LiAlH4 under nitrogen, and then distilled from its sodium naphthalenide solution on a vacuum line.
Potassium tert-butoxide (tBuOK) was prepared by reacting a stoichiometric amount of tert-butanol
with potassium naphthalenide in THF at ꢁ78ꢂC under a high vacuum condition (10ꢁ6 Torr). Potassium
naphthalenide was prepared by the reaction of naphthalene with potassium in THF. Cumylpotassium
was prepared by the reaction of cumyl methyl ether with K=Na alloy in THF according to the previous
method [14]. Both oligo(ꢀ-methylstyryl)lithium and potassium were prepared by the reaction of sec-
BuLi or potassium naphthalenide with a 3-fold excess of ꢀ-methylstyrene in THF at 25ꢂC for 30s and
subsequently by allowing to stand at ꢁ78ꢂC for 15 min.
Measurements
1
Both H and 13C NMR spectra were recorded on a Bruker DPX300 in CDCl3. Chemical shifts were
1
recorded in ppm downfield relative to tetramethylsilane (ꢁ ¼ 0) for H NMR and relative to CDCl3
(ꢁ ¼ 77.1) for 13C NMR. Size exclusion chromatography (SEC) was performed on a Tosoh HLC-8020
with ultraviolet (254 nm) and refractive index detection using THF as a carrier solvent at a flow rate of
1.0 cm3=min at 40ꢂC. Calibration curves were made to determine number-average molecular weight
(Mn) and molecular weight distribution (Mw=Mn) with standard polystyrene samples. Vapor pressure
osmometry (VPO) measurements were made with a Corona 117 instrument in benzene at 40ꢂC with a
highly sensitive thermoelectric couple (TM-32K: sensitivity 35 000ꢂV ꢃ 10%=1 M) and with equip-
ment of very exact temperature control. Right angle laser light scattering (RALLS) was performed by
an Asahi Techneion AT-2002 equiped with a Viscotek TDA model 301 triple detector array using THF
as a carrier solvent at a flow rate of 1.0 cm3=min at 30ꢂC.
4-Isopropenylstyrene (4)
Under nitrogen, the Grignard reagent was prepared by adding slowly 4-chlorostyrene (20.0 g,
144 mmol) to magnesium (4.80 g, 196 mmol) in THF (140cm3) at 70ꢂC for 1 h, followed by allowing
to react at 70ꢂC for additional 2 h. The Grignard reagent thus prepared was cooled to 0ꢂC and acetone
(11.6g, 200 mmol) was added dropwise and the reaction mixture was allowed to react at 25ꢂC
for additional 15 h. The reaction mixture was then neutralized with 2N HCl, extracted with ether,
washed with brine, and dried over MgSO4. Removal of the solvent under reduced pressure yielded
crude 4-(2-hydroxy-2-propyl)styrene (23.2 g, 99%). It was used in the next reaction without purifica-
tion. 4-(2-Hydroxy-2-propyl)styrene (23.2 g, 113 mmol) and a small amount of p-toluenesulphonic
acid were dissolved in benzene (80 cm3) and the reaction mixture was refluxed for 3 h. It was then
neutralized with NaHCO3, extracted with ether, and dried over MgSO4. Removal of the solvent under
reduced pressure followed by column chromatography and fractional distillation (51ꢂC=1 mm Hg)
1
yielded 4-isopropenylstyrene (10.3 g, 50%) as a white crystal (mp 34–35ꢂC). H NMR (300 MHz,
CDCl3): ꢁ ¼ 7.40–7.49 (m, 4H, Ar), 6.75 (dd, 1H, J ¼ 10.9 and 19.0Hz, CH2¼CH–Ar), 5.28 and
5.79 (2d, 2H, J ¼ 10.8 and 17.5Hz, CH2¼CH–Ar), 5.12 and 5.43 (2s, 2H, CH2¼C(Ar)CH3), 2.19 (s,
3H, –CH3) ppm; 13C NMR (75 MHz, CDCl3): ꢁ ¼ 142.9 (CH2¼C(Ar)CH3), 140.7, 136.5, 126.1, 125.7

866
A. Hirao et al.
(Ar), 136.8 (CH2¼CH–Ar), 113.7 (CH2¼CH–Ar), 112.4 (CH2¼C(Ar)CH3), 21.8 (–CH3) ppm; Anal
(C11H12): calcd C 91.61, H 8.39; found C 91.62 H 8.39.
3-Isopropenylstyrene (5)
The title monomer 5 was similarly synthesized by the reaction of the Grignard reagent of 3-bromo-
styrene with acetone, followed by dehydration. After usual work-up, 5 was purified by column chro-
matography, followed by fractional distillation at 48ꢂC=2 mm Hg to give 5.83 g (47%) of 5 as a
1
colorless liquid. H NMR (300MHz, CDCl3): ꢁ ¼ 7.31–7.43 (m, 4H, Ar), 6.76 (dd, 1H, J ¼ 10.9
and 19.0Hz, CH2¼CH–Ar), 5.19 and 5.70 (2d, 2H, J ¼ 10.8 and 17.6Hz, CH2¼CH–Ar), 5.04 and
5.33 (2s, 2H, CH2¼C(Ar)CH3), 2.10 (s, 3H, –CH3) ppm; 13C NMR (75 MHz, CDCl3): ꢁ ¼ 143.2,
141.6, 128.4, 125.2, 125.1, 123.7 (Ar), 137.5 (CH2¼C(Ar)CH3), 137.0 (CH2¼CH–Ar), 113.9
(CH2¼CH–Ar), 112.7 (CH2¼C(Ar)CH3), 22.1 (–CH3) ppm; Anal (C11H12): calcd C 91.61, H 8.39;
found C 91.63, H 8.39.
2-Isopropenylstyrene (6)
The title monomer 6 was similarly synthesized by the reaction of the Grignard reagent of 2-bromo-
styrene with acetone, followed by dehydration. After usual work-up, 6 was purified by column
chromatography and fractional distillation twice at 49ꢂC=2 mm Hg to give 2.11g (21%) of 6 as a
1
colorless liquid. H NMR (300MHz, CDCl3): ꢁ ¼ 7.06–7.46 (m, 4H, Ar), 6.84 (dd, 1H, J ¼ 10.9
and 19.0Hz, CH2¼CH–Ar), 5.14 and 5.59 (2d, 2H, J ¼ 10.8 and 17.6Hz, CH2¼CH–Ar), 4.80 and
5.16 (2s, 2H, CH2 ¼ C(Ar)CH3), 1.97 (s, 3H, –CH3) ppm; 13C NMR (75 MHz, CDCl3): ꢁ ¼ 144.9
(CH2¼C(Ar)CH3), 143.0, 134.9, 128.1, 127.6, 127.1, 125.5 (Ar), 135.7 (CH2¼CH–Ar), 123.7
(CH2¼CH–Ar), 112.7 (CH2¼C(Ar)CH3), 21.9 (–CH3) ppm; Anal (C11H12): calcd C 91.61, H 8.39;
found C 91.62, H 8.41.
4-(1-Isopropylvinyl)styrene (7)
Under nitrogen, the Grignard reagent prepared from 4-chlorostyrene (24.7 g, 178 mmol) and magne-
sium (5.30 g, 218 mmol) in THF (100 cm3) was added dropwise to isobutyric anhydride (43.7 g,
276 mmol) dissolved in THF (40 cm3) at 0ꢂC. The reaction mixture was stirred at 25ꢂC for additional
15h and neutralized with 2 N HCl, extracted with ether, and dried over MgSO4. Removal of the
solvent, followed by flash column chromatography (hexanes) yielded 4-vinylisobutyrophenone
(17.1g, 56%) as a viscous yellowish liquid.
Under nitrogen, 4-vinylisobutyrophenone (9.00 g, 51.7mmol) dissolved in THF (40 cm3) was
added dropwise to a THF (50 cm3) solution of methylenetriphenylphosphorane prepared from methyl-
triphenylphosphonium bromide (22.7 g, 63.6mmol) and potassium tert-butoxide (7.92 g, 70.6mmol) at
0ꢂC. The reaction mixture was stirred at 25ꢂC overnight and quenched with water. The organic layer
was extracted with ether and dried over MgSO4. It was concentrated and poured into hexane to remove
triphenylphosphine oxide. After removal of solvents, flash column chromatography (hexanes), fol-
lowed by fractional distillation twice at 65ꢂC=1 mm Hg gave 7 as a colorless liquid (5.16 g, 61%).
1H NMR (300MHz, CDCl3): ꢁ ¼ 6.71 (dd, 1H, J ¼ 10.8 and 17.5Hz, CH2¼CH–Ar), 5.23 and 5.47
(2d, 2H, J ¼ 10.8Hz, CH2¼CH–Ar), 5.03 and 5.21 (2s, 2H, CH2¼C(Ar)CH(CH3)2), 2.77–2.90 (m,
1H, –CH(CH3)2), 1.10 (d, 6H, J ¼ 6.9 Hz, –CH(CH3)2) ppm; 13C NMR (75 MHz, CDCl3): ꢁ ¼ 155.3
(CH2¼(Ar)CH(CH3)2), 142.3, 130.4, 126.8, 126.1 (Ar), 136.6 (CH2¼CH–Ar), 113.6 (CH2¼CH–Ar),
110.0 (CH2¼C(Ar)CH(CH3)2), 32.1 (–CH(CH3)2), 22.1 (–CH(CH3)2) ppm; Anal (C13H16): calcd
C 90.64, H, 9.31; found C 90.81, H 9.31.
Anionic Polymerization
All the monomers 4–7 thus synthesized were distilled over CaH2 under reduced pressure and finally
distilled over dibutylmagnesium (ca. 3 mol%) on the vacuum line.
The anionic polymerization was carried out by adding the monomer to an appropriate initiator,
followed by allowing to polymerize in THF at ꢁ78ꢂC under high vacuum conditions in a glass

Living Anionic Polymerization
867
apparatus equipped with break-seals. The polymerization was then carefully terminated with a 5-fold
excess of degassed methanol in THF at ꢁ78ꢂC and the reaction mixture was poured into a large
amount of methanol to precipitate the polymer. The polymer was collected by filtration, purified by two
reprecipitations from THF to methanol, and then freeze-dried from its benzene solution. A typical
procedure is as follows: The anionic initiator was prepared by mixing oligo(ꢀ-methylstyryl)lithium
t
(0.104 mmol) with BuOK (0.625 mmol) in THF (20.0 cm3) at ꢁ78ꢂC, followed by allowing the
reaction mixture to stand for additional 10min. To this initiator, 4 (0.901g, 6.25mmol) in THF solution
(10.5cm3) chilled to ꢁ78ꢂC was added at once with vigorous shaking and the polymerization mixture
was allowed to react at ꢁ78ꢂC for 5 min. The polymerization was terminated with degassed methanol
and the resulting mixture was poured into a large amount of methanol (300cm3) to precipitate the
polymer. The resulting polymer was reprecipitated twice from its THF solution into methanol and
freeze-dried from its benzene solution for 24h.
References
[1] Worsfold DJ, Zilliox JG, Rempp R (1969) Can J Chem 47: 3379
[2] Eschwey H, Burchard W (1975) Polymer 16: 180
[3] Eschwey H, Burchard W (1975) J Polym Sci: Symp 53: 1
[4] Bauer BJ, Fetters LJ (1978) Rubber Chem Technol 51: 406
[5] Okay O, Funke W (1990) Makromol Chem 191: 1565
[6] Okamoto A, Mita I (1978) J Polym Sci: Polym Chem Ed 16: 1187
[7] Hiller JCH, Funke W (1979) Angew Makromol Chem 76: 161
[8] Lutz P, Beinert G, Rempp P (1982) Makromol Chem 183: 2787
[9] Hirao A, Kubota S, Sueyoshi T, Sugiyama K (2001) Macromol Chem Phys 202: 1044
[10] Hirao A, Loykulnant S, Ishizone T (2002) Prog Polym Sci 27: 1399
[11] Hirao A, Kitamura M, Loykulnant S (2004) Macromolecules 37: 4770
[12] Hirao A, Kitamura M, Hayashi M, Loykulnant S, Sugiyama K (2005) Macromol Symp: in press
t
[13] The anionic polymerization of 4 was carried out with the initiator prepared from BuOK and
oligo(ꢀ-methylstyryllithium) under the conditions in THF at ꢁ78ꢂC for 5 min. The living
polymer produced was then end-capped with a 1.5-fold excess of 1,1-bis(4-trimethylsilylphe-
nyl)ethylene in THF at ꢁ78ꢂC for 1 h. The resulting polymer was carefully purified and
1
characterized by H NMR (end-group analysis) to determine the Mn value by comparing two
signal areas at 6.1–7.6 and 0.2–0.3 ppm assignable to aromatic protons of the main chain and the
terminal silylmethyl protons, respectively.
[14] Ziegler K, Dislich H (1957) Chem Ber 90: 1107