Living Anionic Polymerization of 4-(4-(2-isopropenylphenoxy)butyl)styrene: A New Dual-Functionalized Styrene Derivative Having α-Methylstyrene Functionality

Article abstract of DOI:10.1021/ma0497106

The anionic polymerization of a substituted styrene with α-methylstyryl moiety, 4-(4-(2-isopropenylphenoxy)butyl)styrene (1), was carried out in THF at -78 deg C with sec-BuLi as an initiator. In the anionic polymerization, only the styryl group of 1 can

Full text of DOI:10.1021/ma0497106

4770
Macromolecules 2004, 37, 4770-4775
Living Anionic Polymerization of
4-(4-(2-Isopropenylphenoxy)butyl)styrene: A New Dual-Functionalized
Styrene Derivative Having R-Methylstyrene Functionality
Ak ir a Hir a o* a n d Ma sa h ir o Kita m u r a
Polymeric and Organic Materials Department, Graduate School of Science and Engineering,
2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8552, J apan
Su r a p ich Loyk u ln a n t
National Metal and Materials Technology Center, 73/ 1, Rama VI Road,
Rajdhevee, Bangkok 10400, Thailand
Received February 11, 2004; Revised Manuscript Received April 19, 2004
ABSTRACT: The anionic polymerization of a substituted styrene with R-methylstyryl moiety, 4-(4-(2-
isopropenylphenoxy)butyl)styrene (1), was carried out in THF at -78 °C with sec-BuLi as an initiator. In
the anionic polymerization, only the styryl group of 1 can be selectively polymerized, and on the other
hand, the R-methylstyryl moiety remains intact to afford a stable living polymer carrying R-methylstyryl
functionality in each monomer unit. The resulting polymers possessed precisely controlled molecular
weights and narrow molecular weight distributions. Furthermore, well-defined AB and BA diblock
copolymers, poly(1)-block-polystyrene and polystyrene-block-poly(1), could also be synthesized by a two-
step sequential monomer addition, namely, 1 followed by styrene, or vice versa. The anionic polymerization
of the para-isomeric monomer, 4-(4-(4-isopropenylphenoxy)butyl)styrene (2), proceeded quantitatively
within 5 min under similar conditions in THF at -78 °C. The resulting polymers were observed to possess
precisely controlled molecular weights and narrow molecular weight distributions, but with small amounts
(2-15%) of high molecular weight shoulders, which were presumably arose from the attack of the anionic
species on the pendant R-methylstyrene functionality after the conclusion of the polymerization. With
use of the meta-isomeric monomer 4-(4-(3-isopropenylphenoxy)butyl)styrene (3) in the polymerization
with sec-BuLi, gelation occurred immediately. An insoluble polymer was obtained in 100% yield after 5
min. All attempts to obtain soluble polymers failed in the anionic polymerization of 3. We discussed such
different polymerization behaviors of 1-3 in terms of electron-donation to the R-methylstyryl vinyl group
via the resonance effect and steric hindrance.
In tr od u ction
Herein, we report on the selective living anionic
polymerization of 1 and the related substituted styrene
derivatives with R-methylstyryl moiety. The objective
of this study is to explore the possibility and limitation
of living anionic polymerization of such dual-function-
alized styrene derivatives with R-methylstyryl moiety
as a part of our program to investigate the anionic
polymerization of a series of functionalized styrene
derivatives.11
It is known that both styrene and R-methylstyrene
undergo living anionic polymerization under the identi-
cal conditions to produce stable living polymers.1,2 The
living anionic polymer of styrene thus produced readily
and quantitatively initiates the polymerization of R-
methylstyrene and vice versa to afford well-defined AB
diblock copolymers of polystyrene-block-poly(R-methyl-
styrene) as well as poly(R-methylstyrene)-block-poly-
styrene.3-6 Accordingly, the chain-end anion of living
polystyrene appears similar in reactivity to that of
R-methylstyrene. This indicates that R-methylstyrene
cannot coexist as such with living anionic polymer of
styrene.
During our studies on the living anionic polymeriza-
tion of a series of functionalized styrene derivatives,7-10
we have recently found that the anionic polymerization
of a new dual-functionalized styrene derivative with
R-methylstyryl moiety, 4-(4-(2-isopropenylphenoxy)-
butyl)styrene, (1), proceeds in a living manner in THF
at -78 °C with sec-BuLi. Indeed, the styryl group of 1
could be selectively polymerized, while the R-methyl-
styrene functionality remained completely intact in the
polymerization. This finding may present an exciting
opportunity for the synthesis of polymers of precisely
controlled chain lengths as well as R-methylstyrene
functionality.
Exp er im en ta l Section
Ma ter ia ls. The reagents were purchased from Aldrich
J apan, unless otherwise stated. Styrene (98%), R-methylsty-
rene (98%), tetrahydrofuran (99%, THF), and benzene (98%)
were purified using standard high-vacuum anionic polymer-
ization techniques reported by Hadjichristidis and co-work-
ers.12 sec-BuLi (1.3 M, in cyclohexane) was used as received.
Potassium naphthalenide was prepared according to the
procedure previously described.11
1
Mea su r em en ts. Both H (300 MHz) and 13C (75 MHz) NMR
spectra were measured in CDCl3 using a Bruker DPX300
spectrometer. Chemical shifts were reported in ppm downfield
1
relative to tetramethylsilane (δ 0.00) for H NMR and to CDCl3
(δ 77.1) for 13C NMR. Size-exclusion chromatograms (SEC)
were performed with a TOSOH HLC-8020 instrument with
UV (254 nm) or refractive index detection. THF was used as
a carrier solvent at a flow rate of 1.0 mL/min at 40 °C. Three
polystyrene gel columns of bead size 5 µm and pore size of
200, 75, and 20 Å or bead size 9 µm and pore size of 650, 200,
and 75 Å were used. These sets of the column covered the
molecular weight ranges 103-4 × 105 g/mol and 104-4 × 106
g/mol, respectively. A calibration curve was made to determine
* Corresponding author: Tel +81-3-5734-2131; Fax +81-5734-
2887; e-mail ahirao@polymer.titech.ac.jp.
10.1021/ma0497106 CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/26/2004

Macromolecules, Vol. 37, No. 13, 2004
4-(4-(2-Isopropenylphenoxy)butyl)styrene 4771
Ta ble 1. An ion ic P olym er iza tion of 1 w ith sec-Bu Li in
THF a t -78 °C for 0.5 h a
Mn and Mw/Mn values with standard polystyrenes. Static light
scattering (SLS) equipped with a He-Ne laser (λ ) 632.8 nm)
was performed with Ohotsuka Electronics DSL-600R instru-
ment in benzene at 25 °C. The refractive index increment (dn/
dc) in benzene at 25 °C was determined with an Ohotsuka
Electronics DRM-1020 refractometer operating 632.8 nm.
Vapor pressure osmometry (VPO) measurements were made
with a Corona 117 instrument in benzene at 40 °C with a
highly sensitive thermoelectric couple (TM-32K: sensitivity
35 000 µV ( 10%/1 M) and with equipment of very exact
temperature control. Therefore, molecular weight can be
measured up to 100 kg/mol with an error of about 5%. The
apparatus constant was obtained by measuring standard
polystyrene samples (Mn ) 5.05, 10.2, 20.5, and 45.0 kg/mol)
and calibrating their values against Mn values. FT-IR spectra
were recorded on a J EOL J IR-AQS20M FT-IR spectrophotom-
eter.
Mn × 10-3
e
[1]0/[sec-BuLi]0 calcd SEC 1H NMRb SLSc (VPO)d Mw/Mn
18.2
47.7
106
215
5.38 4.76
14.0 12.8
31.1 24.0
63.0 49.2
5.40
13.7
31.8
66.7
(5.74)
(13.9)
32.5
1.04
1.02
1.03
1.03
64.5
a
b
Yields of polymers were quantitative in all cases. Mn (1H
NMR) values were calculated from the area ratio of 1H NMR
signals corresponding to aromatic side chains (7.3-6.3 ppm) and
initiator fragment (0.7-0.5 ppm). c Mn(SLS) values were calculated
from Mw values measured by SLS (dn/dc ) 0.0874, in benzene)
d
and Mw/Mn estimated by SEC. Mn(VPO) values were determined
by VPO in benzene. e Mw/Mn values were estimated by SEC using
standard polystyrene calibration curve.
4-(4-Br om obu tyl)styr en e. The title styrene derivative was
synthesized by the Li2CuCl4-mediated coupling reaction of
4-vinylphenylmagnesium chloride with 1,4-dibromobutane ac-
cording to the similar procedure previously reported.13
4-(4-(2-Isop r op en ylp h en oxy)bu tyl)styr en e (1). The title
styrene derivative was synthesized by the reaction of 4-(4-
bromobutyl)styrene with the sodium salt of 2-hydroxyac-
etophenone, followed by treatment with CH3Ph3PBr and
potassium tert-butoxide. Under nitrogen, NaH (0.576 g, 24
mmol) was added dropwise to a dry DMF solution (50 mL)
containing 4-(4-bromobutyl)styrene (5.00 g, 21 mmol) and
2-hydroxyacetophenone (3.26 g, 24 mmol) at 0 °C. The reaction
mixture was stirred at 25 °C for 12 h. It was acidified with 1
N HCl, extracted with ether, and dried over MgSO4. The
solvent was removed under reduced pressure, and the residue
was purified by column chromatography on silica gel using a
mixture of hexane and ethyl acetate (8/2, v/v). The eluted
portions showing one spot were collected, and the solvent was
evaporated to afford 2-(4-(4-vinylphenyl)butoxy)acetophenone
a white crystal; mp 51.2-51.3 °C. 1H NMR (CDCl3) δ: 7.42
(d, 2H, CH2dC(CH3)-HAr, J ) 8.73 Hz), 7.36 (d, 2H, CH2d
CH-HAr, J ) 8.01 Hz), 7.18 (d, 2H, CH2dCH-HAr, J ) 8.01
Hz), 6.87 (d, 2H, CH2dC(CH3)-HAr, J ) 8.73 Hz), 6.72 (dd,
1H, CH2dCH-, J ) 10.9, 17.6 Hz), 5.73 (d, 1H, CH2dCH-, J
) 17.6 Hz), 5.31 (s, 1H, -CH2dC-CH3), 5.22 (d, 1H, CH2d
CH-, J ) 10.9 Hz), 5.01 (s, 1H, -CH2dC-CH3), 4.01 (t, 2H,
-CH2-CH2-O-, J ) 5.67 Hz), 2.70 (t, 2H, -Ph-CH2-CH2-,
J ) 6.87 Hz), 2.15 (s, 3H, -CH2dC-CH3), 1.84 (m, 4H, -CH2-
CH2-CH2-CH2-). 13C NMR (CDCl3): 158.6, 142.7, 142.0
(CH2dCH), 136.7, 135.4, 133.7, 128.7, 126.6, 126.3, 114.2,
113.0 (CH2dCH), 110.6 (CH2dC(CH3)), 67.8, 35.4, 28.9, 27.8.
Anal. Calcd for C21H24O: C, 86.26; H, 8.27; O; 5.47. Found:
C, 86.54; H; 8.62; O; 5.84.
4-(4-(3-Isop r op en ylp h en oxy)bu tyl)styr en e (3). The title
styrene derivative was synthesized by the reaction of 4-(4-
bromobutyl)styrene with the sodium salt of 3-hydroxyac-
etophenone, followed by treatment with CH3Ph3PBr and
potassium tert-butoxide, similar to the synthetic procedure
employed for 1. The styrene, 3, was obtained in 66% yield as
1
as a colorless oil (5.20 g, 18 mmol, 85%). H NMR (CDCl3) δ:
7.76-6.90 (m, 8H, HAr), 6.71 (dd, 1H, CH2dCH-, J ) 10.9,
17.6 Hz), 5.72 (d, 1H, CH2dCH-, J ) 17.6 Hz), 5.21 (d, 1H,
CH2dCH-, J ) 10.9 Hz), 4.07 (t, 2H, -CH2-CH2-O-, J )
5.67 Hz), 2.70 (t, 2H, -Ph-CH2-CH2-, J ) 6.87 Hz), 2.62 (s,
3H, -Ph-C(O)-CH3), 1.85 (m, 4H, -CH2-CH2-CH2-CH2-
).
1
a colorless oil. H NMR (CDCl3) δ: 7.41-6.84 (m, 8H, HAr),
6.76 (dd, 1H, CH2dCH-, J ) 10.9, 17.6 Hz), 5.86 (d, 1H, CH2d
CH-, J ) 17.6 Hz), 5.42 (s, 1H, -CH2dC-CH3), 5.26 (d, 1H,
CH2dCH-, J ) 10.9 Hz), 5.14 (s, 1H, -CH2dC-CH3), 4.04
(t, 2H, -CH2-CH2-O-, J ) 5.46 Hz), 2.74 (t, 2H, -Ph-CH2-
CH2-, J ) 6.42 Hz), 2.20 (s, 3H, -CH2dC-CH3), 1.90 (m, 4H,
-CH2-CH2-CH2-CH2-). 13C NMR (CDCl3): 159.1, 143.3,
142.8, 142.0, 136.7 (CH2dCH), 135.3, 129.2, 128.7, 126.3,
118.0, 113.2, 113.0 (CH2dCH), 112.7 (CH2dC(CH3)), 112.2,
67.7, 35.4, 29.0, 27.9, 21.9. Anal. Calcd for C21H24O: C, 86.26;
H, 8.27; O; 5.47. Found: C, 86.60; H; 8.50; O; 5.90.
Under nitrogen, a suspension of CH3Ph3PBr (2.86 g, 22
mmol) and potassium tert-butoxide (7.85 g, 26 mmol) in THF
(30 mL) were stirred for 30 min; 2-(4-(4-Vinylphenyl)butoxy)-
acetophenone (5.20 g, 18 mmol) dissolved in dry THF (20 mL)
was added dropwise to this suspension at 0 °C, and the
reaction mixture was stirred at 25 °C for 12 h. Water was
added to the reaction mixture, and the organic layer was
extracted with ether and dried over MgSO4. After the solvent
was removed under reduced pressure, hexane was added to
precipitate triphenylphoshine oxide. After filtration, hexane
was removed under reduced pressure, and the residue was
purified by column chromatography on silica gel using a
mixture of hexane and ethyl acetate (30/1, v/ v). The eluted
portions showing one spot were collected, and the solvent was
evaporated to afford 1 as a colorless oil (3.73 g, 13 mmol, 72%).
1H NMR (CDCl3) δ: 7.34-6.87 (m, 8H, HAr), 6.69 (dd, 1H,
CH2dCH-, J ) 10.9, 17.6 Hz), 5.70 (d, 1H, CH2dCH-, J )
17.6 Hz), 5.19 (d, 1H, CH2dCH-, J ) 10.9 Hz), 5.11 (s, 1H,
-CH2dC-CH3), 5.06 (s, 1H, -CH2dC-CH3), 3.98 (t, 2H,
-CH2-CH2-O-, J ) 5.67 Hz), 2.66 (t, 2H, -Ph-CH2-CH2-,
J ) 6.81 Hz), 2.12 (s, 3H, -CH2dC-CH3), 1.80 (m, 4H, -CH2-
CH2-CH2-CH2-). 13C NMR (CDCl3): 156.2, 144.4, 142.0,
136.8 (CH2dCH), 135.3, 133.0, 129.5, 128.7, 128.3, 126.3,
120.5, 115.1, 113.0 (CH2dCH), 111.9 (CH2dC(CH3)), 68.0, 35.3,
28.9, 27.9, 23.3. Anal. Calcd for C21H24O: C, 86.26; H, 8.27;
O; 5.47. Found: C, 86.19; H; 8.32; O; 5.49.
An ion ic P olym er iza tion of 1-3. The anionic polymeri-
zation was carried out under a high-vacuum condition (10-6
Torr) in sealed glass reactors with break-seals. The reactors
were always prewashed with the initiator solutions after being
sealed off from the vacuum line. A typical polymerization
experiment was as follows: A THF (12.6 mL) solution of 1 (3.21
mmol) kept at -78 °C was added to a heptane (1.44 mL)
solution of sec-BuLi (0.0331 mmol) through the break-seal with
vigorous stirring at -78 °C. The reaction mixture was allowed
to stand for additional 0.5 h at -78 °C and quenched with
degassed methanol. The polymer was precipitated in methanol,
reprecipitated twice from THF to methanol, and freeze-dried
from its absolute benzene solution for 24 h. A polymer yield
was 100%. The polymer was characterized by 1H and 13C NMR,
SEC, and SLS, and the results are summarized in Table 1.
Similarly, the anionic polymerizations of 1-3 were carried
out in THF at -78 or -95 °C and in benzene at 25 °C.
Block Cop olym er iza tion . An AB diblock copolymer of 1
and styrene was synthesized by the sequential addition of 1
followed by styrene in a manner similar to the homopolym-
erization. The first stage polymerization was carried out in
THF at -78 °C by mixing a THF (14.2 mL) solution of 1 (3.41
mmol) with sec-BuLi (0.0714 mmol) in heptane (2.11 mL). The
reaction mixture was allowed to stir for an additional 0.5 h,
and then a small portion was sampled to determine the
4-(4-(4-Isop r op en ylp h en oxy)bu tyl)styr en e (2). The title
styrene derivative was synthesized by the reaction of 4-(4-
bromobutyl)styrene with the sodium salt of 4-hydroxyac-
etophenone, followed by treatment with CH3Ph3PBr and
potassium tert-butoxide, similar to the synthetic procedure
employed for 1. The styrene, 2, was obtained in 75% yield as

4772 Hirao et al.
Macromolecules, Vol. 37, No. 13, 2004
Ta ble 2. Block Cop olym er iza tion of 1 a n d Styr en e w ith
°C. The polymeric products were not obtained in both
cases after 0.5 h. Therefore, sec-BuLi was reacted with
each of the monomers at around 1:3 molar ratios under
the same conditions, and after treatment of the reaction
mixtures with (CH3)3SiCl, the reaction products were
examined. Very surprisingly, both monomers were
recovered nearly quantitatively, and the addition prod-
ucts were obtained in <5% yields. It was further
confirmed by careful analyses of the reaction products
that neither ortho-lithiation nor oligomerization occur-
red. Thus, it was found that the reactivity of the CdC
bond of R-methylstyrene toward sec-BuLi was signifi-
cantly lowered by introducing a methoxy group at either
ortho or para position of the phenyl ring.
sec-Bu Li in THF a t -78 °Ca
Mn × 10-3
first
second [M1]0/ [M2]0/
[I]0
Mw/
Mn
monomer monomer [I]0
calcd
obsdb
1
styrene
1
47.7 138
14.0-14.4 13.7-15.0 1.02
styrene
154
60.9 16.1-17.9 17.0-18.3 1.04
a
b
Yields of polymers were quantitative in all cases. Molecular
weights of block copolymers were determined from Mn values of
the first polymers by VPO and compositions of block copolymers
determined by 1H NMR.
On the basis of this unexpected finding, we speculate
that if the R-methylstyrene molecule was introduced
into styrene skeleton via methoxy linkage and the
resulting styrene monomer was treated with an anionic
initiator, the selective anionic polymerization of the
CdC bond of the styrene part would occur, and on the
other hand, the R-methylstyrene part thus introduced
would remain as such. We therefore designed a substi-
tuted styrene derivative with a R-methylstyryl moiety
in such a way that the R-methylstyryl molecule was
introduced into styrene skeleton by OCH2CH2CH2CH2
linkage similar to methoxy group in structure and
electronic effect. The following three substituted styrene
derivatives with R-methylstyryl moiety, 1, 4-(4-(4-iso-
propenylphenoxy)butyl)styrene (2), and 4-(4-(3-isopro-
penylphenoxy)butyl)styrene (3) have been newly syn-
thesized and polymerized under the conditions of usual
anionic polymerization.
F igu r e 1. SEC profiles of poly(1).
An ion ic P olym er iza tion of 4-(4-(2-Isop r op en yl-
p h en oxy)bu tyl)styr en e (1). The anionic polymeriza-
tion of 1 was first carried out in THF at -78 °C for 0.5
h with sec-BuLi as an initiator ([1]0/[sec-BuLi]0 ) 18.2).
The addition of the first aliquot of 1 to sec-BuLi
instantaneously turns to an orange color, indicating the
generation of styrene-derived anion from 1. This color
remains unchanged and disappeared immediately by
quenching with degassed methanol. The polymer was
quantitatively obtained. It was purified by reprecipita-
tion twice from THF to methanol and freeze-dried from
its absolute benzene solution.
F igu r e 2. 1H NMR spectra of 1 (A) and poly(1) (B).
molecular weight and molecular weight distribution. The
second block was prepared by adding a THF (7.90 mL) solution
of styrene (6.56 mmol) to the living polymer solution (0.0476
mmol) obtained at the first stage polymerization. After 0.5 h,
the reaction mixture was quenched with degassed methanol,
and the polymer was precipitated in methanol. A yield of
polymer was quantitative. The polymer was purified by
reprecipitation twice from THF to methanol and freeze-dried.
The polymers obtained at the first and second stages of the
1
polymerization were characterized by H and 13C NMR, SEC,
As shown in Figure 1, SEC profile of the polymer
exhibits a sharp symmetrical monomodal distribution,
the Mw/Mn value being 1.04. Neither shoulder nor
and SLS, and the results are summarized in Table 2.
Resu lts a n d Discu ssion
1
tailing was observed. Figure 2 shows H NMR spectra
During our studies on the anionic polymerization of
the protected vinylphenol derivatives,14 we found that
the anionic polymerization of either 2-methoxy-R-
methylstyrene or 4-methoxy-R-methylstyrene proceeded
unexpectedly sluggishly with sec-BuLi in THF at -78
of 1 and the resulting polymer. The signals at 6.69, 5.70,
and 5.19 ppm corresponding to the styryl CH2dCH
protons of 1 completely disappeared, and on the other
hand, the signals at 5.11 and 5.06 ppm assigned to the
R-methylstyryl CH2dC protons remained in expected

Macromolecules, Vol. 37, No. 13, 2004
4-(4-(2-Isopropenylphenoxy)butyl)styrene 4773
Ta ble 3. An ion ic P olym er iza tion of 2 in THF a t -78 °C for
5 m in a
Mn × 10-3
[2]0/[I]0
initiator
calcd
SEC 1H NMR VPO Mw/Mn
18.6
58.2
55.3d
53.3
19.1
sec-BuLi
sec-BuLi
sec-BuLi
5.50
17.4
16.2
4.94
15.1
13.9
13.9
14.6
5.66
16.5
15.1
16.0
5.90
17.0
16.7
16.0
17.7
1.06b
1.06c
1.09e
1.08g
1.12i
(R-MS)nLif 16.0
K-Naphh
11.2
a
b
Yields of polymers were quantitative in all cases. 2% Shoul-
der. c 5% Shoulder. -95 °C. e 9% shoulder. f Oligo(R-methylsty-
d
ryl)lithium. n ) av 2. g 10% shoulder. Potassium naphthalenide.
h
i
15% shoulder.
F igu r e 3. SEC profiles of poly(1) (A) and poly(1)-block-
polystyrene (B).
molecular weights, molecular weight distributions, and
composition by SEC, VPO, and H NMR listed in Table
1
2 indicate that the block copolymerization proceeds as
desired to afford the expected AB diblock copolymer of
poly(1)-block-polystyrene. The success of this block
copolymerization further confirms the living character
of the polymerization of 1. A well-defined BA diblock
copolymer, polystyrene-block-poly(1), was also success-
fully synthesized by reversing the sequence of monomer
addition, namely, styrene followed by 1 (see also Table
2). These results clearly indicate that the electrophi-
licities of 1 and styrene as well as the nucleophilicities
of their living anionic polymers are very similar in
reactivity.
The anionic polymerization of 1 with sec-BuLi was
also attempted under the conditions in benzene at 25
°C. A characteristic orange color was immediately
developed by the addition of 1 to sec-BuLi. After a few
minutes, however, the color changed to a dark red in
color, indicating the generation of R-methylstyrene-
derived anion presumably by attack of the chain-end
styrene-derived anion on the pendant R-methylstyrene
functionality. The subsequent addition of the anion thus
formed to the R-methylstyrene functionality among
polymer chains occurred to cross-link. An insoluble
polymer was obtained in 80% yield after 1 h. Thus, the
selective anionic polymerization of 1 failed under the
conditions in benzene at 25 °C.
intensities. As expected in spectrum B, all peaks ap-
peared broader after the polymerization. New signals
corresponding to the CH2CH protons appeared at 1.1-
2.0 ppm. The broad signals that newly appeared at 0.5-
0.7 ppm were those of methyl protons of the initiator
fragment. Furthermore, ortho-aromatic protons toward
the former vinyl bond were shifted due to the polym-
erization. The 13C NMR spectra also showed that the
styryl CH2dCH carbons had completely reacted, while
the resonance at 111.9 ppm assignable to the â-carbon
of CH2dC of the R-methylstyryl moiety was present as
such. Thus, evidently, only the styryl group was selec-
tively polymerized, and on the other hand, the R-me-
thylstyryl moiety completely remained intact.
Three more sets of the polymerization were carried
out at higher monomer-to-initiator ratios under the
same conditions.15 The characterization results of these
polymers are summarized in Table 1. Although the
estimated Mn values by SEC relative to polystyrene
were always somewhat smaller than those calculated
from [1]0 to [sec-BuLi]0 ratios, all of the observed values
of molecular weight by VPO and SLS agreed quite well
with those calculated. Their molecular weight distribu-
tions were extremely narrow, and Mw/Mn values were
less than 1.04. These results clearly indicate that the
selective anionic polymerization of 1 proceeds in a living
manner to afford polymers with precisely controlled
chain lengths and R-methylstyrene functionality in each
of all repeating unit.
The orange color of the styrene-derived anion re-
mained unchanged even after 3 h. Furthermore, no
change was observed in shape and molecular weight
distribution at all in SEC profiles of the polymers
terminated after 0.5 and 3 h. Thus, the styrene-derived
anion was sufficiently stable and R-methylstyrene func-
tionality remained as such for at least 3 h under the
conditions in THF at -78 °C.
To further elucidate the living character of the po-
lymerization of 1, the block copolymerization of 1 and
styrene was carried out with sec-BuLi in THF at -78
°C by a two-step sequential monomer addition, 1 fol-
lowed by styrene. The first and second polymerization
times were 0.5 and 0.5 h, respectively. Yields of poly-
mers were quantitative. The results are summarized in
Table 2.
An ion ic P olym er iza tion of 4-(4-(4-Isop r op en yl-
p h en oxy)bu tyl)styr en e (2). The anionic polymeriza-
tion of 2 was carried out under the identical conditions
in THF at -78 °C with sec-BuLi. In each polymerization,
an orange color characteristic of the styrene-derived
anion was immediately developed by the addition of
2 to sec-BuLi. The polymerizations were rapid and
complete within 5 min. The results are summarized in
Table 3.
The polymers always exhibited sharp monomodal
SEC peaks along with small high molecular weight
shoulders whose Mn values were doubly increased.
Undoubtedly, the formation of high molecular weight
shoulder was attributable to the addition reaction of the
chain-end anion to the R-methylstyrene functionality
among polymer chains. The high molecular weight
shoulder becomes more significant with a longer reac-
tion time to 30 min as expected (5 min; 5%; 30 min,
20%). The formation could not be completely suppressed
by lowering the polymerization temperature to -95 °C,
changing the initiator to oligo(R-methylstyryllithium)
or potassium naphthalenide, and the addition of LiCl
or (C4H9)2Mg. The extents were usually in the range of
2-15% relative to the main peak area. The Mn values
Figure 3 shows SEC profiles of the polymers obtained
at the first and second stages of the polymerization. The
SEC peak of poly(1) obtained at the first stage of the
polymerization moves toward higher molecular weight
after the addition of styrene, whereas the peak of poly-
(1) completely disappears. All analytical results on
1
of the polymers determined by H NMR and VPO were
very close to those calculated from the ratios of [2]0/[sec-

4774 Hirao et al.
Macromolecules, Vol. 37, No. 13, 2004
Sch em e 1. Reson a n ce Effect of Mon om er s 1-3
BuLi]0. It is therefore likely that 2 undergoes the
selective anionic polymerization in a living manner
similar to the polymerization of 1, and after the conclu-
sion of the polymerization, the resulting chain-end anion
attacks gradually with the pendant R-methylstyrene
functionality of another polymer chain. Additional
evidence for the anion attack on the R-methylstyrene
functionality was provided by the observation that the
orange color changed with time to a dark red in color
possibly for the R-methylstyene-derived anion.
The anionic polymerization of the meta-isomeric
monomer, 3, was more problematic. On mixing 3 with
sec-BuLi in THF at -78 °C, gelation immediately
occurred, and an insoluble polymer was obtained virtu-
ally quantitatively after 5 min. Several attempts to
obtain soluble polymers from 3 by using various initia-
tors (sec-BuLi/R-methylstyrene, Li and K naphthalen-
ides) and additives (LiCl and KOtBu) were not success-
ful. Thus, the influence of substituted position of the
isopropenyl group is of significance on the anionic
polymerization behavior.
We tentatively consider the reason for success of the
selective living anionic polymerization of 1 as follows:
As shown in Scheme 1, the electron density on the
â-carbon of R-methylstyryl CH2dC group becomes higher
by the electron-donating character of the ortho-substi-
tuted butoxy group via the resonance effect, thereby
suppressing the attack of anionic species on the R-me-
thylstyrene functionality of 1. A similar effect can be
expected in the case of 2. However, the anion attack
occurred after the conclusion of the polymerization of
2, although it was found to be slow in this case.
Therefore, the steric hindering effect of the ortho
substituent in 1 may also play an important role to
suppress the anion attack. In the case of 3 as shown in
Scheme 1, the electron donation to the R-methylstyryl
CH2dC group of 3 cannot be expected by the meta-
substituted butoxy group. Accordingly, the R-methyl-
styryl CH2dC group of 3 may be similar in reactivity
to that of R-methylstyrene and therefore readily at-
tacked by anionic species, resulting in the occurring of
the cross-linking reaction.
called dual-functionality monomers, are now under
investigation in order to elucidate the reason for the
successful polymerization of 1 and to find extra ex-
amples amenable to the selective living anionic polym-
erization.
Con clu sion s
We have successfully demonstrated the selective
living anionic polymerization of 1 in THF at -78 °C with
sec-BuLi in which only the styryl group can be selec-
tively polymerized in a living manner with the remain-
ing R-methylstyrene functionality as such. The resulting
living anionic polymers of 1 were sufficiently stable to
afford quite new functionalized polystyrenes with pre-
cisely controlled chain lengths and R-methylstyrene
functionality in each monomer unit. Well-defined AB
as well as BA functionalized diblock copolymers, poly-
(1)-block-polystyrene and polystyrene-block-poly(1), were
successfully synthesized by a two-step sequential mono-
mer addition. The para-isomeric monomer, 2, also
underwent the selective anionic polymerization, but the
undesirable anion attack on the R-methylstyrene func-
tionality could not be completely suppressed under the
identical conditions. Gelation occurred immediately on
mixing the meta-isomeric monomer, 3, with sec-BuLi.
Soluble polymers were not obtained in the anionic
polymerization of 3 under various conditions.
Needless to say, the synthetic significance of the
present polymerization of 1 lies in the fact that a stable
living anionic polystyrene carrying R-methylstyrene
functionality can be obtained for the first time.16 New
aspects on precise polymer syntheses will be expected
by molecular design based on the living anionic polym-
erization of 1, followed by further modification of the
highly reactive R-methylstyrene functionality.
Refer en ces a n d Notes
(1) Morton, M. Anionic Polymerization: Principles and Practice;
Academic Press: New York, 1983.
(2) Hsieh, H. L.; Quirk, R. P. Anionic Polymerization: Principles
and Practical Applications; Marcel Dekker: New York, 1996.
(3) Baer, M. J . Polym. Sci., Part A 1964, 2, 417.
(4) Dunn, D. J .; Krause, S. J . Polym. Sci., Polym. Lett. Ed. 1974,
12, 591.
More detailed studies on the anionic polymerization
of a series of similar styrene derivatives substituted
with styrene and R-methylstyrene functionalities, so-
(5) Hansen, D. R.; Shen, M. Macromolecules 1975, 8, 903.

Macromolecules, Vol. 37, No. 13, 2004
4-(4-(2-Isopropenylphenoxy)butyl)styrene 4775
(6) Rahlwes, D.; Kirste, R. G. Makromol. Chem. 1977, 178, 793.
(7) Nakahama, S.; Hirao, A. Prog. Polym. Sci. 1990, 15, 299.
(8) Hirao, A.; Nakahama, S. Prog. Polym. Sci. 1992, 17, 283.
(9) Hirao, A.; Nakahama, S. Acta Polym. 1998, 49, 133.
(10) Hirao, A.; Loykulnant, S.; Ishizone, T. Prog. Polym. Sci. 2002,
27, 1399.
(11) Hirao, A.; Ando, Y.; Ishizone, T.; Nakahama, S. Macromol-
ecules 2003, 36, 5081.
(12) Hadjichristidis, N.; Iatrou, H.; Pispas, S.; Pitsikalis, M. J .
Polym. Sci., Part A: Polym. Chem. 2000, 38, 3211.
(13) Hirao, A.; Hayashi, M.; Nakahama, N. Macromolecules 1996,
29, 3353.
(14) Recently, we have successfully demonstrated that the pro-
tected vinylphenol derivatives such as 2-, 3-, and 4-methoxy-
styrenes, 3- and 4-methoxymethoxystyrenes, and 4-tetrahy-
dropyranyloxystyrene undergo living anionic polymerization
with sec-BuLi in THF at -78 °C. On the other hand,
polymerization of neither 2- nor 4-methoxy-R-methylstyrene
occurred at all under the identical conditions as mentioned
in this section.
(15) The addition of Bu2Mg was needed to kill the impurities in
1 in the polymerization where the target molecular weight
was 30 kg/mol or higher molecular weight. Otherwise,
polymers with higher molecular weights than those predicted
were always obtained. For example, a polymer of a Mn value
of 55 kg/mol (Mw/Mn ) 1.04) was quantitatively obtained in
the polymerization of 1 with sec-BuLi in THF at -78 °C for
0.5 h without Bu2Mg. (The target Mn value was 30 kg/mol in
this polymerization.) Taking into consideration on the amount
of impurities estimated from the results of the above polym-
erization, ca. 2 mol % of Bu2Mg to 1 was added and allowed
to stand for 1 h prior to the polymerization of 1. A similar
additive effect of Bu2Mg on the anionic polymerization was
observed in our previous paper (see: Loykulnant, S.; Hirao,
A. Macromolecules 2000, 33, 4757).
(16) The anionic polymerizations of distyryl monomers such as
p-divinylbenzene and m- and p-diisopropenylbenzenes were
previously reported. As expected, gelation occurred im-
mediately in the anionic polymerization of p-divinylbenzene
(see: Eschwey, H.; Burchard, W. Polymer 1975, 16, 180; J .
Polym. Sci., Polym. Symp. 1975, 53, 1 and Worsfold, D. J .;
Zilliox, J . G.; Rempp, R. Can. J . Chem. 1969, 47, 3379). On
the other hand, soluble polymers with relatively narrow
molecular weight distributions were obtained at relatively
low conversion (∼50%) in the anionic polymerization of
diisopropenylbenzenes, but branching and cross-linking oc-
curred at higher conversions (see: Lutz, P.; Beinert, G.;
Rempp, P. Makromol. Chem. 1982, 183, 2787; Okamoto, A.;
Mita, I. J . Polym. Sci., Polym. Chem. Ed. 1978, 16, 1187).
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