Synthesis of well-defined (AB)n multiblock copolymers composed of polystyrene and poly(methyl methacrylate) segments using specially designed living AB diblock copolymer anion

Article abstract of DOI:10.1021/ma902473t

We have developed a new iterative methodology using α-chain-end- functionalized living AB diblock copolymer anion as a key building block in order to synthesize a series of well-defined (AB)_n multiblock copolymers composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The methodology involves the following three reaction steps in the entire iterative synthetic sequence: (1) a sequential living anionic block copolymerization to prepare α-chain-end-functionalized living AB diblock copolymer anion with the 3-tert-butyldimethylsilyloxypropyl (SiOP) group, (2) an introduction of α-phenyl acrylate function (PA) via the SiOP group by deprotection followed by Mitsunobu esterification, and (3) a linking reaction of α-cham-end-PA-functionalized AB diblock copolymer with α-chain-end-SiOP-functionalized living AB diblock copolymer anion. The same iterative synthetic sequence involving the three reaction steps was repeated several times to successively synthesize a series of (AB)_n multiblock copolymers (n = 2, 3, 4, and 5) with precisely controlled molecular weights and compositions and very narrow molecular weight distributions (M _wM_n ≤ 1.06). Furthermore, different two series of (AB)_n multiblock copolymers (n = 2 and 3) composed of PS and either poly(tert-butyl methacrylate) or poly(2-vinylpyridine) blocks were successfully synthesized by the same methodology using the corresponding α-chain-end- SiOP-functionalized living AB block copolymer anions.

Full text of DOI:10.1021/ma902473t

Macromolecules 2010, 43, 1403–1410 1403
DOI: 10.1021/ma902473t
Synthesis of Well-Defined (AB) Multiblock Copolymers Composed of
n
Polystyrene and Poly(methyl methacrylate) Segments Using Specially
Designed Living AB Diblock Copolymer Anion
Kenji Sugiyama, Toshiyuki Oie, Ahmed Abou El-Magd, and Akira Hirao*
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering,
Tokyo Institute of Technology, H-127, 2-12-1 Ohokayama, Meguro-ku, Tokyo 152-8552, Japan
Received November 8, 2009; Revised Manuscript Received December 22, 2009
ABSTRACT: We have developed a new iterative methodology using R-chain-end-functionalized living AB
diblock copolymer anion as a key building block in order to synthesize a series of well-defined (AB)
n
multiblock copolymers composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The
methodology involves the following three reaction steps in the entire iterative synthetic sequence: (1) a
sequential living anionic block copolymerization to prepare R-chain-end-functionalized living AB diblock
copolymer anion with the 3-tert-butyldimethylsilyloxypropyl (SiOP) group, (2) an introduction of R-phenyl
acrylate function (PA) via the SiOP group by deprotection followed by Mitsunobu esterification, and (3) a
linking reaction of R-chain-end-PA-functionalized AB diblock copolymer with R-chain-end-SiOP-functio-
nalized living AB diblock copolymer anion. The same iterative synthetic sequence involving the three reaction
steps was repeated several times to successively synthesize a series of (AB) multiblock copolymers (n = 2, 3,
n
4, and 5) with precisely controlled molecular weights and compositions and very narrow molecular weight
distributions (M /M e 1.06). Furthermore, different two series of (AB) multiblock copolymers (n = 2
w
n
n
and 3) composed of PS and either poly(tert-butyl methacrylate) or poly(2-vinylpyridine) blocks were
successfully synthesized by the same methodology using the corresponding R-chain-end-SiOP-functionalized
living AB block copolymer anions.
Introduction
In order to synthesize block copolymers with well-defined
structures, the use of living polymerization is essential. Although
many living/controlled polymerization systems have been devel-
oped especially in recent 25 years, the living anionic polymeriza-
tion of styrene, 1,3-butadiene, isoprene, 2-vinylpyridine, and
alkyl methacrylates and their derivatives with certain functional
Recent development of living/controlled polymerization systems
has allowed to synthesize a variety of architectural polymers, such
as block copolymers, star-branched polymers, graft copolymers,
comb-like polymers, dendrimer-like star-branched polymers, and
other branched polymers with complex structures.
them, block copolymers have been widely investigated for a long
time from the viewpoints of both syntheses and physical proper-
1
-14
Among
groups is still the best living polymerization system from the
1,46-50
following features:
First, molecular weights can be pre-
3
6
cisely controlled in a wide range from 10 to even 10 . Second,
extremely narrow molecular weight distributions are realized,
M /M values being less than 1.05 or even smaller. Moreover, the
1
,15-20
ties as well as practical applications.
Since block segments
are generally thermodynamically incompatible in almostall block
copolymers, theyare phase-separated atmolecular level, followed
by self-organizing, to form composition-sensitive morphological
nanostructures. Morphologies of AB diblock copolymers com-
posed of amorphous segments are now well-established as the
w
n
resulting living polymers from these monomers have active chain-
end anions that are highly reactive but stable under appropriate
conditions. These characteristics are ideally suited for the synth-
esis of well-defined block copolymers. In fact, most of well-
defined AB diblock copolymers, ABC triblock terpolymers, and
two-component multiblock copolymers have been successfully
synthesized by using this living anionic polymerization system
where the corresponding monomers are sequentially added.
A further consideration for successful design and synthesis of
block copolymers is the order of monomer addition in the
sequential living anionic block copolymerization mentioned
21
Molau rule. Very recently, novel characteristic morphological
behaviors have been observed in the three-component ABC
terpolymers, although they are more complicated due to many
variables originated from the three components such as the Flory
parameters between A-B, B-C, and C-A interfaces and the
22-32
unit numbers of A, B, and C segments.
diblock copolymers, several two-component multiblock copoly-
mers composed of perfectly-(AB) alternating blocks and (AB)
blocks with additional longer blocks have been synthesized.
Although the morphological parameters of such block copoly-
mers are limited similar to those of AB diblock copolymers, these
block copolymers also show unique and interesting morphologies
with ordered nanophase structures originated from the two-
component segments connected by covalent bonds.
In addition to AB
1
above. There is no limitation of the addition order among the
n
3
1,33-45
monomers with similar reactivities. For instance, styrene and
the structural analogous derivatives like R-methylstyrene and
4-methoxystyrene, styrene and 1,3-diene monomers, 2-vinylpyr-
idine and 4-vinylpyridine, and methyl methacrylate (MMA) and
alkyl methacrylates. On the other hand, the order of monomer
addition must be considered among the monomers with different
reactivities. In the case to synthesize a block copolymer of styrene
and MMA, for example, it is necessary first to polymerize styrene
and then add MMA to polymerize to result in the block
*
Corresponding author. Akira Hirao, Tel: þ81-3-5734-2131,
Fax: þ81-3-5734-2887, email:ahirao@polymer.titech.ac.jp.
r 2010 American Chemical Society
Published on Web 01/13/2010
pubs.acs.org/Macromolecules

1
404 Macromolecules, Vol. 43, No. 3, 2010
Sugiyama et al.
˚
copolymer. As is known, MMA is much higher than styrene in
reactivity in anionic polymerization because of strong electron-
withdrawing effect of the carbonyl group and, on the other hand,
the resulting poly(methyl methacrylate) (PMMA) chain-end eno-
late anion is less reactive than polystyrene (PS) chain-end anion
because of the same reason. As a result, PMMA chain-end
enolate anion cannot initiate the polymerization of less reactive
styrene under normal conditions. This means that the synthesis of
PS-block-PMMA is possible, but PMMA-block-PS cannot be
synthesized by the living anionic block copolymerization with
sequential monomer addition, i.e., MMA first followed by
addition of styrene. Accordingly, the synthesis of triblock copo-
lymer, PS-block-PMMA-block-PS, and the multiblock copoly-
mers composed of PS and PMMA blocks is not possible by this
polymerization technique.
(A/μm). The relative molecular weight of polymer (Mn,SEC) was
calculated by RI detection using standard polystyrene calibra-
tion. The combination of viscometer, right angle laser light
scattering detection (RALLS), and RI detection was applied
for the online SEC system in order to determine the absolute
1
molecular weight of block copolymers (Mn,RALLS). Both H and
1
3
C NMR spectra were measured on a Bruker DPX300 in
CDCl . Chemical shifts were recorded in ppm downfield relative
to CHCl
standards, respectively.
3
1
13
3
3
(δ 7.26) and CDCl (δ 77.1) for H and C NMR as
5
3
Synthesis of r-Phenylacrylic Acid. 3-Hydroxy-2-phenylpro-
panoic acid (31.3 g, 188 mmol) was dissolved in 10% potassium
hydroxide solution (350 mL) and refluxed for 10 h. After cooling
down to room temperature, concentrated 2N HCl (45 mL) was
carefully added to quench the reaction. The organic layer was
extracted with chloroform, washed with water, and dried over
In order to overcome such a synthetic limitation and realize the
facile synthesis of multiblock copolymers, we have herein devel-
oped a new iterative methodology using R-chain-end-functiona-
lized living AB diblock copolymer anion specially designed for
the synthesis of well-defined multiblock copolymers composed of
PS and PMMA blocks. As mentioned above, such multiblock
copolymers cannot be synthesized by the sequential living anionic
block copolymerization. Furthermore, the synthesis of different
4
MgSO . Removal of chloroform under reduced pressure gave
the object compound (17.9 g, 121 mmol) in 64% yield as a
1
yellowish solid: H NMR (300 MHz): δ = 10.3-9.0 (broad, 1H,
COOH), 7.6-7.3 (m, 5H, Ar), 6.52 and 6.01 (d, 2H, CdCH ).
2
1
3
C NMR (75 MHz): δ = 172.1 (COOH), 140.8 (CdCH ), 136.2
2
(CdCH ), 129.4, 128.5, 128.4, 128.2 (Ar).
Preparation of r-Chain-End-3-(tert-Butyldimethylsilyloxy)-
propyl (SiOP) Functionalized Living AB Diblock Copolymer
2
(
tions were carried out under high-vacuum conditions (10
PS-block-PMMA) Anion. All of the polymerizations and reac-
two series of multiblock copolymers composed of PS with poly-
-
6
t
(
(
tert-butyl methacrylate) (P BMA) or poly(2-vinylpyridine)
P2VP) blocks are performed in order todemonstrate the general-
Torr) in handmade sealed glass reactors. The reactors were
always prewashed with a heptane solution of 1,1-diphenylhex-
yllithium prior to the polymerizations and reactions. R-Chain-
end-SiOP-functionalized polystyryllithium (PSLi) was prepared
by the polymerization of styrene (19.9 mmol) in tert-butylben-
zene (15.0 mL) initiated with SiOPLi (0.394 mmol) in the
presence of TMEDA (1.40 mmol) at 0 °C for 30 min. THF
solutions (10.0 mL, 4.00 mL) containing DPE (0.778 mmol) and
LiCl (1.55 mmol) were sequentially added to the PSLi solution
at -78 °C, and the reaction mixture was allowed to stand for
additional 15 min at -78 °C. Then, a THF solution (22.3 mL) of
MMA (20.0 mmol) was added at -78 °C with vigorous shaking,
and the reaction mixture was allowed to stand for 30 min.
The R-chain-end-SiOP-functionalized living PS-block-PMMA
anion thus prepared is used for the linking reaction in the
iterative synthetic sequence as mentioned below. In order to
carry out the chain-end modification reactions in the first
reaction step, the living PS-block-PMMA anion was quenched
with degassed methanol and precipitated in methanol by pour-
ing into a large excess of methanol. The resulting polymer was
reprecipitated twice from THF to methanol and freeze-dried
from its absolute benzene solution for 48 h. The resulting PS-
ity and versatility of this iterative methodology. Recently, East-
wood and Dadmun have reported the possible synthesis of
multiblock copolymers composed of PS and PMMA blocks by
the living/controlled radical polymerization with sequential
51,52
monomer addition.
Although the resulting polymers were
undoubtedly penta- and heptablock copolymers, their molecular
weight distributions were broad, the M /M values being 1.5 or
w
n
even higher.
Experimental Section
Materials. All reagents were purchased from Aldrich, Japan
and used as received, unless otherwise stated. Tetrahydrofuran
(
under nitrogen, and then distilled from its sodium naphthale-
THF) was refluxed over sodium wire, distilled over LiAlH
4
-
6
nide solution under high vacuum conditions (10 Torr). Hep-
tane and tert-butylbenzene were washed with concentrated
H SO , water, and aqueous NaHCO , dried over P O , and
2
4
3
2
5
finally distilled in the presence of 1,1-diphenylhexyllithium.
Styrene, MMA, and tert-butyl methacrylate ( BMA) were
t
washed with aqueous NaOH (10 wt %) and water, and dried
over MgSO . After filtration, they were distilled twice over
block-PMMA obtained in 95% yield was characterized by SEC,
4
1
CaH
over Bu
2
under reduced pressures. Finally, styrene was distilled
Mg and dissolved in tert-butylbenzene under high
RALLS, and H NMR, respectively. Mn,RALLS = 11 400, M
w
/
1
2
M
n
= 1.03. H NMR (300 MHz): δ = 7.24-6.26 (m, 289H, Ar),
3.63-3.58 (m, 182H, O-CH ), 2.01-1.76 (m, 157H, main
chain), 0.88 (s, 144H, C-CH ), 0.90 (s, 9H, C (CH ) ), -0.02
t
vacuum conditions. Both MMA and BMA were distilled over
trioctylaluminum and dissolved in THF under high vacuum
conditions. 2-Vinylpyridine (2 VP) was distilled over CaH twice
3
3
3 3
2
3 2
(s, 6H, Si(CH ) ).
under reduced pressures, finally under high vacuum, and dis-
solved in THF under high vacuum conditions. 1,1-Dipheny-
lethylene (DPE) was distilled over butyllithium and dissolved in
Preparation of r-Chain-End-(r-Phenyl Acrylate) (PA) Func-
tionalized PS-block-PMMA. The R-chain-end-SiOP-functiona-
lized PS-block-PMMA (M = 11 400, 3.89 g, 0.341 mmol for
n
0
0
THF under high vacuum conditions. N,N,N ,N -Tetramethy-
lethylenediamine (TMEDA) was distilled over Bu Mg and
4
SiOP terminus) was carefully treated with Bu NF (11.2 mmol) in
absolute THF (45 mL) at 0 °C for 6 h to remove the silyl
protective group and regenerate hydroxyl group. The reaction
2
dissolved in heptane under high vacuum conditions. LiCl was
dried under high vacuum conditions for 3 days with heating and
dissolved in THF. 3-tert-Butyldimethylsilyloxy-1-proxylithium
was repeated two or even three times until the disappearance of
methyl protons of the Si-CH group by H NMR. It should be
1
3
(
SiOPLi, in cyclohexane, FMC Corporation Lithium Division)
noted that raising the reaction temperature and longer reaction
times than 24 h caused undesirable side reactions such as ester
hydrolysis. After quenching the reaction with a small amount
of methanol and removing the solvent, the polymer dissolved
in THF was poured into a large excess of methanol to precipi-
tate. The polymer was purified by reprecipitation twice and
freeze-drying from its absolute benzene solution under vacuum.
The polymer was obtained in 95% yield. Mn,RALLS = 12 000,
was diluted in an appropriate concentration with heptane under
high vacuum conditions.
Measurements. Size exclusion chromatography (SEC) was
performed on a Viscotek GPC max equipped with a Viscotek
TDA 302 triple detector array using THF as a carrier solvent at a
flow rate of 1.0 mL/min at 30 °C. Three polystyrene gel columns
were used, where pore size/bead size = 650/9, 200/5, and 75/5

Article
Macromolecules, Vol. 43, No. 3, 2010 1405
1
1
M
w
/M
Ar), 3.63-3.58 (m, 174H, O-CH
chain), 0.88 (s, 132H, C-CH3).
Under a nitrogen atmosphere, the hydroxyl-terminated PS-
block-PMMA (M = 12 000, 3.62 g, 0.302 mmol for hydroxyl
terminus), R-phenylacrylic acid (2.31 g, 15.6 mmol), and PPh
4.12 g, 15.6 mmol) were dissolved in THF (50 mL). Diisopro-
n
= 1.03. H NMR (300 MHz): δ = 7.24-6.26 (m, 289H,
H NMR to determine the absolute molecular weights, molecular
weight distributions, composition ratios, and degree of SiOP-
chain-end-functionalities.
3
), 2.03-1.72 (m, 155H, main
Synthesis of ABABAB Hexa-, ABABABAB Octa-, and ABA-
BABABAB Decablock Copolymers Composed of PS and PMMA
Blocks. The title multiblock copolymers were synthesized by
repeating the same iterative synthetic sequence as that employed
for the synthesis of tetrablock copolymer mentioned above. The
characterization results of these polymers are as follows: ABA-
BAB hexablock copolymer (2.21 g, 0.0545 mmol, 92% yield),
n
3
(
pylazodicarboxylate (DIAD, 3.50 g, 17.3 mmol) was added
dropwise at 0 °C and the reaction mixture was allowed to stir
at 20 °C for 24 h. After quenching the reaction with a small
amount of methanol and removing the solvent, the polymer
dissolved in THF was poured into a large excess of methanol to
precipitate. The resulting block copolymer was purified by the
reprecipitation twice with THF/methanol and once with THF/
hexane and then freeze-dried from its absolute benzene solution
under vacuum. Yield of the polymer was quantitative (3.59 g).
The H NMR analysis showed that the PA function was
introduced quantitatively. M
.03. H NMR (300 MHz): δ = 7.24-6.26 (m, 287H, Ar),
2
.32 (s, 1H, C = CH ), 5.88 (s, 1H, CdCH
74H, O-CH ), 2.02-1.73 (m, 158H, main chain), 0.88 (s,
47H, C-CH3).
Synthesis of ABAB Tetrablock Copolymers Composed of PS
and PMMA Blocks. R-Chain-end-SiOP-functionalized living
PS-block-PMMA anion (M = 14 500) was first prepared by
the block copolymerization of MMA (24.3 mmol) with R-chain-
1
Mn,RALLS = 40 500, M /M = 1.03. H NMR (300 MHz): δ =
w
n
7.23-6.23 (m, 860H, Ar), 3.67-3.54 (m, 677H, O-CH3),
2.02-1.72 (m, 562H, main chain), 0.87 (s, 528H, C-CH3),
0.90 (s, 9H, C(CH ) ), -0.02 (s, 6H, Si(CH ) ). ABABABAB
3
3
3 2
octablock copolymer (1.16 g, 0.0216 mmol, 88% yield),
1
Mn, RALLS = 53 600, M /M = 1.04. H NMR (300 MHz):
w
n
1
δ = 7.21-6.31 (m, 1129H, Ar), 3.71-3.51 (m, 894H, O-CH3),
= 11 900, M /Mn
w
=
2.01-1.72 (m, 745H, main chain), 0.88 (s, 713H, C-CH ), 0.90
n,RALLS
3
1
1
6
1
1
(s, 9H, C(CH ) ), -0.02 (s, 6H, Si(CH ) ). ABABABABAB
3
3
3 2
2
), 3.63-3.58 (m,
decablock copolymer (0.501 g, 0.00755 mmol, 90% yield),
Mn,RALLS = 66 400, M /M = 1.06. H NMR (300 MHz):
1
3
w
n
δ = 7.22-6.33 (m, 1491H, Ar), 3.66-3.58 (m, 1079H, O-CH3),
1.98-1.74 (m, 1013H, main chain), 0.89 (s, 1060H, C-CH3),
0.90 (s, 9H, C(CH ) ), -0.02 (s, 6H, Si(CH ) ).
3
3
3 2
n
Synthesis of r-Chain-End-SiOP-Functionalized Di-, Tetra-,
t
and Hexablock Copolymers Composed of PS and P BMA Blocks.
The title multiblock copolymers were synthesized in a similar
manner by developing the same iterative methodology using
end-SiOP-functionalized PSLi (M
end-capped with DPE) in THF at -78 °C for 30 min in the
presence of LiCl (1.44 mmol). To this solution, a THF solution
25.4 mL) of R-chain-end-PA-functionalized PS-block-PMMA
= 11 900, 2.23 g, 0.187 mmol for PA moiety) was slowly
n
=5870, 0.281 mmol, ω-chain-
t
R-chain-end-SiOP-functionalized living PS-block-P BMA an-
ion as a key building block. In the synthesis of the block
(
(
t
copolymer anion, the polymerization time of BMA was 2 h.
M
n
added at -78 °C and the reaction mixture was allowed to stand at
40 °C for 48 h. The reaction was terminated with degassed
methanol and the polymers were precipitated by pouring a
large excess of methanol. The ABAB tetrablock copolymer was
isolated in 85% yield by the fractional precipitation men-
tioned below, reprecipitated from THF solution to methanol, and
The introduction of PA function via the SiOP group and the
coupling reactions were carried out under the identical condi-
tions mentioned above. These reactions proceeded cleanly and
essentially quantitative in all cases. The linking reactions were
carried out in mixtures of tert-butylbenzene and THF (1/4, v/v)
with use of a 1.5-fold excess, followed by a 3-fold excess of living
-
t
freeze-dried from its absolute benzene solution. Mn,RALLS=28 200,
PS-block-P BMA anion with the progress of the iteration. The
1
M /M
w
3
0
n
=1.03. H NMR (300 MHz): δ=7.23-6.28 (m, 625H, Ar),
objective multiblock copolymers were always isolated in ca.
60% yields by fractional precipitation with use of acetone/
methanol system. The resulting multiblock copolymers were
.64-3.55 (m, 429H, O-CH ), 1.93-1.62 (m, 333H, main chain),
3
.78 (s, 299H, C-CH
).
General Procedure for Synthesis of (AB)
3
), 0.90 (s, 9H, C (CH
3
)
3
), -0.02 (s, 6H, Si
1
(
3 2
CH )
characterized by SEC, RALLS, and H NMR. The details of
the synthesis are given in the Supporting Information. AB
n
Multiblock Copoly-
1
diblock copolymer: Mn,RALLS = 12 700, M /M = 1.04. H
mers. A series of (AB) multiblock copolymers (n = 2, 3, 4, and 5)
n
w
n
were synthesized by repeating the iterative synthetic sequence
involving the three reaction steps mentioned in the Introduction.
In the first reaction step of the iterative synthetic sequence, a 1.5-fold
excess of R-chain-end-SiOP-functionalized living PS-block-PMMA
anion was reacted with the R-chain-end-PA-functionalized
PS-block-PMMA at -40 °C for 48 h. The molar ratio of living
polymer to PA-functionalized polymer increased gradually from
NMR (300 MHz): δ = 7.2-6.3 (broad, 320H, Ar), 0.80-2.27
(
broad, 417H, main chain and C(CH
CH ). ABAB tetrablock copolymer: Mn,RALLS = 25 300,
/M
18H, Ar), 2.68-0.80 (s, 802H, main chain and C(CH
s, 6H, Si(CH ). ABABAB hexablock copolymer: Mn,RALLS
8 300, M /M = 1.04. H NMR (300 MHz): δ = 7.2-6.3
3 3
) ), -0.01 (s, 6H, Si-
(
M
6
(
3 2
)
1
w
n
= 1.04. H NMR (300 MHz): δ = 7.2-6.3 (broad,
), -0.03
3 3
)
3
)
2
=
1
3
w
n
1
.5 to 5.0 as the iteration proceeded. After quenching the reaction
(
(
broad, 854H, Ar), 2.40-0.80 (broad, 1201H, C(CH ) ), -0.03
3
3
with a small amount of degassed methanol, the reaction mixture
was poured into a large excess of methanol to precipitate the
polymers. The objective coupled polymer was isolated by frac-
tional precipitation using mixed solvents of THF, ether,
and hexane as follows: The polymer (1 g) was dissolved in THF
s, 6H, Si(CH ) ).
Synthesis of Di-, Tetra-, and Hexablock Copolymers Com-
3
2
posed of PS and P2VP Blocks. The title multiblock copolymers
were synthesized in a similar manner by developing the same
iterative methodology using R-chain-end-SiOP-functionalized
living PS-block-P2VP anion as a key building block. The
R-chain-end-SiOP-functionalized living PS-block-P2VP anion
was prepared by the sequential block copolymerization of
styrene, DPE, and 2 VP with SiOPLi at 0 °C for 30 min, -78 °C
for 10 min, and -78 °C for 30 min, respectively. The polymer-
ization was quenched with a small amount of degassed metha-
nol. The polymer solution was then concentrated followed by
pouring into a large excess of hexane to precipitate the polymer.
The block copolymer was purified by reprecipitation from THF
to hexanes twice, freeze-dried from its absolute benzene solution
(
10 mL) and ether (ca. 100 mL) was added at 0 °C where the
solution became cloudy. Then, hexane (10-40 mL) was added
and the reaction mixture was kept at 0 °C for 30 min with stirring.
With this treatment, higher molecular weight multiblock copo-
lymers were precipitated, while the diblock copolymer remained
in the solution. The multiblock copolymers were isolated in
g85% yields by repeating the same treatment. In some cases,
the sampling by SEC fractionation was carried out to completely
remove very small amounts of high and low molecular weight
polymers for the characterization. The isolated polymer was
reprecipitated from THF solution to methanol twice and freeze-
dried from its absolute benzene solution for 48 h. The resulting
multiblock copolymers were characterized by SEC, RALLS and
1
for 48 h, and characterized by SEC, RALLS, and H NMR
measurements. M
n,RALLS
w n
= 13 100, M /M = 1.03. 300 MHz
1
H NMR (CDCl , ppm): δ = 8.4-8.1 (broad, 61H, NdCH),
3

1
406 Macromolecules, Vol. 43, No. 3, 2010
Scheme 1. Synthesis of a Series of Multiblock Copolymers by Iterative Methodology
Sugiyama et al.
7
(
.4-6.2 (broad, 460H, Ar), 5.81 (d, 2H, CdCH
broad, 337H, main chain).
Both the introduction of PA function via the SiOP group
2
), 2.3-1.6
(broad, 191H, NdCH), 7.4-6.2 (broad, 1707H, Ar), 2.3-1.4
(broad, 1679H, main chain), 0.84 (s, 9H, C(CH ), -0.03 (s, 6H,
Si(CH ) ). The details of the synthesis are given in the Supporting
3 3
)
3
2
and the linking reactions were carried out under the iden-
tical conditions mentioned above. These reactions proceeded
cleanly and essentially quantitative in all cases. The linking
reactions were carried out in a mixture of tert-butylbenzene and
THF (1/4, v/v) at -78 °C for 24 h with the use of a 1.5-fold
Information.
Results and Discussion
We have herein proposed a new iterative methodology, in
which R-chain-end-SiOP-functionalized living AB diblock
copolymer anion is employed as a key building block specially
(
or more) excess of PS-block-P2VP anion. The objective multi-
block copolymers were always isolated in ca. 60% yields by
fractional precipitation with use of acetone/methanol system. In
some cases, the sampling by SEC fractionation was carried out to
completely remove very small amounts of high and low polymers
for the characterization. The resulting multiblock copolymers
designed for the synthesis of well-defined (AB) multiblock
n
copolymers composed of PS and PMMA blocks. The synthetic
outline is illustrated in Scheme 1. As can be seen, the living AB
diblock copolymer anion is designed in order to simultan-
eously introduce both A and B blocks. Furthermore, the SiOP
R-terminus is also designed to link two block copolymer chains
by converting the SiOP group to a R-phenyl acrylate function
capable of reacting with the ω-chain-end enolate anion in a 1:1
addition manner. The following three reaction steps are used
for the entire iterative synthetic sequence: (1) a sequential
living anionic block copolymerization with SiOPLi to prepare
1
were characterized by H NMR, SEC, and RALLS. (Figures S3
w
and S4). ABAB tetrablock copolymer, Mn,RALLS = 25 800, M /
1
M
1
8
n
=1.03. 300 MHz H NMR (CDCl
15H, NdCH), 7.4-6.2 (broad, 847H, Ar), 2.3-1.4 (broad,
32H, main chain), 0.84 (s, 9H, C(CH ), -0.028 (s, 6H, Si-
). ABABAB hexablock copolymer, Mn,RALLS = 46600,
3
, ppm): 8.4-8.1 (broad,
3 3
)
(
CH
3
)
2
1
w n 3
M /M = 1.03. 300 MHz H NMR (CDCl , ppm): δ = 8.4-8.1

Article
Macromolecules, Vol. 43, No. 3, 2010 1407
R-chain-end-SiOP-functionalized living AB diblock copoly-
mer anion, (2) an introduction of R-phenyl acrylate (PA)
function via the SiOP group by deprotection of the silyl group
of the SiOP R-terminus followed by Mitsunobu esterification
reaction, and (3) a linking reaction of the R-chain-end-PA-
functionalized AB block copolymer prepared in step 2 with the
R-chain-end-SiOP-functionalized living AB block copolymer
anion prepared in step 1. Since the polymer obtained in step 3
possesses the same SiOP R-terminus as the starting material
prepared in step 1, the same reaction sequence involving the
above three reaction steps can be repeated to result in a series
of multiblock copolymers.
converted to a PA function by reacting with R-phenyl acrylic
acid, DIAD, and Ph P (the so-called Mitsunobu reaction). These
3
1
end-group modification reactions were followed by H NMR and
found to be virtually quantitative by H NMR analyses. It can be
1
observed that the signal corresponding to the silyl methyl protons
at -0.02 ppm was completely disappeared after deprotection and
the PA vinyl proton signals at 5.88 and 6.32 ppm were subse-
quently emerged by the esterification as shown in Figure 1. As can
be seen in Table 1, the resulting polymer possesses a predictable
molecular weight and a narrow molecular weight distribution.
1
Moreover, the composition observed by H NMR was consistent
with that calculated from the feed ratio. These results clearly
indicate that the resulting polymer is the objective R-chain-end-
PA-functionalized PS-block-PMMA with well-defined and ex-
pected structures. Unless otherwise stated, molecular weight of
the block copolymer was adjusted to be around 10000 g/mol and
the composition (w/w) of A/B was ca. 50/50.
In the first step of the iterative synthetic sequence, R-chain-
end-SiOP-functionalized living PS-block-PMMA anion was pre-
pared as follows: The living anionic polymerization of styrene
was first carried out with SiOPLi in tert-butylbenzene at 0 °C for
5
4
3
0 min in the presence of a 3-fold excess of TMEDA. The
resulting R-chain-end-SiOP-functionalized PSLi was end-capped
with DPE in a 1:1 mixture of tert-butylbenzene and THF at -78 °C
followed by the polymerization of MMA at -78 °C for 30 min to
result in the objective R-chain-end-SiOP-functionalized living PS-
block-PMMA anion. Prior to the polymerization of MMA, a
In the final step, the R-chain-end-PA-functionalized PS-block-
PMMA thus prepared was reacted with a 1.5-fold excess of
R-chain-end-SiOP-functionalized living PS-block-PMMA anion
separately prepared. The linking reaction was carried out under
the conditions in a 1:4 mixture of tert-butylbenzene and THF at
-40 °C for 48 h. As shown in Figure 2, the SEC profile of the
reaction mixture exhibits only two distinct sharp peaks corre-
sponding to the objective linked product and the deactivated
block copolymer anion used in excess in the reaction. No higher
molecular weight peak was observed, indicating that the linking
reaction between the living chain-end anion and the PA terminus
undergoes in a 1:1 addition manner and no more addition of the
3
-fold excess of LiCl toward the PSLi was added to narrow the
molecular weight distribution of PMMA block.
The resulting living PS-block-PMMA anion was quenched
with a small amount of degassed methanol. The silyl protective
group of the SiOP R-terminus was completely removed by
treatment with Bu NF and the regenerated hydroxyl group
4
5
3
PA terminus occurs at all under such conditions. The linking
efficiency was found to be virtually quantitative by comparing the
two peak areas. The linked product was isolated in 85% yield by
fractional precipitation. The results are also summarized in
Table 1.
1
Figure 1. H NMR spectra of R-chain-end-functionalized (PS-block-
PMMA)s with (a) SiOP terminus, (b) hydroxyl terminus, and (c) PA
function.
Figure 2. SEC profiles of ABAB tetrablock copolymer (a) before and
(b) after fractional precipitation.
Table 1. Synthesis of a Series of Multiblock Copolymers Composed of PS (A) and PMMA (B) Blocks
-
3
M
n
ꢀ 10 (g/mol)
RALLS
M
w
/M
n
composition (PS/PMMA, w/w)
a
b
a
b
code
AB
type
calcd
NMR
SEC
calcd
obsd
diblock
10.5
26.4
37.0
51.0
64.5
11.4
28.2
40.5
53.6
12.2
27.5
40.7
53.6
1.03
1.03
1.03
1.04
1.06
51/49
48/52
45/55
45/55
45/55
48/52
47/53
43/57
43/57
45/55
(
(
(
(
AB)
AB)
AB)
AB)
a
2
3
4
5
tetrablock
hexablock
octablock
decablock
66.4
b
67.6
1
Determined by SEC equipped with triple detectors. Determined by H NMR.

1
408 Macromolecules, Vol. 43, No. 3, 2010
Sugiyama et al.
synthesized by the sequential living anionic block copolymeriza-
tion of styrene with MMA.
Synthesis of ABAB Tetra- and ABABAB Hexablock Co-
t
polymers Composed of PS Blocks and Either P BMA or P2VP
Blocks. In order to demonstrate the generality and versatility
of the iterative methodology developed in this study, the
synthesis of other two series of multiblock copolymers
t
composed of PS blocks and either P BMA or P2VP blocks
were carried out by using the corresponding R-chain-end-
functionalized living AB diblock copolymer anions. The
t
choice of P BMA and P2VP segments is to be expected that
they can be transformed into poly(methacrylic acid) and
poly(2-vinylpyridinium salt) by hydrolysis and quaterniza-
tion with either HX or RX, respectively. As is known,
poly(methacrylic acid) is a typical weak polyelectrolyte and
soluble in water depending on pH. On the other hand,
poly(2-vinylpyridinium salt) is a cationic polyelectrolyte
and soluble in water. Accordingly, the resulting multiblock
copolymers may be amphiphilic in character with many
potential applications.
Figure 3. SEC profiles for a series of multiblock copolymers: (a) (AB)
decablock, (b) (AB) octablock, (c) (AB) hexablock, (d) (AB) tetra-
block, and (e) AB diblock copolymers.
5
4
3
2
Synthesis of the multiblock copolymers composed of PS
blocks and either P BMA or P2VP blocks followed essen-
t
The molecular weight calculated was in good agreement with
that determined by either RALLS or H NMR and a narrow
1
tially the same iterative methodology as that employed for
the synthesis of the multiblock copolymers composed of PS
and PMMA blocks. The first PS block was prepared by the
polymerization of styrene with SiOPLi in tert-butylbenzene
in the presence of TMEDA at 0 °C as mentioned before. The
molecular weight distribution was attained. The composition
1
observed by H NMR was very close to the calculated value.
Thus, obviously, the linking reaction proceeds quantitatively to
resultin the object tetrablock copolymer composed of two PS and
two PMMA blocks referred to as ABAB or (AB)2.
t
block copolymer, PS-block-P BMA, anion was prepared by
t
sequential addition of DPE at first and then BMA to
Similarly, an ABABAB hexablock copolymer was synthesized
by repeating the same reaction sequence (the second iterative
process), which involved the chain-end modification of the SiOP
group into PA function of the ABAB tetrablock copolymer
obtained by the first iterative process, the preparation of an
R-chain-end-SiOP-functionalized living (PS-block-PMMA) an-
ion, and the linking reaction between R-chain-end-PA-functio-
nalized ABAB tetrablock copolymer and R-chain-end-SiOP-
functionalized living (PS-block-PMMA) anion. All these three
reaction steps were observed to effectively proceed with nearly
quantitative efficiencies under the same conditions. The charac-
terization results listed in Table 1 clearly show that the expected
and well-defined ABABAB hexablock copolymer was success-
fully synthesized.
polymerize in a 1:2 mixture of tert-butylbenzene and THF
at -78 °C for 2 h. Similar to the polymerization of MMA, the
addition of a 3-fold excess of LiCl was essential to narrow the
t
molecular weight distribution of P BMA block prior to the
polymerization of BMA. Then, the block copolymer was
t
treated carefully with Bu NF in THF to remove the silyl
4
protective group of the SiOP R-terminus without affecting
ester functionalities. The subsequent Mitsunobu esterifica-
tion with R-phenyl acrylic acid was carried out under the
1
same conditions as mentioned above. H NMR analysis
confirmed that the silyl protective group was quantitatively
removed and the degree of the PA functionalization with a
value of almost 100% was achieved (Figure S1). The result-
t
Likewise, the same reaction sequence was repeated two more
times in order to synthesize ABABABAB octa- and ABABA-
BABAB decablock copolymers. The SEC profiles always showed
two distinct peaks corresponding to the object linked products
and the block copolymer anions used in excess in the reactions.
Higher molecular weight products were not observed at all in
both cases. After isolation of the object products by fractional
ing R-chain-end-PA-functionalized PS-block-P BMA was
reacted with the R-chain-end-SiOP-functionalized living
PS-block-P BMA anion separately prepared. A 1.5-fold excess
t
of the living diblock copolymer anion was used to complete
the reaction under the conditions in a 1:4 mixture of tert-
butylbenzene and THF at -40 °C for 48 h.
The SEC curve of the crude product showed two peaks
corresponding to the object tetrablock copolymer and the
deactivated diblock copolymer anion used in excess in the
reaction. The linking efficiency was observed to be essen-
tially quantitative by comparing the two peak areas. The
objective polymer isolated in 60% yield by fractional pre-
cipitation showed a sharp monomodal distribution. It can be
seen in Table 2 that the resulting polymer is confirmed to be
the expected ABAB tetrablock copolymer by good agree-
ment of the molecular weight as well as composition between
calculated and observed.
1
precipitation (>85% yields), they were characterized by SEC, H
NMR, and RALLS, respectively. It can be seen from the results
listed in Table 1 that the agreement of the molecular weights
1
between calculated and observed by both RALLS and H NMR
is quite satisfactory in each of both cases and the narrow
molecular weight distributions are attained. The resulting block
polymers possessed the expected compositions close to 50/50 (w/w).
The SEC peaks of all the isolated multiblock copolymers shown
in Figure 3 clearly exhibit that all of the multiblock copolymers
herein synthesized possess sharp monomodal peaks. These results
strongly support the conclusion that the first, second, third, and
fourth iterative processes proceeded satisfactory as desired to
Deprotection of silyl group of the SiOP R-terminus with
Bu NF followed by esterification yielded the R-chain-end-
4
result in a series of well-defined (AB) multiblock copolymers,
PA-functionalized tetrablock copolymer. The chain-end
modification reactions were observed by H NMR to be
n
1
(
n = 2, 3, 4, and 5), composed of PS and PMMA blocks. Since the
ABABABABAB decablock copolymer possesses the same SiOP
R-terminus, the same reaction sequence can be repeated to result
in multiblock copolymers composed of more blocks. Once again,
it should be noted that such multiblock copolymers are not
quantitative. The second iteration was performed by the
linking reaction of the PA-functionalized tetrablock copo-
lymer with a 3-fold excess of R-chain-end-SiOP-functiona-
t
lized living PS-block-P BMA anion under the identical

Article
Macromolecules, Vol. 43, No. 3, 2010 1409
t
Table 2. Synthesis of Multiblock Copolymers Composed of PS Blocks and P BMA or P2VP Blocks
-
3
polymer
M
n
ꢀ 10 (g/mol)
RALLS
M /M
w
n
composition (A/B, wt/wt)
a
b
a
b
A
B
type
AB
ABAB
ABABAB
AB
calcd
NMR
SEC
calcd
obsd
t
P BMA
PS
PS
PS
PS
PS
PS
11.3
24.3
37.2
10.4
24.4
41.5
12.7
25.3
38.3
13.1
25.8
13.4
25.7
37.6
11.6
22.5
43.7
1.04
1.04
1.04
1.03
1.03
1.06
52/48
49/51
49/51
47/53
47/53
48/52
50/50
49/51
49/51
46/54
46/54
46/54
t
P BMA
t
P BMA
P2VP
P2VP
P2VP
ABAB
ABABAB
46.6
a
b
1
Determined by SEC equipped with triple detectors. Determined by H NMR.
conditions. The characterization results listed in Table 2
clearly indicate the successful formation of the requisite
ABABAB hexablock copolymer with well-defined structure.
Thus, the synthesis of ABAB tetra- and ABABAB hexablock
copolymers composed of PS and PtBMA blocks is realized
by developing the same iterative methodology using R-chain-
SiOPLi to prepare R-chain-end-SiOP-functionalized living PS-
block-PMMA anion, (2) an introduction of PA function via the
SiOP group by deprotection of the silyl protective group followed
by esterification with R-phenyl acrylic acid, and (3) a linking
reaction of R-chain-end-PA-functionalized PS-block-PMMA
with R-chain-end-SiOP-functionalized living PS-block-PMMA
anion. Since the three reaction steps proceeded cleanly and
quantitatively, the iterative synthetic sequences involving the
three reaction steps could be repeated at least four times to
successively synthesize a series of multiblock copolymers up to
the stage of ABABABABAB decablock copolymer composed of
PS and PMMA blocks.
t
end-SiOP-functionalized living PS-block-P BMA anion
(Figure S2).
In a similar fashion, an R-chain-end-SiOP-functiona-
lized living PS-block-P2VP anion was prepared by sequen-
tial addition of styrene, DPE, and 2-vinylpyridine with
SiOPLi as an initiator at 0 °C for 30 min, -78 °C for
1
0 min, and -78 °C for 30 min, respectively. Then, the SiOP
The resulting multiblock copolymers all possessed pre-
cisely controlled molecular weights, compositions, and very
R-terminus of the resulting AB diblock polymer was
deprotected with Bu NF and the subsequent Mitsunobu
esterification to introduce PA functionality was carried out
under the same conditions. H NMR analysis confirmed
narrow molecular weight distributions (M /Mn e 1.06). It
4
w
should be noted that the molecular weight and composition
can be readily and intentionally changed by changing the
monomers to initiator ratios in this methodology by means of
living anionic polymerization. Moreover, it may be possible
to synthesize the multiblock copolymers with more blocks,
since the final block copolymer has the same SiOP terminus
capable of continuing the iterative process. Further-
more, other two series of well-defined multiblock copolymers
(up to ABABAB hexablock) composed of PS with either
1
that the two end-functionalization reactions proceeded
essentially quantitatively (Figure S3). The resulting PA-
functionalized polymer was carefully freeze-dried several
times and reacted with a 1.5-fold excess of R-chain-end-
SiOP-functionalized living PS-block-P2VP anion in a 1:4
mixture of tert-butylbenzene and THF at -78 °C for 24 h.
The linking reaction was observed by SEC to proceed
quantitatively without the formation of any higher molec-
ular weight product than the 1:1 linked product under such
conditions. The results are also listed in Table 2. It can be
seen that the expected ABAB tetrablock copolymer is
successfully obtained with a predictable molecular weight,
a controlled composition, and a very narrow molecular
weight distribution.
t
P BMA or P2VP blocks were also successfully synthesized
by developing the same iterative methodology using the
corresponding R-chain-end-SiOP-functionalized living AB
block copolymer anions. The generality and versatility of
this iterative methodology is thus obvious. It should be
emphasized that the multiblock polymers composed of PS
t
and PMMA, P BMA, or P2VP blocks herein synthesized
Likewise, the ABABAB hexablock copolymer was synthe-
sized by repeating the same reaction sequence one more time
cannot be synthesized by sequential addition of two mono-
mers in the living anionic polymerization due to a big
difference between PS and PMMA, P BMA, or P2VP chain-
t
(Figure S4). Generally, a living anionic P2VP potentially
initiates the polymerization of styrene under the conditions
in THF at -78 °C. However, SEC profile of the resulting
polymer showed a multimodal distribution with the residual
end anions in reactivity.
On the basis of the successful synthesis of well-defined multi-
block copolymers, the iterative methodology developed in this
study offers the potential of providing a general and versatile
procedure for a variety of well-defined multiblock copolymers.
Furthermore, this iterative methodology may be applied to the
synthesis of a series of multiblock copolymers composed of PS,
5
5-57
peak corresponding to the starting P2VP.
Both of the
slow initiation reaction due to rather low nucleophilicity of
P2VP anion and the fast propagation reaction of styrene may
cause the starting P2VP being left behind, result in failure of
the multiblock copolymer synthesis by the living anionic
block copolymerization based on sequential addition of the
two monomers. Accordingly, the method herein developed is
only the procedure for the synthesis of well-defined (AB)n
multiblock copolymers composed of PS and P2VP.
P2VP, and PMMA blocks refer to as (ABC) , which is now under
investigation.
n
Acknowledgment. A.H. and K.S. acknowledge the JSPS
Gant-in-Aid for Scientific Research (No. B21350060 and
C21550114) from the Ministry of Education, Science, Sport,
and Culture of Japan, for financial support which funded this
research.
Conclusions
Herein, we have developed a new iterative methodology using
R-chain-end-functionalized living AB diblock copolymer anion
as a key building block specially designed for the synthesis of a
series of well-defined multiblock copolymers copolymer com-
posed of PS and PMMA blocks. The methodology involves the
following three reaction steps in the iterative synthetic sequence:
Supporting Information Available: Text giving synthetic
details of (AB)
n
multiblock copolymers composed of PS and
P BMA and synthetic details of (AB) multiblock copolymers
t
n
1
composed of PS and P2VP including figures showing H NMR
spectra and SEC curves. This material is available free of charge
via the Internet at http://pubs.acs.org.
(
1) a sequential living anionic block copolymerization with

1
410 Macromolecules, Vol. 43, No. 3, 2010
Sugiyama et al.
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31) Matsushita, Y. Macromolecules 2007, 40, 771.
w n
relatively broad molecular weight distributions (M /M = 1.3-1.5).
The asymmetric SEC peaks with significant tailings were
always observed. This curious behavior in the polymerization of
styrene with SiOPLi was also reported by Hutchings et al.:
Hutchings,
(
(
(
L. R.; Robert-Bleming, S. J. Macromolecules 2006, 39, 2144.
(55) El-Magd, A. A.; Sugiyama, K.; Hirao, A. Unpublished results.
(56) Matsushita, Y.; Nakao, Y.; Saguchi, R.; Choshi, H.; Nagasawa, M.
Polym. J. 1986, 18, 493.
(57) Ishizone, T.; Hirao, A.; Nakahama, S. Macromolecules 1993, 26,
6964.
(
(
(
(