Synthesis of polybenzamide-b-polystyrene block copolymer via combination of chain-growth condensation polymerization and atom transfer radical Polymerization

Article abstract of DOI:10.1002/pola.24068

Researchers at the Department of Material and Life Chemistry, Kanagawa University, Rokkakubashi have developed chain growth condensation polymerization (CGCP) to provide rod-like polymers with controlled molecular weight, low polydispersity, and functiona

Full text of DOI:10.1002/pola.24068

Synthesis of Polybenzamide-b-Polystyrene Block Copolymer via
Combination of Chain-Growth Condensation Polymerization
and Atom Transfer Radical Polymerization
CHIH-FENG HUANG, AKIHIRO YOKOYAMA, TSUTOMU YOKOZAWA
Department of Material and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
Received 13 March 2010; accepted 9 April 2010
DOI: 10.1002/pola.24068
Published online in Wiley InterScience (www.interscience.wiley.com).
KEYWORDS: atom transfer radical polymerization; diblock copolymer; polyamides; chain-growth condensation polymerization
INTRODUCTION Rod-coil block copolymers have received
polybenzamide (PSt-b-PBzAm) was successfully synthesized
1
4
enormous attentions due to their fascinating self-assembly
by the combined use of anionic polymerization or reversi-
ble addition-fragmentation chain transfer (RAFT) polymeriza-
1
behaviors in solution and solid state. With the development
1
5
of living polymerizations, such as living free-radical polymer-
tion. In the case of first anionic polymerization of St fol-
lowed by CGCP, PSt macroinitiators (MI) with high molecular
weight hindered the sequential CGCP resulting in the occur-
rence of self-condensation. In the case of first CGCP followed
by RAFT polymerization of St, the hindrance problem could
be overcome with CGCP as the first polymerization sequence,
but elaborate work was needed for the preparation of
PBzAms as macromolecular chain transfer agents for RAFT
polymerization.
2
3
ization, ring-opening (metathesis) polymerization , many
types of well-defined diblock copolymer with coil chains can
now be easily obtained through the use of dissimilar poly-
4
merization techniques via difunctional initiators or chain-
end transformations. However, the preparation of well-
5
defined rod segments is still a challenge due to the tedious
6
nature of the synthetic steps and the problem of low
7
solubility.
We have developed chain-growth condensation polymeriza-
tion (CGCP) to provide rod-like polymers with controlled
molecular weight, low polydispersity, and functionalities
through manipulating the resonance effect (þR effect) and
The strategy of using CGCP first, followed by atom-transfer
radical polymerization (ATRP) of St for the synthesis of well-
defined polybenzamide-b-polystyrene block copolymers has
not been reported yet. This ‘‘CGCP first’’ approach might
overcome the above-mentioned hindrance problem resulting
from the use of high-molecular-weight MI and also avoid the
tedious synthesis of macromolecular chain transfer agent. An
anticipated problem during ATRP is that the metal-catalyzed
system might be interrupted by coordination of the amide
structure with the catalyst leading to interference with the
activation/deactivation equilibrium constant of the metal
complex. Therefore, metal/ligand complexes with appropri-
ate redox affinity are needed.
8
the inductive effect (þI effect) on aromatic monomers. Dif-
ferent from conventional polycondensation, the monomers
show high selectivity and react preferentially with the poly-
mer end groups than the other monomers. The þR effect
was efficiently mediated through deprotonation of the amino
group of 4-aminobenzoic acid esters using a commercially
available base (lithium hexamethyldisilazide [LiHMDS]) and
9
well-defined polybenzamides (PBzAm) were obtained.
Explorations of para-type monomers with various leaving
groups could diversify the access to well-defined poly(para-
benzamide).
Herein, we first synthesized three monomers by one-step
reaction from commercially available methyl 4-aminoben-
zoate, ethyl 4-aminobenzoate, and methyl 3-aminobenzoate,
respectively. Two difunctional initiators for CGCP were exam-
ined and an efficient initiator was chosen (Scheme 1). In
addition, poly(meta-benzamide) with the N-octyloxybenzyl
(OOB) side group (PmOOBBzAm), which can be further
deprotected to poly(N-H-meta-benzamide) (PmNHBzAm),
was synthesized. For chain extension with styrene (St) via
Essentially, well-defined condensation polymers yield tele-
chelic structures, which can be used or modified for the pro-
duction of block copolymers by polymer–polymer coupling
or sequential polymerizations. By using this strategy, we
have developed efficient approaches in the preparation of
1
0–12
aromatic polyamide (i.e., PBzAm)
and aromatic poly-
1
3
ether block/star copolymers. In addition, polystyrene-b-
Additional Supporting Information may be found in the online version of this article. Correspondence to: T. Yokozawa (E-mail: yokozt01@
kanagawa-u.ac.jp)
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2948–2954 (2010) V
2010 Wiley Periodicals, Inc.
C
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RAPID COMMUNICATION
SCHEME 1 Synthetic routes to polystyrene-b-polybenzamide (PSt-b-PBzAm) block copolymers. [Color figure can be viewed in the
online issue, which is available at www.interscience.wiley.com.]
ATRP, PBzAm MIs with quantitative chain end modifications
were obtained. Afterward, copper-catalyzed systems composed
of different ligands were examined to understand the influence
of amide structure on ATRP. Eventually, we developed an effi-
cient synthetic approach using the combination of CGCP and
ATRP for the synthesis of well-defined polybenzamide-b-poly-
styrene block copolymers with high molecular weights. Poly
slightly basic (pH ¼ 8), and the mixture was extracted with
ethyl acetate. The combined organic layers were washed
with brine and dried over MgSO . The solvent was removed
4
and the residue was recrystallized from methanol to give
the monomer 4 as colorless crystals with melting point:
ꢀ
80-82 C (7.80 g, yield 62%).
1
H NMR (600 MHz, CDCl , d, ppm): 7.87-7.84 (m, 2H), 6.54-
3
(N-H-meta-benzamide)-b-polystyrene (PmNHBzAm-b-PSt), which
6
7
.52 (m, 2H), 4.31 (q, J ¼ 7.2 Hz, 2H), 4.05 (s, 1H), 3.15 (t, J ¼
has strong intermolecular multiple hydrogen bonding between
the amide bonds and pAp stacking of the aromatic rings, was
synthesized through removal of the OOB group.
.2 Hz, 2H), 1.65-1.60 (q, J ¼ 7.6 Hz, 2H), 1.42-1.26 (m, 13H),
13
0.88 (t, J ¼ 6.9 Hz, 3H); C NMR (150 MHz, CDCl , d, ppm):
1
2
3
66.88, 152.03, 131.46, 118.35, 111.24, 60.11, 43.38, 31.78,
9.33, 29.31, 29.21, 27.06, 22.63, 14.45, 14.08.
EXPERIMENTAL
CGCP for the Synthesis of PBzAms from Initiator 2
General Methods
A 10-mL flask equipped with a three-way stopcock was
charged with 1.0 M LiHMDS/THF solution (0.5 mL, 0.5 mmol).
A mixture of the monomer 4 (132 mg, 0.5 mmol) and the ini-
tiator 2 (14 mg, 0.05 mmol) in dry THF (1 mL) was added to
Conversion of the monomer was monitored by analytical gas
chromatography on a Shimadzu GC-2010 gas chromatograph
equipped with a Shimadzu Rtx-1 column (15 m) and an FID
detector. Naphthalene and anisole were used as internal
standards for CGCP and ATRP, respectively. H and C NMR
spectra were obtained on a JEOL ECA-600 instrument. The
ꢀ
the flask under nitrogen at ꢁ10 C. To examine CGCP kinetics,
1
13
aliquots were withdrawn at intervals during the polymeriza-
tion to monitor the conversion of monomer by GC with naph-
thalene as an internal standard. After reaction had finished,
1
internal standards for H NMR experiments in CDCl3 and
deuterated dimethylformamide (DMF-d ) were tetramethylsi-
7
the mixture was quenched with saturated NH Cl. The whole
4
lane (0.00 ppm) and the midpoint of DMF (2.74 ppm),
solution was extracted with CH Cl and the organic layer was
2
2
1
3
respectively; for C NMR experiments in CDCl it was the
3
washed with water; then dried over MgSO . The crude oil was
4
1
3
midpoint of CDCl (77.0 ppm), and for C NMR experiments
3
dissolved in CH Cl and twice precipitated in methanol/water
2
2
6 6
in DMSO-d it was the midpoint of DMSO-d (39.5 ppm).
¼
9/1 (v/v) to afford yellowish viscous poly(para-benzamide)
with the tert-butyldimethylsilyl protecting end group
PpBzAm-OTBS) (M ¼ 3010, M /M ¼ 1.07, yield 72%).
FT-IR spectra were recorded on a JASCO FT/IR-410. The Mn
and M /M values of polymers were measured with a Sho-
w
n
(
n
w
n
dex GPC-101 gel permeation chromatography (GPC) unit
eluent: tetrahydrofuran [THF]; calibration: polystyrene
Chain Extension with Styrene via ATRP to Synthesize
(
Polybenzamide-b-Polystyrene Block Copolymers
standards) equipped with two Shodex KF-804L columns,
Shodex UV-41, and Shodex RI-71S.
(PBzAm-b-PSt)
Preparations of para- and meta-type PBzAm MIs (i.e.,
PpBzAm-Br and PmOOBBzAm-Br) involve similar synthetic
steps, as detailed in the Supporting Information. The result-
ing MIs were further used for St chain extension via ATRP.
For example, St/MI/CuBr/tris(2-dimethylaminoethyl)amine
Synthesis of Monomer 4
Ethyl 4-aminobenzoate (8.23 g, 50 mmol) and octanal (7.08
mL, 45 mmol) were mixed with THF (100 mL). Acetic acid
(
2.9 mL, 50 mmol) was gradually added and the mixture
was stirred at room temperature for another 10 min. Then,
sodium triacetoxyborohydride (16.30 g, 77 mmol) was added
directly. The mixture was stirred at room temperature for 24
h, then saturated NaHCO3 was added to make the solution
6
(Me TREN) reagents were used in the ratio of 600/1/1/1/1
in 13% (v/v) anisole ([St]0 ¼ 7.56M). Styrene, Me TREN,
6
PpBzAm-Br, and anisole were added to a Schlenk flask. The
mixture was deoxygenated by three freeze-pump-thaw cycles
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Conditions of CGCP and Characterization of Polybenzamide
a
b
5
ꢁ1
)
Entry
M
I
[M] /[I]
0 0
Time (h)
M
n
M /M
w n
Conv. (%)
k
appꢂ10 (s
1
2
3
4
5
3
3
3
4
4
5
1
2
2
2
2
2
10
10
40
10
40
10
19
12
19
24
26
1
–
–
21
99
92
85
75
88
–
–
3,000
7,600
3,010
5,900
4,520
1.07
1.09
1.07
1.09
1.09
5.34
–
1.69
–
c
6
a
c
12
M
n
was determined by GPC (eluent: THF) using polystyrene calibra-
Five-fold molar excess of LiCl to base was added.
tion standards.
b
Conversion of monomer was determined by GC with 10 mol.% naph-
thalene as an internal standard.
and the flask was backfilled with nitrogen. CuBr was then
added to the frozen solution. The flask was closed, evac-
uated, and deoxygenated by additional two freeze-pump-
thaw cycles. An initial sample was taken via a syringe and
not be achieved from initiator 1 with the ATRP initiating
site.
In our previous study, we obtained well-defined PBzAms via
CGCP of the methyl ester monomer 3. The ethyl ester mono-
mer 4, which can be easily synthesized via one-step reaction
from commercially available reagents, would also be a suita-
ble monomer for preparing well-defined PBzAms. The influ-
ence of the alkoxy group of the ester moiety on the mono-
mer reactivity can be rationalized on the basis of the CGCP
the flask was then immersed in an oil bath preheated at
ꢀ
7
0 C to start the polymerization. Aliquots were withdrawn
at intervals during the polymerization to monitor the conver-
sion by GC, with anisole as an internal standard. The poly-
merization was stopped by placing the flask in an ice bath
and exposing the contents to air. The resulting mixture was
diluted with THF and passed through a neutral aluminum
oxide column to remove the copper catalyst. The mixture
was precipitated in methanol, filtered, and dried in a vacuum
kinetic study. CGCP of monomers 3 and 4 was carried out at
ꢀ
ꢁ
10 C in THF, using 2 and LiHMDS as initiator and base,
respectively, (M/I/LiHMDS ¼ 40/1/40, [M]
0
¼ 0.3M). As
shown in Figure 1(A), a linear first-order kinetic plot was
(
M ¼ 23,400, M /M ¼ 1.24, conversion ¼ 40%).
n
w
n
RESULTS AND DISCUSSION
Three monomers were first synthesized via one-step reaction
from commercially available methyl-4-aminobenzoate, ethyl-
4-aminobenzoate, and methyl-3-aminobenzoate. Based on the
combination of CGCP and ATRP reported, two difunctional
initiators 1 and 2 were synthesized. As outlined in Scheme
1, the major advantage of the initiator 1 having an ATRP ini-
tiating site is that the sequential polymerizations from CGCP
to ATRP can proceed without the need for chain end modifi-
cations. In CGCP, addition of a base that abstracts a proton of
the amino group of monomer generates the aminyl anion.
This anionic group deactivates the electrophilic carbonyl site
on the para-position through the resonance effect (þR
effect), resulting in the suppression of self-condensation of
the monomer, and allowing selective reaction with initiator
and the propagating end. A possible problem arises from the
halogen atom at the ATRP initiating site, which might react
with the aminyl anion of monomer, leading to quenching of
the anion, and side reactions. To examine this issue, CGCP of
the monomer 3 from two initiators 1 and 2 was carried out.
As shown in Table 1 (entry 1) and can be seen from the GPC
profile (see Fig. S1 in the Supporting Information), low
monomer conversion (21%) and tailing GPC traces were
obtained using initiator 1. On the contrary, CGCP from the
initiator 2 with tert-butyldimethylsilyl (TBS) group (entry 2
in Table 1) proceeded with high monomer conversion
FIGURE 1 Chain-growth condensation polymerization (CGCP):
(A) kinetic plots of ln(M /M) versus time, and (B) M and
0
n
(
99%), giving a product with a narrow molecular weight
M /Mn versus conversion plots with monomers
3
and 4
w
ꢀ
distribution (M /M ¼ 1.07). Hence, effective CGCP could
(M/I/LiHMDS ¼ 40/1/40 at ꢁ10 C in THF with [M]
0
¼ 0.3 M).
w
n
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RAPID COMMUNICATION
1
FIGURE 2 H NMR (600 MHz, CDCl
3
) spectra of chain end modifications of (A) PpBzAm: (i) TBS endprotected, (ii) deprotection of
TBS, and (iii) acylation, and (B) PmOOBBzAm: (iv) TBS end-protected, (v) deprotection of TBS, and (vi) acylation.
1
6
obtained in each polymerization. The faster consumption of
the methyl ester monomer 3 (triangles) indicated its higher
reactivity, when compared with the ethyl ester monomer 4
structure can chelate metal ions and chelation might affect
the activation/deactivation equilibrium of metal-catalyzed
systems. Therefore, kinetic studies were conducted to exam-
ine the efficiency of various ligands with copper(I) bromide
ꢁ
5
(
s
circles). The apparent rate constant of 3 (k ¼ 5.34 ꢂ 10
app
ꢁ
1
) was about three times higher than that of 4 (k ¼ 1.69
app
using tris(2-dimethylaminoethyl)amine (Me TREN), tris[(2-
6
pyridyl)methyl]amine (TPMA), N,N,N ,N ,N -pentamethyldie-
thylenetriamine (PMDETA), and 2,2 -bipyridyl (Bpy). In the
ꢁ
5
ꢁ1
0
00 00
ꢂ 10
s
). Figure 1(B) shows a linear increase in molecular
0
weight (M ) with respect to conversion and a narrow molecu-
w
lar weight distribution (M /M < 1.10). From Figure 1, we
cases of PpBzAm-Br as an MI [solid symbols in Fig. 3(A)],
four linear first-order kinetic plots for the St polymerization
were obtained (entries 1-4 in Table 2: St/PpBzAm-Br/CuBr/
w
n
can conclude that monomers 3 and 4 both undergo chain-
growth polymerization and the monomer 4 has a slower
CGCP rate than the monomer 3, which is consistent with the
ethoxy carbonyl group having lower electrophilicity than the
methoxy carbonyl group. Well-defined tert-butyldimethylsilyl-
protected poly(para-benzamide) (PpBzAm-OTBS) can be
obtained from either monomer. The conditions and character-
istics of the CGCP are summarized in Table 1.
L ¼ 600/1/1/1; PpBzAm-Br: M
¼ 3010, M
/M
¼ 1.07). As
n
w
n
shown in Figure 3(B) (solid symbols), these four polymeriza-
tions proceeded with a linear increase in molecular weight
with respect to conversion, and with low polydispersity
w n
(M /M < 1.25). When conversion was higher than 30%,
however, molecular weight deviations were observed. This
might be ascribed to the difference of hydrodynamic radius
between the high-molecular-weight block copolymers and
polystyrene standards. Monomodal GPC traces for the chain
extensions are shown in Figure 3(C). Furthermore, a block co-
For the next chain extension with styrene (St) via ATRP,
chain-end modification to synthesize PBzAm-Br MI was car-
ried out. As outlined in Scheme 1, the TBS group was
removed with 1.0 M tetrabutylammonium fluoride/THF solu-
tion. The purified PBzAm-OH polymer was acylated with
polymer with low polydispersity (entry 5 in Table 2: M
n
¼
3
7,200, M /M ¼ 1.25) was synthesized from high-molecular-
w
n
2
-bromoisobutyryl bromide to obtain PBzAm-Br MI. As
weight MI (PpBzAm-Br: M ¼ 7600, M /M ¼ 1.09; footnote
1
n
w
n
revealed from the H NMR spectra of Figure 2(A), quantita-
tive conversion in chain-end modification was obtained, as
can be distinguished from peaks a (4.67 ppm, singlet), a
in Table 2). These results suggest that well-defined poly(N-
octyl-para-benzamide)-b-polystyrene block copolymers can
0
be efficiently synthesized. Interestingly, TPMA (k
¼ 5.11 ꢂ
app
ꢁ6 ꢁ1
00
(
4.61 ppm, doublet, J ¼ 6.5 Hz), and a (5.14 ppm, singlet).
ꢁ6 ꢁ1
1
0
s
) and Me TREN (k
¼ 5.74 ꢂ 10
s ) as ligands
6
app
A poly(N-octyl-para-benzamide) with the 2-bromoisobutyryl
end group (PpBzAm-Br: Mn ¼ 3010, M /M ¼ 1.07) was
show faster polymerization rates than those obtained with
PMDETA (k
w
n
ꢁ6 ꢁ1
¼ 0.80 ꢂ 10
s
) and Bpy (kapp ¼ 0.74 ꢂ
app
obtained. Similarly, poly(N-octyloxylbenzyl-meta-benzamide)
ꢁ6 ꢁ1
10
s ) as ligands. This is due to the different redox poten-
with the 2-bromoisobutyryl end group (PmOOBBzAm-Br: M
4520, M /M
n
17
tial of the copper complex. Chain extension results are sum-
marized in Table 2. Thus, the results of kinetic studies indicate
that N-substituted PBzAms have an insignificant effect on the
ATRP copper complex structures, although rather slow poly-
merization rates were obtained with less-active copper com-
plexes. Further studies of chain extensions with various
monomers and ATRP initiating sites are under way.
¼
w
n
¼ 1.09) was synthesized after CGCP of the
monomer 5; this can be quantitatively distinguished from
0
peaks c (4.60 ppm, singlet), c (4.50 ppm, doublet, J ¼ 5.5
0
0
Hz) and c (5.05 ppm, singlet) in Figure 2(B).
Thus, the functionalized polymers, PBzAm-Br, were used for
chain extension with St. It has been reported that amide
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 St chain extension: (a) kinetic plots of ln(M
PmOOBBzAm-Br as an MI), (b) M and M /M versus conversion plots, (c) GPC traces of chain extension from PpBzAm-Br, and
d) GPC traces of chain extension from PmOOBBzAm-Br and precipitation (red line) of the resulting block copolymer (St/MI/CuBr/L
0
/M) versus time (solid symbols: PpBzAm-Br as an MI; hollow symbol:
n
w
n
(
ꢀ
¼
600/1/1/1 at 70 C in 13% (v/v) anisole).
TABLE 2 Reaction Conditions and Characterization of St Chain Extension Products Generated from Polybenzamide
Macroinitiators via ATRP
a
b
a
c
d
6
ꢁ1
)
Entry
MI
Ligands
Time (h)
Conv. (%)
M
n
M /M
w n
k
appꢂ10 (s
1
2
3
4
5
6
a
PpBzAm-Br (M
n
¼ 3,010)
¼ 7,600)
TPMA
20
35
40
12
18
25
27
18,000
23,400
8,400
1.16
1.24
1.09
1.15
1.25
5.11
5.74
0.80
0.74
6
Me TREN
25
PMDETA
Bpy
45
72.5
8.25
24
12,580
37,200
e
PpBzAm-Br (M
n
Me
6
TREN
TREN
–
f
f
PmOOBBzAm-Br (M
n
¼ 4,520)
Me
6
20,000 (26,420)
1.37 (1.13)
3.30
ꢀ
c
In 13% (v/v) anisole at 70 C with St/MI/CuBr/L ¼ 600/1/1/1, except for
Conversion of St was determined by GC with anisole as an internal
standard.
entries 4 (St/MI/CuBr/Bpy ¼ 600/1/1/2) and 5 (St/MI/CuBr/Me TREN ¼
6
d
1
b
000/1/1/1).
n
M was determined by GPC (eluent: THF) using polystyrene calibra-
tion standards.
PpBzAm-Br (M
n
¼ 3,010, M
w
/M
n
¼ 1.07) for entries 1–4; PpBzAm-Br
e
(M
n
¼ 7,600, M
w
/M
n
¼ 1.09) for entry 5; and PmOOBBzAm-Br (M
n
¼
Not determined.
f
4
,520, M /M
w
n
¼ 1.09) for entry 6.
After precipitation into 2-propanol/ethyl acetate ¼ 50/6 (v/v).
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RAPID COMMUNICATION
CONCLUSIONS
Two difunctional initiators (1 and 2) and three monomers
3, 4, and 5) were synthesized. An initiator 2 with a TBS-
(
protecting group was chosen to avoid the problem of
quenching between the aminyl anion of monomer and the
halogen atom of initiator 1 during CGCP. The kinetics of
CGCP was investigated for the para-type monomers 3 and 4
with different ester moieties. Polycondensation of each
monomer proceeded in a CGCP fashion, and the apparent
rate constants (kapp) showed a three-fold difference between
ꢁ
5
ꢁ1
the methyl ester 3 (5.34 ꢂ 10
s
) and ethyl ester 4 (1.69
ꢁ
5
ꢁ1
ꢂ 10
s ). Then, quantitative chain end modifications
were conducted for syntheses of para- and meta-PBzAm MIs.
Various ligands, such as tris(2-dimethylaminoethyl)amine
(
Me TREN), TPMA, PMDETA, and Bpy with copper(I) bro-
6
1
7
FIGURE 4 H NMR (600 MHz, DMF-d ) spectra before and after
mide (CuBr), were used for ATRP. In chain extensions with
St, a linear increase in molecular weight with respect to con-
version, low polydispersity, and monomodal GPC traces was
obtained. The kinetic studies indicated that N-substituted
PBzAms are not detrimental to the ATRP copper complexes,
although rather slow polymerization rates were obtained
with less-active copper complexes (herein, CuBr/PMDETA
and CuBr/Bpy). Thus, we were able to develop an efficient
approach, by the combination of CGCP and ATRP, to the syn-
thesis of well-defined PBzAm-b-polystyrene block copoly-
treatment of block copolymer with TFA: (a) PSt-b-PmOOBB-
zAm, treatment for (b) 1 day and (c) 4 days.
Moreover, synthesis of poly(N-OOB-meta-benzamide)-b-poly-
styrene block copolymer was carried out. Compared with the
same catalytic system with a different MI [entries 2 and 6 in
Table 2: solid circles and hollow diamonds in Figs. 3(a, b)],
chain extension with St showed a slower polymerization rate
ꢁ
6
ꢁ1
mers with high molecular weight and low polydispersity (Mn
(
kapp ¼ 3.3 ꢂ 10
s
), which might be attributed to the
¼
37,200, M /Mn ¼ 1.25). Selective removal of the OOB
higher M
w
and bulkier nature of the PmOOBBzAm-Br MI.
w
group was further carried out with TFA to obtain poly(N-H-
meta-benzamide)-b-PSt block copolymers. Selective deprotec-
tion and good stability of the ester linkage between the poly-
amide and polystyrene segments were attained. Exploration
of the self-assembly behavior of the PmNHBzAm-b-PSt block
copolymers in solution and in the solid state is under way.
The GPC traces show some tailing toward low Mw [Fig.
(d)], which would be due to self-condensation polymer
without the initiator unit, resulting from the high reactivity
3
1
1,12
of the meta-type monomer during the first step of CGCP.
For removal of the MI, the block copolymer was purified by
precipitation into 2-propanol/ethyl acetate ¼ 50/6 (v/v).
A well-defined poly(N-OOB-meta-benzamide)-b-polystyrene
This study was supported by a Scientific Frontier Research Pro-
ject Grant from the Ministry of Education, Science, Sport and
Culture, Japan.
block copolymer was obtained [Fig. 3(d) red line: Mn
¼
2
6,420, M /M ¼ 1.13].
w
n
Selective removal of the OOB group was further carried out
to synthesize poly(N-H-meta-benzamide)-based block copoly-
mers with strong hydrogen bonding and good solubility in
highly polar solvents. To examine the removal of the OOB
group and the stability of the ester linkage between the PSt
and PmOOBBzAm segments, reactions were carried out with
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