Chain-growth condensation polymerization of 4-aminobenzoic acid esters bearing tri(ethylene glycol) side chain with lithium amide base

Article abstract of DOI:10.1002/pola.23897

Chain-growth condensation polymerization of paminobenzoic acid esters 1 bearing a tri(ethylene glycol) monomethyl ether side chain on the nitrogen atom was investigated by using lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base. The methyl ester

Full text of DOI:10.1002/pola.23897

Chain-Growth Condensation Polymerization of 4-Aminobenzoic Acid
Esters Bearing Tri(ethylene glycol) Side Chain with Lithium Amide Base
KAZUO YOSHINO, KOTARO HACHIMAN, AKIHIRO YOKOYAMA, TSUTOMU YOKOZAWA
Department of Material and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
Received 12 November 2009; accepted 18 December 2009
DOI: 10.1002/pola.23897
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Chain-growth condensation polymerization of p-
aminobenzoic acid esters 1 bearing a tri(ethylene glycol) mono-
methyl ether side chain on the nitrogen atom was investigated
by using lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a
base. The methyl ester monomer 1a afforded polymer with
low molecular weight and a broad molecular weight distribu-
tion, whereas the polymerization of the phenyl ester monomer
1b at ꢀ20 ꢁC yielded polymer with controlled molecular weight
(Mn ¼ 2800–13,400) and low polydispersity (Mw/Mn ¼ 1.10–
1.15). Block copolymerization of 1b and 4-(octylamino)benzoic
acid methyl ester (2) was further investigated. We found that
block copolymer of poly1b and poly2 with defined molecular
weight and low polydispersity was obtained when the poly-
merization of 1b was initiated with equimolar LiHMDS at
ꢀ20 ꢁC and continued at ꢀ50 ꢁC, followed by addition of 2 and
equimolar LiHMDS at ꢀ10 ꢁC. Spherical aggregates were
formed when a solution of poly1b in THF was dropped on a
glass plate and dried at room temperature, although the block
copolymer of poly1b and poly2 did not afford similar aggre-
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gates under the same conditions. 2010 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 48: 1357–1363, 2010
KEYWORDS: block copolymers; chain-growth condensation poly-
merization; living polymerization; polyamides; self-assembly
INTRODUCTION Oligomers and polymers containing aro-
matic rings in the backbone and oligo(oxyethylene) units in
the side chain possess unique character derived from the dif-
ferent solvophobicity of the backbone and side chain.1–9 For
example, m-phenyleneethynylene oligomers bearing tri(ethyl-
ene glycol) side chains fold to a helix in polar solvents, such
as acetonitrile.1 We have reported that poly(p-benzamide)5
and poly(naphthalenecarboxamide)6 bearing methyl-substi-
tuted tri(ethylene glycol) as a chiral side chain on the nitro-
gen atom take helical structures in solution, whereas the cor-
responding poly(m-benzamide) takes a chiral conformation
in solution.7 Furthermore, poly(m-benzamide)s bearing tri-
and tetra(ethylene glycol) side chains on the nitrogen atom
are soluble in water and exhibit lower critical solution tem-
peratures (LCST) in water.8
LiHMDS, but a polymerization method using LiHMDS for the
synthesis of poly(p-benzamide) bearing oligo(oxyethylene)
side chains has not been established. An oligo(oxyethylene)
side chain on the amide anion would have a strong affinity for
the lithium cation derived from LiHMDS, and this is expected
to reduce the reactivity of the amide anion. Furthermore, the
amide anions of para-aminobenzoic acid ester monomers are
less reactive than those of the meta-substituted counterparts
because of the electron-withdrawing resonance effect of the
ester moiety in the para monomer. Therefore, the polymeriza-
tion of N-oligo(oxyethylene) 4-aminobenzoic acid esters with
LiHMDS is thought not to proceed in the same manner as that
of the meta-substituted counterparts.
In this article, we report LiHMDS-promoted chain-growth
condensation polymerization of 4-aminobenzoic acid esters 1
bearing a tri(ethylene glycol) monomethyl ether side chain
on the nitrogen atom and the copolymerization of 1 and 4-
These aromatic polyamides, except the poly(p-benzamide),
were synthesized in a controlled manner by chain-growth
condensation polymerization of the corresponding aromatic
amino acid esters with lithium 1,1,1,3,3,3-hexamethyldisila-
zide (LiHMDS) as a base.10 However, the poly(p-benzamide)
with the chiral tri(ethylene glycol) side chain was prepared
by polymerization with a prototype base system using N-
octyl-N-(triethylsilyl)aniline/CsF/18-crown-6, instead of com-
mercially available LiHMDS.5 This silyl aniline is readily
hydrolyzed by moisture in air. N-Alkyl poly(p-benzamide)s
have already been synthesized by polymerization with
(octylamino)benzoic acid methyl ester
2 with LiHMDS
(Scheme 1). Self-assembly of poly1 and the block copolymer
was also examined.
EXPERIMENTAL
Materials
Commercially available dehydrated tetrahydrofuran (stabi-
lizer-free, Kanto) and CH2Cl2 (Kanto) were used as dry
Correspondence to: T. Yokozawa (E-mail: yokozt01@kanagawa-u.ac.jp)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 1357–1363 (2010) 2010 Wiley Periodicals, Inc.
CHAIN-GROWTH CONDENSATION POLYMERIZATION, YOSHINO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 A: Polymerization
of 1. B: Block copolymerization
of 1 and 2.
solvents. Lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS,
1.0 M solution in THF, Aldrich) was used as received.
N,N,N0,N0-Tetramethylethylenediamine (TMEDA) was distilled
over CaH2. Methyl 4-(octylamino)benzoate (2)10 and phenyl
4-methylbenzoate (3)11 were prepared as described
previously.
and dried over anhydrous MgSO4. The solvent was removed
under reduced pressure, and the residue was purified by
flash chromatography on silica gel (ethyl acetate/hexane ¼
5/1) to give 5.1 g of 4a as a yellow viscous oil (54%).
1H NMR (500 MHz, CDCl3, d, ppm): 8.97 (br s, 1 H), 8.06 (d,
J ¼ 8.9 Hz, 2 H), 7.62 (d, J ¼ 8.9 Hz, 2 H), 4.13 (s, 2 H), 3.90
(s, 3 H), 3.79–3.77 (m, 2 H), 3.74–3.72 (m, 4 H), 3.60–3.58
(m, 2 H), 3.37 (s, 3 H). 13C NMR (126 MHz, CDCl3, d, ppm):
168.6, 166.6, 141.6, 130.7, 125.7, 119.1, 71.7, 71.2, 70.7,
70.4, 70.0, 58.9, 51.9. IR (neat, cmꢀ1): 3332, 2882, 1719,
1282, 1176, 1109, 858.
Characterization
Conversion of monomer was determined by HPLC with a
Japan Analytical Industry LC-909 HPLC unit (eluent: THF)
using a JAIGEL column (1H-A). The Mn and Mw/Mn values of
polymers were measured with a TOSOH HLC-8120 gel-per-
meation chromatography (GPC) unit (eluent: THF; volume
flow rate: 1 mL/min; calibration: polystyrene standards)
using two TSK-gel columns (2 ꢂ Multipore HXL-M). Isolation
of polymer was carried out with a Japan Analytical Industry
LC-908 Recycling Preparative HPLC unit (eluent: CHCl3)
using two TSK-gel columns (2 ꢂ G2000HHR-M). 1H and 13C
NMR spectra were obtained on JEOL ECA-600 and ECA-500
spectrometers with tetramethylsilane (TMS) as an internal
standard. IR spectra were recorded on a JASCO FT/IR-410.
Scanning electron microscopy (SEM) was carried out with a
Hitachi S-4000. Samples were prepared by dropping a THF
solution of polymer on a glass slide, and allowing it to dry
under THF vapor at 25 ꢁC for 3 days. This glass plate was
sputter-coated with carbon before SEM analysis.
Synthesis of 4-{2-[2-(2-Methoxyethoxy)ethoxy]ethylamino}-
benzoic Acid Methyl Ester (1a)
A three-necked flask, equipped with a dropping funnel, a
reflux condenser, and a gas inlet tube, was purged with ar-
gon and then charged with 1.15 M borane-THF complex in
THF (15 mL, 17 mmol). The solution was cooled to 0 ꢁC
under an argon atmosphere with stirring for 10 min. A solu-
tion of 4a (4.1 g, 13 mmol) in dry THF (20 mL) was added
dropwise from the dropping funnel, and the mixture was
refluxed for 3.5 h. After cooling to room temperature, 6 M
HCl (23 mL) was added to it, and the whole was heated
under reflux for 1 h. The solution was diluted with water
and neutralized to approximately pH 8 with NaHCO3, then
extracted with CH2Cl2. The combined organic layer was
washed with water and dried over anhydrous MgSO4. The
Synthesis of Monomer 1
Monomer 1 was synthesized by the procedure as shown in
Scheme 2.
Synthesis of 4-{2-[2-(2-Methoxyethoxy)ethoxy]acetylamino}
benzoic Acid Methyl Ester (4a)
A mixture of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (6.0
mL, 39 mmol), methyl 4-aminobenzoate (4.5 g, 30 mmol),
and 4-(dimethylamino)pyridine (DMAP, 4.8 g, 39 mmol) in
ꢁ
dry CH2Cl2 (45 mL) was stirred at 0 C for 10 min. Into the
flask was added N-ethyl-N0-(3-dimethylaminopropyl)carbodii-
mide hydrochloride (EDCI) (7.5 g, 39 mmol) with stirring at
ꢁ
0 C. The reaction mixture was stirred at room temperature
for 65 h, and then the reaction was quenched with water, fol-
lowed by extraction with CH2Cl2. The combined organic layer
was washed with 1 M HCl and saturated aqueous NaHCO3,
SCHEME 2 Synthesis of Monomer 1.
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ARTICLE
solvent was removed under reduced pressure, and the resi-
due was purified by flash chromatography on silica gel (ethyl
acetate/hexane ¼ 7/1) to give 2.6 g of 1a as an orange vis-
cous oil (67%).
3.40 (s, 3 H), 3.38 (t, J ¼ 5.3 Hz, 2 H). 13C NMR (126 MHz,
CDCl3, d, ppm): 165.3, 152.6, 151.3, 132.2, 129.3, 125.4,
121.9, 117.4, 111.7, 72.0, 70.6, 70.4, 69.2, 59.0, 42.9. IR
(neat, cmꢀ1): 3369, 2876, 1704, 1607, 1278, 1109, 771.
1H NMR (500 MHz, CDCl3, d, ppm): 7.86 (d, J ¼ 8.9 Hz, 2 H),
6.57 (d, J ¼ 8.9 Hz, 2 H), 4.69 (br s, 1 H), 3.84 (s, 3 H), 3.71
(t, J ¼ 5.2 Hz, 2 H), 3.67–3.65 (m, 6 H), 3.57–3.55 (m, 2 H),
3.39 (s, 3 H), 3.35 (q, J ¼ 4.6 Hz, 2 H). 13C NMR (126 MHz,
CDCl3, d, ppm): 167.2, 152.0, 131.4, 118.1, 115.5, 71.8, 70.4,
70.2, 69.1, 61.8, 58.9, 51.4, 42.8. IR (neat, cmꢀ1): 3369,
2876, 1704, 1607, 1278, 1109, 771.
Polymerization
Polymerization of 1b
A round-bottomed flask equipped with a three-way stopcock
was purged with argon and then charged with dry THF
(0.5 mL) and 1.0 M LiHMDS in ꢁTHF (0.50 mL, 0.50 mmol).
The solution was cooled to ꢀ20 C with stirring under an ar-
gon atmosphere. A solution of 1b (0.180 g, 0.50 mmol) and
3 (0.0053 g, 0.025 mmol) in dry THF (0.5 mL) at ꢀ20 ꢁC
was added at once with a syringe into the flask containing
LiHMDS through the three-way stopcock under a stream of
Synthesis of 4-{2-[2-(2-Methoxyethoxy)ethoxy]acetylamino}
benzoic Acid Phenyl Ester (4b)
A mixture of 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (8.0
mL, 52 mmol), phenyl 4-aminobenzoate (8.6 g, 40 mmol),
and DMAP (6.4 g, 52 mmol) in dry CH2Cl2 (180 mL) was
stirred at 0 ꢁC for 10 min. Into the flask was added EDCI
ꢁ
dry nitrogen. Stirring was continued at ꢀ20 C for 4 h, then
the reaction was quenched with saturated aqueous NH4Cl,
and the whole was extracted with CH2Cl2. The organic layer
was washed with water and dried over anhydrous MgSO4.
Concentration in vacuo gave a crude product, whose Mn and
ꢁ
(10.0 g, 52 mmol) with stirring at 0 C. The reaction mixture
was stirred at room temperature for 48 h, and then the reac-
tion was quenched with water, followed by extraction with
CH2Cl2. The combined organic layer was washed with 1 M
HCl and saturated aqueous NaHCO3, and dried over anhy-
drous MgSO4. The solvent was removed under reduced pres-
sure, and the residue was purified by flash chromatography
on silica gel (ethyl acetate/hexane ¼ 2/1) to give 12.8 g of
4b as a pale yellow viscous oil (83%).
Mw/Mn were determined by GPC (Mn ¼ 4000, Mw/Mn
¼
1.15). The residue was purified by preparative HPLC to give
0.063 g of poly1b as a yellow viscous oil (46%).
Poly1b: Mn ¼ 6400 (determined by 1H NMR), Mn (calcd.) ¼
5500, Mw/Mn ¼ 1.15.
1H NMR (600 MHz, CDCl3, d, ppm): 7.08 (d, J ¼ 7.2 Hz, 2n
H), 6.89 (d, J ¼ 7.9 Hz, 2n H), 4.15–3.88 (m, 2n H), 3.79–
3.46 (m, 10n H), 3.39–3.30 (m, 3n H). IR (neat, cmꢀ1): 3059,
2873, 1644, 1603, 1509, 1107, 849.
1H NMR (600 MHz, CDCl3, d, ppm): 9.05 (br s, 1 H), 8.17 (d,
J ¼ 8.9 Hz, 2 H), 7.81 (d, J ¼ 8.9 Hz, 2 H), 7.42 (t, J ¼ 7.4
Hz, 2 H), 7.23 (t, J ¼ 7.5 Hz, 1 H), 7.21 (d, J ¼ 7.7 Hz, 2 H),
4.12 (s, 2 H), 3.80–3.78 (m, 2 H), 3.75–3.73 (m, 4 H), 3.61–
3.59 (m, 2 H), 3.38 (s, 3 H). IR (neat, cmꢀ1): 3332, 2882,
1719, 1282, 1176, 1109, 858.
Synthesis of Block Copolymer
A round-bottomed flask equipped with a three-way stopcock
was purged with argon and then charged with dry THF (0.5
mL) and 1.0 M LiHMDS in THF (0.50 mL, 0.50 mmol). The
ꢁ
solution was cooled to ꢀ20 C with stirring under an argon
Synthesis of 4-{2-[2-(2-Methoxyethoxy)ethoxy]ethylamino}-
benzoic Acid Phenyl Ester (1b)
atmosphere. A solution of 1b (0.180 g, 0.50 mmol) ꢁand 3
(0.0053 g, 0.025 mmol) in dry THF (0.5 mL) at ꢀ20 C was
added at once with a syringe into the flask containing
LiHMDS through the three-way stopcock under a stream
of dry nitrogen. After having been stiꢁrred for 10 min at
A three-necked flask, equipped with a dropping funnel, a
reflux condenser, and a gas inlet tube, was purged with ar-
gon and then charged with 0.98 M borane-THF complex in
THF (40 mL, 39 mmol). The solution was cooled to 0 ꢁC
under an argon atmosphere with stirring for 10 min. A solu-
tion of 4b (11.6 g, 30 mmol) in dry THF (50 mL) was added
dropwise from the dropping funnel, and the mixture was
refluxed for 3 h. It was then cooled to room temperature,
6 M HCl (5 mL) was added to it, and the whole was heated
under reflux for 1 h. The solution was diluted with water
and neutralized to approximately pH 8 with NaHCO3, then
extracted with CH2Cl2. The combined organic layer was
washed with water and dried over anhydrous MgSO4. The
solvent was removed under reduced pressure, and the resi-
due was purified by flash chromatography on silica gel (ethyl
acetate/hexane ¼ 3/4) to give 4.6 g of 1b as an orange oil
(43%).
ꢁ
ꢀ20 C, the mixture was cooled to ꢀ50 C with stirring. Stir-
ꢁ
ring was continued at ꢀ50 C for 6 h, then 0.1 mL of the so-
lution was withdrawn and quenched with saturated aqueous
NH4Cl to measure the Mn value and Mw/Mn ratio of poly1b
[Mn (GPC) ¼ 3600, Mw/Mn ¼ 1.11]. Immediately after the
sampling, the reaction mixture was warmed to ꢀ10 ꢁC, and
then 1.0 M LiHMDS in THF (0.50 mL, 0.50 mmol) at room
temperature was slowly added, followed by fast addition of a
solution of 2 (0.123 g, 0.47 mmol) in dry THF (1.0 mL) at
ꢀ10 ꢁC. The mixture was stirred at ꢀ10 ꢁC for 15 h. The
reaction was quenched with saturated aqueous NH4Cl, and
the whole was extracted with CHCl3. The organic layer was
washed with water and dried over anhydrous MgSO4. Con-
centration in vacuo gave a crude product, whose Mn and
1H NMR (600 MHz, CDCl3, d, ppm): 8.01 (d, J ¼ 8.6 Hz, 2 H),
7.40 (t, J ¼ 8.1 Hz, 2 H), 7.23 (t, J ¼ 7.4 Hz, 1 H), 7.19 (d, J
¼ 8.4 Hz, 2 H), 6.63 (d, J ¼ 8.6 Hz, 2 H), 4.80 (s, 1 H), 3.74
(t, J ¼ 5.2 Hz, 2 H), 3.71–3.65 (m, 6 H), 3.59–3.56 (m, 2 H),
Mw/Mn were determined by GPC (Mn ¼ 6700, Mw/Mn ¼
1.15). The residue was purified by preparative HPLC to give
0.188 g of the block copolymer of poly1b and poly2 as a yel-
low viscous oil (75%).
CHAIN-GROWTH CONDENSATION POLYMERIZATION, YOSHINO ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 Polymerization of 1aa
Additiveb
Temp. (ꢁC)
Time (days)
Mn calcd.
Mn GPC
Mw/Mn
c
c
Entry
e
1
2
3
4
5
6
a
–
0
12d
7d
9
–
600
900
1.22
1.30
1.63
1.72
1.52
1.73
e
LiCl
TMEDAf
0
–
0
5,500
5,500
5,500
5,500
2,100
1,700
1,200
1,600
–
25
25
25
2
LiCl
TMEDAf
3
2
d
Polymerization of 1a with 3 was carried out in the presence of 1.0
equiv. of LiHMDS in THF ([1a]0/[3]0 ¼ 20, [1a]0 ¼ 0.33 M).
1a was not completely consumed.
e
f
Not calculated because the conversion of 1a was not determined.
N,N,N0,N0-Tetramethylethylenediamine.
b
Five equivalents.
c
Determined by GPC based on polystyrene standards (eluent: THF).
Poly1b-b-poly2: Mn ¼ 10,000 (determined by 1H NMR), Mn
(calcd.) ¼ 10,200, Mw/Mn ¼ 1.15.
low molecular weight and a broad molecular weight distri-
bution (Mn ¼ 2100, Mw/Mn ¼ 1.63).
1H NMR (600 MHz, CDCl3, d, ppm): 7.16–6.98 (m, 2(nþm)
H), 6.89 (d, J ¼ 8.0 Hz, 2n H), 6.77 (d, J ¼ 8.0 Hz, 2m H),
4.03–3.90 (m, 2n H), 3.85–3.74 (m, 2m H), 3.68–3.48 (m,
10n H), 3.35 (s, 3n H), 1.57–1.44 (m, 2m H), 1.39–1.08 (m,
10m H), 0.87 (t, J ¼ 7.0 Hz, 3m H). IR (KBr, cmꢀ1): 3065,
2926, 2856, 1569, 1017, 949, 763.
The polymerization was then carried out at room tempera-
ture. The monomer 1a was completely consumed even in
the absence of LiCl or TMEDA, but the Mn value of the poly-
mer obtained was lower than the calculated value based on
the feed ratio of [1a]0/[3]0 and the molecular weight distri-
bution was broad (entry 4). LiCl or TMEDA was not effective
for controlling polymerization of 1a at room temperature,
giving similar polymers with low Mn and broad molecular
weight distribution (entries 5 and 6). We speculated that the
low reactivity of 1a might reduce the difference of activation
energy between the reaction of 1a with the polymer end
group, leading to chain-growth polymerization, and the self-
condensation of 1a, leading to step-growth polymerization.
RESULTS AND DISCUSSION
Polymerization of Methyl Ester Monomer 1a
The methyl ester monomer 1a bearing a tri(ethylene glycol)
monomethyl ether side chain on the nitrogen atom was poly-
merized in the presence of phenyl 4-methylbenzoate (3)
([1a]0/[3]0 ¼ 20) as an initiator and 1.0 equiv. of lithium
1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base9 in THF
under several conditions (Table 1). The polymerization at 0
ꢁC, like the polymerization of 4-(octylamino)benzoic acid
methyl ester (2) with LiHMDS, proceeded very slowly, and
1a was not completely consumed even after 12 days (entry
1). Addition of 5 equiv. of LiCl12–14 gave similar results
(entry 2). In contrast, addition of 5 equiv. of TMEDA8,15–18
resulted in complete consumption of 1a (entry 3), implying
that the unusually slow polymerization of 1a stems from
coordination of the lithium cation to the tri(ethylene glycol)
side chain on the nucleophilic nitrogen atom. However, the
polymerization was still slow, and afforded polymer with a
Polymerization of Phenyl Ester Monomer 1b
We next polymerized more reactive phenyl ester monomer
1b in the presence of 3 ([1b]0/[3]0 ¼ 20) and LiHMDS
(Table 2). The polymerization proceeded rapidly at ꢀ10 ꢁC,
and the molecular weight of the obtained polymer became
larger than in the case of the polymerization of 1a (entry 1).
However, the GPC elution curve showed a shoulder in the
higher-molecular-weight region [Fig. 1(A)]. In the polymer-
ization at ꢀ20 ꢁC, the minor shoulder disappeared, and the
molecular weight distribution became narrower [entry 2, Fig.
ꢁ
1(B)]. At ꢀ30 C, however, a shoulder appeared again in the
higher-molecular-weight region [entry 3, Fig. 1(C)]. There-
fore, the optimum temperature for the polymerization of 1b
TABLE 2 Polymerization of 1ba
b
c
b
Entry
[1b]0/[3]0
Temp. (ꢁC)
Time (h)
Mn calcd
Mn GPC
Mn NMR
Mw/Mn
1
2
3
4
5
6
a
20.0
20.0
20.0
10.0
31.2
50.0
ꢀ10
ꢀ20
ꢀ30
ꢀ20
ꢀ20
ꢀ20
2.5
4
5,500
5,500
5,500
2,900
8,200
13,500
4,200
4,100
3,800
2,200
4,800
7,500
6,200d
6,400
1.20
1.15
1.16
1.11
1.10
1.10
5
5,600
2
2,800
2
7,200
4
13,400
c
Polymerization of 1b with 3 was carried out in the presence of 1.0
equiv. of LiHMDS in THF ([1b]0 ¼ 0.33 M).
Determined by 1H NMR.
Polymer in the shoulder was removed with preparative HPLC.
d
b
Determined by GPC based on polystyrene standards (eluent: THF).
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ARTICLE
FIGURE 2 GPC profiles of poly1b as a prepolymer (dashed line)
and poly1b-b-poly2 as a postpolymer (solid line) obtained by
two-stage polymerization of 1b ([1b]0/[3]0 ¼ 20) and 2 ([added
2]0/[3]0 ¼ 20) with 3 in the presence of LiHMDS in THF. The
data in parentheses are Mn GPC and Mw/Mn values of the prod-
uct in this order, unless otherwise stated. A: Polymerization of
1b with 2.0 equiv. of LiHMDS at ꢀ20 ꢁC (3800, 1.28) followed
by 2 (8100, 1.37). B: Polymerization of 1b with 1.0 equiv. of
LiHMDS at ꢀ20 ꢁC (3300, 1.13) followed by 2 with 1.0 equiv.
of LiHMDS (5700, 1.33). C: Polymerization of 1b with 1.0 equiv.
of LiHMDS at ꢀ20 ꢁC for 10 min and at ꢀ50 ꢁC for 6 h (3600,
1.11) followed by 2 with 1.0 equiv. of LiHMDS at ꢀ10 ꢁC [Mn GPC
¼ 6700, Mn NMR ¼ 10,000 (Mn calcd ¼ 10,200), Mw/Mn ¼ 1.15].
FIGURE 1 GPC profiles of poly1b obtained by the polymerization
of 1b with 3 in the presence of LiHMDS in THF ([1b]0/[3]0 ¼ 20,
[1b]0 ¼ 0.33 M) at (A) ꢀ10 ꢁC (Mn GPC ¼ 4200, Mw/Mn ¼ 1.20, entry
1 in Table 2), (B) ꢀ20 ꢁC (Mn GPC ¼ 4100, Mw/Mn ¼ 1.15, entry 2),
and (C) ꢀ30 ꢁC (Mn GPC ¼ 3800, Mw/Mn ¼ 1.16, entry 3).
ꢁ
was ꢀ20 C. These temperature effects can be accounted for
by assuming that the shoulder was due to products generated
by the coupling reaction of chain-growth polymer and self-
condensed polymer. In the polymerization at ꢀ10 ꢁC, the
deprotonated 1b would be sufficiently reactive to undergo
self-polymerization. At ꢀ30 ꢁC, abstraction of the proton from
the amino group of 1b with LiHMDS would be slow, and the
reaction of undeprotonated 1b with deprotonated 1b would
take place, resulting in self-condensation of 1b.
converted to the methyl ester monomer 1a, the polymeriza-
tion of which was uncontrolled as mentioned earlier, by
transesterification if the methyl ester monomer 2 were poly-
merized in the first stage of the one-pot copolymerization.
Thus, 1b was polymerized first in the presence of 3 as an
initiator ([1b]0/[3]0 ¼ 20) and LiHMDS (2.0 equiv.) in THF
at ꢀ20 ꢁC, and then a fresh feed of 1 equiv. of 2 ([2]0/[3]0
¼ 20) was added to the reaction mixture. The GPC elution
curve of the product was shifted toward the higher-molecu-
lar-weight region, but showed a shoulder in the region of the
prepolymer peak, indicating that not all of the end groups of
the prepolymer, poly1b, initiated polymerization of 2, and a
part of poly1b remained unreacted [Fig. 2(A)]. The large
excess of LiHMDS in the first stage was thought to have
reacted with a part of the terminal phenyl ester moiety of
poly1b, inactivating it.
With the optimized conditions in hand, the polymerization
was carried out with various feed ratios of monomer to ini-
tiator ([1b]0/[3]0) to synthesize poly1b with different values
of molecular weight. The Mn value was determined by 1H
NMR, because the Mn value of poly1b obtained by GPC based
on polystyrene standards deviated from the real Mn value.
The polymerization at the [1b]0/[3]0 ratios of 10, 31, and 50
gave well-defined poly1b, the molecular weight values of
which agreed well with the calculated values based on those
feed ratios. The molecular weight distributions were all nar-
row (entries 4–6).
Synthesis of Block Copolymers
Since we have already established a method for the chain-
growth condensation polymerization of 4-(octylamino)ben-
zoic acid methyl ester (2) with LiHMDS,10 one-pot block
copolymerization of 1b and 2 with LiHMDS was investigated
[Scheme 1(B)]. Such a block aromatic copolyamide having
hydrophilic tri(ethylene glycol) and hydrophobic octyl side
chains might afford unprecedented self-assembled structures.
In this block copolymerization, the polymerization order is
important, because the phenyl ester monomer 1b would be
On this assumption, LiHMDS equivalent to each monomer
was added in both the first and second stage. Thus, 1b was
polymerized in the presence of 3 ([1b]0/[3]0 ¼ 20) and 1.0
equiv. of LiHMDS in THF at ꢀ20 ꢁC to give a prepolymer. A
fresh feed of 1.0 equiv. of LiHMDS and 2 ([2]0/[3]0 ¼ 20)
were added to the prepolymer in the reaction mixture. The
shoulder in the GPC elution curve of the product became
TABLE 3 Block Copolymerization of 1b and 2a
Poly1b
Poly1b-b-Poly2
Reaction
Reaction
b
b
b
c
b
Entry
[1b]0/[3]0
Time (h)
Mn GPC
Mw/Mn
[2]0/[3]0
Time (h)
Mn calcd.
Mn GPC
Mn NMR
Mw/Mn
1
2
3
4
a
20.0
20.0
10.0
40.0
6
3,600
3,300
1,900
5,600
1.11
1.10
1.14
1.12
20.4
43.3
50.0
13.3
b
15
18
15
8
10,200
15,500
14,400
14,100
6,700
7,700
9,500
6,100
10,000
14,900
15,900
14,400
1.15
1.19
1.10
1.26
8
3
20
Polymerization of 1b with 1.0 equiv. of LiHMDS was carried out in
THF at ꢀ20 ꢁC for 10 min then at ꢀ50 ꢁC for the indicated period, fol-
lowed by polymerization of 2 with 1.0 equiv. of LiHMDS at ꢀ10 ꢁC.
Determined by GPC based on polystyrene standards (eluent: THF).
Determined by 1H NMR.
c
CHAIN-GROWTH CONDENSATION POLYMERIZATION, YOSHINO ET AL.
1361

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 3 SEM images of poly1b self-
assembled from a THF solution on a glass
plate. A and B: 10 wt % Solution of poly1b
(Mn NMR ¼ 6400, entry 2 in Table 2). C: 5 wt %
of the same polymer. D: 5 wt % of poly1b
(Mn NMR ¼ 13,400, entry 6 in Table 2).
smaller, but still remained [Fig. 2(B)]. A small amount of
LiHMDS might have reacted with the terminal phenyl ester
moiety to give an unreactive amide terminal moiety, prob-
ably because the phenyl ester terminal moiety was too reac-
tive at ꢀ20 ꢁC. Polymerization at a temperature lower than
organic solvents, such as chloroform and 2-propanol. Further-
more, other N-alkyl poly(p-benzamide)s did not afford spheri-
cal aggregates from a THF solution. Therefore, interactions
between the tri(ethylene glycol) side chain in poly1b and THF
and/or different solubility of the tri(ethylene glycol) side chain
and aromatic polyamide backbone in THF may underlie the
formation of these aggregates. Further studies are necessary
to establish the reason for the formation of the spherical
aggregates from the homopolymer, poly1b.
ꢁ
ꢀ20 C might prevent this termination reaction. Accordingly,
ꢁ
the polymerization of 1b was initiated at ꢀ20 C for 10 min,
then the reaction mixture was stirred at ꢀ50 ꢁC for 6 h,
followed by addition of LiHMDS and 2 to the prepolymer in
ꢁ
the reaction mixture at ꢀ10 C. The GPC elution curve of the
product did not show a shoulder and was shifted toward the
higher-molecular-weight region, while the polydispersity
remained below 1.20, indicating successful production of the
block copolymer of poly1b and poly2 [Fig. 2(C)].
CONCLUSIONS
We have demonstrated that the tri(ethylene glycol) mono-
methyl ether side chain on the nitrogen atom of 4-aminoben-
zoic acid esters 1 makes the polymerization of 1 with
LiHMDS sluggish, compared to the polymerization of the N-
alkyl counterparts, and the phenyl ester 1b is necessary for
controlled chain-growth condensation polymerization. By
using this established polymerization method, poly1b-b-
poly(N-octyl-4-benzamide) was synthesized by the successive
polymerization of 1b and 2 in one pot in the presence of ini-
tiator 3 and LiHMDS. The obtained block copolymer did not
self-assemble, but when a THF solution of poly1b was
allowed to dry on a glass plate, spherical aggregates were
formed. Synthesis and properties of star polymers containing
poly1b will be reported elsewhere.
Under the optimized conditions in hand, poly1b-b-poly2
with different compositions was synthesized by varying the
feed ratio of 1b to 2 (Table 3). The Mn value of the block
copolymers agreed well with the calculated value, and the
molecular weight distribution was narrow. It should be
noted that the block copolymer with the longer poly1b seg-
ment (entry 4) is soluble not only in general organic sol-
vents but also in water.
Self-Assembly
We studied self-assembly of the obtained block copolymer
(Table 3, entry 4). Dilute aqueous, chloroform, and THF solu-
tions of the block copolymer were dropped on a glass plate
and dried at room temperature. However, the scanning elec-
tron microscopy (SEM) images of these samples did not show
any assembled structures; flat films might have been formed.
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