Synthesis of poly(naphthalenecarboxamide)s with low polydispersity by chain-growth condensation polymerization

Article abstract of DOI:10.1002/pola.24737

Condensation polymerization of 6-(N-substituted-amino)-2-naphthoic acid esters (1) was investigated as an extension of chain-growth condensation polymerization (CGCP). Methyl 6-(3,7-dimethyloctylamino)-2-naphthoate (1b) was polymerized at -10 °C in the presence of phenyl 4-methylbenzoate (2) as an initiator and lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base. When the feed ratio [1a]₀/[2]₀ was 10 or 20, poly(naphthalenecarboxamide) with defined molecular weight and low polydispersity was obtained, together with a small amount of cyclic trimer. However, polymer was precipitated during polymerization under similar conditions in [1a]₀/[2]₀ = 34. To increase the solubility of the polymer, monomers 1c and 1d with a tri(ethylene glycol) (TEG) monomethyl ether side chain instead of the 3,7-dimethyloctyl side chain were synthesized. Polymerization of the methyl ester monomer 1c did not proceed well, affording only oligomer and unreacted 1c, whereas polymerization of the phenyl ester monomer 1d afforded well-defined poly(naphthalenecarboxamide) together with small amounts of cyclic oligomers in [1d]₀/[2]₀ = 10 and 29. The polymerization at high feed ratio ([1d]₀/[2]₀ = 32.6) was accompanied with self-condensation to give polyamide with a lower molecular weight than the calculated value. Such undesirable self-condensation would result from insufficient deactivation of the electrophilic ester moiety by the electron-donating resonance effect of the amide anion.

Full text of DOI:10.1002/pola.24737

Synthesis of Poly(naphthalenecarboxamide)s with Low Polydispersity by
Chain-Growth Condensation Polymerization
KOICHIRO MIKAMI, HIROAKI DAIKUHARA, JYUNYA KASAMA, AKIHIRO YOKOYAMA, TSUTOMU YOKOZAWA
Department of Material and Life Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
Received 1 January 2011; accepted 9 April 2011
DOI: 10.1002/pola.24737
Published online 16 May 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Condensation polymerization of 6-(N-substituted-
amino)-2-naphthoic acid esters (1) was investigated as an
extension of chain-growth condensation polymerization
(CGCP). Methyl 6-(3,7-dimethyloctylamino)-2-naphthoate (1b)
was polymerized at ꢀ10 ꢁC in the presence of phenyl 4-methyl-
benzoate (2) as an initiator and lithium 1,1,1,3,3,3-hexamethyl-
disilazide (LiHMDS) as a base. When the feed ratio [1a]0/[2]0
was 10 or 20, poly(naphthalenecarboxamide) with defined mo-
lecular weight and low polydispersity was obtained, together
with a small amount of cyclic trimer. However, polymer was
precipitated during polymerization under similar conditions in
[1a]0/[2]0 ¼ 34. To increase the solubility of the polymer, mono-
mers 1c and 1d with a tri(ethylene glycol) (TEG) monomethyl
ether side chain instead of the 3,7-dimethyloctyl side chain
were synthesized. Polymerization of the methyl ester monomer
1c did not proceed well, affording only oligomer and unreacted
1c, whereas polymerization of the phenyl ester monomer 1d
afforded well-defined poly(naphthalenecarboxamide) together
with small amounts of cyclic oligomers in [1d]0/[2]0 ¼ 10 and
29. The polymerization at high feed ratio ([1d]0/[2]0 ¼ 32.6) was
accompanied with self-condensation to give polyamide with a
lower molecular weight than the calculated value. Such unde-
sirable self-condensation would result from insufficient deacti-
vation of the electrophilic ester moiety by the electron-
C
V
donating resonance effect of the amide anion.
2011 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3020–
3029, 2011
KEYWORDS: chain-growth condensation polymerization; living
polymerization; molecular weight distribution/molar mass dis-
tribution; naphthalene; polyamides; polycondensation
the polymer end group, the amide anion of the monomer is
converted to an amide linkage, which is a much weaker elec-
tron-donating group than the amide anion, and so the newly
extended polymer terminal ester moiety becomes more reac-
tive than the ester moiety of the monomer bearing the amide
anion. Accordingly, another monomer is selectively reacted
with the polymer end group, and chain growth continues
(Scheme 1).12 In the polymerization of m-substituted mono-
mer, the amide anion can deactivate the electrophilic ester
moiety at the meta position through the electron-donating
inductive effect, and self-condensation is suppressed.13 The
following amidation of the monomer induces the activation
of the newly elongated polymer end group as in the p-substi-
tuted monomer. In general, inductive effects become much
weaker through three or more successive carbon–carbon r
bonds, whereas resonance effects can work between func-
tional groups not only at the para position of benzene but
also at the 1,5- or 2,6-positions of naphthalene. Therefore,
we were interested to know whether the long-distance reso-
nance effects in the naphthalene ring can be utilized for
CGCP. If so, monomers available for CGCP could be not only
simply extended from those with a benzene backbone to
those with a naphthalene backbone but also utilized for
INTRODUCTION Living polymerization has enormously pro-
gressed over the last few decades,1–10 and is indispensable
for the production of nanoarchitecture, which serves as
the backbone of nanotechnology. However, it remains im-
portant to develop new living polymerization methods to
extend the range of well-defined polymers that can be
accessed.
We have developed a novel living polymerization, chain-
growth condensation polymerization (CGCP), which can pro-
vide condensation polymers with controlled molecular
weight and low polydispersity. To achieve chain-growth poly-
merization in condensation polymerization while suppressing
conventional step-growth polymerization, selective activation
of the polymer end group is necessary. In the synthesis of
well-defined N-substituted polybenzamides, we have used
two kinds of substituent effects for the selective activation
of the polymer end group.6,11–13 In the polymerization of
p-substituted monomer, the strong electron-donating reso-
nance effect of the amide anion deactivates the electrophilic
ester moiety at the para position, resulting in the suppres-
sion of self-condensation of the monomer. Once the
monomer has reacted with the ester moiety of an initiator or
Correspondence to: T. Yokozawa (E-mail: yokozt01@kanagawa-u.ac.jp)
C
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 3020–3029 (2011) 2011 Wiley Periodicals, Inc.
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SCHEME 1 CGCP of (a) p-substituted and (b) m-substituted benzene-based monomers.
more fused aromatic system, for instance pyrene and por-
phyrin, which have interesting properties. However, reso-
nance effect also becomes weak as the distance between the
functional groups is longer. If the amide anion cannot suffi-
ciently convey the electron-donating effect on the ester
moiety through the resonance effect, self-condensation of
monomer would be caused, resulting in difficulty on control-
ling molecular weight and polydispersity of the obtained
polymer.
CGCP of the benzene-based monomers that we have hitherto
reported.
RESULTS AND DISCUSSION
Polymerization of Monomers with Alkyl Side Chain
The methyl ester monomer 1a having an octyl side chain
was first polymerized in the presence of 2 ([1a]0/[2]0 ¼ 10)
and 1.0 equiv of LiHMDS in tetrahydrofuran (THF) at
ꢀ10 ꢁC (Scheme 2). However, the produced polymer was
precipitated in the reaction mixture within 1 h. The N-octyl
side chain, which permits polyamides with the benzene back-
bone to dissolve in THF,12–14 was not effective to solubilize
polyamide with the naphthalene backbone.
In this article, we focus on the condensation polymerization
of 6-amino-2-naphthoic acid esters (1) bearing an alkyl or a
tri(ethylene glycol) (TEG) side chain on the amino group in
the presence of lithium 1,1,1,3,3,3-hexamethyldisilazide
(LiHMDS) as a base and phenyl 4-methylbenzoate (2) as an
initiator. We found that the polymerization proceeded in a
chain-growth polymerization manner to yield poly(naphtha-
lenecarboxamide)s with defined molecular weight and low
polydispersity (Scheme 2). This result demonstrates that the
resonance effect at the 2,6-position of naphthalene ring
is sufficient for CGCP, working in the same way as in
To suppress precipitation of polymer during polymerization,
we synthesized monomer 1b bearing a 3,7-dimethyloctyl
side chain, which was easily derived from citronellal. The
polymerization of 1b with initiator 2 and LiHMDS was
carried out under several conditions (Table 1). At the
feed ratio [1b]0/[2]0
¼
10, at which poly1a was
SYNTHESIS OF POLY(NAPHTHALENECARBOXAMIDE)S, MIKAMI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 2 CGCP of naphthalene-based monomers.
precipitated during polymerization, the polymerization pro-
ceeded homogeneously throughout to yield polymer with
low polydispersity. The number-average molecular weight
(Mn) value of the obtained polymer, determined from the H
NMR spectrum, agreed well with the theoretical value of Mn
uct was shifted toward the higher molecular weight region,
maintaining low polydispersity (Fig. 1). The Mn values and
Mw/Mn ratio, determined by GPC, were plotted as a function
of monomer conversion, and these relationships showed that
the Mn value increased in proportion to conversion, being
consistent with the theoretical Mn value based on the feed
ratio, and Mw/Mn remained at 1.1 over the whole conversion
range (Fig. 2). These results clearly demonstrate that the
polymerization proceeds via the CGCP mechanism.
1
on the basis of the feed ratio (Entry 1).
The polymerization at [1b]0/[2]0 ¼ 20 also proceeded
homogeneously, although the reaction solution increased in
viscosity, to afford polymer with double the initial Mn value
(Entry 2). The polymerization at this feed ratio was studied
in more detail. As the polymerization progressed, the gel
permeation chromatography (GPC) elution curve of the prod-
However, the GPC traces had a small peak in the low molec-
ular weight region after 5 min, the intensity of which
remained almost unchanged (Fig. 1). This product was
TABLE 1 Polymerization of 1b with 2a
Mn
[1b]0 Temperature (ꢁC) Time (h) Conversionc (%) Calculatedd GPCe NMRf Mw/Mn
b
e
Entry [1b]0/[2]0
1
2
3
4
5
6
10.0
20.0
34.0
32.8
32.7
34.0
0.44
0.45
0.45
0.15
ꢀ10
ꢀ10
ꢀ10
ꢀ10
18
4
100
99
3,240
6,340
3,680 2,780 1.15
5,720 5,540 1.13
3.5
93
10,670
10,300
10,270
10,670
8,180
7,450
5,200
7,720
–
–
–
–
1.20
1.20
1.22
1.20
6
18
4
100
93
0.044 ꢀ10
0.148
0
98
a
b
c
d
e
f
Polymerization was carried out in the presence of 1.0 equiv of LiHMDS in THF.
Feed ratio of the monomer 1b to the initiator 2.
Estimated by HPLC (eluent: THF).
Calculated from the feed ratio of [1b]0/[2]0.
Determined by GPC based on polystyrene standards (eluent: THF).
Determined by 1H NMR.
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ARTICLE
zene monomer, resulting in the occurrence of the reaction of
deprotonated 1b with nondeprotonated 1b. This decrease in
the acidity of the amino group of 1b can be ascribed to a
weaker electron-withdrawing resonance effect of the ester
moiety at the 2-position of the naphthalene ring, compared
with the ester moiety at the para position of the benzene
monomer.
The polymerization was further carried out at the feed ratio
[1b]0/[2]0 ¼ 34. The reaction mixture became slightly turbid
after 1 h, and then polymer was precipitated at 3 h. The Mn
value of the obtained polyamide was lower than the theoreti-
cal value, and Mw/Mn was slightly increased (Entry 3). To sup-
press the precipitation, the polymerization was carried out in
dilute solution (Entry 4). The polymerization proceeded
homogeneously, but again the Mn value did not reach the theo-
retical value and the Mw/Mn was slightly increased (Entries 4
and 5). Low concentration might be liable to induce self-con-
densation of 1b, resulting in polymer with lower molecular
weight. The polymerization at 0 ꢁC did not afford good results,
either, because of precipitation of polymer during polymeriza-
tion (Entry 6). As a consequence, the polymerization of 1b can
be well controlled up to the feed ratio [1b]0/[2]0 ¼ 20,
although even then, a small amount of cyclic trimer was
formed in the early stage of the polymerization.
FIGURE 1 GPC profiles of the product obtained by the poly-
merization of 1b with 5 mol % of 2 in the presence of LiHMDS
in THF at ꢀ10 ꢁC (Table 1, Entry 2).
isolated by high-performance liquid chromatography (HPLC)
and analyzed by matrix-assisted laser desorption/ionization
time-of-flight mass spectrometry. It turned out to be a cyclic
trimer of 1b, which had been synthesized in a different man-
ner by Azumaya and coworkers.15 This cyclic trimer, the
amount of which did not increase with the progress of poly-
merization, was probably formed by self-condensation of 1b
in the early stage of polymerization, where deprotonated 1b
could react with 1b untreated with base. As the polymeriza-
tion of the corresponding p-substituted benzene monomer
did not afford cyclic oligomers as byproducts under the
same conditions,14 the proton abstraction by the base from
the amino group of 1b might be slower than that in the ben-
Polymerization of Monomers with Oligo(ethylene glycol)
Side Chain
To increase the solubility of poly(naphthalenecarboxamide),
we synthesized monomers with an oligo(ethylene glycol)
side chain. The oligo(ethylene glycol) side chain not only
provides good solubility in a variety of solvents but also
affords unique functionality.16–23 Indeed, m-substituted poly-
benzamides with an oligo(ethylene glycol) side chain showed
a lower critical solution temperature in water.23 However,
CGCP of some monomers with an oligo(ethylene glycol) side
chain is more difficult than CGCP of those with an alkyl side
chain, because oligo(ethylene glycol) has high affinity for
lithium cation, inducing undesired reactions.24,25
The methyl ester monomer 1c bearing a TEG side chain was
first polymerized with LiHMDS in the presence of 10 mol %
of 2 at ꢀ10 ꢁC for 24 h in a similar manner to that
described for 1b (Scheme 1). However, an oligomer with Mn
¼ 780 was obtained and unreacted monomer was recovered.
As in the polymerization of m-substituted benzene mono-
mers with an oligo(ethylene glycol) side chain,24 the
polymerization was then carried out in the presence of
N,N,N0,N0-tetramethylethylenediamine (TMEDA), which is
known to strongly coordinate lithium cation, but similar
results were obtained. We next increased the reactivity of
the ester moiety of the monomer by changing to phenyl
ester. Thus, the phenyl ester monomer 1d was polymerized
with 1.0 equiv of LiHMDS in the presence of initiator 2
([1d]0/[2]0 ¼ 10) at ꢀ10 ꢁC to afford polymer with a
slightly broadened molecular weight distribution (Table 2,
Entry 1). When the polymerization was examined at lower
FIGURE 2 Mn and Mw/Mn values of poly1b, obtained by poly-
merization with 5 mol % of 2 in the presence of LiHMDS in
THF at ꢀ10 ꢁC (Table 1, Entry 2).
ꢁ
temperature, ꢀ20 C, to suppress self-condensation, the GPC
profile of the product showed a narrower molecular weight
SYNTHESIS OF POLY(NAPHTHALENECARBOXAMIDE)S, MIKAMI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Polymerization of 1d with 2a
Mn
Calculatedc
GPCd
Mw/Mn
b
d
Entry
[1d]0/[2]0
Additive
Temperature (ꢁC)
Time (h)
1
2
3
4
5
6
a
10.0
10.0
10.0
28.6
10.0
32.6
None
None
None
None
LiCl
ꢀ10
ꢀ20
ꢀ30
ꢀ30
ꢀ30
ꢀ30
1
2
3,370
3,370
3,370
9,430
3,370
10,490
3,460
3,130
3,170
5,690
3,190
6,800
1.23
1.18
1.17
1.16
1.17
1.21
2
19
2
LiCl
5
Polymerization was carried out in the presence of 1.0 equiv of LiHMDS in THF ([1d]0 ¼ 0.44 M).
Feed ratio of the monomer 1d to the initiator 2.
Calculated from the feed ratio of [1d]0/[2]0.
b
c
d
Determined by GPC.
distribution (Entry 2). Further lowering the polymerization
oligomers, observed as the small peak. We thought that the
undesirable self-condensation probably resulted from insuffi-
cient deactivation of the electrophilic ester moiety by the
electron-donating resonance effect of the amide anion due to
the longer distance between the positions 2 and 6 of
the naphthalene ring, compared with the positions 1 and 4
of p-substituted benzene ring.
temperature to ꢀ30 ꢁC also yielded polyamide with con-
trolled molecular weight and narrow molecular weight dis-
tribution (Entry 3). Although the GPC profile of the products
showed a small peak, which might be due to cyclic oligomers
[Fig. 3(a)], the controlled Mn and narrow polydispersity of
the products suggest that the polymerization of 1d at ꢀ20
ꢁ
and ꢀ30 C proceeded mainly in a chain-growth polymeriza-
To suppress the self-condensation completely, the polymer-
ization was carried out in the presence of LiCl as an additive,
as we expected stabilization of the amide anion to reduce
the nucleophilicity.26 When the polymerization was carried
out at the feed ratio of [1d]0/[2]0 ¼ 10.0 in the presence of
5.0 equiv of LiCl to 1d, the Mn value of the polymer was
consistent with the calculated value (Entry 5). However,
polymerization at high feed ratio ([1d]0/[2]0 ¼ 32.6) was
accompanied with self-condensation, affording polyamide
with a lower molecular weight than the calculated value
(Entry 6). Thus, we found that the introduction of the TEG
side chain into the naphthalene monomer improved the solu-
bility of the poly(naphthalenecarboxamide) in THF, and that
CGCP proceeded well at low feed ratios.
tion manner. On the other hand, when the polymerization
was carried out with a smaller amount of the initiator 2
([1d]0/[2]0 ¼ 28.6), the Mn value of the polymer was not
consistent with the calculated value [Entry 4, Fig. 3(b)], and
the GPC profiles of the product showed a shoulder in the
higher molecular weight region, as well as a small peak in
the lower molecular weight region [Fig. 3(b)], although no
polyamide precipitate was seen, indicating that the
side chain improved the solubility of the polyamide. The
shoulder peak might be attributed to coupling between the
chain-growth and the self-condensation polyamides, and self-
condensation would also result in the formation of cyclic
EXPERIMENTAL
General
1H and 13C NMR spectra were obtained on JEOL ECA-500
and ECA-600 spectrometers. The internal standards of 1H
NMR spectra in CDCl3 and CD3OD were tetramethylsilane
(0.00 ppm) and the midpoint of CD3 (3.35 ppm), respec-
tively, and the internal standards of 13C NMR spectra in
CDCl3 and DMSO-d6 were the midpoints of CDCl3 (77.0 ppm)
and CD3 (39.8 ppm), respectively. IR spectra were recorded
on a JASCO FT/IR-410. All melting points were measured
with a Yanagimoto hot stage melting point apparatus without
correction. Column chromatography was performed on silica
gel (Kieselgel 60, 230–400 mesh, Merck) with a specified
solvent. The conversion of monomers during the polymeriza-
tion was determined by HPLC with a Japan Analytical Indus-
try LC-909 HPLC unit (eluent: THF) fitted with a JAIGEL
column (1H-A). The Mn and Mw/Mn values of polymers were
measured on a Shodex GPC-101 GPC unit equipped with
FIGURE 3 GPC profiles of the products obtained by the poly-
merization of 1d with 1.0 equiv of LiHMDS in the presence of 2
in THF. The polymerization was carried out at ꢀ30 ꢁC with the
feed ratio (a) [1d]0/[2]0 ¼ 10.0 for 2 h (Table 2, Entry 3) and (b)
[1d]0/[2]0 ¼ 28.6 for 19 h (Entry 4).
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ARTICLE
Shodex UV-41, Shodex RI-71S, and two Shodex KF-804L col-
and 2.6 Hz, 1H), 2.11–1.98 (m, 1H), 1.53 (m, 1H), 1.39–1.09
(m, 6H), 0.97 (d, J ¼ 6.6 Hz, 3H), 0.86 (d, J ¼ 6.6 Hz, 6H); IR
(neat) 2955, 2928, 2870, 2717, 1725, 1560, 1466, 1409,
umns (bead size ¼ 7 lm, pore size ¼ 200 Å). THF was used
ꢁ
as the eluent (temperature ¼ 40 C, flow rate ¼ 1 mL/min).
Calibration was carried out using polystyrene standards. The
isolation of polyamides was carried out with a Japan Analyti-
cal Industry LC-908 recycling preparative HPLC (eluent:
1383, 1366, 1215, 1147, 1119, 1091, 1050, 880 cmꢀ1
.
Synthesis of 1b
Into a solution of 6-amino-2-naphthoic acid methyl ester
(797.5 mg, 3.96 mmol) in dry dichloromethane (50 mL) at
0
chloroform) using two TOSOH TSK-gel columns (2
ꢂ
G2000HHR). Commercially available dehydrated THF (stabi-
lizer-free, Kanto), dehydrated dichloromethane (Kanto),
dehydrated methanol (Kanto), and dehydrated N,N-dimethyl-
formamide (Wako) were used as dry solvents. LiHMDS
(1.0 M) solution in THF (Aldrich) and 1 M borane–THF com-
plex in THF (Kanto) were used as received. TMEDA was
distilled over CaH2 before use.
ꢁC, 3 (752 mg, 4.75 mmol) and NaBH(OAc)3 (1.097 g,
5.15 mmol) were successively added (Scheme 4). The mix-
ꢁ
ture was stirred at 0 C for 1 h and at room temperature for
1 h. The reaction was quenched with aqueous NaHCO3, and
the whole was extracted with dichloromethane. The collec-
ted organic layers were washed with water and dried
over MgSO4. The solvent was removed under reduced
pressure and the residue was purified by column chromato-
graphy [SiO2, hexane/EtOAc ¼ 8/1 (twice), hexane/dichloro-
methane ¼ 1/1] to afford pale red solid (1.2195 g, 95%).
Synthesis of 1a
Into a solution of 6-amino-2-naphthoic acid methyl ester
(1.004 g, 4.99 mmol) in dry THF (14 mL), n-octanal
(0.77 mL, 5.0 mmol), glacial acetic acid (0.31 mL, 5.5 mmol),
and NaBH(OAc)3 (1.589 g, 7.5 mmol) were successively
added (Scheme 3). The mixture was stirred at room temper-
ature for 14 h. The reaction was quenched with aqueous
NaHCO3, and the whole was extracted with dichloromethane.
The combined organic layers were washed with water and
dried over MgSO4. The solvent was removed under reduced
pressure and the residue was purified by column chromatog-
raphy (SiO2, hexane/ethyl acetate ¼ 8/1) followed by recrys-
tallization from hexane to afford monomer 1a as white solid
ꢁ
mp 90.7–91.5 C.
1H NMR (500 MHz, CDCl3): d 8.41 (br s, 1H), 7.93 (dd, J ¼
8.6 and 1.7 Hz, 1H), 7.69 (d, J ¼ 8.6 Hz, 1H), 7.60 (d, J ¼ 8.6
Hz, 1H), 6.88 (dd, J ¼ 8.6 and 2.3 Hz, 1H), 6.77 (br s, 1H),
3.97 (br s, 1H), 3.94 (s, 3H) 3.31–3.18 (m, 2H), 1.76–1.49
(m, 5H), 1.41–1.10 (m, 5H), 0.97 (d, J ¼ 6.6 Hz, 3H), 0.87 (d,
J ¼ 6.6 Hz, 6H); 13C NMR (126 MHz, CDCl3): d 167.6,
147.4, 137.8, 131.0, 130.5, 126.4, 126.0, 125.8, 123.3, 118.6,
104.4, 51.9, 42.2, 39.2, 37.2, 36.3, 30.9, 28.0, 24.7, 22.7,
22.6, 19.6; IR (KBr) 3389, 2928, 1689, 1624, 1537, 1494,
1479, 1434, 1418, 1382, 1343, 1297, 1214, 1133, 1101, 851,
ꢁ
(0.76 g, 48%). mp 92.3–94.6 C.
1H NMR (500 MHz, CDCl3): d 8.41 (br s, 1H), 7.93 (dd, J ¼
8.6 and 1.7 Hz, 1H), 7.70 (d, J ¼ 8.9 Hz, 1H), 7.60 (d, J ¼ 8.6
Hz, 1H), 6.89 (dd, J ¼ 8.9 and 2.3 Hz, 1H), 6.78 (br s, 1H),
3.94 (s, 3H), 3.23 (t, J ¼ 7.2 Hz, 2H), 1.69 (quint, J ¼ 7.4 Hz,
2H), 1.48–1.22 (m, 10H), 0.89 (t, J ¼ 7.2 Hz, 3H); 13C NMR
(151 MHz) 167.7, 148.1, 138.0, 131.0, 130.5, 126.0, 125.9,
125.6, 122.9, 118.4, 103.3, 51.9, 43.7, 31.8, 29.4, 29.3, 29.2,
27.2, 22.6, 14.1; IR (KBr) 3372, 2954, 2922, 2855, 1691,
817 cmꢀ1
.
Synthesis of 4
To a mixture of 6-amino-2-naphthoic acid (5.00 g, 26.8
ꢁ
mmol) and dry methanol (250 mL) at 0 C, thionyl chloride
(52 mL, 0.71 mol) was added dropwise, and the whole was
stirred at room temperature overnight under an argon
atmosphere. The reaction mixture was poured into water,
neutralized with saturated aqueous NaHCO3, and extracted
with dichloromethane. The organic layer was washed with
saturated aqueous NaHCO3 and water, dried over Na2SO4,
and concentrated. The residue was purified by silica gel col-
umn chromatography (AcOEt/hexane ¼ 1/2) to give 4 as
1624, 1536, 1491, 848, 815 cmꢀ1
.
Synthesis of 3,7-Dimethyloctanal (3)
A mixture of 5% Pd/C (156 mg, 5 mol %), citronellal
(1.512 g, 9.802 mmol), and ethyl acetate (120 mL) was
stirred at room temperature for 2 h under an H2 atmos-
phere. The reaction mixture was filtered through Celite and
the filtrate was concentrated under vacuum to afford 3 as
colorless liquid (1.526 g, 99%).
ꢁ
pale red solid (4.73 g, 88%). mp 163.0–164.3 C.
1H NMR (500 MHz, CDCl3): d 8.45 (d, J ¼ 1.1 Hz, 1H), 7.94
(dd, J ¼ 8.6 and 1.7 Hz, 1H), 7.76–7.74 (m, 1H), 7.58 (d, J ¼
8.6 Hz, 1H), 6.98–6.96 (m, 2H), 4.04 (br s, 2H), 3.94 (s, 3H);
13C NMR (126 MHz, CDCl3): d 167.6, 146.5, 137.4, 131.1,
130.9, 126.6, 125.9, 125.7, 123.8, 118.6, 107.8, 52.0; IR
1H NMR (500 MHz, CDCl3): d 9.76 (t, J ¼ 2.3 Hz, 1H), 2.39
(ddd, J ¼ 16.0, 7.7, and 2.0 Hz, 1H), 2.22 (ddd, J ¼ 16.0, 8.0,
SCHEME 3 Synthesis of 1a.
SYNTHESIS OF POLY(NAPHTHALENECARBOXAMIDE)S, MIKAMI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Synthesis of 1c
A three-neck flask equipped with a dropping funnel, a reflux
condenser, and a gas inlet tube was purged with argon and
then charged with 1.01 M borane–THF complex in THF
(14.6 mL, 14.8 mmol; Scheme 5). A solution of 5 (3.42 g,
9.86 mmol) in THF (30 mL) was added dropwise from the
dropping funnel at 0 ꢁC, and the mixture was stirred at
room temperature for 30 min, then refluxed for 4 h. After
the mixture had cooled to room temperature, 6 M hydrochlo-
ric acid (3.0 mL) was added, and the whole was heated at
reflux for 1 h. It was allowed to cool to room temperature,
then diluted with water, neutralized to pH ꢃ 8 with NaHCO3,
and extracted with dichloromethane. The combined organic
layers were washed with water and dried over MgSO4.
The crude product was purified by silica gel column
chromatography (hexane/AcOEt ¼ 1/2) to give 1c (797 mg,
24%) as pale yellow viscous liquid.
SCHEME 4 Synthesis of 1b.
(KBr) 3405, 3340, 3236, 2945, 1688, 1620, 1577, 1509,
1481, 1438, 1393, 1350, 1299, 1212, 1133, 1103, 983, 955,
914, 876 cmꢀ1
.
1H NMR (500 MHz, CDCl3): d 8.40 (br s, 1H), 7.92 (dd, J ¼
8.6 and 1.7 Hz, 1H), 7.66 (d, J ¼ 8.6 Hz, 1H), 7.57 (d, J ¼ 8.6
Hz, 1H), 6.91 (dd, J ¼ 8.9 and 2.3 Hz, 1H), 6.74 (d, J ¼ 2.0
Hz, 1H), 4.69 (br s, 1H), 3.91 (s, 3H), 3.71 (t, J ¼ 5.2 Hz,
2H), 3.65–3.61 (m, 6H), 3.53–3.51 (m, 2H), 3.37–3.35 (m,
5H); 13C NMR (126 MHz, CDCl3): d 167.6, 148.0, 137.8,
131.0, 130.4, 126.2, 125.9, 125.7, 123.1, 118.7, 103.6, 71.9,
70.5, 70.3, 69.2, 59.0, 51.9, 43.1; IR (neat) 3512, 3374, 3059,
2948, 2877, 2047, 1927, 1714, 1623, 1577, 1530, 1493,
1459, 1436, 1417, 1403, 1382, 1288, 1209, 1096, 1028, 990,
Synthesis of 5
To a mixture of 4 (103 mg, 0.511 mmol), 2-[2-(2-methoxy-
ethoxy)ethoxy]acetic acid (0.1 mL, 0.7 mmol), 4-(dimethyla-
mino)pyridine (DMAP; 79.2 mg, 0.648 mmol), and dry
dichloromethane (20 mL) at 0 ꢁC, 1-ethyl-3-(3-dimethylami-
nopropyl)carbodiimide hydrochloride (EDCI; 124 mg,
0.646 mmol) was added, and the whole was stirred at room
temperature for 1 h. Water was added, and the mixture
was extracted with dichloromethane. The organic layer was
washed with 1 M hydrochloric acid, saturated aqueous
NaHCO3, and water, dried over MgSO4, and concentrated. The
residue was purified by silica gel column chromatography
(AcOEt/hexane ¼ 1/2) to give 5 as yellow viscous liquid
(156 mg, 88%).
967, 939, 915, 853 cmꢀ1
.
Synthesis of 6
To
a
mixture of 6-amino-2-naphthoic acid (5.20 g,
1H NMR (500 MHz, CDCl3): d 9.03 (br s, 1H), 8.54 (br s, 1H),
8.38 (d, J ¼ 2.0 Hz, 1H), 8.04 (dd, J ¼ 8.6 and 1.7 Hz, 1H),
7.90 (d, J ¼ 8.9 Hz, 1H), 7.84 (d, J ¼ 8.9 Hz, 1H), 7.64 (dd,
J ¼ 8.6 and 2.3 Hz, 1H), 4.17 (s, 2H), 3.97 (s, 3H), 3.82–3.80
(m, 2H), 3.77–3.74 (m, 4H), 3.62–3.60 (m, 2), 3.36 (s, 3H);
13C NMR (126 MHz, CDCl3): d 168.6, 167.2, 137.1, 136.2,
130.6, 130.1, 129.6, 127.8, 126.4, 125.8, 120.7, 116.3, 71.7,
71.2, 70.7, 70.4, 70.1, 59.0, 52.1; IR (neat) 3511, 3335, 2948,
2882, 1933, 1717, 1631, 1608, 1582, 1542, 1496, 1483,
1436, 1407, 1391, 1342, 1287, 1246, 1201, 1099, 1029,
28.8 mmol), NaHCO3 (4.67 g, 55.6 mmol), and dry THF
(840 mL) at 0 ꢁC, benzyl chloroformate (2.0 mL, 14 mmol)
was added, and the whole was stirred at room temperature
for 1 h. Further benzyl chloroformate (2.0 mL, 14 mmol)
was added to the reaction mixture at 0 ꢁC, and the whole
was stirred at room temperature for 17 h, then poured into
water, adjusted to pH around 1 with 1 M hydrochloric acid,
and extracted with dichloromethane. The organic layer was
washed with water, dried over MgSO4, and concentrated. The
residue was recrystallized from THF–CHCl3 to give 6 as
990 cmꢀ1
.
ꢁ
white solid (8.20 g, 92%). mp 236.8–239.7 C.
SCHEME 5 Synthesis of 1c.
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ARTICLE
1H NMR (500 MHz, CD3OD): d 8.56 (br s, 1H), 8.17 (br s,
1H), 8.03 (dd, J ¼ 8.6 and 1.7 Hz, 1H), 7.96 (d, J ¼ 8.9 Hz,
1H), 7.84 (d, J ¼ 8.6 Hz, 1H), 7.63 (dd, J ¼ 8.9 and 2.0 Hz,
2H), 7.50–7.48 (m, 2H), 7.44–7.41 (m, 2H), 7.39 (t, J ¼ 7.3
Hz, 1H), 5.28 (s, 2H); 13C NMR (126 MHz, DMSO-d6): d
167.8, 153.7, 139.3, 136.7, 136.1, 130.6, 130.4, 128.8, 128.6,
128.5, 128.4, 127.6, 126.6, 126.0, 120.3, 113.4, 66.3; IR
(KBr) 3314, 3061, 3033, 2954, 2895, 2852, 2685, 2639,
2565, 1670, 1634, 1579, 1542, 1501, 1428, 1307, 1242,
Synthesis of 9
To a mixture of 8 (2.49 g, 9.50 mmol), 2-[2-(2-methoxyethoxy)-
ethoxy]acetic acid (1.9 mL, 12 mmol), DMAP (1.51 g, 12.4
mmol), and dry dichloromethane (250 mL) at 0 ꢁC, EDCI
(2.38 g, 12.4 mmol) was added, and the whole was stirred
at room temperature for 2 h, then poured into water
and extracted with dichloromethane. The organic layer was
washed with 1 M hydrochloric acid, saturated aqueous
NaHCO3, and water, dried over MgSO4, and concentrated. The
residue was purified by silica gel column chromatography
(AcOEt/hexane ¼ 4/1) to give 9 as yellow viscous liquid
(3.43 g, 86%).
1066 cmꢀ1
.
Synthesis of 7
To a mixture of 6 (8.19 g, 25.5 mmol), phenol (3.16 g,
33.5 mmol), DMAP (4.05 g, 33.2 mmol), and dry DMF
(500 mL) at 0 C, EDCI (6.35 g, 33.3 mmol) was added, and
1H NMR (500 MHz, CDCl3): d 9.06 (br s, 1H), 8.72 (br s, 1H),
8.44 (d, J ¼ 1.7 Hz, 1H), 8.18 (dd, J ¼ 8.6 and 1.7 Hz, 1H),
7.96 (d, J ¼ 8.9 Hz, 1H), 7.91 (d, J ¼ 8.6 Hz, 1H), 7.67 (dd,
J ¼ 8.9 and 2.3 Hz, 1H), 7.45 (dd, J ¼ 8.3 and 7.4 Hz, 2H),
7.31–7.25 (m, 3H), 4.19 (s, 2H), 3.84–3.81 (m, 2H), 3.79–
3.75 (m, 4H), 3.63–3.62 (m, 2H), 3.38 (s, 3H); 13C NMR (151
MHz, CDCl3): d 168.6, 165.1, 150.9, 137.3, 136.4, 131.3,
130.1, 129.4, 129.3, 127.9, 125.8, 125.6, 125.5, 121.6, 120.7,
116.1, 71.5, 71.1, 70.5, 70.3, 69.9, 58.8; IR (neat) 3334,
3065, 2881, 1731, 1692, 1630, 1580, 1541, 1494, 1407,
ꢁ
the whole was stirred at room temperature for 17 h. Then,
water was added, and the mixture was extracted with
dichloromethane. The organic layer was washed with 1 M
hydrochloric acid, saturated aqueous NaHCO3, and water,
dried over MgSO4, and concentrated. The residue was puri-
fied by recrystallization from CHCl3 to give 7 as colorless
ꢁ
needles (7.21 g, 71%). mp 193.4–196.2 C.
1391, 1342, 1281, 1241, 1188, 1106, 1024, 942 cmꢀ1
.
1H NMR (500 MHz, CDCl3): d 8.71 (br s, 1H), 8.17 (dd, J ¼
8.6 and 1.7 Hz, 1H), 8.12 (br s, 1H), 7.93 (d, J ¼ 8.9 Hz, 1H),
7.86 (d, J ¼ 8.6 Hz, 1H), 7.47–7.35 (m, 8H), 7.31–7.24 (m,
3H), 6.92 (br s, 1H), 5.27 (s, 2H); 13C NMR (151 MHz,
Synthesis of 1d
A three-neck flask, equipped with a dropping funnel, a reflux
condenser, and a gas inlet tube, was purged with argon and
then charged with 1.20 M borane–THF complex in THF
(9.5 mL, 11 mmol; Scheme 6). A solution of 9 (3.19 g,
7.53 mmol) in THF (100 mL) was added dropwise from the
dropping funnel, and the mixture was stirred at room tem-
perature for 30 min, refluxed for 4 h, and allowed to cool to
room temperature. Then, 6 M hydrochloric acid (5.0 mL)
was added, and the whole was refluxed for 1 h. After cooling
to room temperature, the mixture was neutralized to pH ꢃ 8
with NaHCO3, and extracted with dichloromethane. The com-
bined organic layers were washed with water and dried over
MgSO4. The crude product was purified by silica gel column
chromatography (hexane/AcOEt ¼ 1/3) to give 1d (2.42 g,
79%) as pale yellow viscous liquid.
DMSO-d6):
d 165.1, 153.7, 151.1, 139.9, 136.7, 136.6,
131.6, 130.8, 129.9, 129.2, 128.8, 128.53, 128.46,
128.1, 126.3, 125.9, 124.6, 122.3, 120.6, 113.4, 66.4; IR
(KBr) 3324, 3182, 3094, 3066, 3030, 2954, 1714, 1631,
1584, 1552, 1483, 1348, 1285, 1226, 1190, 1163, 1139,
1047 cmꢀ1
.
Synthesis of 8
To a mixture of 7 (4.31 g, 10.9 mmol) and dry dichlorome-
thane (450 mL), Et3SiH (7.0 mL, 44 mmol), Et3N (1.22 mL,
8.66 mmol), and PdCl2 (0.583 g, 3.29 mmol) were added and
the whole was stirred at room temperature for 1.5 h. The
reaction mixture was filtered through Celite and concen-
trated. Then, dry dichloromethane (500 mL) and trifluoro-
acetic acid (30 mL) were added to the residue at room tem-
perature, and the mixture was stirred at room temperature
for 0.5 h. After neutralizing with saturated aqueous NaHCO3,
the mixture was extracted with dichloromethane, and the or-
ganic layer was washed with water, dried over MgSO4, and
concentrated. The residue was purified with silica gel col-
umn chromatography (AcOEt/hexane ¼ 2/3) to give 8 as
1H NMR (500 MHz, CDCl3): d 8.59 (d, J ¼ 1.4 Hz, 1H), 8.06
(dd, J ¼ 8.6 and 1.7 Hz, 1H), 7.75 (d, J ¼ 8.9 Hz, 1H),
7.65 (d, J ¼ 8.9 Hz, 1H), 7.44 (dd, J ¼ 8.4 and 7.5 Hz, 2H),
7.29–7.24 (m, 3 H), 6.97 (dd, J ¼ 8.9 and 2.6 Hz, 1H), 6.82
(d, J ¼ 2.0 Hz, 1H), 4.67 (br s, 1H), 3.80 (t, J ¼ 5.2 Hz, 2H),
3.72–3.67 (m, 6H), 3.58–3.56 (m, 2H), 3.45 (t, J ¼ 5.2 Hz,
2H), 3.40 (s, 3H); 13C NMR (151 MHz, CDCl3): d 165.7,
151.2, 148.3, 138.2, 131.8, 130.6, 129.4, 126.2, 126.1, 125.9,
125.6, 122.3, 121.8, 118.9, 103.6, 71.9, 70.6, 70.5, 70.3, 69.2,
59.0, 43.1; IR (neat) 3334, 3065, 2881, 1731, 1692, 1630,
1580, 1541, 1494, 1407, 1391, 1342, 1281, 1241, 1188,
ꢁ
pale red solid (2.61 g, 92%). mp 193.2–194.7 C.
1H NMR (500 MHz, CDCl3): d 8.63 (d, J ¼ 1.1 Hz, 1H),
8.07 (dd, J ¼ 8.6 and 1.7 Hz, 1H), 7.81 (d, J ¼ 9.2 Hz, 1H),
7.65 (d, J ¼ 8.6 Hz, 1H), 7.44 (dd, J ¼ 8.6 and 7.6 Hz, 2H),
7.29–7.24 (m, 3H), 7.02–7.00 (m, 2H), 4.09 (br s, 2H);
1106, 1024, 942 cmꢀ1
.
13C NMR (126 MHz, CDCl3):
d
165.6, 151.2, 146.9,
Polymerization
137.8, 132.0, 131.1, 129.4, 126.6, 126.2, 125.9, 125.7, 123.0,
121.8, 118.8, 107.8; IR (KBr) 3414, 3343, 3238, 3057, 1708,
1640, 1618, 1478, 1431, 1390, 1348, 1290, 1202, 1188,
Synthesis of Poly1b
A flask equipped with a three-way stopcock was purged
with argon and then charged with 1.0 M LiHMDS in THF
(0.4 mL, 0.4 mmol). The flask was cooled to ꢀ10 ꢁC under
1065, 869 cmꢀ1
.
SYNTHESIS OF POLY(NAPHTHALENECARBOXAMIDE)S, MIKAMI ET AL.
3027

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 6 Synthesis of 1d.
an argon atmosphere with stirring. A solution of monomer
1b (130.9 mg, 0.4022 mmol), initiator (2.5 mg,
of 1b bearing a 3,7-dimethyloctyl side chain in the presence
of initiator 2 and LiHMDS gave well-defined poly(naphthale-
necarboxamide), together with a very small amount of a
cyclic trimer, formed by self-condensation of 1b in the early
stage of the polymerization, in [1b]0/[2]0 ¼ 10 and 20.
Attempts to obtain higher molecular weight polymers
resulted in the formation of polymer insoluble in the reac-
tion solvent. On the other hand, polymerization of 1d with
the TEG side chain yielded poly(naphthalenecarboxamide)
with high solubility, but the molecular weight was well con-
trolled only in [1d]0/[2]0 ¼ 10. Polymerization at higher
feed ratio was accompanied with self-condensation to afford
polyamides via chain-growth and step-growth polymeriza-
tion, so that the Mn value of the polymer did not reach the
theoretical value. The undesirable self-condensation is
accounted for by insufficient deactivation of the electrophilic
ester moiety by the electron-donating resonance effect of the
amide anion, due to the greater distance between the posi-
tions 2 and 6 of the naphthalene ring, in comparison with
the corresponding p-substituted benzene monomer, which
can undergo CGCP without self-condensation until the feed
ratio reaches 100.
2
0.012 mmol), and naphthalene (51.6 mg, 0.403 mmol) as an
ꢁ
internal standard in dry THF (0.5 mL) cooled to ꢀ10 C was
added all at once into the flask containing LiHMDS via a
syringe through the three-way stopcock in a stream of dry
ꢁ
nitrogen. The reaction mixture was stirred at ꢀ10 C for 4 h,
then the reaction was quenched with saturated aqueous
NH4Cl, and the mixture was extracted with dichloromethane.
The organic layer was washed with saturated aqueous
NaHCO3 and water, dried over MgSO4, and concentrated
under vacuum. The residue was purified by preparative
HPLC (eluent: CHCl3) using a polystyrene gel column to give
poly1b (65.1 mg) as brown solid.
1H NMR (600 MHz, CDCl3): d 7.81–7.75 (m, 1H), 7.53–7.41
(m, 1H), 7.37–7.21 (m, 2H), 7.18–7.02 (m, 2H), 4.12–3.88
(m, 2H), 1.72–1.01 (m, 10H), 0.95–0.69 (m, 9H).
Synthesis of Poly1d
The polymerization was carried out as in 1b, using 1.0 M
LiHMDS in THF (0.4 mL, 0.4 mmol) and a solution of 1d
(164 mg, 0.400 mmol) and 2 (8.5 mg, 0.040 mmol) in dry
THF (0.5 mL). After the reaction mixture had been stirred at
This study was supported by a Scientific Frontier Research
Project Grant from the Ministry of Education, Science, Sport
and Culture, Japan.
ꢁ
ꢀ10 C for 1 h, the reaction was quenched, and the mixture
was extracted and purified in the same manner as in 1b to
give poly1d (127 mg) as yellow solid.
1H NMR (500 MHz, CDCl3): d 7.88–7.14 (m, 6H), 4.25–4.09
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SYNTHESIS OF POLY(NAPHTHALENECARBOXAMIDE)S, MIKAMI ET AL.
3029