Well-defined star-shaped aromatic polyamides from chain-growth polymerization of phenyl 4-(alkylamino)benzoate with multifunctional initiators

Article abstract of DOI:10.1021/ma0473420

For the synthesis of well-defined star-shaped aromatic polyamides, triphenyl benzene-1,3,5-tricarboxylate (2a), tetraphenyl benzene-1,2,4,5- tetracarboxylate (2b), and 1,3,5-tris(4-phenyloxycarbonylbenzyloxy)benzene (3) were synthesized and then employed

Full text of DOI:10.1021/ma0473420

5526
Macromolecules 2005, 38, 5526-5531
Well-Defined Star-Shaped Aromatic Polyamides from Chain-Growth
Polymerization of Phenyl 4-(Alkylamino)benzoate with Multifunctional
Initiators
Ryuji Sugi,†,‡ Yoshio Hitaka,† Akihiro Yokoyama,† and Tsutomu Yokozawa*,†,‡
Department of Applied Chemistry, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama
221-8686, Japan, and “Synthesis and Control”, PRESTO, Japan Science and Technology Agency (JST)
Received December 23, 2004; Revised Manuscript Received May 2, 2005
ABSTRACT: For the synthesis of well-defined star-shaped aromatic polyamides, triphenyl benzene-1,3,5-
tricarboxylate (2a), tetraphenyl benzene-1,2,4,5-tetracarboxylate (2b), and 1,3,5-tris(4-phenyloxycarbo-
nylbenzyloxy)benzene (3) were synthesized and then employed as multifunctional initiators for the chain-
growth polymerization of phenyl 4-(octylamino)benzoate (1). The polymerization with 2a or 2b did not
proceed smoothly from all of the phenyl ester moieties in the initiators and afforded polymers with high
polydispersities. In contrast, initiator 3 having the benzyloxy spacers resulted in three-armed aromatic
polyamide (I) with low polydispersity. Furthermore, the benzyloxy linkages of the core of I were cleaved
by hydrogenolysis to yield a polymer with low polydispersity, the Mn of which was one-third that of I,
indicating that I exactly possesses three arm chains of a uniform and controlled length. However, the
polymerization at higher feed ratios of [1]0/[3]0 afforded not only the three-armed polymer but also a
linear polymer formed by self-polymerization of 1.
Introduction
employed herein possess tri- or tetraphenyl ester moi-
eties per molecule, such as simple triphenyl benzene-
1,3,5-tricarboxylate (2a) and tetraphenyl benzene-1,2,4,5-
tetracarboxylate (2b), and 1,3,5-tris(4-phenyloxycar-
bonylbenzyloxy)benzene (3) having the benzyloxy spac-
ers (Scheme 1). The presence of a spacer unit in the
initiator was found to be crucial for the synthesis of the
star-shaped polyamides, and the polymerization behav-
ior with 2a or 2b was different from that with 3.
The synthesis of well-defined star polymers has
become an important field in macromolecular chemistry
due to their unique spatial shapes and rheological
properties. Among a variety of synthetic approaches to
star polymers, living polymerization is the most ap-
propriate for the synthesis of well-defined star polymers,
which can be divided into three methods: (1) living
polymerization with a multifunctional initiator, (2)
coupling reaction of linear living polymers with a
multifunctional coupling agent, and (3) linking reaction
of linear living polymers with a divinyl compound.
Method 1 can yield star polymers with a determined
number of arms and has been successfully employed in
various living polymerizations, including anionic,1 cat-
ionic,2 radical polymerization,3 and ring-opening pro-
cesses.4 However, polycondensation is not applicable to
this method for the synthesis of well-defined star-shaped
polymers because polycondensation does not proceed in
a chain polymerization manner. Star-shaped condensa-
tion polymers have been prepared by copolycondensa-
tion of a star-center molecule with an AB-type monomer
or with A2 and B2 monomers,5 in which the arm lengths
of the polymers obtained are not controlled. Well-defined
star-shaped condensation oligomers have been synthe-
sized by the coupling reaction between a star-center
molecule and linear oligomers with monodispersity,
which was prepared by sequential condensation proce-
dure.6
Experimental Section
Measurements. 1H and 13C NMR spectra were obtained
on a JEOL ECA-600, 500, and FX-200 operating in the pulsed
Fourier transfer (FT) modes, using tetramethylsilane (TMS)
as an internal standard. IR spectra were recorded on a JASCO
FT/IR-410. Elemental analyses were performed by a Perkin-
Elmer 2400 II CHN. The Mn and Mw/Mn of polymers were
measured with a TOSOH HLC-8020 gel permeation chroma-
tography (GPC) unit (eluent: tetrahydrofuran (THF); calibra-
tion: polystyrene standards) using two TSK-gel columns (2 ×
Multipore HXL-M). Isolation of polyamides was carried out with
a Japan Analytical Industry LC-908 recycling preparative
HPLC (eluent: chloroform) using two TSK-gel columns (2 ×
G 2000HHR). MALDI-TOF mass spectra were recorded on a
Shimadzu/Krotos Kompact MALDI IV tDE in the reflection
mode using laser (λ ) 337 nm). A sample solution of 3,
dithrarnol as a matrix, and silver trifluoromethanesulfonate
as a cationizing salt was made in THF.
Materials. Phenyl 4-(octylamino)benzoate (1) and N-octyl-
N-triethylsilylaniline were prepared according to the previ-
ously established procedures.7a Triphenyl benzene-1,3,5-
tricarboxylate (2a) was prepared according to the literature.9
Phenyl benzoate (2c), CsF (Wako), and dehydrated tetrahy-
drofuran (dry THF; Kanto) as a solvent were used as received
without purification. 18-Crown-6 (TCI) was dried under re-
duced pressure at 40 °C for more than 6 h prior to use.
We have developed condensative chain-growth po-
lymerization,7 which yields well-defined condensation
polymers as well as block copolymers.8 In this paper,
we synthesize star-shaped aromatic polyamides by the
chain-growth polymerization of phenyl 4-(octylamino)-
benzoate (1) on the basis of the multifunctional initiator
method (method 1 mentioned above). The initiators
Synthesis of Tetraphenyl Benzene-1,2,4,5-tetracar-
boxylate (2b). Into the mixture of phenol (4.6 g, 52 mmol)
and benzene-1,2,4,5-tetracalboxylic acid (1.3 g, 5.0 mmol) was
added phosphorus oxy chloride (2.2 mL, 24 mmol) at 120 °C
with stirring. The reaction mixture was stirred at 120 °C for
8 h and poured into water, followed by extraction with CH2-
† Kanagawa University.
‡ Japan Science and Technology Agency (JST).
10.1021/ma0473420 CCC: $30.25 © 2005 American Chemical Society
Published on Web 05/27/2005

Macromolecules, Vol. 38, No. 13, 2005
Star-Shaped Aromatic Polyamides 5527
Scheme 1
Cl2. The combined organic layer was washed with 1 M NaOH
and dried over anhydrous MgSO4. The solvent was removed
in vacuo, and the residue was recrystallized from hexane-
ethyl acetate to give 0.73 g of 2b as a white solid (26%): purity
>99% by HPLC; mp 147.1-150.8 °C. IR (KBr): 1737, 1590,
1486, 748, 688 cm-1. 1H NMR (200 MHz, CDCl3) δ: 8.58 (s, 2
H), 7.44 (t, J ) 7.3 Hz, 8 H), 7.45-7.13 (m, 12 H). 13C NMR
(50 MHz, CDCl3) δ: 164.2, 150.6, 134.7, 130.7, 129.8, 126.6,
121.5. Anal. Calcd for C20H16O3: C, 73.11; H, 3.97. Found: C,
73.25; H, 3.99.
Synthesis of Phenyl (4-Chloromethyl)benzoate (4).
Into the mixture of phenol (3.2 g, 34 mmol) and triethylamine
(4.3 mL, 31 mmol) in CH2Cl2 (100 mL) was added a solution
of 4-chloromethylbenzoyl chloride (4.9 g, 25 mmol) in CH2Cl2
(100 mL) at 0 °C with stirring. The reaction mixture was
stirred at ambient temperature for 15 h and poured into water,
followed by extraction with CH2Cl2. The combined organic
layer was washed with water and dried over anhydrous
MgSO4. The solvent was removed in vacuo, and the residue
was recrystallized from hexane to give 4.6 g of 4 as a white
solid (72%): mp 89.0-91.0 °C. IR (KBr): 2924, 1734, 1609,
1275, 1074, 742, 704 cm-1. 1H NMR (200 MHz, CDCl3) δ: 8.18
(d, J ) 8.3 Hz, 2 H), 7.51 (d, J ) 8.3 Hz, 2 H), 7.42 (t, J ) 7.4
Hz, 2 H), 7.26 (t, J ) 7.0 Hz, 1 H), 7.20 (d, J ) 7.3 Hz, 2 H),
4.62 (s, 2 H). 13C NMR (50 MHz, CDCl3) δ: 164.7, 150.9, 143.0,
130.7, 130.6, 129.6, 128.7, 126.0, 121.7, 45.3.
Synthesis of 1,3,5-Tris(4-phenyloxycarbonylbenzyloxy)-
benzene (3). The mixture of K2CO3 (3.2 g, 23 mmol), phenyl
(4-chloromethyl)benzoate (2.5 g, 10 mmol), KI (2.4 g, 15 mmol),
and 18-crown-6 (0.19 g, 0.70 mmol) in acetone (10 mL) was
stirred at 60 °C for 1 h, and a solution of phloroglucinol (0.38
g, 3.0 mmol) in acetone (1.8 mL) was added at 60 °C with
stirring. The reaction mixture was stirred at 60 °C for 5 h.
After cooling to room temperature, K2CO3 was filtered off and
poured into water, followed by extraction with CH2Cl2. The
combined organic layer was washed with water and dried over
anhydrous MgSO4. The solvent was removed in vacuo, and the
residue was purified by flash chromatography on silica gel
(hexane/ethyl acetate ) 3/1) and was then recrystallized by
hexane-ethyl acetate to give 0.13 g of 3 as a white solid (6%):
purity >99% by HPLC; mp 180.0-181.5 °C. IR (KBr): 2924,
Polymerization Procedures. Monomer 1 was polymerized
with initiator 3 for the preparation of polymers I-III. An
example of the procedure is described for I. CsF (0.076 g, 0.5
mmol) was placed in a round-bottomed flask, equipped with a
three-way stopcock, and dried at 250 °C under reduced pres-
sure for 20 min. The flask was cooled to room temperature
under an argon atmosphere. Into the flask was added a solu-
tion of 1 (0.165 g, 0.5 mmol), 3 (0.0076 g, 2 mol %), N-octyl-
N-triethylsilylaniline (0.160 g, 0.5 mmol), and naphthalene
(internal standard for HPLC analysis, 0.064 g, 0.5 mmol) in
dry THF (1.25 mL) and a solution of 18-crown-6 (0.266 g, 1.0
mmol) in dry THF (0.25 mL) successively. After stirring at
ambient temperature for 7 h, the reaction was quenched with
saturated NH4Cl. A small portion of the THF layer was with-
drawn by a syringe and analyzed by HPLC to determine the
degree of consumption of 1 and extracted with CHCl3. The
organic layer was washed with saturated NH4Cl and dried over
anhydrous MgSO4. Concentration in vacuo gave crude product
I as a yellow oil. The GPC trace of the crude poduct is shown
in Figure 3A. Mn(GPC) ) 8000 and Mw/Mn ) 1.12. Subsequent-
ly, the residue was purified by preparative HPLC to give puri-
1
fied product I as a white powder. The H NMR spectra and
the GPC trace of I are shown in Figures 4A and 5A, respec-
tively. Mn(NMR) ) 11 000, Mn(GPC) ) 8000, Mw/Mn ) 1.12.
Hydrogenolysis of Triarmed Star Polymer. Hydro-
genolysis of the benzyl ether moieties of polymers I and II was
performed to determine the length of arms. An example of the
procedure is described for hydrogenolysis of I. A mixture of
1735, 1609, 1593, 1484, 1270, 1197, 1140, 1074, 743, 689 cm-1
.
Figure 1. (A) GPC profiles of polymer obtained in the
polymerization of 1 with (i) 2a and (ii) 2b. (B) Time-conversion
curves for the polymerization of 1 with 2a, 2b, or 2c in the
presence of N-octyl-N-triethylsilylaniline and CsF/18-crown-6
in THF ([1]0 ) [N-octyl-N-triethylsilylaniline]0 ) [CsF]0 ) 0.33
M, [18-crown-6]0 ) 0.66 M) at 25 °C: [1]0/[2a]0 ) 50.0, [1]0/
[2b]0 ) 66.7, [1]0/[2c]0 ) 16.7. Initiator: (O) 2a; ([) 2b; (0)
2c.
1H NMR (200 MHz, CDCl3) δ: 8.21 (d, J ) 8.0 Hz, 6 H), 7.55
(d, J ) 8.1 Hz, 6 H), 7.43 (t, J ) 7.6 Hz, 6 H), 7.29-7.20 (m,
9 H), 6.27 (s, 3 H), 5.12 (s, 6 H). 13C NMR (50 MHz, CDCl3) δ:
164.9, 160.5, 151.0, 142.8, 130.6, 129.6, 129.3, 127.2, 126.0,
121.8, 95.3, 69.5. MALDI-TOF MS: m/z calcd for [3 + Ag]+
863.70; found 865.36. Anal. Calcd for C48H36O9: C, 76.18; H,
4.79. Found: C, 75.77; H, 4.55.

5528 Sugi et al.
Macromolecules, Vol. 38, No. 13, 2005
Figure 2. 1H NMR spectrum of 3 in CDCl3 at 25 °C.
Figure 5. GPC profiles of (A) I and (B) the product obtained
by the hydrogenolysis of I.
Figure 3. GPC profiles of polymers I, II, and III, obtained
by the polymerization of 1 with 3 in the presence of N-octyl-
N-triethylsilylaniline and CsF/18-crown-6 in THF ([1]0
)
cleaved linear polymer as a white powder. The 1H NMR
spectra and the GPC trace of this product are shown in Figures
4B and 5B, respectively: Mn(NMR) ) 3900, Mn(GPC) ) 4000,
Mw/Mn ) 1.14.
[N-octyl-N-triethylsilylaniline]0 ) [CsF]0 ) 0.33 M, [18-crown-
6]0 ) 0.66 M) at 25 °C: [1]0/[3]0 ) 50.0 (A), 100 (B), and 200
(C).
Fractionation of III Using Preparative HPLC. Product
III (Mn(GPC) ) 16 800, Mw/Mn ) 1.26) was fractionated into
two parts (III-a and III-b) using preparative HPLC. The
product III (0.057 g) was dissolved in chloroform (3.0 mL), and
the solution was injected into the preparative HPLC. The
chromatogram of the eluent exhibted two peaks in the higher
and lower molecular weight regions. The respective eluents
were fractionated, concentrated, and dried in vacuo to give
white powders. The 1H NMR spectrum of III-a is shown in
Figure 6B: 0.027 g (23%); Mn(GPC) ) 30 000, Mw/Mn ) 1.07.
The 1H NMR spectrum of III-b is shown in Figure 6C: 0.012
g (10%); Mn(GPC) ) 15 400, Mw/Mn ) 1.05.
Results and Discussion
1. Chain-Growth Polymerization with Multi-
functional Initiators 2. Simple benzenepoly(carboxylic
acid) phenyl esters (2a and 2b) were first employed as
multifunctional initiators. Thus, the polymerization of
1 with 2 mol % of trifunctional initiator 2a ([1]0/[2a]0 )
50) and with 1.5 mol % of tetrafunctional initiator 2b
([1]0/[2b]0 ) 66.7) was carried out in the presence of 1.0
equiv of N-octyl-N-triethylsilylaniline and CsF and 2.0
equiv of 18-crown-6 in THF at room temperature, re-
spectively.7a The amounts of 2 were chosen for the same
length of arms in each star polymer ([1]0/[-CO2Ph]0 )
Figure 4. 1H NMR spectra in CDCl3 at 25 °C: (A) I; (B) the
product obtained by the hydrogenolysis of I.
5% Pd/C (0.010 g) and I (0.081 g) in ethyl acetate (10 mL) was
stirried under H2 atmosphere at 50 °C for 20 h. Pd/C was
filtered off, and the filtrate was concentrated in vacuo to give
a crude product (Mn(GPC) ) 4000 and Mw/Mn ) 1.14), followed
by purification with preparative HPLC to give 0.079 g of a core-

Macromolecules, Vol. 38, No. 13, 2005
Star-Shaped Aromatic Polyamides 5529
Figure 6. 1H NMR spectra in CDCl3 at 25 °C: (A) III, obtained by the polymerization of 1 with 3 in the presence of N-octyl-
N-triethylsilylaniline and CsF/18-crown-6 in THF ([1]0 ) [N-octyl-N-triethylsilylaniline]0 ) [CsF]0 ) 0.33 M, [18-crown-6]0
0.66 M) at 25 °C: [1]0/[3]0 ) 200. (B) III-a and (C) III-b, which were separated from III by preparative HPLC.
)
Scheme 2. Synthesis of Initiator 3 Having Benzyloxy
Spacers
(b) Polymerization with Initiator 3. The polym-
erization with 2 mol % of 3 ([1]0/[3]0 ) 50) was completed
in 7 h to yield a polymer I with Mn(GPC) of 8000 and
Mw/Mn of 1.12 (Figure 3A), the polydispersity of which
was lower than that of the polymer obtained with 2a
and 2b under the same conditions. This result implies
that each of the three phenyl ester moieties of 3
homogeneously initiated the polymerization of 1. Fur-
thermore, the fact that the Mn(GPC) value of I was
lower than the calculated value based on the feed ratio
of [1]0/[3]0 (Mn(calcd) ) 12 000) agreed with the feature
of star-shaped polymers because the Mn values of linear
polymer from 1 estimated by GPC were in good agree-
ment with the theoretical values.12
16.7). Figure 1A shows the GPC chromatograms of the
polymers obtained in each polymerization for 3 h. Both
of the GPC curves exhibit broad molecular weight
distributions (Mw/Mn > 1.2), implying that the arm
lengths of those products were not completely controlled.
To check each polymerization behavior, the polymer-
ization of 1 with 6 mol % of benzoic acid phenyl ester
2c ([1]0/[2c]0 ) 16.7) as a monofunctional initiator was
conducted under the same initial concentrations of the
phenyl ester moiety as for 2a and 2b. The polymeriza-
tion rates from 2a or 2b would be the same as that from
2c, if the polymerization is initiated and propagated
smoothly from all the phenyl ester moieties of the
initiators.8b As shown in the curves of monomer conver-
sion against polymerization time (Figure 1B), the po-
lymerization with both 2a and 2b was slower than that
with 2c, which yielded a linear polyamide with lower
polydispersity (Mn(GPC) ) 4050, Mw/Mn ) 1.15). Ac-
cordingly, the polymerization with 2a and 2b did not
proceed homogeneously from all the initiation sites of
2. This might be caused by steric hindrance around the
phenyl ester moieties in those initiators.
1
In the H NMR spectrum of I (Figure 4A), there can
be seen characteristic signals of the benzyloxy group b
and the aromatic proton c of the core unit, in addition
to the signals of the repeating units d-i and the
aromatic proton a at the ortho position of the terminal
phenyl ester. The integral ratio of c:b:a is 3:6:6, and
the signal of the benzyl proton of 3 at 5.1 ppm com-
pletely disappeared, indicating that one initiator mol-
ecule formed three polymer chains. The Mn values
estimated by the integral ratio of the signal of the
methylene in the repeating units (f) to that of the
terminal group (a) was 11 000, which was in good
agreement with the theoretical value mentioned above.
These results indicate that 3 served as a trifunctional
initiator to yield a three-armed polyamide.
To confirm the uniformity in length of the three arm
chains of I, the benzyloxy linkages connected to the core
were cleaved by hydrogenolysis. Figure 4B shows the
1H NMR spectrum of the product after the hydrogenoly-
sis of I at 50 °C for 20 h. Comparison between the
spectra of Figure 4A,B shows complete conversion of the
triarmed star polymer into a linear polymer because the
signals b and c of the core unit in star polymer I
completely disappeared and the signal of the methyl
proton j derived from the benzyloxy group was observed,
in which the integral ratio of j:a was 3:2. The Mn value
of the product estimated similarly by the 1H NMR
spectrum was 3900, which was nearly one-third of the
Mn value of I (Mn ) 11 000). The GPC chromatogram
of the product also shifted toward the low molecular
weight region while retaining low polydispersity (Figure
5). This arm-cleavage experiment clearly indicates that
I has three arm polyamide chains with a uniform and
controlled length.
2. Chain-Growth Polymerization with Initiator
3. (a) Synthesis of Initiator 3. We prepared initiator
3 bearing benzyloxy spacers to avoid steric hindrance
for initiation around the phenyl ester moieties (Scheme
2). Thus, 4-chloromethylbenzoyl chloride was converted
to the corresponding phenyl ester 4, followed by etheri-
fication with phloroglucinol. The yield of 3 was only 6%,
although similar etherification of 4 with phenol instead
of phloroglucinol gave the corresponding ether in 66%
yield. The low yield of 3 stemmed from C-alkylation of
phloroglucinol, which is a well-known side reaction.10
Indeed, the 1H NMR spectra of the isolated byproducts
showed the signal derived from C-alkylation at 4.0 ppm,
the methylene protons of the benzyl group adjacent to
an aromatic carbon.11 However, this signal was not
observed in the 1H NMR spectrum of purified 3 (Figure
2). 13C NMR spectroscopy, elemental analysis, analytical
HPLC and mass spectroscopy indicated that 3 was
essentially pure.

5530 Sugi et al.
Macromolecules, Vol. 38, No. 13, 2005
To synthesize the star polymers with higher molec-
ular weights, the polymerization of 1 with 3 was carried
out at higher feed ratios of [1]0/[3]0. The polymerization
with 1 mol % of 3 ([1]0/[3]0 ) 100) was completed in 6 h
to yield product II with Mn(GPC) of 15 100 and Mw/Mn
of 1.16. The GPC chromatogram of II appeared in a
higher molecular region than that of I, but a shoulder
peak was observed in the lower molecular weight region
(Figure 3B). In the polymerization with 0.5 mol % of 3
([1]0/[3]0 ) 200) for 12 h, the GPC chromatogram of
product III exhibited a bimodal (Figure 3C). The
undesirable products in the lower molecular weight
region seem to increase with decreasing 3 in the
polymerization.
(c) Origin of Undesirable Products. Two peaks of
bimoldal product III shown in Figure 3C were fraction-
1
ated by preparative HPLC. In the H NMR spectrum
of isolated III-a (Mn(GPC) ) 30 000, Mw/Mn ) 1.07), the
signal of a singlet of the aromatic proton a of the core
at 6.2 ppm was observed, and the integral ratio of a:b
was 3:6 (Figure 6B). Therefore, III-a is the three-armed
polyamide yielded by the chain-growth polymerization
Figure 7. GPC profiles of (A) II and (B) the product obtained
by the hydrogenolysis of II.
1
of 1 from 3. The Mn value of III-a determined by H
NMR was 39 000, which was lower than calculated
value on the basis of the feed ratios of [1]0/[3]0 (Mn(calcd)
) 47 000). On the other hand, the 1H NMR spectrum of
isolated III-b (Mn(GPC) ) 15 400, Mw/Mn ) 1.05)
showed the doublet signal e of the aromatic proton
adjacent to the octylamino group at 6.2 ppm (Figure
6C),8c indicating a linear polyamide derived from self-
polymerization of 1. The fact that the Mn of 14 000
determined by 1H NMR was close to the Mn(GPC) value
was also consistent with the feature of linear polymer
from 1.12 Accordingly, the Mn of III-a being lower than
the theoretical Mn is due to occurrence of not only chain-
growth polymerization from 3 but also self-polymeriza-
tion of 1. These results would suggest that the shoulder
in the lower molecular weight region of sample II is also
derived from the self-condensed linear polyamide with-
out the 3 unit.
Cleavage of the arms of the isolated product III-a was
attempted by hydrogenolysis at 50 °C for a week, but
the linear polymer could not be obtained. It is probably
difficult for long arm chains to be cleaved due to steric
hindrance between the arms and the Pd/C catalyst for
hydrogenolysis. However, sample II, obtained by the
polymerization with 1 mol % of 3, underwent cleavage
of the arms by hydrogenolysis at 50 °C for 3 days. Figure
7 shows the GPC chromatogram of II before and after
hydrogenolysis. The main peak of II clearly shifted to
the lower molecular weight region maintaing narrow
distribution, and the peak became unimodal. Further-
more, the top position of this peak is surprisingly the
same elution time as that of the shoulder peak of II
before hydrogenolysis. This result implies that the
degree of polymerization of each arm in star polymer
II and that of the linear polyamide from the self-
polymerization of 1 were almost identical. In the case
of product III, the Mn value of star polymer III-a (Mn
) 39 000) was also nearly 3 times higher than that of
the linear polymer III-b (Mn ) 14 000).
Figure 8. GPC profiles of polymer obtained by the polymer-
ization of 1 with 3 in the presence of N-octyl-N-triethylsily-
laniline and CsF/18-crown-6 in THF ([1]0 ) [N-octyl-N-
triethylsilylaniline]0 ) [CsF]0 ) 0.33 M, [18-crown-6]0 ) 0.66
M) at 25 °C: [1]0/[3]0 ) 100.
in the early stage, and the chain-growth polymerization
from the dimer and that from 3 would proceed at the
same propagation rates to afford the linear polymer and
the star polymer whose arm length is the same as that
of the linear polymer. The propagation of both polymers
can be seen by GPC traces of the polymerization of 1
with 1 mol % of 3 (Figure 8). The shoulder peak was
observed in the middle stage of polymerizaion and
shifted toward the higher molecular weight region, as
well as the main peak, with polymerization time.
In the polymerization of 1 with a monofunctional
initiator, no self-polymerization of 1 takes place as long
as the feed ratio of [1]0/[initiator]0 is 100 and less.7a In
the polymerization with trifunctional initiator 3, how-
ever, the self-polymerization occurred even at the feed
ratio of [1]0/[initiator site of 3]0 ) 33, which is much
less than 100. Easy occurrence of the self-polymerization
in the polymerization of 1 with multifunctional initiator
3 is presumably ascribed to the low local concentration
of the initiator site in the whole solution, except for the
area around 3. Thus, monofunctional initiators homo-
geneously exist in the solution, whereas multifunctional
initiators make both the area of high local concentration
We propose the polymerization mechanism as follows.
We have recently reported that the polymerization of 1
without an initiator yields aromatic polyamides with low
polydispersities (Mw/Mn e 1.1) and that this polymeri-
zation proceeds in a chain polymerization manner from
the dimer of 1 formed in situ.13 Accordingly, also in the
polymerization of 1 with 3, the dimer of 1 may be formed

Macromolecules, Vol. 38, No. 13, 2005
Star-Shaped Aromatic Polyamides 5531
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tration of them where self-polymerization would be
liable to occur. Contamination of the homopolymer in
the synthesis of star polymers with multifunctional
initiators turned out to be a unique problem in conden-
sative chain-growth polymerization, in which there is
a possibility of self-polymerization of monomers because
it does not occur in the living addition polymerization
method with multifunctional initiators.
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Conclusion
We have demonstrated that a condensative chain-
growth polymerization technique is applicable to prepa-
ration of star-shaped aromatic polyamides with con-
trolled arm length by the use of multifunctional initiators.
The polymerization of 1 with phenyl benzenepolycar-
boxylates (2a and 2b) as multifunctional initiators did
not proceed homogeneously from each initiator site
probably because of steric hindrance around the phenyl
ester moieties in 2. In contrast, in the polymerization
with trifunctional initiator 3 containing the benzyloxy
spacers, the three phenyl ester moieties of 3 initiated
polymerization of 1 homogeneously to yield a three-
armed aromatic polyamide with a controlled arm length.
However, the polymerization at higher feed ratios of [1]0/
[3]0 afforded not only the three-armed polymer but also
a linear polymer without the 3 unit from the self-
polymerization of 1. This approach to star polymers by
condensative chain-growth polymerization will permit
the production of star block copolyamides having dif-
ferent aminoalkyl side chains and a well-defined se-
quence, as well as star block copolymers consisting of
aromatic polyamide and polymers from the living po-
lymerization of vinyl and cyclic monomers. Those results
will be reported in the near future.
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Acknowledgment. This work was supported in part
by a Grant-in-Aid (12450377) for Scientific Research
from the Ministry of Education, Science, and Culture,
Japan.
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(12) The Mn values of linear polyamide determined by GPC based
on polystyrene standards were in good agreement with those
determined by 1H NMR spectra (see ref 7a).
References and Notes
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