C O M M U N I C A T I O N S
polycondensation of 1b followed by deprotection with TFA. By
this method we synthesized a soluble diblock copolymer of poly-
(p-benzamide) and poly(N-octyl-p-benzamide) with a narrow mo-
lecular weight distribution, which was arranged in a supramolecular
self-assembly in THF to give intriguing µm-sized bundles probably
by virtue of the multiple intermolecular hydrogen bondings of the
poly(p-benzamide) unit. The self-assembly of block copolymers
and star polymers containing the well-defined poly(p-benzamide)
units will be a versatile protocol for nanoarchitectures of aromatic
polyamides. Experiments along these lines are in progress.
Figure 1. GPC profile of polymer (eluent: THF). (A) Synthesis of the
block copolymer of 1a and 1b by monomer addition method: (a) poly1a
as a prepolymer ([1a]0/[2]0 ) 9.6), Mn ) 2490, Mw/Mn ) 1.10; (b) poly1a-
b-poly1b as a postpolymer ([added 1b]0/[2]0 ) 10.2), Mn ) 6420, Mw/Mn
) 1.10. (B) The block copolymer of poly(N-octyl-p-benzamide) and poly(p-
benzamide) obtained by the deprotection of the 4-octyloxybenzyl groups
on poly1a-b-poly1b with TFA.
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.
Supporting Information Available: Synthesis and polymerization
of monomer 1b and the synthesis of diblock copolymer of 1a and 1b,
followed by deprotection (PDF). This material is available free of charge
References
(1) Herlinger, H.; Knoell, H.; Menzel, H.; Schlaefer, J. Appl. Polym. Symp.
1973, 21, 215-224.
(2) Yokozawa, T.; Asai, T.; Sugi, R.; Ishigooka, S.; Hiraoka, S. J. Am. Chem.
Soc. 2000, 122, 8313-8314. Recently, the same polyamides were
synthesized by using a different leaving group of monomer and base:
Shibasaki, Y.; Araki, T.; Okazaki, M.; Ueda, M. Polym. J. 2002, 34, 261-
266.
(3) For chain-growth polycondensation for other polymers, see the following.
Polyesters: Yokozawa, T.; Suzuki, H. J. Am. Chem. Soc. 1999, 121,
11573-11574. Polyethers: Yokozawa, T.; Suzuki, Y.; Hiraoka, S. J. Am.
Chem. Soc. 2001, 123, 9902-9903. Poly(ether sulfone)s: Yokozawa, T.;
Taniguchi, T.; Suzuki, Y.; Yokoyama, A. J. Polym. Sci. Part A: Polym.
Chem. 2002, 40, 3460-3464.
Figure 2. SEM images (A, B) of the supramolecular assemblies of the
block copolymer of poly(N-octyl-p-benzamide) and poly(p-benzamide) from
the copolymer solution in THF dried at 25 °C on a silicon wafer and sputter
coated with carbon. (A) is magnified in the inset in (A).
ppm completely disappeared. The GPC chromatogram of the
product (Figure 1B) in the low molecular weight region slightly
shifted toward the lower molecular weight region, while keeping
the low polydispersity. Consequently, deprotection of the 4-octyl-
oxybenzyl groups proceeded quantitatively without scission of the
amide linkage of polymer, and a soluble diblock copolymer of
aromatic N-H polyamide and N-octyl polyamide was successfully
synthesized (Scheme 1).
(4) Lee, M.; Cho, B.-K.; Zin, W.-C. Chem. ReV. 2001, 101, 3869-3892.
(5) For examples of diblock copolymers containing aromatic polyamides from
conventional polycondensation, see: (a) Marsano, E.; Bianchi, E.; Conio,
G.; Mariani, A.; Russo, S. Polym. Commun. 1991, 32, 45-46. (b) Wang,
H.-H.; Lin, M.-F. J. Appl. Polym. Sci. 1991, 43, 259-269. (c) Conio, G.;
Marsano, E.; Bonfiglioli, F.; Tealdi, A.; Russo, S.; Bianchi, E. Macro-
molecules 1991, 24, 6578-6581. (d) Tagami, T. JP Pat. 05112651 A2,
1991; Chem. Abstr. 1993, 119, 226723. (e) Tagami, T. JP Pat. 05132563
A2, 1991; Chem. Abstr. 1993, 119, 227191. (f) Conio, G.; Tealdi, A.;
Marsano, E.; Mariani, A.; Ponomarev, I. Polymer 1994, 35, 1115-1117.
(g) Cavalleri, P.; Chavan, N. N.; Ciferri, A.; Dell’Erba, C.; Novi, M.;
Marrucci, G.; Renamayor, C. S. Macromol. Chem. Phys. 1997, 198, 797-
808.
It should be noted that the GPC chromatogram (eluent: THF)
of the above block copolymer showed a large peak in the high
molecular weight region as well as the peak corresponding to the
block copolymer (Figure 1B). The observed high molecular weight
region peak implies that this block copolymer was arranged in a
supramolecular self-assembly in THF. Scanning electron micros-
copy (SEM) was used to visualize the supramolecular assemblies
of the block copolymer after drying the THF solution on a silicon
wafer. Surprisingly, the SEM images revealed that µm-sized bundles
were formed as well as aggregates of flake structures;14 the reason
for the formation of two kinds of structures is unclear at present
time (Figure 2). The length of the bundles was in the range of 4-15
µm and their diameter was in the range of 150-250 nm. The DMF
solution of the block copolymer, however, did not show the high
molecular weight peak in the GPC chromatogram, and the bundle
structures were not observed in the SEM, either. The SEM image
of homopolymer of 1a having the N-octyl groups also did not show
the bundle structures even by use of the THF solution. Therefore,
the hydrogen bondings of the poly(p-benzamide) unit of the block
copolymer are probably responsible for supramolecular bundle
structures. Further studies by X-ray diffraction methods will be
essential to achieving a detailed understanding of the supramolecular
structures of the block copolymer.
(6) Phenyl 4-aminobenzoate, which would lead directly to poly(p-benzamide),
did not polymerize under our polymerization conditions.
(7) The observed low reactivity of the Boc-protected monomer may be caused
by steric hindrance of the monomer, because it did not react even with
4-nitrobenzoyl chloride.
(8) The Mn value of polyamide was estimated by the 1H NMR spectra based
on the ratios of signal intensities of the repeating units to those of the
initiator unit.
(9) A living polymerization nature was also ascertained by a linear correlation
between the Mn values and monomer conversion, retaining low polydis-
persities.
(10) Longer poly1b units (DP ) 20) could be introduced to the block copolymer
of 1a and 1b in the postpolymerization from poly1a without precipitation
(see ref 13).
(11) The polymer solubility was not changed even though the dodecyloxy group
was introduced to monomer instead of the octyloxy group in 1b.
(12) For examples of the deprotection of the 4-methoxybenzyl group with TFA,
see: (a) Brooke, G. M.; Mohammed, S.; Whiting, M. C. Chem. Commun.
1997, 1511-1512. (b) Miki, Y.; Hachiken, H.; Kashima, Y.; Sugimura,
W.; Yanase, N. Heterocycles 1998, 48, 1-4. (c) Bouzide, A.; Sauve, G.
Tetrahedron Lett. 1999, 40, 2883-2886.
(13) Other block copolymers (1a)n-(1b)m were also synthesized in a controlled
fashion. n ) 5, m ) 10: Mn ) 4630 (Mn(calcd) ) 4770), Mw/Mn ) 1.10.
n ) 10, m ) 5: Mn ) 4150 (Mn(calcd) ) 4270), Mw/Mn ) 1.12. n ) 10,
m ) 14: Mn ) 8130 (Mn(calcd) ) 7270), Mw/Mn ) 1.08. n ) 17, m )
9: Mn ) 8890 (Mn(calcd) ) 7160), Mw/Mn ) 1.06. n ) 20, m ) 5: Mn
) 6070 (Mn(calcd) ) 6530), Mw/Mn ) 1.08. n ) 20, m ) 20: Mn
11900 (Mn(calcd) ) 11500), Mw/Mn ) 1.08.
)
(14) Similar bundles were also observed in the SEM image of the block
copolymer without the terminal nitro group, which was obtained by
successive chain-growth polycondensation of 1a and 1b initiated with
phenyl benzoate instead of 2, followed by deprotection.
In conclusion, our chain-growth polycondensation method for
well-defined aromatic polyamides has been developed to the
synthesis of poly(p-benzamide) with a low polydispersity by the
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