Despite the remote location of the chiral group, the CD
intensity in the polyacetylene chromophore region of poly-
J.-L. Hou and C. Li, Acc. Chem. Res., 2008, 41, 1343;
(
(
l) J. G. Rudick and V. Percec, Acc. Chem. Res., 2008, 41, 1641;
m) E. Yashima, K. Maeda, H. Iida, Y. Furusho and K. Nagai,
148
was almost identical to that of poly-129 (Fig. 2e). Although
Chem. Rev., 2009, 109, 6102.
poly-170 showed a slight decrease in CD intensity, it can be
presumed that the helix-sense excess of the polyacetylene
backbone in poly-170 is still rather high judging from its
relatively large De compared with those of previously reported
3 (a) O. Pieroni, F. Matera and F. Ciardelli, Tetrahedron Lett., 1972,
13, 597; (b) H. Nakako, Y. Mayahara, R. Nomura, M. Tabata and
T. Masuda, Macromolecules, 2000, 33, 3978; (c) J. Tabei,
M. Shotsuki, F. Sanda and T. Masuda, Macromolecules, 2005,
38, 5860; (d) F. Ishiwari, K. Nakazono, Y. Koyama and T. Takata,
Chem. Commun., 2011, 47, 11739.
2
m,14
helical poly(phenylacetylene) derivatives (Fig. 2f).
On the
4
5
N. Ousaka, Y. Takeyama, H. Iida and E. Yashima, Nat. Chem.,
2
basis of these results, we can conclude that the preferred-
handed helical chirality of the pendant polyisocyanate chains
induced by the chiral group at the a-end would play an
essential role in the remote control of the helicity of the
011, 3, 856.
(a) Y. Okamoto, M. Matsuda, T. Nakano and E. Yashima, Polym.
J., 1993, 25, 391; (b) Y. Okamoto, M. Matsuda, T. Nakano and
E. Yashima, J. Polym. Sci., Part A: Polym. Chem., 1994, 32, 309.
(a) Y. Inai, K. Tagawa, A. Takasu, T. Hirabayashi, T. Oshikawa and
M. Yamashita, J. Am. Chem. Soc., 2000, 122, 11731; (b) Y. Inai,
Y. Ishida, K. Tagawa, A. Takasu and T. Hirabayashi, J. Am.
Chem. Soc., 2002, 124, 2466.
6
polyacetylene backbone in the polymer brush. As with poly-129
,
the amplification of the helix-sense excess of the pendant poly-
isocyanate chains after conversion to the polymer brush was also
observed for poly-148 and poly-1 , showing a more intense CD
70
7 (a) K. Maeda, M. Matsuda, T. Nakano and Y. Okamoto, Polym. J.,
995, 27, 141; (b) K. Maeda and Y. Okamoto, Polym. J., 1998, 30, 100.
S. Lifson, C. E. Felder and M. M. Green, Macromolecules, 1992,
5, 4142.
9 Y. Kishimoto, M. Itou, T. Miyatake, T. Ikariya and R. Noyori,
Macromolecules, 1995, 28, 6662.
1
signal in the absorption region of the polyisocyanate (o325 nm)
than that of the corresponding macromonomers macro-148 and
macro-170, respectively (Fig. 2b, c, e and f). This amplification may
be caused by the chiral interaction between the pendants and/
or a reduction in the number of helix reversals in the polyiso-
cyanate chains caused by the interaction between adjacent
pendants as observed for polyisocyanates and polyacetylenes in
8
2
1
0 The polymerization of macro-1
Rh(nbd)Cl] , which is often employed for stereospecific polymer-
ization of phenylacetylene derivatives, was used as a catalyst.
11 It was difficult to evaluate the stereoregularity of poly-1 using
m
did not proceed when
[
2
m
1
15
H NMR spectroscopy because the peak caused by the main chain
protons, which are highly useful for assigning the conformation
and configuration of the polyacetylene backbone, could hardly be
observed because of their very weak intensities relative to those of
the protons of the pendant polyisocyanates (Fig. S2, ESIz). There-
a liquid crystal state.
In conclusion, we have demonstrated that poly(phenylacetylene)-
based polymer brushes bearing poly(phenyl isocyanate) pendants
form a preferred-handed helical structure when a chiral group is
introduced only at the pendant terminal. In these polymers, the
pendant helical polyisocyanate chains are arranged in a helical
array with a preferred-handed helix-sense along the helical
polyacetylene backbone, which is accompanied by amplification
of the helix-sense excess of the pendants. This method will be
applicable to the combination of other dynamic helical poly-
mers to arrange pendant helical polymer chains in preferred-
handed helical arrays using chiral amplification. We believe that
such helical polymer brushes may be useful as novel chiral
materials for possible application as asymmetric catalysts and
enantioselective selectors.
m
fore, the stereoregularity of poly-1 was evaluated using laser
Raman spectroscopy (Fig. S3, ESIz).
1
2 The vibrational CD (VCD) spectra of poly-129 in THF at 25 and
ꢀ10 1C were measured in order to clearly demonstrate that the
change of the CD intensity of poly-129 in the polyisocyanate
chromophore region with temperature is due to the change of the
helical screw sense preference of the polyisocyanate backbone, not
due to the change of conformation adoption for the 3-methoxy-
phenyl side group against the polyisocyanate backbone. The VCD
spectra of poly-129 showed a bisignate couplet in the CQO
stretching band region of the polyisocyanate backbone, whose
intensity increased reversibly with decreasing temperature (Fig.
S6, ESIz). These VCD results support that the polyisocyanate
pendants have a dynamic nature.
1
3 The CD intensity in the polyacetylene chromophore region (above
25 nm) of poly-129 was apparently changed by solvents, whereas
This work was partially supported by Grants-in-Aid for Scientific
Research from the Japan Society for the Promotion of Science
3
that in the polyisocyanate chromophore region (260–325 nm) of
poly-129 as well as macro-129 was almost the same independent of
solvent (see Fig. S4 in the ESIz). Poly-129 exhibited the most
intense CD in the absorption region of the polyacetylene backbone
in DMSO. Therefore, the CD and absorption spectra of poly-148
and poly-170 with longer pendant chains were measured in DMSO.
(JSPS). We also acknowledge Professor E. Yashima (Nagoya
University) for his help with laser Raman and VCD spectroscopy.
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This journal is c The Royal Society of Chemistry 2012