Synthesis, liquid-crystalline properties, and supramolecular nanostructures of dendronized poly(isocyanide)s and their precursors

Article abstract of DOI:10.1002/chem.200500868

A series of novel dendronized π-conjugated poly(isocyanide)s were synthesized successfully by using a Pd-Pt μ-ethynediyl dinuclear complex ([ClPt{C₂H₅)₃}₂C≡CPt-(P(C ₂H₅)₃}₂Cl]) as the initiator. The polymerizations of the dendronized monomers follow first-order kinetics, indicating that living polymerization takes place. The obtained polymers exhibit narrow polydispersities in the range of 1.03-1.20. Thermal properties of the poly(isocyanide)s as well as their isocyanide monomers and precursors with formamido (HCONH-) moieties as apexes were investigated by using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). Both the peripheries and the apex groups of the dendrons affect the formation of supramolecular column and/or cubic phases of the precursors and monomers. The formamido precursor forms a liquid-crystalline phase due to intermolecular hydrogen bonding. The isocyanide monomer lacks this hydrogen-bonding ability and does not display an organized mesophase. All of the rigid poly(isocyanide)s with the monodendrons exhibit columnar liquid-crystalline phases. Interestingly, cylindrical structures of a poly(isocyanide) were directly visualized by using transmission electron microscopy (TEM).

Full text of DOI:10.1002/chem.200500868

DOI: 10.1002/chem.200500868
Synthesis, Liquid-Crystalline Properties, and Supramolecular Nanostructures
of Dendronized Poly(isocyanide)s and Their Precursors
Yanqing Tian,*[a, b] Kaori Kamata,[a, c] Hirohisa Yoshida,[a] and Tomokazu Iyoda*[a, c]
Abstract: A series of novel dendron-
ized p-conjugated poly(isocyanide)s
were synthesized successfully by using
with formamido (HCONH-) moieties
as apexes were investigated by using
cursors and monomers. The formamido
precursor forms liquid-crystalline
a
differential
scanning
calorimetry
phase due to intermolecular hydrogen
bonding. The isocyanide monomer
lacks this hydrogen-bonding ability and
does not display an organized meso-
phase. All of the rigid poly(isocya-
nide)s with the monodendrons exhibit
columnar liquid-crystalline phases. In-
terestingly, cylindrical structures of a
poly(isocyanide) were directly visual-
ized by using transmission electron mi-
croscopy (TEM).
ꢀ
a Pd Pt m-ethynediyl dinuclear com-
(DSC), polarized optical microscopy
(POM) and wide-angle X-ray diffrac-
tion (WAXD). Both the peripheries
and the apex groups of the dendrons
affect the formation of supramolecular
column and/or cubic phases of the pre-
plex
([ClPt{P(C2H5)3}2CꢁCPt-
{P(C2H5)3}2Cl]) as the initiator. The
polymerizations of the dendronized
monomers follow first-order kinetics,
indicating that living polymerization
takes place. The obtained polymers ex-
hibit narrow polydispersities in the
range of 1.03–1.20. Thermal properties
of the poly(isocyanide)s as well as their
isocyanide monomers and precursors
Keywords: dendrimers
· liquid
crystals · living polymerization ·
nanostructures · polymers
Introduction
existing polymer.[1h] Most of the reported dendronized poly-
mers are have flexible polymethacrylates, polystyrenes, and/
or functional poly(p-phenylene)s as the backbones.[1c–e,h]
Herein, we will report the synthesis and investigation of
new dendronized polymers with the rigid poly(isocyanide)
backbone. In this study, we have placed the emphasis on
both the rigidity of the rodlike polymer backbone and the
living polymerization character which allows us to build
macromolecular nanostructures.
Poly(isocyanide)s are quite different from conventional
polymers, such as polystyrene and polymethacrylate, and
may keep a rigid helical conformation with the 41-type helix
with a pitch of about 0.4 nm even in the racemic polymers,
such as the poly(tert-butyl isocyanide).[2,3] Many poly(isocya-
nide)s with chiral and/or achiral functional and/or nonfunc-
tional side-groups have been prepared[4] for the study of the
influence of chiral groups on the helicity, for the demonstra-
tion of nonlinear dynamics of the high-order helical struc-
tures, for the elucidation of the ion-channel properties, and
for direct visualization of the helical structures through mi-
crophase separation of block copolymers by atomic force
microscopy (AFM) and transmission electron microscopy
(TEM). As another strategy to fabricate the poly(isocya-
nide)-based nanostructures, we have attempted to introduce
liquid crystalline (LC) properties into the rigid helical p-
The synthesis of dendronized polymers, which may also be
called polymers with appendant dendrons or dendrimers
with a polymer core, possessing desirable properties of the
dendrimers, that is, high solubility, low intrinsic viscosity,
self-assembly ability, and so forth, have caused scientific in-
terest.[1] Such dendronized macromolecules could be pre-
pared either by polymerization of an appropriate dendron-
ized monomer or by appending dendrimer segments to an
[a] Dr. Y. Q. Tian, Dr. K. Kamata, Prof. H. Yoshida, Prof. T. Iyoda
Department of Applied Chemistry
Graduate School of Engineering, Tokyo Metropolitan University
1-1 Minami-Ohsawa, Hachioji, Tokyo, 192–0397 (Japan)
E-mail: yqtian@u.washington.edu
iyoda@res.titech.ac.jp
[b] Dr. Y. Q. Tian
Present address:
Materials Science and Engineering, University of Washington
Box 352120, Seattle, WA 98195-2120 (USA)
Fax : (+1)206-543-3100
[c] Dr. K. Kamata, Prof. T. Iyoda
Present address:
Chemical Resources Laboratory, Tokyo Institute of Technology
4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503 (Japan)
Fax : (+81)45-924-5266
584
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 584 – 591

FULL PAPER
conjugated poly(isocyanide)s. The combination of the helical
properties and LC properties may not only result in a new
class of functional materials, but also endow the poly(isocya-
nide)s with interesting optical and thermal properties. How-
ever, due to the rigid nature of the poly(isocyanide) back-
bones, only few poly(isocyanide)s were found to show the
liquid crystalline properties.[5] Herein, we utilize monoden-
drons with long alkyl chains,[1d,e,j–m,6] which allow us to
expect interesting self-assembly specific nanostructures, such
as cylindrical or cubic supramolecular structures, as the pe-
ripheral groups of the poly(isocyanide) backbone. Dendron
substituents on the poly(isocyanide) backbone are program-
med to induce self-assembling process to give ordered nano-
structures. To obtain the dendronized poly(isocyanide)s with
defined molecular weights and with narrow polydispersities,
we chose the living polymerization technique developed by
Takahashi et al.,[7] in which the successive and multiple in-
necessary precursors and monomers for the preparation of
poly(isocyanide)s. Though many papers investigated the
monodendrons with different peripheries, generations, and
polar groups at the apex (such as COOH, COONa, COOCs,
CO(OCH2CH2)nOH, metal cations, etc),[6,8] there is still no
report describing the synthesis and liquid-crystalline proper-
ties of the monodendrons with formamido and/or isocyano
units as the polar apex groups.
In the article, we will describe the preparative procedure,
the thermal properties, and the supramolecular structures of
the dendronized poly(isocyanide)s, including their corre-
sponding monodendrons with formamido and isocyano
groups.
Results and Discussion
ꢀ
sertion of the isocyanide into the Pd C bond of the Pd–Pt
m-ethynediyl dinuclear complex may produce polymers with
narrow polydispersities in quantitative yields.
Synthesis and characterization: Isocyanide monomers for
the liquid-crystalline (LC)-dendronized poly(isocyanide)s
were derived from esterification of the known monoden-
drons bearing hydroxyl groups (1 and 2)[6] with 4-formami-
On the other hand, generally, compounds with the form-
amido (HCONH-) group and isocyano (-NC) moiety are
dobenzoic acid to give new monodendrons
3
and
4
Scheme 1.
Table 1. Experimental conditions and properties of the synthesized poly(isocyanide)s.
[b]
[c]
[d]
Runs
Monomer
[M]0/[I]0
Obtained
polymers
Polymerization
time [h]
Conversion [%]
Yield [%]
Mn,GPC
Mn,calcd
Mw/Mn
1
2
3
4
5
6
5
5
5
6
6
6
100
100
170
10
20
100
P5a
P5b
P5c
P6a
P6b
2
22
72
48
57
23
92
98
88
81
22
~10
77
90
70
59
10900
23200
33600
10100
11700
–
26300
102800
186000
20800
36300
49600
1.03
1.06
1.20
1.05
1.03
–
[a]
[a]
–
336
–
[a] Not isolated. [b] Number average molecular weight (Mn) determined by GPC. [c] Mn calculated based on the feed ratio and conversions. [d] Polydis-
persity determined by GPC.
Chem. Eur. J. 2006, 12, 584 – 591
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
585

Y. Q. Tian, T. Iyoda et al.
(Scheme 1) as precursors for the dendronized isocyanide
monomers. After dehydration of the formamido groups in 3
and 4 with (trichloromethyl)carbonate (triphosgene), mono-
dendrons 5 and 6 as monomers were afforded in yields of
~70%. Polymerizations of the monomers (Table 1) were
carried out in THF at 758C. Purities of the monodendrons
and polymers were guaranteed by using IR and 1H NM R
spectroscopy, gel permeation chromatography (GPC), and/
or elemental analysis.
The IR spectra of the purified polymers showed no signal
corresponding to the isocyano moiety. Weak broad bands
from the formed imino groups constituting the polymer
backbone were observed at approximately 1645 cmꢀ1, con-
firming the formation of the poly(isocyanide)sꢁ backbone. A
ꢀ1
ꢀ
ꢀ
very weak band of CꢁC at 2085 cm was detected in the
resulting poly(isocyanide)s, implying that the insertion poly-
merization proceeded successfully and the structure of the
initiator remains in the polymer; this in turn leads to further
living polymerization.[7] The 1H NMR spectra of the poly-
mers just show very broad resonance in both the aromatic
and aliphatic chain regions. All the polymers gave unimodal
GPC profiles with narrow polydispersities from 1.03 to 1.20
(Figure 1 and Table 1).
Figure 2. The first-order kinetic plots of the polymerization of A) mon-
omer 5 with the feed ratio ([M]0/[I]0) of 100 and B) 6 with the feed ratio
of 20 by the m-ethynediyl Pd–Pt dinuclear complex as the initiator in
THF heated under reflux.
Kinetic of the polymerization: Figure 2 shows the kinetic
plots of the polymerization procedures of monodendron 5
with the feed ratio of [5]0/[I]0 =100 and of monodendron 6
with the feed ratio of [6]0/[I]0 =20. A linear dependence of
ln([M]0/[M]) on the polymerization reaction time was ob-
served, demonstrating that the polymerizations of the
dendronized monomers follow first-order kinetics. Taking
the [5]0/[I]0 =100 system as an example, molecular weights
increase with increasing monomer conversion. The polydis-
persities are in the narrow range of 1.03–1.06 (Figure 3).
This behavior confirms the living character of the polymeri-
zation under the present conditions. The molecular weights
determined by GPC are much lower than the molecular
weights calculated according to the feed ratio and conver-
sions. The significant discrepancy is probably due to the
quite different hydrodynamic volumes of the dendronized
polymers from those of the linear polystyrenes that are used
for the calibration materials for GPC columns.
Figure 3. Dependence of molecular weigh (Mn) and polydispersity (Mw/
Mn) on the conversion of the monodendric monomer 5.
Polymerization rates of the two monodendrons of 5 and 6
are quite different. The polymerization of the large mono-
dendron 6 was much slower than that of the small monoden-
dron 5, which may be attributed to their different peripher-
ies resulting in their different weight fractions of the isocya-
no groups in the monomers. Polymers with high polymeri-
zation degrees (e.g., DP=100) with the monodendron 6 as
the monomer could not be obtained. After one week poly-
merization, the conversion of a polymerization of 6, expect-
ed for DP=100, was just about 22%. However, the poly-
merization of 5 with high DP proceeded well. The conver-
sion of the polymerization of 5 for DP=170 reached 98%
only within three days.
Figure 1. The GPC curves of monomer 5; polymers P5a, P5b, and P5c;
monomer 6; and polymers P6a, and P6b.
586
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 584 – 591

Supramolecular Chemistry
FULL PAPER
Thermalproperties of the monodendrons—precursors and
monomers: Figure 4 gives the differential scanning calorime-
try (DSC) curves of the monodendron 3. The first heating of
3 shows two sharp endothermic peaks at 69 and 798C, corre-
sponding to its crystal–crystal (Cr1–Cr2) and crystal–isotrop-
ic-liquid (Cr–I, or melting) transitions. The first cooling of
this compound shows a small exothermic peak at 778C cor-
responding to an isotropic-liquid–mesophase (I–M) transi-
tion and a broad baseline shift at about 338C corresponding
to a mesophase–glass transition (M–g). On the second heat-
ing, the monodendron 3 undergoes a cold crystallization at
about 258C followed by complex melting processes until the
isotropic transition at 778C. The second cooling cycle gives
the same result as the first one. Upon cooling from the iso-
tropic state, clear fan-shaped textures (Figure 5) were ob-
served by polarized optical microscopy (POM), indicating
the possible hexagonal columnar phase (Colh),[9] which was
further confirmed by using wide-angle X-ray diffraction
(WAXD).
The first heating of monodendron 4 shows a sharp endo-
thermic peak at 538C corresponding to the crystal–meso-
phase (Cr–M) transition and a weak endothermic peak at
828C corresponding to the M–I transition, as illustrated in
Figure 4. On cooling, a much wider mesophase temperature
range was observed. Under POM, no birefringence was ob-
served, suggesting that the mesophase is a cubic (Cub)
phase.
The DSC curves of the monodendrons with isocyano
group, 5 and 6, exhibit only a melting peak on heating and a
crystalline peak on cooling with a big enthalpy as given in
Table 2.
Figure 6 illustrates the wide-angle X-ray diffractograms of
the monodendrons 3 and 4. For the monodendron 3, the X-
ray diffractogram at 608C on cooling shows a sharp (100)
and two weak (110) and (200) Bragg reflections in small-
angle region with a lattice spacing ratio of d100:d110:d200 =1/
(1/31/2)/(1/41/2) indicates that the mesophase is a hexagonal
columnar phase (Colh) with a lattice of a=50.1 Š.[10] On
cooling to room temperature, the X-ray diffractogram
changes slightly. The ratio of the lattice spacing still follows
the order of d100:d110:d200 =1/(1/31/2)/(1/41/2), suggesting the
ordered columnar structures were frozen in the glassy state.
The absence of a sharp reflection in the wide-angle region
in its columnar mesophase and existence of a diffuse halo
caused by the liquidlike arrangement of the alkyl side chains
suggest an irregular (disordered) arrangement of the mole-
Figure 4. DSC curves of the monodendron 3 and 4. a) first heating of 3;
b) first cooling of 3; c) second heating of 3; d) first heating of 4; e) first
cooling of 4; f) second heating of 4.
Figure 5. Typical texture of the monodendron 3 at 608C on cooling. Mag-
nification: ”200.
Figure 6. he X-ray diffractograms of 3 (top) measured at 608C (a) and
258C (b) on cooling, and 4 (bottom) measured at 258C on cooling.
Chem. Eur. J. 2006, 12, 584 – 591
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
587

Y. Q. Tian, T. Iyoda et al.
Table 2. The phase behaviors of the monodendrons and their polymers.
bration of
5
appears at
2120 cmꢀ1. Therefore, the re-
sults from IR spectra clearly in-
dicate that intermolecular hy-
drogen bonding does exist in
the formamido moiety contain-
ing precursors. Further study is
in progress by using tempera-
ture-dependent IR and Raman
spectra for more detailed un-
derstandings of the relationship
between the intermolecular hy-
drogen bonding and thermal
properties.
Phase-transition
Measured lattice spacings
and proposed indexes
temperatures [8C][a]
3
4
5
6
Cr1 69 (39.2) Cr2 79 (56.3) I[b]
I 77 (ꢀ3.4) Colh 33 (ꢀ3.8) g[c]
I 72 (ꢀ0.8) Cub ꢀ12 (ꢀ20.8) Cr[c]
Cr ꢀ10 (18.1) Cub 81 (1.3) I[d]
I 37 (ꢀ141.3) Cr[c]
d
d
d
100 =43.3 Š; d110 =25.1 Š; d200 =21.6 Š (608C, cooling)
100 =41.2 Š; d110 =23.1 Š; d200 =20.7 Š (258C, cooling)
200 =43.0 Š; d210 =38.5 Š; d211 =35.3 Š; d320 =23.7 Š (258C, cooling)
Cr 67 (168.7) I[d]
I 30 (ꢀ172.2) Cr[c]
Cr 62 (178.6) I[d]
P5a Cr ~36[e] (91.8) M ~260 decomp[f] d=39.5 Š (308C, after annealing at 1008C)
P5b Cr 43 (40.3) Colh ~260 decomp[f]
P5c Cr 45 (50.6) M ~260 decomp[f]
P6a Cr ꢀ12 (25.9) M ~260 decomp[f]
P6b Cr ꢀ12 (29.2) M ~260 decomp[f]
d100 =39.4 Š; d110 =22.3 Š (1008C)
d=39.6 Š (1008C)
d=36.7 Š (308C, after annealing at 1008C)
d=36.6 Š (808C)
[a] Enthalpies [kJmolꢀ1] are given in parentheses. [b] On the first heating cycle. [c] On the first cooling cycle.
[d] On the second heating cycle. [e] Broad transition. [f] Decomposition on heating. Cr: crystalline phase; M:
Mesophase, possibly columnar phase; Colh: hexagonal columnar phase; Cub: cubic phase; I: isotropic phase;
g: glass state.
Thermalproperties of the poyl-
mers: Thermal properties of the
polymers were first examined
by means of thermogravimetric
analysis, revealing that all of
the polymers are stable up to
cules within the parallel aligned columns independent of the
two-dimensional lattice. For the monodendron 4, four Bragg
reflections corresponding to the (200), (210), (211), and
(320) with a lattice spacing ratio d200:d210:d211:d320=(1/41/2)/(1/
51/2)/(1/61/2)/(1/131/2) were observed, indicating the cubic mes-
ophase with a lattice parameter of a=80.5 Š.[11]
The phase-transition temperatures and transition enthal-
pies obtained from the above thermal investigations are
summarized in Table 2. The phase behavior depends on not
only the peripheries, but also the apex groups. The two mon-
odendrons with formamido apex groups, 3 and 4, form the
column or cubic phases, respectively, which are dependent
on their peripheries. The two monodendrons with isocyano
apex groups, 5 and 6, do not exhibit liquid-crystalline prop-
erties regardless of their peripheries. Comparison of the iso-
tropic transition temperatures of 3 and 4 with their related
dehydrated monodendrons, 5 and 6, it can be seen that the
isotropic transition temperature of each monodendron with
formamido group is about 10 or 158C higher than that of its
related monodendron with an isocyano group. This observa-
tion suggests the formamido group may stabilize the meso-
phase. Considering their structural difference, we think the
different thermal properties might possibly be due to inter-
molecular hydrogen bonding through the formamido apexes.
To confirm the above consideration, typical IR spectra of
the monodendrons 3 and 5 were measured and are illustrat-
ed in Figure 7. For both the two compounds, the ester car-
bonyl vibration at 1717 cmꢀ1 was observed. Two formamido
carbonyl vibrations of 3 at 1683 and 1678 cmꢀ1 were ob-
served, confirming the existence of intermolecular hydrogen
bonding between the formamido groups through the s-cis in-
teraction (dimer, 1683 cmꢀ1) and the s-trans interaction
(polymer, the predominating state for the amide,
1678 cmꢀ1)[12] as illustrated in Scheme 2. Due to the dehy-
dration of the formamido group, the intermolecular hydro-
gen bonding of 3 is broken and the resulting isocyanide vi-
Figure 7. The IR spectra of a) the precursor monodendron 3 and b) its
dehydrated monomer 5.
Scheme 2. The possible intermolecular hydrogen bonding between the
formamido groups.
588
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 584 – 591

Supramolecular Chemistry
FULL PAPER
more information about the mesophormic structures. All of
the polymers show a sharp peak in the small angle region
and a broad hollow in the wide-angle region of 2qꢂ208, in-
dicating formation of their mesophases. Especially, the dif-
fractogram of P5b shows a sharp diffraction peak at
3.94 nm (d100) and a broad peak at 2.23 nm (d110), strongly
confirming its hexagonal columnar phase (Colh). According
to the 41-helical structure of the polymer backbone, the
monodendrons in the side-group might generate a supra-
molecular columnar structure with a diameter of 4.70 nm
(calculated by Chem 3D). The determined diameters (diam-
eter=2hd100i/31/2) of the columns from the X-ray diffraction
measurements are 4.60 nm for P5 and 4.30 nm for P6; these
values are in general accordance with the calculated diame-
ter of the column by Chem 3D (4.70 nm). Therefore, we
may deduce that each of the polymers forms a columnar
mesophase. The above results show that through the intro-
duction of the flexible monodendrons into the rigid poly(iso-
cyanide)s, LC properties, especially the hexagonal columnar
LC phase, can be realized successfully.
Morphologies of the polymer P5b: Very interestingly, cylin-
drical structures (Figure 10) were directly viewed under
TEMby using thin films of P5b after annealing in its col-
umnar phase. The film was prepared by spreading about
5 mL of 1 wt% solution of P5b in toluene on a water sur-
face. The thickness of the thin film was estimated to be
about 50–100 nm. The films were annealed at 1008C for 1 h
in order to get the ordered structures. Small cylinders paral-
lel to the surface with the average diameter of 4.7 nm, perio-
dicity of 5.8 nm, and length of 18.7 nm (calculated using 100
cylinders with parallel orientation) were observed. The
small cylinders found in defined areas, for example, area A
in Figure 10, are tilted or perpendicular to the substrate.
The different contrast reflects the different thickness of the
film. The cylinders of the dendronized poly(isocyanide)s ob-
Figure 8. Top: DSC curves of a) P5a, b) P5b, c) P5c, d) P6a, and
e) P6b for the heating process. Bottom: TG-DTA curve of P5b.
2608C. The DSC profile of polymers of 5 (P5) showed a re-
versible phase transition at about 40–508C (Figure 8) de-
pending on their molecular weights, but no further phase
transitions were observed before their decomposition. The
DSC results for polymers of 6 (P6) showed a reversible
transition at about ꢀ128C. No isotropization transition was
observed for any of the polymers before their decomposi-
tions, as confirmed by temperature-dependent wide-angle
X-ray diffraction and polarized microscopy. The thermal
properties are summarized in Table 2. Under polarized opti-
cal microscopy, very strong birefringence was observed in
the LC phase of P5. The textures are not characteristic of
columnar phases or smectic phases, and are difficult to iden-
tify. No birefringence was observed for P6. The lack of typi-
cal textures of the polymers with monodendrons has already
been reported by Percecꢁs group.[1d,f,j] Therefore, X-ray dif-
fraction analysis (Figure 9) becomes a powerful tool to gain
Figure 9. Wide-angle X-ray diffractograms of the polymer P5b and P6b.
Figure 10. TEMimage of the thin film of P5b.
Chem. Eur. J. 2006, 12, 584 – 591
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
589

Y. Q. Tian, T. Iyoda et al.
carbon supporting film, 4) drying the specimens at room temperature
under vacuum overnight followed by annealing at 1008C for 1 h, and 5)
staining samples by using 2 wt% OsO4 vapor for 5 min to enhance the
contrast for the TEMobservation.
served under TEMare possibly arranged as single mole-
cules. X-ray diffraction shows the d100 of P5b is 3.94 nm, re-
sulting in the diameter of the column is 4.60 nm (diameter=
2<d100 >/31/2), which is very close to the 4.7 nm observed by
TEMand the calculated value by using Chem 3D. This ob-
servation might be compared with the morphologies of
linear polymethacrylates and/or polystyrenes with the simi-
lar monodendrons,[13] showing the richness of the nanostruc-
tures of the dendronized polymers. Further investigations
will be addressed with the controlling of the morphologies
through the adjustment of the film thickness, degree of poly-
merization, and even the rigidity and helicity of the back-
bones.
Materials: Monodendrons 1 and 2, and 4-formamidobenzoic acid were
prepared according to the known procedures.[5,8b] The Pd–Pt m-ethynediyl
complex ([Cl{P(C2H5)3}2PdCꢁCPt{P(C2H5)3}2Cl] Scheme 1) as the initia-
tor for polymerization was prepared according to the literature.[14] THF
was used as the polymerization solvent and was dehydrated by heating to
reflux over sodium and then distillation under nitrogen. The other chemi-
cal reagents and solvents were commercially available and used without
further purification.
Preparation of 3: 4-Formamidobenzoic acid (1.65 g, 10 mmol), 1 (9.79 g,
10 mmol), and catalytic amount of 4-N,N’-dimethylaminopyridine were
dissolved in methylene chloride (150 mL) and cooled to 0–58C. Dicyclo-
hexyl carbodiimide (3.09 g, 15 mmol) in methylene chloride (50 mL) was
added dropwise in under stirring at 08C. After 12 h, the precipitate was
filtered, and the solvent was removed under reduced pressure. Then the
residue was purified by silica column chromatography by using chloro-
form/ethyl acetate as the eluent. A white product (8.1 g) with the yield of
72% was obtained after recrystallization from ethanol. 1H NM R
(270 MHz, CDCl3, 258C, TMS): d=8.86 (d, J=13 Hz, 0.4H; HCO in
trans), 8.41 (s, 0.6H; HCO in cis), 8.02 (d, J=8.9 Hz, 2H; phenyl proton,
Hm to NH), 7.60 (d, J=8.9 Hz, 1.2H; phenyl proton, Ho to NH), 7.29 (d,
J=7.8 Hz, 6H; phenyl proton, Hm to OC12H25), 7.11 (d, J=7.8 Hz, 0.8H;
phenyl proton, Ho to NH), 6.85 (d, J=7.8 Hz, 4H; phenyl proton, Ho to
OC12H25), 6.78 (d, J=7.8 Hz, 2H; phenyl proton, Ho to OC12H25), 6.71 (s,
2H; phenyl proton, Ho to CH2OCO), 5.22 (s, 2H; CH2O), 5.02 (s, 4H;
CH2O), 4.94 (s, 2H; CH2O), 3.93 (m, 6H; CH2O), 1.83–1.26 (m, 60H;
(CH2)10), 0.84 ppm (t, J=6.5 Hz, 9H; CH3); FT-IR (KBr pellet): n˜ =1718
(C=O ester), 1679, and 1683 cmꢀ1 (C=O amide); elemental analysis calcd
(%) for C72H103NO9 (1126.59): C 76.76, H 9.22, N 1.24; found: C 76.63, H
9.44, N 1.27.
Conclusion
We reported the synthesis, liquid-crystalline properties, and
supramolecular nanostructures of novel dendronized poly-
(isocyanide)s with their related precursors and monomers.
Narrow polydispersities of the polymers were obtained
using the Pd–Pt m-ethynediyl dinuclear complex ([Cl-
{P(C2H5)3}2PdꢁPt{P(C2H5)3}2Cl]) as the initiator. The poly-
merizations follow first-order kinetics, even though the mo-
lecular weights of the dendronized monomers are higher
than 1000. Through the introduction of flexible monoden-
drons into the rigid poly(isocyanide)s, liquid-crystalline
properties, especially the hexagonal columnar liquid-crystal-
line properties, are realized successfully. This provides an ef-
ficient route for endowing liquid-crystalline properties and
supramolecular columnar structures on the extreme rigid
poly(isocyanide)s. The cylindrical supramolecular structures
of the poly(isocyanide)s were also clearly visualized using
TEM.
Preparation of 4: This compound was synthesized from 2 by using a pro-
cedure similar to that described for 3. Yield: 63%; 1H NMR (270 MHz,
CDCl3, 258C, TMS): d=8.86 (d, J=13 Hz, 0.4H; HCO in trans), 8.35 (s,
0.6H; HCO in cis), 7.89 (m, 2H; phenyl proton, Hm to NH), 7.80 (d, J=
8.9 Hz, 1.3H; phenyl proton, Ho to NH), 7.55 (d, J=8.9 Hz, 0.7H; phenyl
proton, Ho to NH), 7.41 (s, 0.4H; NH in trans), 7.06 (d, J=7.8 Hz, 0.6H;
NH in cis), 6.63 (m, 2H; phenyl proton), 6.56 (m, 6H; phenyl proton),
5.13 (s, 2H; CH2O), 4.92 (m, 6H; CH2O), 3.83 (m, 18H; CH2O), 1.83–
1.26 (m, 180H; (CH2)10), 0.85 ppm (t, J=6.5 Hz, 27H; CH3); FT-IR (KBr
pellet): n˜ =1718 (C=O ester) and 1679 cmꢀ1 (C=O amide); elemental
analysis calcd (%) for C114H247NO15 (2232.50): C 77.47, H 11.15, N 0.63;
found: C 77.32, H 11.47, N 0.62.
ExperimentalSection
Preparation of 5: Triphosgene (0.24 g, 1 mmol) in methylene chloride
(5 mL) was added slowly into a mixture of 3 (1.126 g, 1 mmol) and trie-
thylamine (0.4 mL, 3 mmol) in methylene chloride (10 mL) at 0–58C.
Two hours later, aqueous NaHCO3 (5 wt%, 10 mL) was added to the
mixture. The organic layer was separated, washed with brine, and dried
by using anhydrous Na2SO4. After the solvent was removed under re-
duced pressure, the crude product was purified by column chromatogra-
phy with methylene chloride as the eluent. A white solid was obtained
(yield: 0.70 g, 70%). 1H NMR (270 MHz, CDCl3, 258C, TMS): d=8.06
(d, J=8.6 Hz, 2H; phenyl proton, Ho to COOCH2), 7.47 (d, J=8.6 Hz,
2H; phenyl proton, Hm to COOCH2), 7.29 (m, 6H; phenyl proton, Hm to
OC12H25), 6.88 (d, J=8.6 Hz, 4H; phenyl proton, Ho to OC12H25), 6.76 (d,
J=8.6 Hz, 2H; phenyl proton, Ho to OC12H25), 6.65 (s, 2H; phenyl
proton, Ho to CH2OCO), 5.22 (s, 2H; CH2O), 5.02 (s, 4H; CH2O), 4.94
(s, 2H; CH2O), 3.93 (m, 6H; CH2O), 1.83–1.26 (m, 60H; (CH2)10),
Characterization: 1H NMR spectra were measured by using a JEOL 270
instrument spectrometer operating at 270 MHz with TMS internal stan-
dard as a reference for chemical shifts. FT-IR spectra were recorded on a
Bio-Rad FTS 3000 spectrophotometer. All of the FT-IR measurements
were performed in KBr pallet.
Molecular weights of the polymers were determined by using a JASCO
860 GPC (Japan Spectroscopic Co., Ltd.) system coupled with a UV de-
tector, with reference to a series of standard polystyrenes as calibration
with THF as eluent.
Thermal behavior was determined by using a SII Extra 6000 DSC system
(Seiko Instruments Inc.) at a scanning rate of Æ58Cminꢀ1 under nitro-
gen. Liquid-crystalline textures were observed under a Nikon Microphot-
UFX polarized optical microscopy (POM) with a Mettler FP-82 hot stage
and a FP-80 central processor. Wide-angle X-ray diffraction (WAXD)
was measured on a MAC Science MPX 3 X-ray diffractometer equipped
with a thermal controller Model 5310.
ꢀ
0.84 ppm (t, J=6.5 Hz, 9H; CH3); FT-IR (KBr pellet): n˜ =2120 ( NC),
1719 cmꢀ1 (C=O ester); elemental analysis calcd (%) for C72H101NO8
(1108.57): C 78.01, H 9.18, N 1.26; found: C 77.87, H 8.97, N 1.22.
Transmission electron microscopy (TEM, JEOL 1200 EXII) experiments
were carried out at an acceleration voltage of 200 kV. TEMsamples were
prepared by: 1) spreading 1 wt% solutions of the sample in solutions
onto water surface, 2) waiting for about 10 min until the complete evapo-
ration of toluene and formation of uniform thin polymer films on water
surface, 3) transferring the thin films onto a copper TEMgrid with
Preparation of 6: This compound was synthesized from 4 by using a pro-
cedure similar to that described for 5. Yield: 67%; 1H NMR (270 MHz,
CDCl3, 258C, TMS): d=8.00 (d, J=8.6 Hz, 2H; phenyl proton, Hm to
ꢀ
ꢀ
NC), 7.48 (d, J=8.6 Hz, 2H; phenyl proton, Ho to NC), 6.67 (m, 8H;
phenyl proton, Ho,m to OCH2), 5.22 (s, 2H; CH2O), 5.00 (m, 6H; CH2O),
590
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 584 – 591

Supramolecular Chemistry
FULL PAPER
3.88 (m, 18H; CH2O), 1.80–1.10 (m, 180H; (CH2)10), 0.88 ppm (t, J=
Edlund, S. D. Hudson, P. A. Heiney, H. Duan, S. N. Magonov, S. A.
Vinogradov, Nature 2004, 430, 764; l) G. Ungar, Y. S. Liu, X. B.
Zeng, V. Percec, W. D. Cho, Science 2003, 299, 1208; m) X. B. Zeng,
G. Ungar, Y. S. Liu, V. Percec, A. E. Dulcey, J. K. Hobbs, Nature
2004, 428, 157; n) A. F. Zhang, L. Okrasa, T. Pakula, A, D. Schlüter,
J. Am. Chem. Soc. 2004, 126, 6658.
ꢀ1
ꢀ
6.5 Hz, 27H; CH3); FT-IR (KBr pellet): n˜ =2119 ( NC), 1718 cm (C=O
ester); elemental analysis calcd (%) for C114H245NO14 (2214.48): C 78.10,
H 11.15, N 0.63; found: C 77.91, H 10.86, N 0.68.
Polymerization: All of the polymerizations were carried out in THF
under reflux as shown in Table 1. An example of the synthesis of P5b is
described in detail.
[2] a) F. Millich, Chem. Rev. 1972, 72, 101; b) F. Millich, Macromol. Rev.
1980, 15, 207.
A mixture of the Pd–Pt m-ethynediyl complex (4.35 mg, 0.005 mmol) as
the initiator (I) and the monodendron 5 (554.3 mg, 0.5 mmol) was de-
gassed under vacuum for 30 min at room temperature, then THF
(20 mL) was added under nitrogen. The polymerization was carried out
at 758C. During the polymerization process, 5 mL of the solution was
taken out at a specific intervals by using micro-syringe to determine the
conversions. The conversion was calculated according to the integration
areas of the GPC curves of the formed polymer (Apolymer) and non-poly-
merized monomer (Amonomer) by using Equation (1).
[3] a) R. J. M. Nolte, A. J. M. van Beijnen, W. Drenth, J. Am. Chem.
Soc. 1974, 96, 5932; b) A. J. M. van Beijnen, R. J. M. Nolte, W.
Drenth, Recl. Trav. Chim. Pays-Bas 1980, 99, 121; c) A. J. M. van
Beijnen, R. J. M. Nolte, W. Drenth, A. N. F. Hezemans, Tetrahedron
1976, 32, 2017.
[4] a) T. J. Deming, B. M. Novak, J. Am. Chem. Soc. 1993, 115, 9101;
b) T. J. Deming, B. M. Novak, Macromolecules 1991, 24, 6043;
c) M. F. M. Roks, R. J. M. Nolte, Macromolecules 1992, 25, 5398;
d) B. Hong, M. A. Fox, Macromolecules 1994, 27, 5311; e) J. P. Chen,
J. P. Gao, Z. Y. Wang, Polym. Int. 1997, 44, 83; f) N. Ohshiro, A. Shi-
mizu, R. Okumura, F. Takei, K. Onitsuka, S. Takahashi, Chem. Lett.
2000, 786; g) F. Takei, K. Kanai, K. Onitsuka, S. Takahashi, Chem.
Eur. J. 2000, 6, 983; h) M. Kauranen, T. Verbiest, C. Boutton, M. N.
Teerenstra, K. Clays, A. J. Schouten, R. J. M. Nolte, A. Persoons,
Science 270, 1995, 966; i) D. B. Amabilino, E. Ramos, J. L. Serrano,
J. Vaciana, Adv. Mater. 1998, 10, 1001; j) J. J. L. M. Cornelissen, M.
Fischer, N. A. Sommerdijk, R. J. M. Nolte, Science 1998, 280, 1427;
k) R. J. M. Nolte, Chem. Soc. Rev. 1994, 23, 11; l) D. B. Amabilino,
E. Ramos, J. L. Serrano, T. Sierra, J. Veciana, J. Am. Chem. Soc.
1998, 120, 9126; m) Y. Q. Tian, Y. Li, T. Iyoda, J. Polym. Sci. A
2003, 41, 1871.
Conversion ¼ Apolymer=ðApolymer þ Amonomer
Þ
ð1Þ
After the solution was heated under refluxing for 22 h, the conversion
was determined to be 92%. The solution was cooled down to room tem-
perature and then the THF was removed under vacuum. The residue was
purified by preparative GPC with CHCl3 as eluent in order to remove
the trace amount of nonpolymerized monomer to afford pure pale yellow
ꢀ
ꢀ
polymer. Yield: 77% (430 mg); FT-IR (KBr pellet): n˜ =2080 ( CꢁC in
the main-chain), 1718 (C=O ester in the side-group), 1653 cmꢀ1 ( N=C=
ꢀ
in the backbone).
[Eq. (2)].
M
n,GPC =23200, Mw/Mn =1.06.
M
n,calcd =102800
[5] C. A. van Walree, J. F. van der Pol, J. W. Zwikker, Recl. Trav. Chim.
Pays-Bas 1990, 109, 561.
Mn,calcd ¼ ½MŠ0=½IŠ0  conversion  1108 þ 869
ð2Þ
[6] a) V. S. K. Balagurusamy, G. Ungar, V. Percec, G. Johansson, J. Am.
Chem. Soc. 1997, 119, 1539, and references therein; b) V. Percec,
W.-D. Cho, G. Ungar, D. J. P. Yeardley, J. Am. Chem. Soc. 2001, 123,
1302; c) V. Percec, B. Barboiu, C. Grigoras, T. K. Bera, J. Am.
Chem. Soc. 2003, 125, 6503; d) V. Percec, G. Johansson, J. Heck, G.
Ungar, S. V. Batty, J. Chem. Soc. Perkin Trans. 1 1993, 1411; e) V.
Percec, J. Heck, D. Tomazos, F. Falkenberg, H. Blackwell, G. Ungar,
J. Chem. Soc. Perkin Trans. 1 1993, 2799.
In Equation (2) 1108 and 869 are the molecular weights of the monomer
and initiator, respectively; the [M]0/[I]0 is the feed ratio of the monomer
to initiator. Elemental analysis calcd (%) for Mn,calcd =102800: C 77.48, H
9.06, N 1.25; found: C 77.12, H 9.35, N 1.01.
[7] a) K. Onitsuka, T. Joh, S. Takahashi, Angew. Chem. 1992, 104, 893;
Angew. Chem. Int. Ed. Eng. 1992, 31, 851; b) K. Onitsuka, F. Yanai,
T. Takei, T. Joh, S. Takahashi, Angew. Chem. 1996, 108, 1634;
Angew. Chem. Int. Ed. Eng. 1996, 35, 1554.
[8] a) G. Ungar, V. Percec, M. N. Holerca, G. Johansson, J. A. Heck,
Chem. Eur. J. 2000, 6, 1258; b) V. Percec, W. D. Cho, G. Ungar,
D. J. P. Yeardley, Angew. Chem. 2000, 112, 1661; Angew. Chem. Int.
Ed. 2000, 39, 1598, and references there in; c) V. Percec, D. Schluet-
er, G. Ungar, S. Z. D. Cheng, A. Zhang, Macromolecules 1998, 31,
1745.
Acknowledgements
This work was partially supported by a Grant-in-Aid from the Ministry
of Education, Culture, Sports, Science, and Technology (MEXT) of the
Japanese Government. We thank Prof. Shigetoshi Takahashi, Prof. Kiyo-
taka Onitsuka, and Dr. Fumie Takei in Osaka University for their kind
supply of the Pd–Pt dinuclear complex. Y.-Q.T. thanks Japan Society for
the Promotion Science for a Postdoctoral Fellowship and financial sup-
ports from MEXT.
[9] C. Destrade, P. Foucher, H. Gasparoux, H. T. Nguyen, A. M. Leve-
lut, J. Malthete, Mol. Cryst. Liq. Cryst. 1984, 106, 121.
pffiffiffi
[1] a) T. H. Mourey, S. R. Turner, M. Rubinstein, J. M. J. FrØchet, C. J.
Hawker, K. L. Wooley, Macromolecules 1992, 25, 2401; b) L. J. Shu,
A. Schäfer, A. D. Schlüter, Macromolecules 2000, 33, 4321; c) G. M.
Stewart, M. A. Fox, Chem. Mater. 1998, 10, 860; d) V. Percec, C. H.
Ann, W. D. Cho, A. M. Jamieson, J. Kim, T. Leman, M. Schmidt, M.
Gerle, M. Moller, S. A. Prokhorova, S. S. Sheiko, S. Z. D. Cheng, A.
Zhang, G. Ungar, D. J. P. Yeardley, J. Am. Chem. Soc. 1998, 120,
8619; e) V. Percec, D. Schlueter, Macromolecules 1997, 30, 5783;
f) V. Percec, C. H. Ann, B. Barboiu, J. Am. Chem. Soc. 1997, 119,
12978; g) Z. S. Bo, A. D. Schlüter, Chem. Eur. J. 2000, 6, 3235;
h) A. D. Schlüter, P. R. Jürgen, Angew. Chem. 2000, 112, 860;
Angew. Chem. Int. Ed. 2000, 39, 864, and references therein; i) V,
Percec, M. Glodde, T. K. Bera, Y. Miura, I. Shiyanovskaya, K. D.
Singer, V. S. K. Balagurusamy, P. A. Heiney, I. Schnell, A. Rapp,
H. W. Spiess, S. D. Husdon, H. Duan, Nature 2002, 419, 384; j) V.
Percec, C. H. Ann, G. Unger, D. J. P. Yeardley, M. Moller, S. S.
Sheiko, Nature 1998 391, 161; k) V. Percec, A. E. Dulcey, V. S. K.
Balagurusamy, Y. Miura, J. Smidrkal, M. Peterca, S. Nummelin, U.
[10] Hexagonal columnar lattice parameter a=2hd100i/ 3, in which,
pffiffiffi
pffiffi
hd100i=(d100
+
3d110
+
42d200)/3.
pffiffi
[11] Cubic lattice parameter a=hd200i, in which hd200i=(d200
pffiffiffi pffiffiffiffiffi
+
5d210 +
6d211 13d320)/4.
+
[12] Spectrometic Identification of Organic Compounds (Eds.: R. M. Sil-
verstein, F. X. Webster), Wiley, 6th ed., 1997, p. 101.
[13] a) S. A. Prokhorova, S. S. Sheiko, M. Moller, C. H. Ann, V. Percec,
Macromol. Rapid Commun. 1998, 19, 359; b) S. A. Prokhorova, S. S.
Sheiko, C. H. Ann, V. Percec, M. Moller, Macromolecules 1999, 32,
2654; c) W. Stocker, B. L. Schürmann, J. P. Rabe, S. Fçrster, P. Lind-
ner, I. Neubert, A. D. Schlüter, Adv. Mater. 1998, 10, 793.
[14] S. Takahashi, Y. Ohyama, E. Murata, K. Sonogashira, N. Hagihara,
J. Polym. Sci. Polym. Chem. Ed. 1980, 18, 349.
Received: July 22, 2005
Published online: September 27, 2005
Chem. Eur. J. 2006, 12, 584 – 591
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
591