Spherical supramolecular minidendrimers self-organized in an 'inverse micellar'-like thermotropic body-centered cubic liquid crystalline phase

Article abstract of DOI:10.1021/ja993915q

An 'inverse micellar'- or 'water-in-oil'-like (similar to the lyotropic type I(II) thermotropic body-centered cubic (BCC) liquid crystal (LC) phase was discovered in a poly(ethyleneimine) with a degree of polymerization (DP) = 20 containing 3,4,5-tri(dode

Full text of DOI:10.1021/ja993915q

1684
J. Am. Chem. Soc. 2000, 122, 1684-1689
Spherical Supramolecular Minidendrimers Self-Organized in an
“Inverse Micellar”-like Thermotropic Body-Centered Cubic Liquid
Crystalline Phase
Duncan J. P. Yeardley,† Goran Ungar,*,† Virgil Percec,*,‡ Marian N. Holerca,‡ and
Gary Johansson‡
Contribution from the Department of Engineering Materials and Center for Molecular Materials,
UniVersity of Sheffield, Sheffield S1 3JD, U.K., and Roy & Diana Vagelos Laboratories, Department of
Chemistry, UniVersity of PennsylVania, Philadelphia, PennsylVania 19104-6323
ReceiVed NoVember 4, 1999
Abstract: An “inverse micellar”- or “water-in-oil”-like (similar to the lyotropic type III) thermotropic body-
centered cubic (BCC) liquid crystal (LC) phase was discovered in a poly(ethyleneimine) with a degree of
polymerization (DP) ) 20 containing 3,4,5-tri(dodecyloxy)benzoyl minidendritic side groups. Fiber X-ray
diffraction (XRD) experiments show that the extinction symbol of this phase is I- - - and, alongside other
evidence, suggested that the space group is Im3hm (Q229). These results point to a supramolecular inverse micellar-
like structure with the polymer backbone and the benzoyl groups aggregated into globules located at the corners
and the center of the unit cell. The n-alkyl groups radiate out of the aromatic part of the globule and make up
the continuos matrix of the lattice. The cubic unit cell parameter is a ) 42.6 Å. Upon shearing, the BCC phase
aligns along the [111] direction. The BCC lyotropic Im3hm inverse micellar phase of III type has not yet been
observed and the experiments reported here will access its design. The present is only the second “inverse
micellar” thermotropic LC phase known. The first one was previously reported from our laboratories
(Balagurusamy, V. S. K.; Ungar, G.; Percec, V.; Johansson, G. J. Am. Chem. Soc. 1997, 119, 1539) and has
a Pm3hn symmetry. Both the Im3hm and the Pm3hn cubic lattices were self-organized from spherical supramolecular
dendrimers. The BCC cubic LC lattice reported here enriches the synthetic capabilities of dendritic building
blocks.
Introduction
Scheme 1. Fan-Shaped and Cone-Shaped Monodendronsa
Dendritic building blocks provide some of the most powerful
synthetic tools for the design and construction of complex
molecular, macromolecular, and supramolecular systems.1 Pre-
vious publications from our laboratories have reported the design
and synthesis of tapered and conical monodendrons which self-
assemble into cylindrical and spherical supramolecular den-
drimers. These supramolecular object-like dendrimers self-
organize in 2-D hexagonal columnar p6mm2,3 and 3-D cubic
Pm3hn,4,5,6 thermotropic liquid crystalline (LC) phases (Scheme
1). Recently, a hexagonal columnar LC superlattice was reported
for a mixture of supramolecular/macromolecular minidendritic
systems.7 These latter experiments have also demonstrated the
synthetic capabilities of minidendrons as models for higher
generations of dendrons.7,8 The analysis of these lattices and
superlattices by X-ray diffraction experiments allows the
† University of Sheffield.
‡ University of Pennsylvania.
(1) For recent reviews on dendritic building blocks see: (a) Fre´chet, J.
M. J. Science 1994, 263, 1710. (b) Newcome, G. R.; Moorefield C, N.;
Vogtle, F. Dendritic Molecules; VCH: Weinheim, 1996. (c) Moore, J. S.
Acc. Chem. Res. 1997, 30, 402. (d) Tomalia, D. A.; Esfand, R. Chem. Ind.
1997, 416. (e) Smith, D. K.; Diederich, F. Chem. Eur. J. 1998, 4, 1353. (f)
Frey, H. Angew. Chem., Int. Ed. Engl. 1998, 37, 2193. (g) Vo¨gtle, F., Ed.
Dendrimers; Topics Curr. Chem. Vol. 197; Springer, Berlin, 1998. (h)
Mathews, O. A.; Shipway, A. N.; Stoddart, F. J. Prog. Polym. Sci. 1998,
23, 1. (i) Fischer, M.; Vo¨gtle, F. Angew. Chem., Int. Ed. Engl. 1999, 38,
884. (j) Bosman, A. W.; Janssen H. M.; Meijer, E. W. Chem. ReV. 1999,
99, 1665. (k) Berresheim, A. J.; Mu¨ller, M.; Mu¨llen, K. Chem. ReV. 1999,
99, 1747. (l) Moore, J. S. Curr. Opin. Coll. Int. Sci. 1999, 4, 108. (m)
Roovers, J.; Comanita, B. AdV. Polym. Sci. 1999, 142, 179.
a Fan-shaped dendrons self-assemble into columns which self-
organize in a 2-D p6mm hexagonal columnar LC lattice.2d Cone-shaped
dendrons self-assemble into quasi-spherical globules which in turn pack
in a Pm3hn 3-D LC cubic lattice4,5a
determination of the shape and size of dendrimers2-7 and
provides access to the rational design and synthesis of functional
dendritic building blocks which are required for the construction
of giant nanosystems with precise shape, size, and functional
10.1021/ja993915q CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/02/2000

Spherical Supramolecular Minidendrimers
J. Am. Chem. Soc., Vol. 122, No. 8, 2000 1685
Scheme 2. Synthesis and Polymerization of
2-[3,4,5-Tris(n-alkan-1-yloxy)phenyl]-2-oxazoline
(t12-APOX)
properties in the bulk state.9 These LC lattices are actively
exploited for rational design both in our and in other
laboratories.2-8
The goal of this publication is to report that spherical
supramolecular dendrimers also self-organize into a second
“inverse micellar”-like thermotropic cubic phase of Im3hm space
group. Both this phase and its analogue from lyotropic systems,
a body-centered inverse micellar cubic phase (“water-in-oil”,
type III), have not actually been observed. However, the lyotropic
“oil-in-water” (type II) analogue is known.10
Results and Discussion
We have selected a poly(ethyleneimine) with degree of
polymerization 20 (DP ) 20) containing 3,4,5-tri(dodecyloxy)-
(2) For selected references on cylindrical supramolecular dendrimers self-
organized in hexagonal columnar LC lattices see: (a) Percec, V.; Johansson,
G.; Heck, J.; Ungar, G.; Batty, S. V. J. Chem. Soc., Perkin Trans. 1 1993,
1411. (b) Johansson, G.; Percec, V.; Ungar, G.; Abramic, D. J. Chem. Soc.,
Perkin Trans. 1 1994, 447. (c) Stebani, U.; Lattermann, G. AdV. Mat. 1995,
7, 578. (d) Percec, V.; Johansson, G.; Ungar, G.; Zhou, J. J. Am. Chem.
Soc. 1996, 118, 9855. (e) Pesak, D.; Moore, J. S. Angew. Chem., Int. Ed.
Engl. 1997, 36, 1636. (f) Suarez, M.; Lehn, J.-M.; Zimmerman, S. C.;
Skoulios, A.; Heinrich, B. J. Am. Chem. Soc. 1998, 120, 9526. (g) Meier,
H.; Lehmann, M. Angew. Chem., Int. Ed. Engl. 1998, 37, 643. (h) Percec,
V.; Cho, W.-D.; Mosier, P. E.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem.
Soc. 1998, 120, 11061. (i) Brewis, M.; Clarkson, G. J.; Holder, A. M.;
McKeon, N. B. Chem. Commun. 1998, 969.
(3) For selected references on cylindrical macromolecular dendrimers
self-organized in hexagonal columnar LC lattices see: (a) Percec, V.; Heck.;
J.; Lee, M.; Ungar, G.; Castillo, A. A. J. Mater. Chem. 1992, 2, 1033. (b)
Percec, V.; Heck, J.; Tomazos, D.; Falkenberg, F.; Blackwell, H.; Ungar,
G. J. Chem. Soc., Perkin Trans. 1 1993, 2799. (c) Percec, V.; Heck, J. A.;
Tomazos, D.; Ungar, G. J. Chem. Soc., Perkin Trans. 2 1993, 2381. (d)
Percec, V.; Tomazos, D.; Heck, J.; Blackwell, H.; Ungar, G. J. Chem. Soc.,
Perkin Trans. 2 1994, 31. (e) Percec, V.; Schlueter, D.; Kwon, Y. K.;
Blackwell, J.; Moller, M.; Slangen, P. J. Macromolecules 1995, 28, 8807.
(f) Johansson, G.; Percec, V.; Ungar, G.; Zhou, J. P. Macromolecules 1996,
29, 646. (g) Percec, V.; Schlueter, D.; Ronda, J. C.; Johansson, G.; Ungar,
G.; Zhou, J. P. Macromolecules 1996, 29, 1464. (h) Percec, V.; Schlueter,
D. Macromolecules 1997, 30, 5783. (i) Percec, V.; Ahn, C.-H.; Cho, W.-
D.; Jamieson, A. M.; Kim, J.; Leman, T.; Schmidt, M.; Gerle, M.; Moller,
M.; Prokhorova, S. A.; Sheiko, S. S.; Cheng, S. Z. D.; Zhang, A.; Ungar,
G.; Yeardley, D. J. P. J. Am. Chem. Soc. 1998, 120, 8619. (j) Prokhorova,
S. A.; Sheiko, S. S.; Moller, M.; Ahn, C.-H.; Percec, V. Macromol. Rapid
Commun. 1998, 19, 359. (k) Percec, V.; Schlueter, D.; Ungar, G.; Cheng,
S. Z. D.; Zhang, A. Macromolecules 1998, 31, 1745. (l) Prokhorova, S.
A.; Sheiko, S. S.; Ahn, C.-H.; Percec, V.; Moller, M. Macromolecules 1999,
32, 2653.
(4) For spherical supramolecular dendrimers self-organized in a Pm3hn
cubic LC lattice see: Balagurusamy, V. S. K.; Ungar, G.; Percec, V.;
Johansson, G. J. Am. Chem. Soc. 1997, 119, 1539.
(5) For macromolecular dendrimers that change their shape from spherical
to cylindrical by increasing their degree of polymerization see: (a) Percec,
V.; Ahn, C.-H.; Ungar, G.; Yeardley, D. J. P.; Moller, M.; Sheiko, S. S.
Nature 1998, 391, 161. (b) Yin, R.; Zhu, Y.; Tomalia, D. A. J. Am. Chem.
Soc. 1998, 120, 2678.
(6) For cylindrical and spherical supramolecular dendrimers that change
their shapes as a function of generation number see: (a) Hudson, S. D.;
Jung, H.-T.; Percec, V.; Cho, W.-D.; Johansson, G.; Ungar, G.; Balaguru-
samy, V. S. K. Science 1997, 278, 449. (b) Percec, V.; Cho, W.-D.; Mosier,
P. E.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem. Soc. 1998, 120, 11061.
(7) For the co-assembly of a hexagonal columnar LC superlattice and
the demonstration of the synthetic capabilities of minidendritic building
blocks see: Percec, V.; Ahn, C.-H.; Bera, T. K.; Ungar, G.; Yeardley, D.
J. P. Chem. Eur. J. 1999, 5, 1070.
benzoyl minidendritic side groups [poly(t12-APOX)] to dem-
onstrate this cubic LC phase. The present cubic phase has been
observed in a large number of supramolecular dendrimers.
However, we have decided to use this polymer for structural
characterization because of its ability to align. The synthesis of
the cyclic imino ether monomer and its living cationic ring-
opening polymerization are outlined in Scheme 2. Oligo- and
poly(ethyleneimine) with minidendritic side groups were in-
vestigated simultaneously in several different laboratories.11
Most of them exhibit a hexagonal columnar LC phase.
The differential scanning calorimetry trace of poly(t12-
APOX) (Figure 1) shows two endothermic transitions on
heating: one at -12 °C (∆H ) 19.5 J/g), into the thermotropic
LC phase, and another at 131 °C (∆H ) 1.7 J/g), into the
isotropic liquid. On cooling the reverse sequence of transitions
occurs, with a small hysteresis (exothermic peaks at 122 and
-16 °C). Thermal optical polarized microscopy of poly(t12-
(8) For additional examples of LCs generated with the aid of miniden-
drons see: (a) Zheng, H.; Swager, T. M. J. Am. Chem. Soc. 1994, 116, 77.
(b) van Nunen, J. L. M.; Folmer, B. F. B.; Nolte, R. J. M. J. Am. Chem.
Soc. 1997, 119, 283. (c) Tschierske, C. J. J. Mat. Chem. 1998, 8, 1485. (d)
Pegenan, A.; Cheng, X. H.; Tschierske, C.; Goring, P.; Diele, S. New J.
Chem. 1999, 23, 465.
(9) (a) Jiang, D.-L.; Aida, T. Nature 1997, 388, 454. (b) Sooklal, K.;
Hanus, L. H.; Ploehn, H. J.; Murphy, C. J. AdV. Mat. 1998, 10, 1083. (c)
Zhao, M.; Sun, Z. L.; Crooks, R. M. J. Am. Chem. Soc. 1998, 120, 4877.
(d) Balogh, L.; Tomalia, D. A. J. Am. Chem. Soc. 1998, 120, 4877. (e)
Kawa, M.; Fre´chet, J. M. J. Chem. Mater. 1998, 10, 286. (f) Bao, Z.;
Amundson, K. R.; Lovinger, A. J. Macromolecules 1998, 31, 8647.
(10) Gulik, A.; Delacroix, H.; Kirschner, G.; Luzzati, V. J. Phys. II
(France) 1995, 5, 445.
(11) (a) Fischer, H.; Ghosh, S. S.; Heiney, P. A.; Maliszewskyj, N. C.;
Plesnivy, T.; Ringsdorf, H.; Seitz, M. Angew. Chem., Int. Ed. Engl. 1995,
34, 795. (b) Fischer, H.; Plesnivy, T.; Ringsdorf, H.; Seitz, M. J. Chem.
Soc., Chem. Commun. 1995, 1615. (c) Stebani, U.; Latterman, G.; Festag,
R.; Wittemberg, M.; Wendorff, J. H. J. Mater. Chem. 1995, 5, 2247. (d)
Stebani, U.; Latterman, G. AdV. Mat. 1995, 7, 578. (e) Seitz, M.; Plesnivy,
T.; Schimossek, K.; Edelmann, M.; Ringsdorf, H.; Fischer, H.; Uyama, H.;
Kobayashi, S. Macromolecules 1996, 29, 6560. (f) Ungar, G.; Abramic,
D.; Percec, V.; Heck, J. A. Liq. Cryst. 1996, 21, 73. (g) Johansson, G.
Ph.D. Thesis Case Western Reserve University, Cleveland, OH, August
1996. (h) Percec, V.; Johansson, G.; Schlueter, D.; Ronda, J. C.; Ungar, G.
Macromol. Symp. 1996, 101, 43. (i) Stebani, U.; Latterman, G.; Wittemberg,
M.; Wendorff, J. H. Angew. Chem., Int. Ed. Engl. 1996, 35, 1858. (j) Fischer,
H.; Plesnivy, T.; Ringsdorf, H.; Seitz, M. J. Mater. Chem. 1998, 8, 343.

1686 J. Am. Chem. Soc., Vol. 122, No. 8, 2000
Yeardley et al.
Table 1. Interplanar Spacings for XRD Reflections Observed for
the Cubic LC Phase of
Poly{N-[3,4,5-tris(n-dodecan-1-yloxy)benzoyl]ethyleneimine} with
DP ) 20
h2+k2+l2
dobs/Å
a/Åa
Iobs
b
hkl
110
200
211
220
310
222
321
400
411
420
332
431
2
4
6
30.3
21.5
17.4
15.1
13.5
12.4
11.4
10.6
10.0
9.4
42.9
42.9
42.7
42.8
42.7
42.8
42.5
42.4
42.4
42.1
42.4
42.6
vs
s
m
m
w
w
w
8
10
12
14
16
18
20
22
24
w
vw
vw
w
Figure 1. DSC thermograms of poly(t12-APOX) with DP ) 20 at
10deg C per min.
9.0
8.7
vw
a Average value of unit cell parameter, a ) 42.6 Å. b vs ) extremely
strong, s ) strong, m ) moderate, w ) weak, vw ) extremely weak.
pattern (Figure 2). This showed that only reflections obeying
the conditions 0kl:k + l ) 2n, hhl:l ) 2n, and h00:h ) 2n
were present. The limited number of reflections shown in Figure
2 are not sufficient to discriminate between primitive and body-
centered cubic (BCC) lattices, more precisely between the Pn-n
and I--- extinction groups, respectively. The two differ by the
reflection condition hkl:h + k + l ) 2n , obeyed by the BCC
lattice. The first set of reflections on which this condition can
be tested is {421}. Diffraction patterns were recorded with long
exposures and the full list of observed reflections is given in
Table 1. {421} reflections are not observed, hence the assign-
ment of extinction symbol I- - - could be made. The I- - -
extinction group contains the space groups Im3hm, I4h3m, I432,
Im3h, I23, and I213, which cannot be separated by extinctions
alone. Since the Laue class could not be determined from the
fiber pattern, all of the above space groups are theoretically
possible. However, the following consideration makes it most
unlikely that the current cubic LC phase belongs to anything
but the highest symmetry space group Im3hm. The argument
below also points to the structure and molecular organization
in the present cubic mesophase.
(a) The nature of the disorder in LCs favors molecular
aggregation of highest symmetry. With only one exception (P43-
32, in a ternary lyotropic system),12 all cubic LCs were found
to belong to the m3hm point group. When applied to the I- - -
extinction group, this singles out the space group Im3hm.
(b) The taper angle of the tri(dodecyloxy) benzoyl miniden-
dritic group used here is too high or just acceptable, at the high
end of the range, for accommodation into infinite columns.
Results to be reported soon from our laboratories have shown
that in fact in most cases this building block is capable of self-
assembly in spheres forming the Pm3hn cubic phase. The Pm3hn
phase is of the “inverse micellar”-type (type III in lyotropics)
rather than bicontinuous (type V). The latter forms when the
interface curvature (in our case the equivalent is the molecular
taper angle) is too low to allow the formation of the columnar
phase. A “micellar” phase implies the existence of insular
regions of one phase in the continuum of the other. In the
thermotropic Pm3hn the two microseparated subphases were
made up of aromatic dendritic cores and the aliphatic end-chains,
respectively.1a,4 Since the same tapered minidendron, which
previously gave rise to the Pm3hn phase,4 is used here as the
polymer side group, it is most likely that the current cubic phase
is also of the “inverse micellar” type. This inference is further
Figure 2. Low-angle X-ray fiber diffraction pattern of poly(t12-
APOX) in the cubic phase at room temperature with an overlay of the
calculated reflection positions. The inner area including {111} reflec-
tions is attenuated 100 times. The fiber axis is vertical and the preferred
orientation is [111].
APOX) at room temperature shows the thermotropic mesophase
to be optically isotropic. On heating, the optically isotropic
texture persists in the isotropic phase. It is apparent, however,
that there is a reduction in viscosity above the isotropization
temperature. The optical isotropy and high viscosity of the
mesophase indicates that the LC phase is most probably cubic.
The crystalline phase formed below -12 °C was not analyzed
by XRD.
In the wide-angle region of the X-ray diffraction pattern only
a diffuse halo is observed at room temperature and above. The
small-angle X-ray scattering (SAXS) fiber pattern of the partially
aligned LC phase is shown in Figure 2. Only the central region
is presented. The first group of reflections, arranged nearly
hexagonally, are 2 orders of magnitude stronger than the next
reflections. To compensate for this, the inner area of Figure 2
is attenuated by a factor of about 100. The diffraction arcs are
arranged in rings with reciprocal spacings in the ratio 1:x2:
x3:x4:x5 etc. (see also Table 1). The innermost reflections
are consistent with a fiber sample of cubic crystals with [111]
direction parallel to the fiber axis. With the first and strongest
reflections indexed as {110}, indexing of the remaining reflec-
tions was consistent with the overlaid calculated diffraction
(12) Mariani, P.; Luzzati, V.; Delacroix, H. J. Mol. Biol. 1998, 204, 165-
189.

Spherical Supramolecular Minidendrimers
J. Am. Chem. Soc., Vol. 122, No. 8, 2000 1687
types VII and VI, respectively. The other subphase is confined
to a pair of independent interpenetrating tubular networks. In
the case of inverse (VII) phases the buckled minimum surfaces
of zero mean curvature allow bilayers to have their outer surface
area slightly larger than the inner surface area. Bicontinuous
phases appear in lyotropic systems close to the lamellar phase.
In thermotropic compounds IPMS structures are likely when
molecules have a small taper angle.
In the case of Im3hm symmetry the bicontinuous type is
referred to as “plumber’s nightmare”.14 If we were to describe
our phase in terms of an IPMS model, there would be two
options: the IPMS is defined either by the methyl groups at
the ends of the alkyl chains (inverse cubic, VII) or by the
polymer backbone (normal cubic, VI). The analogy with the
lyotropic classification is based here on water being replaced
by the poly(ethyleneimine)/aromatic subphase. If the polymer
backbones were located at the minimum surface, alkyl chains
Figure 3. (a) Schematic representation of a unit cell of the “inverse
micellar” (type III) Im3hm (BCC) LC lattice. Spheres represent the
preferred locations of aromatic groups and polymer backbones. The
interstitial space is filled with aliphatic chains. The volume fraction of
the spheres (22.5%, drawn to scale) is equal to the “aromatic” fraction
of the van der Waals volume. (b) Schematic drawing of the “bicon-
tinuous” (tube model) and “inverse micellar” variants of the Im3hm cubic
LC lattice. The latter structure is obtained from the former by closing
off the connecting channels.
1
would have to converge to singularities at 0,0,0 and /2,1/2,1/2.
This is contrary to the geometry of the tapered monodendritic
group with three divergent alkyl chains. On the other hand, the
first option, whereby the methyl groups are near the IPMS, is
compatible with molecular geometry.
The distinction between “bicontinuous” and “micellar” Im3hm
phases is illustrated in Figure 3b. For clarity the tube model is
used to represent schematically the bicontinuous phase. The
minimum surface is not drawn. Referring to the inverse phases,
water or polymer backbones are confined to the tubes in the
bicontinuous cubic phase, and to isolated spheres in the case of
the micellar phase. In the lyotropic case, the main parameter
determining whether the phase is bicontinuous or micellar is
the volume fraction of water. In the case of thermotropic systems
such as ours, in addition to the aromatic volume fraction there
are other dominant parameters of molecular architecture at play,
such as the number and type of pendant chains, structure of the
dendritic core, degree of polymerization in the case of polymers,
etc. The bicontinuous thermotropic LC phase of Im3hm symmetry
is known.15 It involves molecules with very small taper that
are liable to form bilayers.
The inverse lyotropic micellar Im3hm phase (“water-in-oil”,
type III) has not been reported so far, whereas the normal
micellar one (type II) has.10 Only one type of inverse micellar
(type III) cubic phase, with Fd3hm symmetry, has been found so
far in lyotropic systems.16,17
The field of block copolymers has also contributed to the
discovery of phase separated cubic morphologies.18 A “micellar”
type Im3hm phase was first shown by electron microscopy in a
triblock copolymer19 and later by neutron scattering in a diblock
reinforced by the fact that in a number of instances this tapered
minidendron exhibits the present body-centered cubic phase in
addition to the Pm3hn.4
(c) 96% of the Lorentz-corrected Bragg diffraction intensity
is accommodated in the {110} reflections. Consequently, if the
structure factors for all {110} reflections were the same, as is
the case for Im3hm space group, electron density distribution is
dominated by smooth, nearly spherical maxima (or minima) at
positions 000 and 1/2,1/2,1/2 (site symmetry m3hm). These special
positions would be the centers of the insular domains (“mi-
celles”) of the minority subphase which, as in the Pm3hn form
of related compounds, is “aromatic”. Including the oxygens,
the poly(ethyleneimine) backbone, and the triflate anion, the
“aromatic” subphase in poly(t12-APOX) constitutes 22.5% of
the total van der Waals volume. It follows from the above that
the most likely structure of the present cubic phase is the one
with Im3hm (Q229) symmetry shown schematically in Figure 3a.
The spheres at the corners and at the center of the unit cell are
representative of the poly(ethyleneimine)/aromatic cores of the
“inverse micelles”, with the interstitial continuum filled by the
aliphatic side chains in a 22.5%:77.5% volume ratio.
The relationship between the unit cell parameter (a ) 42.6
Å) and molecular dimensions is not inconsistent with the
structure in Figure 3a. Considering that the length of a fully
extended side-group monomer repeat unit is ∼25 Å, we find
that every part of the unit cell is accessible. The furthest an
alkyl chain on a monomer repeat unit anchored at the center of
a “micelle” (0,0,0) must reach is position 0,1/2,1/4 or equivalent
(four per face). These positions are at a distance of 23.8 Å from
the origin, hence are just reachable by extended dodecyl chains.
The distance from the origin to the point closest to a neighboring
“micelle” is 18.4 Å.
(14) Seddon, J.; Temple, R. New Scientist 1991, 130, 45.
(15) For a recent review on thermotropic cubic phases see: (a) Diele,
S.; Go¨ring, P. In Handbook of Liquid Crystals; Demus, D., Goodby, J.,
Gray, G. W., Spiess, H.-W., Vill, V., Eds.; Wiley-VCH: Weinheim, 1998;
Vol. 2B, pp 887-900. For several examples of thermotropic bicontinuous
cubic LC phase of Im3hm symmetry see: (b) Levelut, A. M.; Fang, Y. J.
Phys. Colloq. France 1990, 51, Suppl. C7229. (c) Kutzumizu, S.; Ichikawa,
T.; Nojima, S.; Yano, S. Chem. Commun. 1999, 1181.
(16) Luzzati, V.; Vargas, V.; Gulik, A.; Mariani, P.; Seddon, R. M.;
Rivas, E. Biochemistry 1992, 31, 279.
(17) Seddon, J. M.; Zeb, N.; Templer, R. H.; McElhaney, R. N.;
Mannock, D. A. Langmuir 1996, 12, 5250.
To set the present results in context, in the following we
briefly discuss the different possible Im3hm cubic structures. As
already noted, there are in general two types of cubic LCs: the
“micellar” II (normal micellar) and III (inverse micellar) type,
with III being equivalent to the currently proposed structure,
and the “bicontinuous” (V) type.13 The latter occurs in lyotropic
systems where either aliphatic bilayers or water subphase follow
one of three infinite periodic minimum surfaces (IPMS), phase
(18) For several representative publications on complex phase behavior
in block copolymers see, for example: (a) Bates, F. S. Science 1991, 25,
898. (b) Hillmyer, M. A.; Bates, F. S.; Almdal, K.; Mortensen, K.; Ryan,
A. J.; Fairclough, J. P.A Science 1996, 271, 976. (c) Fredrikson, G. H.;
Bates F. S. Annu. ReV. Mater. Sci. 1996, 26, 501. (d) Thomas, E. L.;
Anderson, D. M.; Henkee, C. S.; Hoffman, D. Nature 1988, 334, 598. (e)
Shefelbine, T. A.; Vigild, M. E.; Matsen, M. W.; Hajduk, D. A.; Hillmyer,
M. A.; Cussler, E. L.; Bates, F. S. J. Am. Chem. Soc. 1999, 121, 8457.
(19) Pedemonte, E.; Turturro, A.; Bianchi, U.; Devetta, P. Polymer 1973,
14, 145.
(13) Seddon, J. M. Biochem. Biophis. Acta 1990, 1031, 1-69.

1688 J. Am. Chem. Soc., Vol. 122, No. 8, 2000
Yeardley et al.
compound.20 However, although the “micellar”-type Im3hm phase
from block copolymers is considered from the symmetry point
of view similar to the thermotropic Im3hm LC phase, it cannot
be differentiated into “inverse” (type III) and “normal” (type II)
“micellar”, as is possible in the case of lyotropic LCs and of
the LC phase reported here.
Returning to the present system, there are 3.2 poly(t12-
APOX) macromolecules with Mw/Mn ) 1.11 per unit cell, or
1.6 per “micelle”, for an experimental density of 0.95 g/cm3.
However, this density was obtained from a sample that was
not annealed to perfect crystallinity and consequently it is lower
than that of the highly ordered lattice sampled by XRD.
Therefore, it would appear that in most cases two macromol-
ecules self-assemble into a spherical object. By analogy with
the spherical polymers containing dendritic side groups which
self-organize in a Pm3hn cubic phase,5a in the present case the
polymer backbones are also believed to be coiled within the
interior of the “micelle”.
was used as solvent and TMS as internal standard unless otherwise
noted. Chemical shifts are reported as δ, ppm. The purity of products
was determined by a combination of techniques including thin-layer
chromatography (TLC) on silica gel plates (Kodak) with fluorescent
indicator and high-pressure liquid chromatography (HPLC). HPLC
measurements were carried out by using a Perkin-Elmer Series 10 high-
pressure liquid chromatograph equipped with an LC-100 column oven,
Nelson Analytical 900 Series integrator data station, and two Perkin-
Elmer PL gel columns of 5 × 102 and 1 × 104 Å. THF was used as
solvent at the oven temperature of 40 °C. Detection was by UV
absorbance at 254 nm. Weight average (Mw) and number average (Mn)
molecular weights were determined with the same instrument and a
calibration plot constructed from polystyrene standards. Mn was also
determined from the 1H NMR analysis of the polymer chain ends.
Thermal transitions of samples that were freeze-dried from benzene
were measured on a Perkin-Elmer DSC-7 differential scanning calo-
rimeter (DSC). In all cases, the heating and cooling rates were 10 °C
min-1 unless otherwise noted. First-order transition temperatures were
reported as the maxima and minima of their endothermic and
exothermic peaks. Glass transition temperatures (Tg) were read at the
middle of the change in heat capacity. Indium and zinc were used as
calibration standards. An Olympus BX-40 optical polarized microscope
(100× magnification) equipped with a Mettler FP 82 hot stage and a
Mettler FP 80 central processor was used to verify thermal transitions
and characterize anisotropic textures.
X-ray diffraction (XRD) experiments were performed using an Image
Plate area detector (MAR Research) with a graphite-monochromatized
pinhole-collimated Cu KR beam and a helium tent. XRD experiments
were also performed at several small-angle stations of the Synchotron
Radiation Source at Daresbury, UK. A double-focused beam and a
quadrant detector were used. In both cases the sample was held in a
capillary within a custom-build temperature cell controlled to within
(0.1 °C. Capillaries holding the dried samples were sealed under
nitrogen. Elemental analysis was carried out at MHW Laboratories,
Phoenix AZ. Densities (F20) were determined by flotation in gradient
columns at 20 °C.
Conclusions
Poly{N-[3,4,5-tris(n-dodecan-1-yloxy)benzoyl]ethylene-
imine} with DP ) 20 displays an “inverse micellar” (type III-
like) body-centered cubic (BCC) LC phase. A multitude of
evidence indicates that the space group is Im3hm (Q229). Two
macromolecules pair up to form “inverse micellar”-like objects
with globular cores centered at 0,0,0 and 1/2,1/2,1/2 positions and
containing polymer backbones and aromatic groups (Figure 3a).
As in the case of Pm3hn cubic LC lattice discovered previously
in our laboratories,4,5a,6 in the present case the n-alkyl side chains
also radiate out of the aromatic core and make up the continuous
matrix. The globular supramolecular minidendrimer contains
approximately forty 3,4,5-tri(dodecyloxy)benzoyl minidendritic
groups. We have observed the present cubic phase in a large
number of other spherical supramolecular dendrimers. As
expected, the shear alignment of this phase is along the [111]
direction, i.e., the direction of closest packing of “micelles”.
This “inverse micellar” Im3hm thermotropic LC phase expands
our capabilities to design and construct functional nanoobjects
from dendritic building blocks. It also provides synthetic
strategies for the design of the lyotropic Im3hm inverse micellar
cubic phase (type III) that was not yet reported. The results
reported here provide access to the investigation of the similari-
ties and differences between the spherical supramolecular
dendrimers which self-organize in Pm3hn (Scheme 1b) and Im3hm
(Figure 3a) cubic lattices and to the elucidation of the mecha-
nism that determines the selection of one of these two lattices.
Synthesis. 3,4,5-Tris(n-dodecan-1-yloxy)benzoic acid was synthe-
sized as previously reported.2a
3,4,5-Tris(n-dodecane-1-yloxy)benzoyl chloride (2).11f 3,4,5-Tris-
(n-dodecan-1-yloxy)benzoic acid (20.5 g, 30.4 mmol) was suspended
in 250 mL of CH2Cl2 and a catalytic amount of DMF was added. SOCl2
(7.3 g, 60.75 mmol) was added dropwise and the mixture was heated
to reflux for 1.5 h. After cooling to room temperature, the solvent and
the excess of SOCl2 were distilled to yield 20.3 g (99.9%) of a white
1
powder that was used without further purification. H NMR (CDCl3,
δ, ppm, TMS): 0.88 (overlapped t, 9H, CH3), 1.26 (m, 54H, CH3-
(CH2)9), 1.78 (m, 6H, CH2CH2OAr), 4.02 (t, 4H, CH2OAr, 3,5-position,
J ) 6.2 Hz), 4.08 (t, 2H, CH2OAr, 4-position, J ) 6.2 Hz), 7.33 (s,
2H, Ar).
N-[3,4,5-Tris(n-dodecan-1-yloxy)benzoyl]-2-aminoethanol (3).11g
Compound 2 (17.63 g, 25.45 mmol) was dissolved in 400 mL of CH2-
Cl2 and slowly added to ice-cooled ethanolamine (25 mL) under
vigorous stirring. The mixture was stirred at 0 °C for 1 h and then the
temperature was raised to 40 °C for another 4 h. The solution was
poured into a separatory funnel and washed three times with H2O, dried
over MgSO4, and filtered. The solvent was removed by rotary
evaporation and the crude product was recrystallized twice from acetone
at 0 °C to yield 16.08 g (87.6%) of a white powder, mp 68-70 °C.
Purity (HPLC), 99+%; TLC (1:1 hexanes:EtOAc), Rf ) 0.42. 1H NMR
(CDCl3, δ, ppm, TMS): 0.88 (t, 9H, CH3, J ) 6.3 Hz), 1.27-1.65 (m,
54H, CH3(CH2)9), 1.78 (m, 6H, CH2CH2OAr), 2.68 (bs, 1H, OH), 3.62
(q, 2H, CH2OH, J ) 4.5 Hz) 3.83 (t, 2H, NHCH2, J ) 4.8 Hz), 3.99
(overlapped t, 6H, CH2OAr), 6.53 (m, 1H, CONH), 6.97 (s, 2H, Ar).
13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.7 (CH3CH2), 26.1 (CH2-
CH2CH2O), 29.4, 29.6 (CH3CH2CH2(CH2)6), 30.3 (CH2CH2OAr), 31.9
(CH3CH2CH2), 43.0 (NHCH2), 62.5 (CH2OH), 69.3 (CH2OAr, 4-posi-
tion), 73.4 (CH2OAr, 3,5-position), 105.7 (ortho to O), 128.9 (ipso to
CONH), 140.8 (para to CONH), 153.1 (meta to CONH), 168.4
(CONH).
Experimental Section
Materials. Hexanes (Fisher, A.C.S. reagent) was used as received.
THF (Fisher, A.C.S. reagent) was refluxed over sodium ketyl and
freshly distilled before use. CH2Cl2 (Fisher, A. C. S. reagent) was
refluxed over CaH2 and freshly distilled before use. Benzene (Fisher,
ACS reagents) was shaken with concentrated H2SO4, washed twice with
water, dried over MgSO4, and finally distilled over CaH2 or sodium
ketyl, respectively. Dimethylformamide (DMF), KOH, K2CO3, and
NaHCO3 (all Fisher, A.C.S. reagents) were used as received. SOCl2
(97%), 3,4,5-trihydroxybenzoic acid (97%), ethanolamine (EtOH)
(99+%), and LiAlH4 (95+%) (all from Aldrich) were used as received.
1-Bromododecane (98+%) (Lancaster) was used as received. Methyl
trifluoromethanesulfonate (MeOTf) (Fluka, g97%) was freshly distilled
under vacuum before use.
1
General Methods. H NMR (200 MHz) and 13C NMR (50 MHz)
spectra were recorded on a Varian Gemini 200 spectrometer. CDCl3
2-[3,4,5-Tris(n-dodecan-1-yloxy)phenyl]-2-oxazoline (4). 11g Com-
pound 3 (15 g, 21 mmol) and a catalytic amount of DMF were dissolved
(20) Bates, F. S.; Cohen, R. E.; Berney, C. V. Macromolecules 1982,
15, 589.

Spherical Supramolecular Minidendrimers
J. Am. Chem. Soc., Vol. 122, No. 8, 2000 1689
in 250 mL of CH2Cl2 and SOCl2 (15.25 mL, 0.21 mol) was added
dropwise. After 0.5 h, H NMR as well as TLC (1:1 hexanes:EtOAc)
magnetic stirrer was dried at 180 °C overnight and charged with 4
(0.30 g, 0.43 mmol). The monomer was dissolved in 1 mL of benzene
and freeze-dried in the septum-sealed Schlenk tube. After freeze-drying,
the Schlenk tube was flushed with Ar. The initiator MeOTf (3.51 mg,
0.021 mmol) was added under a stream of N2 via a syringe. The Schlenk
tube was immersed in an oil bath that was preheated to 160 °C and
stirred. After 60 min the monomer conversion was higher than 99%
(HPLC). The polymerization was cooled to room temperature and
diluted with 2 mL of CH2Cl2, then the polymer was precipitated in
cold acetone, filtered, dried, redissolved in benzene and freeze-dried.
Yield 92.3%. Mn,th ) 14140, Mn,NMR ) 12050, Mn,GPC ) 9010, Mn/Mw
) 1.11. F20 ) 0.95 g/cm3. 1H NMR (CDCl3, δ, ppm, TMS): 0.88 (m,
CH3), 1.26-2.00 (m, CH3(CH2)11), 2.86-3.5 (br, NCH2CH2N, NCH3),
3.8-4.0 (br, CH2OAr), 6.38-6.82 (br, Ar).
1
analysis indicated complete consumption of 3. The reaction was
neutralized by addition of 400 mL of saturated NaHCO3 solution
accompanied by vigorous stirring of the two-phase system for 1 h. The
organic layer was separated, washed three times with 200 mL of water,
dried over MgSO4, and filtered. The solvent was removed on a rotary
evaporator and the product was recrystallized twice from hexanes at 0
°C to yield 11.54 g (79.9%) of a white solid, mp 50-52 °C. Purity
(HPLC), 99+%; TLC (CH2Cl2), Rf ) 0.30. 1H NMR (CDCl3, δ, ppm,
TMS): 0.88 (t, 9H, CH3, J ) 6.3 Hz), 1.26 (m, 54H, CH3(CH2)9),
1.77 (m, 6H, CH2CH2OAr), 4.00 (t, 6H, CH2OAr, J ) 6.5 Hz), 4.04
(t, 2H, OCH2CH2N, J ) 10.0 Hz), 4.42 (t, 2H, OCH2CH2N, J ) 9.5
Hz), 7.15 (s, 2H, Ar). 13C NMR (CDCl3, δ, ppm): 14.1 (CH3), 22.7
(CH3CH2), 26.1 (CH2CH2CH2OAr), 29.3, 29.6 (CH3CH2CH2(CH2)6),
30.3 (CH2CH2OAr), 31.9 (CH3CH2CH2), 54.9 (NCH2), 67.6 (dCOCH2),
69.1 (CH2OAr, 4-position), 73.4 (CH2OAr, 3,5-position), 106.6 (ortho
to O), 122.4 (ipso to C), 140.9 (para to C), 152.9 (meta to C), 164.6
(C)N). Anal. Calcd for C45H81O4N: C, 77.19, H, 11.66. Found: C,
76.97, H, 11.76.
Acknowledgment. Financial support from the National
Science Foundation (DMR-97-08581) and the Engineering and
Physical Science Research Council (UK) are gratefully ac-
knowledged. We thank Professor S. Z. D. Cheng from Akron
University for the density measurements.
Poly{N-[3,4,5-Tris(n-dDodecan-1-yloxy)benzoyl]ethylene-
imine} [poly(t12-APOX), 5].11g A Schlenk tube equipped with a
JA993915Q