J. Am. Chem. Soc. 2001, 123, 4617-4618
Polymerization of a Phosphonium Diene Amphiphile
4617
in the Regular Hexagonal Phase with Retention of
Mesostructure
Bradford A. Pindzola, Benjamin P. Hoag, and
Douglas L. Gin*
Department of Chemistry, UniVersity of California
Berkeley, California 94720-1460
Figure 1. Schematic of a generic LLC mesogen and an illustration of
some common LLC phases.
ReceiVed December 7, 2000
A promising approach to the design of functional, nanostruc-
tured materials is the polymerization of amphiphilic monomers
in lyotropic liquid crystalline (LLC) phases (Figure 1).1 Previous
work has shown that it is possible to polymerize reactive
amphiphiles in the lamellar (L),1c inverted hexagonal (HII),2-6 and
bicontinuous cubic (QII)3 phases with retention of nanostructure.
These polymerized assemblies have been used as biomembrane
mimetics,1c scaffolds for functional nanocomposites,5-10 catalytic
organic zeolite analogues,11 and media for potential bioencapsu-
lation and controlled-release applications.1b
Polymerization of amphiphiles in the regular hexagonal (HI)
phase would afford ordered arrays of either linear polysoaps or,
with cross-linking, polymer nanofibrils. These ordered polysoaps
and nanofibrils could be useful for nanocomposite synthesis or
as novel mineralization platforms, in much the same way as lipid
microtubules.12-14 Initial work by Luzatti and co-workers em-
ployed a cross-linker to stabilize the phase but afforded network
gels rather than discreet fibrils.2 Additionally, a number of
attempts to homopolymerize amphiphilic monomers in the HI
phase have been made but resulted in either loss of phase or low
degrees of conversion.15-18 Friberg and co-workers observed
complete conversion to the L phase when attempting to polymer-
ize sodium 11-undecenoate in the HI phase.15,16 McGrath reported
radical polymerization of 11-undecenyltrimethylammonium bro-
mide in the HI phase with retention of mesostructure, but the
reaction only proceeded to ca. 40% conversion.14 Shibasaki
reported similar results with salts of 10-undecenoic acid.15
Previous homopolymerization studies in the HI phase all
employed amphiphiles with an unactivated terminal olefin as the
polymerizable moiety, likely contributing to the limited success
of these systems. Herein, we report a new family of LLC
monomers that can be homopolymerized in the HI phase at
ambient temperature with retention of phase mesostructure and
with a degree of polymerization greater than 90%. The soluble
polysoap from homopolymerization can be diluted to an isotropic
solution or desiccated, and it reversibly re-forms the HI phase
upon returning to the original concentration.19 Additionally, the
LLC monomers can be copolymerized with divinylbenzene (DVB)
to generate a cross-linked structure, again with retention of the
nanostructure. These amphiphiles incorporate a polymerizable
hydrocarbon 1,3-diene tail and a phosphonium headgroup.20 The
diene tail is more reactive than a terminal alkyl olefin and is closer
in character to n-alkyl chains than traditional (meth)acrylate and
styrenic groups. Additionally, the larger phosphonium group
should better direct the formation of the HI phase21 and give
enhanced X-ray diffraction contrast22 compared to the corre-
sponding ammonium or carboxylate groups.
Three phosphonium diene mesogens (1a-c) were synthesized
from the corresponding ω-bromoalkyldienes by reaction with
trimethylphosphine in 2-propanol at 85 °C.23 The ω-bromoalkyl-
dienes were prepared from the reaction of a ω-bromoalkanal with
Matteson’s reagent24 and subsequent acid-catalyzed elimination,
as described previously.25 The ω-bromoalkanals were synthesized
by PCC oxidation of the appropriate ω-bromoalkanols.19
Compound 1b demonstrated the best LLC behavior and will
be the focus of this communication.26 A two-component am-
phiphile/water, and three-component amphiphile/water/DVB phase
diagram were prepared for 1b using polarized light microscopy
(PLM) to map the phase boundaries and X-ray diffraction (XRD)
to confirm the identity of each phase region. The two-component
phase diagram of 1b and water exhibits the HI phase from 50 to
75 wt % amphiphile between 25 and 80 °C. Additionally, 1b
exhibits a QII phase from 75 to 85 wt % amphiphile at 37-75
°C, and a L phase between 85 and 95 wt % amphiphile from 63
(1) For reviews of nanostructured materials synthesis using polymerizable
LLCs, see: Miller, S. A.; Ding, J. H.; Gin, D. L. Curr. Opin. Colloid Interfac.
Sci. 1999, 4, 338. (b) O’Brien, D. F.; Armitage, B.; Benedicto, A.; Bennett,
D. E.; Lamparski, H. G.; Lee, Y.-S.; Srisiri, W.; Sisson, T. M. Acc. Chem.
Res. 1998, 31, 861. (c) Ringsdorf, H.; Schlarb, B.; Venzmer, J. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 113.
(2) Herz, J.; Reiss-Husson, F.; Rempp, P.; Luzzati, V. J. Polym. Sci., Part
C: Polym. Lett. 1963, 4, 1275.
(3) Lee, Y.-S.; Yang, J.-Z.; Sisson, T. M.; Frankel, D. A.; Gleeson, J. T.;
Aksay, E.; Keller, S. L.; Gruner, S. M.; O’Brien, D. F. J. Am. Chem. Soc.
1995, 117, 5573.
(4) Srisiri, W.; Sisson, T. M.; O’Brien, D. F.; McGrath, K. M.; Han, Y.;
Gruner, S. M. J. Am. Chem. Soc. 1997, 119, 4866.
(5) Smith, R. C.; Fischer, W. M.; Gin, D. L. J. Am. Chem. Soc. 1997, 119,
4092.
(6) Gray, D. H.; Hu, S.; Juang, E.; Gin. D. L. AdV. Mater. 1997, 9, 731.
(7) Sellinger, A.; Weiss, P. M.; Nguyen, A.; Lu, Y.; Assink, R. A.; Gong,
W.; Brinker, C. J. Nature 1998, 394, 256.
(8) Werkman, P. J.; Wieringa, R. H.; Schouten, A. J. Thin Solid Films
1998, 323, 251.
(9) Deng, H.; Gin, D. L.; Smith, R. C. J. Am. Chem. Soc. 1998, 120, 3522.
(10) Gray, D. H.; Gin, D. L. Chem. Mater. 1998, 10, 1827.
(11) Miller, S. A.; Kim, E.; Gray, D. H.; Gin, D. L. Angew. Chem., Int.
Ed. 1999, 38, 3021.
(19) See Supporting Information.
(20) Polymerizable analogues of alkyltrimethylammonium salts (which are
known to form the HI phase) containing (meth)acrylate and styrene groups
were synthesized initially. However, these compounds did not exhibit
significant LLC behavior.
(21) Israelachvili, J. N. Intermolecular and Surface Forces with Applications
to Colloidal and Biological Systems; Academic: London, 1985; p 249.
(22) Jenkins, R.; Snyder R. L. Introduction to X-ray Powder Diffraction,
Wiley-Interscience: New York, 1996; p 76.
(23) Pindzola, B. A.; Gin, D. L. Langmuir 2000, 16, 6750.
(24) Hoffmann, R. W.; Brinkmann, H.; Frenking, G. Chem. Ber. 1990,
123, 2387.
(25) Hoag, B. P.; Gin, D. L. Macromolecules 2000, 33, 8549.
(26) When mixed with water, compound 1a has a smaller HI domain than
1b (ca. 65-85 wt %). Compound 1c forms phases above 30 °C but has no HI
phase.
(12) Schnur, J. M. et al. Thin Solid Films 1987, 152, 181.
(13) Chappell. J. S.; Yager, P. J. Mater. Sci. Lett. 1992, 11, 633.
(14) Archibald, D. D.; Mann, S. Nature 1993, 364, 430.
(15) Friberg, S. E.; Thundathil, R.; Stoffer, J. O. Science 1979, 205, 607.
(16) Thundathil, R.; Stoffer, J. O.; Friberg, S. E. J. Polym. Sci., Polym.
Chem. Ed. 1980, 18, 2629.
(17) Shibasaki, Y.; Fukuda, K. Colloids Surf. 1992, 67, 195.
(18) McGrath, K. M. Colloid Polym. Sci. 1996, 274, 399.
10.1021/ja0058583 CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/19/2001