This work describes the self-assembly behavior, the structure, the state, and phase diagrams of comblike liquid-crystalline polymers obtained by supramolecular ionic complexation of cationic dendronized polymers (PG1-PG3) and anionic sulfonated lipid surfactants. In order to characterize the influence of both the polymer and the surfactant on the microphase separation of these complexes, dendronized polymers with generation 1 e n e 3, carrying 2 n positive charges per monomer, were complexed with a stoichiometric amount of anionic sodium alkyl monosulfate surfactants with hydrocarbon chain of C 8 , C 12 , C 14 , and C 18 lengths. Supramolecular complexes were obtained in water, and the complexation process was monitored by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance. After drying and thermal annealing under high vacuum, the complexes showed thermotropic liquid-crystalline behavior as demonstrated by both cross-polarized optical microscopy and differential scanning calorimetry. Small-angle X-ray scattering allowed determining the respective lattice parameters and type of structures for all the complexes considered. Depending on both generation and lipid chain length, amorphous isotropic fluid, columnar rectangular, columnar hexagonal, columnar tetragonal, and lamellar phases were observed, each characterized by a specific order-disorder transition temperature (T ODT ).

During the past decade, ionic complexation of polyelectrolytes and oppositely charged low molecular mesogenic units has been gaining increasing attention as a viable route to design liquidcrystalline (LC) polymers with long-range order. 1,2 The main advantage of this strategy over other self-assembly methods is the simplicity with which complex architectures can be accessed by putting together simple constituents from a "toolbox". At the same time, the liquid-crystalline phases obtained for the ionic supramolecular complexes are comparable to those obtained in systems where mesogenic units are covalently attached to macromolecules. [3][4][5] Various molecular architectures have been investigated for cationic and anionic polymers, including linear, 6 dendritic, 7 and hyperbranched polyelectrolytes. 8 Hydrocarbon-based cationic and anionic surfactants, which have been the most widely investigated class of mesogenic units, have also been shown to directly control the period and the structure of the complex mesophases. 9 Here we report for the first time the use of cationic dendronized polymers 10 and anionic lipids as a model system in which the molecular architecture can be rationally controlled by two factors, the generation of the dendrons attached to the polymer backbone and the length of the lipid tail. Scheme 1 shows the molecular structures of the first (PG1) and second (PG2) generation dendronized polymers used in this study. They have two and four ammonium triflate end groups, respectively. The syntheses (see Supporting Information) follow closely the lines given for a similar PG2 polymer. 11 The polymers were isolated on the multigram scale in their tert-butyloxycarbonyl (Boc)-protected form. The molar masses were determined by gel permeation chromatography (in DMF, 1% LiCl, 80°C, referenced to PMMA standards using twoangle light scattering, refractive index, and viscometry detectors): PG1 (M w ) 1.5 × 10 6 ), PG2 ) (M w ) 2.5 × 10 6 ). 12 The deprotection was achieved quantitatively by treatment with neat trifluoroacetic acid. Complexation with the lipids was carried out by mixing polymers and lipids at a stoichiometric ratio in water at pH ) 3, so that the dendrons' primary amines and the lipids' sulfonic groups are positively and negatively charged, respectively. Upon complexation, the comb-like supramolecule precipitates in water. After its re-precipitation into water from an ethanol/butanol mixture as solvent, drying, and annealing at 50°C under ultrahigh vacuum (10 -8 mBar), the complete complexation of NH 3 + /SO 4 -in the solid polymer/lipid complex was demonstrated by the appearance of the FTIR band at 1074 cm -1 corresponding to the bound sulfonic groups. All the comb-like complexes obtained as described above showed liquid-crystalline behavior as indicated by birefringency in cross-polarized optical microscopy.Small-angle X-ray scattering allowed us to determine the specific group space of the LC complexes as a function of the lipid tail length and dendron generation. The effect of the alkyl ch...