Polyampholyte-Dressed Micelles of Fluorinated and Hydrogenated Dodecanoic Acid Andreas F. Thu ¨ nemann,* Kathrin Sander, and Werner Jaeger Fraunhofer Institute for Applied Polymer Research, Geiselbergstrasse 69, D-14476 Golm, Germany Rumiana Dimova Max Planck Institute of Colloid and Interfaces, Am Mu ¨ hlenberg 2, D-14476 Golm, Germany Received February 20, 2002. In Final Form: April 15, 2002 Polyampholytes with alternating cationic and anionic monomers were synthesized and complexed with fatty acids (dodecanoic acid and perfluorododecanoic acid). The formation of the polyelectrolyte-fatty acid complexes is self-assembled and generates nanoparticles with sizes in the range of 3-5 nm that were named dressed micelles. A defined arrangement of the ionic charges of three polyampholytes was achieved by the copolymerization of a cationic vinyl monomer (N,N′-diallyl-N,N′-dimethylammonium chloride) and anionic vinyl monomers (maleamic acid, phenylmaleamic acid, and 4-butylphenylmaleamic acid). The zeta potentials of the polyampholyte dressed micelles were adjusted in the range of -56 to 25 mV. They increase when replacing the alkylated dodecanoic acid by its perfluorinated counterpart, and they also increase when enhancing the hydrophilicity of the polyampholyte. Analytical ultracentrifugation, dynamic light scattering, and isothermal titration calorimetry were used for the characterization of the fluorinated and the hydrogenated complexes. Introduction The complexation of polyelectrolytes with low molecular weight amphiphiles (ionic surfactants, fatty acids) pro- duces self-assembled soft matter that combines the properties of polymers such as mechanical stability with the capability of surfactants to form supramolecular ordered structures, for example, smectic and hexagonal phases. Reviews of this field are given by Thou and Chu, 1 by Ober and Wegner, 2 and also by Tirrell et al. 3 The interaction of polymers and surfactants results typically in the formation of water-insoluble complexes 4 if the stoichiometry of the charges is 1:1. By contrast, dispersions of nanoparticles can be produced easily for nonstoichio- metric complexes. An example is the complex of poly- (ethylene imine) with dodecanoic acid. It forms a water- insoluble solid-state complex with a smectic A-like structure for a 1:1 stoichiometry. 5 The same complex with an excess of poly(ethylene imine) of 50 mol % forms nanoparticles of the core-shell type that are useful as carriers for lipophilic drugs such as Q 10 and triiodothy- ronine. 6 These particles exhibit hydrodynamic radii of 80- 150 nm and high positive surface charges with zeta potentials of about +40 mV. Another way of producing nanoparticles is to use diblock copolymers with a com- plexing block and a noncomplexing block that stabilizes these particles. An example of this is shown in the complexes of dodecanoic acid with poly(ethylene oxide)- block-poly(ethylene imine)s with linear, branched, and cyclic poly(ethylene imine) blocks. 7 These complexes form core-shell particles with sizes around 200 nm, but their zeta potential is zero due to their electrostatic neutral shells of poly(ethylene oxide). The aim of this work is also to prepare nanoparticles of complexes, but their diameters should be significantly smaller than the particles produced in our earlier studies (>50 nm). High specific interface areas between the particles and their surroundings should be generated in this way, and the zeta potentials of the particles should be adjustable. We prepared six different complexes for this purpose, whose molecular structures are shown in Figure 1. An alkylated (H) and a fluorinated fatty acid (F) of the same chain length (12 carbon atoms) will be compared in their complexation properties with the polyampholytes P 1 , P 2 , and P 3 . It can be seen that the hydrophobicity of the rest, R, increases from P 1 to P 3 . Experimental Section Materials. The maleamic acid, N,N′-diallyl-N,N′-dimethyl- ammonium chloride, n-dodecanoic acid, perfluorododecanoic acid, sodium hydroxide, and toluene (HPLC grade) were supplied by Aldrich and used as received. Monomer Synthesis. N-Phenylmaleamic Acid. A total of 98.06 g (1 mol) of maleic anhydride was dissolved in 500 mL of toluene and heated to 80 °C. Then 93.12 g (1 mol) of aniline, dissolved in 100 mL of toluene, was added in droplets and stirred at 80 °C for a further 2 h. The N-phenylmaleamic acid was observed as a precipitate after cooling the reaction mixture to room temperature. This product was separated, washed with 200 mL of toluene, and further purified by crystallization twice in ethanol (2 g of N-phenylmaleamic acid in 100 mL of ethanol). The yield was 138.6 g (72.5%). The composition was determined by 400 MHz 1 H NMR (Bruker DPX-400) in DMSO-d6, δ (ppm): 6.3 (d, 1 H), 6.45 (d, 1H), 7.1 (t, 1 H), 7.35 (t, 2 H), 7.65 (d, 2 H), 10.4 (s, 1 H), 13.15 (s, 1 H). The purity was checked by elemental * Corresponding author. E-mail: andreas.thuenemann@iap.fhg. de. (1) Zhou, S. Q.; Chu, B. Adv. Mater. 2000, 12, 545-556. (2) Ober, C. K.; Wegner, G. Adv. Mater. 1997, 9, 17-31. (3) MacKnight, W. J.; Ponomarenko, E. A.; Tirrell, D. A. Acc. Chem. Res. 1998, 31, 781-788. (4) Goddard, E. D.; Ananthapadmanabhan, K. P. Interactions of Surfactants with Polymers and Proteins; CRC Press: Boca Raton, FL, 1993. (5) Thu ¨ nemann, A. F.; General, S. Langmuir 2000, 16, 9634-9638. (6) Thu ¨ nemann, A. F.; General, S. J. Controlled Release 2000, 75, 237-247. (7) Thu ¨ nemann, A. F.; General, S. Macromolecules 2001, 34, 6978- 6984. 5099 Langmuir 2002, 18, 5099-5105 10.1021/la020188v CCC: $22.00 © 2002 American Chemical Society Published on Web 06/01/2002