Ionic Complexes of Polyacids and Cationic Surfactants Ainhoa Tolentino, Antxon Martı´nez de Ilarduya, Abdelilah Alla, Sebastia´nMun ˜ oz-Guerra * Summary: Comb-like ionic complexes were prepared from polyuronic acids (pectinic and alginic acids) and alkyltrimethylammonium surfactants bearing linear alkyl chains with 18, 20 and 22 carbon atoms. In the condensed state, these complexes were able to self-assemble in ordered structures which were thermally stable up to 200 8C. The complexes were analysed by DSC and WAXS/SAXS and compared to their analogous made from poly(g-glutamic acid). They all adopt a biphasic layered structure in which the main chain and the alkyl side chain alternate with a nanometric periodicity. Alkyl side chains were partially crystallized in these com- plexes and they show reversible melting at temperatures within the 60-80 8C range depending on the length of the polymethylene segment. Keywords: alginic acid; comb-like ionic complexes; pectinic acid; Poly(gamma glutamic acid); polyelectrolyte surfactant complexes; polygalacturonic acid; polyuronic acid Introduction It is known that comb-like polymers made of a rigid main chain and a flexible side chain are able to self-assemble in biphasic layered structures sensitive to temperature changes. [1] As early as 1985, Watanabe described comb-like polymer structures made of long alkyl esters of polygluta- mates. [2] In these systems the alkyl side chain is linked to the main chain by an ester bond. It is well established that in these comb-like polypeptides the main chain is in helical conformation with hydrogen bonds intramolecularly formed and the side chains coming out from the helix to fill up the interlayer space. [3] Upon heating, the alkyl side chains melt but the con- formation of the main chain remains essentially unaltered retaining the helical arrangement and keeping its position in the lattice. The layered structure is therefore preserved although the interlayer spacing decreases due to the slightly contraction undergone by the polymethylene chain. Such thermal behaviour has interesting phenomenological consequences with potential technological applications such as responsive temperature membranes and thermochromic sensors. [4–6] Recently it has been shown that comb- like systems with structure and properties similar to those described above can be generated by ionic coupling between ionic alkyl surfactants and charged polyelectro- lytes (Figure 2). First work published on this type of systems was reported by Antonietti in 1994. [7] The clear advantage afforded by the systems based on ionic coupling respect to the covalent ones is simplicity of preparation; ionic complexes can be readily obtained by direct mixing of the corresponding components in aqueous medium avoiding laborious synthetic work. In this contribution a comparative study of the complexes produced by ionic cou- pling of alkyltrimethyl ammonium surfac- tants (nATMA) with either poly(g-gluta- mic acid) (PGGA) or polyuronic acids (pectinic and alginic acids) is reported. PGGA is a biotechnological polypeptide obtained by aerobic fermentation of organic substrates with bacteria Macromol. Symp. 2010, 296, 265–271 DOI: 10.1002/masy.201051037 265 Departament d’Enginyeria Quı´mica, Universitat Poli- te ` cnica de Catalunya ETSEIB, Diagonal 647, 08028 Barcelona, Spain E-mail: sebastian.munoz@upc.edu Copyright ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com