Complexes of octadecyltrimethylammonium polyacrylate: properties in solution, gel and solid forms

A polymer-surfactant complex (OTAPA) was prepared by titration of aqueous poly(sodium acrylate) with stoichiometric amounts of octadecyltrimethylammonium chloride. The resulting product is not water-soluble and does not dissolve in most polar and nonpolar, liquids. OTAPA has peculiar thermal behaviour and interesting structural properties. It has a high melting temperature and decomposes around 350 degreesC. According to preliminary X-ray findings, the complex is formed by an arrangement of alkyl chains around the polymer skeleton, packed into a layered structure. The complex forms an elastic gel in ethylene glycol, and, to a much lesser extent, in glycerol or tetrahydrofuran, but is hardly water-soluble. Indeed, the occurrence of micelle-assisted dissolution and the precipitation of OTAPA from such mixtures, upon dilution with water, have been observed. Applications of OTAPA as a hydrophobic modifier of surfaces can be considered.