Soluble Complexes from Poly(ethylene oxide)-<i>block</i>-polymethacrylate Anions and <i>N</i>-Alkylpyridinium Cations

Complexes from poly(ethylene oxide)-b-poly(sodium methacrylate) (PEO-b-PMANa) and N-alkylpyridinium bromides are water soluble, in marked contrast to those from poly(sodium methacrylate). These systems are studied using potentiometric titration, microcalorimetry, ζ-potential measurement, light scattering and electron microscopy. Three regions (A−C) are observed with a complex from PEO-b-PMANa and cetylpyridinuim bromide (C16PyBr) when the composition of the mixture (Z = [C16PyBr]/[COO-]) is varied. (A) At Z < 1 C16PyBr binds electrostatically to the polyion to form soluble complex with a negative ζ-potential. (B) The size of the complex decreases and reaches minimum (o.d. 67 nm) at Z = 1 when ζ = 0. Those stoichiometric complexes are soluble and stable. They appear to be micelles with a core formed by C16PyBr neutralized polyion chains and a shell of PEO chains. (C) With a further increase in Z, the surfactant cations incorporate in the particles (ζ > 0). The particles formed at saturating concentrations of C16PyBr are spherical and remarkably monodisperse. Overall, these systems represent a new class of lyophilic colloids that exhibit combined properties of amphiphilic block copolymers and polyelectrolyte−surfactant complexes.