Water-soluble complexes formed by sodium poly(4-styrenesulfonate) and a poly(2-vinylpyridinium)-block-poly(ethyleneoxide) copolymer

Formation of interpolyelectrolyte complexes (IPEC) between sodium poly(4-styrenesulfonate) (PSSO3Na) and a diblock copolymer consisting of a protonated poly(2-vinylpyridine) (P2VP) block and a neutral poly(ethylene oxide) (PEO) one was investigated in water. The main experimental variables were the molecular weight (MW) of the PSSO3Na polyanion, the molar ratio of the cationic and anionic species (i.e., the stoichiometry of the complex), and the pH of the aqueous solution. It was observed that (i) the interpolyelectrolyte complexes self-assemble at least at low pH into the core of monodisperse spherical micelles surrounded by a corona of PEO blocks and possibly of uncomplexed PSSO3Na segments, (ii) their stability depends on the pH in relation to the degree of protonation of the P2VP block, whatever the MW of the PSSO3Na polyanion and the cation/anion stoichiometry, (iii) the complexes are dissociated above a critical pH and are salt-sensitive, falling apart above a critical salt concentration, and (iv) a cooperative mechanism operates, which is completely reversible.