Self-organization of sulfonated polystyrene ionomers with various contents of ionogenic groups in toluene: Neutron scattering study

The structural organization of sulfonated polystyrene-based ionomers containing different amounts of sodium sulfonate groups (SO3Na) in the concentration range from 0.5 to 5.8 mol % in deuterotoluene has been studied by cold neutron scattering. An analysis of molecular correlations shows that ionomer chains retain the Gaussian coil conformation even at a degree of sulfonation of 5.8 mol %, when the distance between ionogenic groups along a chain is comparable with the Kuhn segment length. At a content of SO3Na groups of 1.35 mol %, the mutual penetration of polymer chains predominates and is accompanied by the formation of associates including up to seven macromolecules (effective chains) and functioning as main structural elements of the system. At a higher content of SO3Na groups, the mutual penetration of macromolecules becomes weaker owing to the enhanced intramolecular association of ionogenic groups. As a result, the effective chains with sizes smaller than the size of the PS coil arise. These chains are composed of 1-2 ionomer macromolecules and are compacted structures in which the concentration of PS units is a factor of 4 higher than the concentration of units in the nonsulfonated PS coil. The self-organization of such particles in toluene yields secondary structures in the form of clusters composed of four to five effective chains.