Dynamic light scattering and rheology of associating sulfonated polystyrene ionomers in non-polar solvents

Dynamic light scattering and reduced viscosity measurements on dilute solutions of sodium sulfonated polystyrene (NaSPS) ionomers of molecular weight 1 x 10(5) g mol(-1) and sulfonation levels of 0, 0.62, 0.95 and 1.39 mol% in xylene are described and compared with earlier static light and small-angle neutron scattering studies. The unsulfonated polystyrene and 0.62 mol% ionomer are present in dilute xylene solutions as single expanded chains. The 0.95 mol% ionomer, however, forms an equilibrium between single chains and aggregates of three chains in the concentration range studied (i.e. closed association). The dimensions of both the aggregates and single chains with the latter ionomer are closer to those observed for polystyrene under theta conditions rather than in xylene. With the 1.39 mol% ionomer single chains are found to be in equilibrium with aggregates of all sizes (i.e. open association). The single chains are more compact than expected for polystyrene even in a theta solvent. The aggregates, however, are lower density structures. The viscosities of the ionomer solutions were found to be determined by the total volumes occupied by the single chains and aggregates only in very dilute solutions ( < 0.4 g dl(-1)). Comparison of the behaviour of these ionomers dissolved in xylene with previous rheological and light scattering studies on different ionomers dissolved in a range of other solvents suggest that the variations in the extent of single-chain collapse and aggregation behaviour with charge level observed in this work could be a common feature of randomly charged ionomers in non-polar solvents. The charge levels at which transitions between different types of behaviour occur are determined primarily by the strengths of the ionic interactions and the dielectric constant of the solvent. (C) 1997 Elsevier Science Ltd. All rights reserved.