DYNAMIC LIGHT-SCATTERING AND RHEOLOGY OF ASSOCIATING SULFONATED POLYSTYRENE IONOMERS IN NONPOLAR-SOLVENTS

Dynamic light scattering and reduced viscosity measurements on dilute solutions of sodium sulfonated polystyrene (NaSPS) ionomers of molecul ar 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 po lystyrene and 0.62 mol% ionomer are present in dilute xylene solutions as single expanded chains. The 0.95 mol% ionomer, however, forms an e quilibrium 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 ev en in a theta solvent. The aggregates, however, are lower density stru ctures. The viscosities of the ionomer solutions were found to be dete rmined by the total volumes occupied by the single chains and aggregat es only in very dilute solutions ( < 0.4 g dl(-1)). Comparison of the behaviour of these ionomers dissolved in xylene with previous rheologi cal and light scattering studies on different ionomers dissolved in a range of other solvents suggest that the variations in the extent of s ingle-chain collapse and aggregation behaviour with charge level obser ved in this work could be a common feature of randomly charged ionomer s in non-polar solvents. The charge levels at which transitions betwee n different types of behaviour occur are determined primarily by the s trengths of the ionic interactions and the dielectric constant of the solvent. (C) 1997 Elsevier Science Ltd. All rights reserved.