EFFECT OF SULFONATION LEVEL ON THE SINGLE-CHAIN DIMENSIONS AND AGGREGATION OF SULFONATED POLYSTYRENE IONOMERS IN XYLENE

Small angle neutron scattering has been used to determine the dimensio ns and extent of aggregation of dilute solutions of sodium sulfonated polystyrene (SPS) ionomers of molecular weight 10(5)gmol(-1) and sulfo nation levels of 0.95 and 1.65 mol% in p-xylene. At concentrations bel ow 0.1x10(-2)gml(-1) the 0.95 mol% SPS was present as mainly single ch ains of considerably smaller dimension than that of the 'parent' polys tyrene. Above this concentration small compact aggregates consisting o f three chains were formed. These data could be analysed using the clo sed association model. The higher sulfonation level ionomer was presen t as even more compact single chains in very dilute solution. It assoc iated, however, to form a distribution of much less dense aggregates w ith an average size that increased as the polymer concentration was ra ised. This type of behaviour was interpreted using the open associatio n model and used to explain why semi-dilute solutions of this latter i onomer can gel.