LIGHT-SCATTERING-STUDIES OF BLOCK IONOMER AGGREGATION CHARACTERISTICSIN NONPOLAR SOLVENT

Static and dynamic light scattering studies are presented on the aggre gation characteristics of a block ionomer in nonpolar solvent. In the dilute solution regime (1-5 mg/mL), the solution behavior of poly(tert -butylstyrene)-b-lightly sulfonated polystyrene (sodium neutralized wi th a 2.3 mol % sulfonation content) dissolved in cumene was compared w ith that of the parent neutral copolymer. For the block ionomer studie d, reverse aggregates with the salt groups in the interior were obtain ed as expected. However, in all cases, as indicated by combining stati c and dynamic light scattering measurements, a dominating portion of s ingle chains (approximately 83 wt %) and a small amount of reverse agg regates (approximately 17 wt %, each aggregate consisting of, on avera ge, about 10 unimers) coexist in a nearly constant weight ratio. There seems to be no real equilibrium between these two distinctive species . Most likely, the aggregates detected are essentially made up of less soluble, but higher ionic content, copolymer chains, as resulted from the composition heterogeneity in terms of the ionic content among ind ividual block ionomer chains.