LIGHT-SCATTERING-STUDIES OF BLOCK IONOMER AGGREGATION CHARACTERISTICS IN NONPOLAR SOLVENT

Static and dynamic light scattering studies are presented on the aggregation 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 with a 2.3 mol % sulfonation content) dissolved in cumene was compared with that of the parent neutral copolymer. For the block ionomer studied, reverse aggregates with the salt groups in the interior were obtained as expected. However, in all cases, as indicated by combining static and dynamic light scattering measurements, a dominating portion of single chains (approximately 83 wt %) and a small amount of reverse aggregates (approximately 17 wt %, each aggregate consisting of, on average, 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 individual block ionomer chains.