Light-scattering studies of styrene-(ethylene-co-butylene)-styrene triblock copolymer and its sulfonated ionomers in tetrahydrofuran

A combination of static and dynamic laser light scattering (LLS) was used to study a styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEES) and its sulfonated ionomers in THF at 25 degrees C. We found that the SEES solution unexpectedly contained a small amount of clusters whose dissolution in THF is an extremely slow process. On average, each initial SEES aggregate contains 15-20 individual SEES chains. As for the SEES ionomers, the solutions contained species much larger than individual sulfonated SEES chains. This study revealed that these large species can very slowly dissolve in THF and the dissolution process follows a first-order kinetics. Moreover, we found that the solubility of sulfonated SEES ionomers decreased with increasing storage time even when the solids were under sealed and dry conditions. These results suggest that the origin of ''association of sulfonated SEES ionomers'' should be reconsidered; namely, these large species were not formed from individual chains in solution, but instead were fragments produced in the dissolution process. In addition, the study of the complexation of sulfonated SEES ionomers respectively with poly(styrene-co-4-vinylpyridine) (PSVP) and poly(methyl methacrylate-co-4-vinylpyridine) (PMMAVP) showed a maximum (in terms of the size or amount of the formed complexes or viscosity) at an equimolar condition, no matter what kind of metal counterions were used. This suggests a complexation mechanism different from coordination between small molecules.