| Abstract: | Previous studies have shown that metal sulfonated ionomers display unusual solution behavior. Typically, inomers, such as metal sulfonated EPDM or sulfonated polystyrene, are readily dissolved in mixed solvents, such as hydrocarbons plus alcohols. Such mixed solvents can provide unusual viscosity-temperature behavior due to the strong inter-or intramolecular interactions of the ionic groups. This paper is concerned with studies directed at a variety of polar cosolvents, including amines, alcohols, acids, amides, and esters, in interactions with zinc sulfonated ethylene propylene diene monomer (sulfo-EPDM). Within various classes of compounds the structural effects of such cosolvents on the solution viscosities of sulfonate ionomers have been elucidated. Generally, amines and alcohols have been found to be the most effective cosolvents. Amines appear to form a specific complex with zinc and can virtually eliminate ion pair association at extremely low levels. Within a homologous series, those compounds of shortest hydrocarbon chain length provide the most effective solvation of the ionic groups of sulfonated EPDM. The effect of structure of the amines or alcohols on solution viscosity has shown the efficiency of cosolvent interaction proceeding as normal > iso > secondary > tertiary in the alcohol series. These results are interpreted as a consequence of the cosolvent solvating the ionic groups wherein the more bulky cosolvents are least effective in solvating the metal cations. |
