The solution behavior of metal sulfonate‐containing ionomers has been investigated in various mixed solvent systems. Ionomers, such as lightly sulfonated polystyrene (sodium salt) and sulfonated ethylene‐propylene‐diene terpolymer (metal salts) are generally insoluble in typical hydrocarbon solvents, but readily dissolve when small amounts of alcohols or other polar cosolvents are present. At relatively low polymer concentration these ionomers display unusually high thickening behavior in nonpolar solvents when compared with nonionic polymers because of association of the metal sulfonate groups. The addition of modest levels of polar cosolvent markedly decreases the solution viscosity and gives rise to viscosity‐temperature relationships different from those of conventional polymer solutions. For example, such solutions can display vicosities which increase, are relatively constant, or display maxima or minima over broad temperature ranges. These observations are interpreted as arising from a temperature‐dependent preferential interaction of the cosolvent with the sulfonate groups. While these ionomers can be regarded as polyelectrolytes of low charge density, they do not display the typical “polyelectrolyte” behavior often observed in aqueous solutions. This anomalous behavior is attributed to the fact that the metal sulfonate groups are largely un‐ionized in solvents of low dielectric constant. Therefore, the solution behavior is dominated by ion pair interactions rather than free ions.
Metal sulfonate groups were introduced into an ethylene--propylene-diene monomer terpolymer (EPDM) via reaction of its residual unsaturation with acetyl sulfate, followed by neutralization of the resultant polymeric sulfonic acid with metal acetates. The composition, structure, and molecular weight of the EPDM and the sulfonate content, cation borne by the sulfonate group, and metal acetate concentration of the ionomer were found to substantially affect the rheological and mechanical properties of the ionomer. Through the proper selection of EPDM backbone, EPDM molecular weight, and sulfonate content, and through the use of the zinc cation, it was possible to prepare EPDM--based ionomers with excellent mechanical properties and with the lowest possible melt viscosities. Although formulations derived from these zinc sulfonate-containing EPDM's possess melt viscosities that are higher than desirable for facile processability, in many respects they are truly thermoplastic elastomers.HPhe presence of small amounts of ionic groups in hydrocarbon polymers exerts a profound effect on their physical properties (1,2). The polymers are effectively cross-linked through the association of these ionic groups forming multiplets or higher order associations described as "domains." These associations can be thermally relaxed to a greater or lesser extent depending on the composition of the ionic domains. In elastomeric systems, if the degree of ionic association at processing temperatures is sufficiently reduced to permit adequate melt flow, then the ion-containing elastomer is a thermoplastic elastomer.Carboxylate-containing elastomers and the effects of the free acid and metal carboxylate groups on elastomer properties have been studied 0-8412-0482-9/80/33-187-003$05.00/0
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