Three different sets of styrene-based ionomer homoblends containing ca. 5 mol% of ionic repeat units, i.e. poly(styrene-co-sodium itaconate) [P(S-co-ITANa)]/ poly(styrene-co-sodium methacrylate) [P(S-co-MANa)] ionomer blends, sodium sulfonated polystyrene [P(S-co-SSNa)]/P(S-co-MANa) ionomer blends, and P(S-co-ITANa)/P(S-co-SSNa) ionomer blends, were prepared and their dynamic mechanical properties were investigated. It was observed that with increasing itaconate content in the blend of P(S-co-ITANa)/P(S-co-MANa) ionomers the multiplet of the P(S-co-MANa) ionomer disrupted initially very rapidly, and ionic modulus of the blend increased drastically. In the case of P(S-co-ITANa)/P(S-co-SSNa) ionomer blends, again, the ionic modulus increased significantly with increasing itaconate content. In these two ionomer blend systems, the itaconate, having two ionic groups per ionic repeat unit, influenced the properties of the blends more noticeably than the other two ionic units, containing only one ionic group per ionic repeat unit. In the blend system of P(S-co-SSNa)/P(S-co-MANa), as expected, the cluster loss tangent peak shifted to higher temperature, ionic modulus decreased, but the ionic plateau extended more with increasing the ratio of the P(S-co-SSNa) content. However, it should be mentioned that when the ion contents of the methacrylate and sulfonate ionomers increased to over 6 mol%, at which the cluster phase of the P(S-co-MANa) ionomers is known to become dominant, compared to the matrix phase, the three loss tangent peaks were observed, which implies that methacrylate-rich and sulfonaterich phases exist together. This might be due to the fact that a copolymerization effect becomes stronger; that is, with increasing ion content the role of ionic units in random copolymer ionomers becomes more important, compared to the role of host non-ionic units. As a concluding remark, the properties of these three ionomer blend systems depend on the degree of clustering, type of ionic groups, and the number of ionic groups per repeat unit.

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Summary: Spectroscopic methods were employed to evaluate the thermodynamics of aggregates formation of P(S-co-MANa) in aqueous solution containing a trace of DMF(0.2 mol%) using pyrene as an optical probe. The mol %s of methacrylate unit in poly(styrene-co-sodium methacrylate)[P(S-co-MANa)] were 3.6, 5.0, 6.2 and 9.4. Measurements were made at a series of temperatures in the range 10-80 8C. Based on the temperature dependence of the critical aggregation concentration (CAC) and by the use of van't Hoff equation, thermodynamic parameters were calculated. At low temperature the aggregation is accomplished by a large positive entropy change and a small negative enthalpy changes. As the temperature increases, the magnitude of entropy change becomes smaller and the enthalpy change is more exothermic. Moreover, the changes in enthalpy and entropy compensate each other for all samples we have studied, and the compensation temperature was $320 K.

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