DYNAMIC MECHANICAL-PROPERTIES OF TRIBLOCK IONOMERS OF POLYSTYRENE AND POLY(SODIUM METHACRYLATE)

The dynamic mechanical properties of poly(sodium methacrylate)-b-polystryrene-b-poly (sodium methacrylate) triblock ionomers were investigated as a function of the length of the ionic blocks at constant styrene block length. The glass transition temperature (T(alpha), subsequently referred to as T(g)) of the styrene blocks was very slightly higher than that of bulk polystyrene, and was independent of the ion content. The T(g) of the ionic domains increased as the length of the ionic blocks increased. This increase is explained as being due to the dependence of T(g) on the molecular weight of the short ionic segments, and possibly also to an increase in the dimensions of the ionic regions as the length of the ionic blocks increased. The height of the rubbery plateau located between the two T(g) also increased as the ion content increased, suggesting a change in the morphology of the ionic domains with increasing ion content. Because of the very high T(g) of the ionic component, the rubbery plateau extends to very high temperatures. This is not observed in the non-ionic precursors, and the triblock copolymers with poly(methacrylic acid) endblocks.