Breakdown of time-temperature superposition in miscible polymer blends

The authors demonstrate that time-temperature superposition is in fact invalid for a miscible blend of poly(ethylene oxide) and poly(methyl methacrylate). This blend is a model blend system in two respects. Both polymers can be prepared with narrow molecular weight distributions by anionic polymerization. This represents a major advantage over the blends of polydisperse polymers used in previous rheological studies, as the relaxation of each component is obvious in blends of nearly monodisperse polymers. The enthalpy of mixing for these polymers, reflected in the Flory-Huggins interaction parameter, is negative, but indistinguishable from zero within experimental error. Thus the blend is miscible, but free from strong specific interactions between the components, which might complicate the blend rheology.