Viscoelastic properties of mixtures of polystyrene with low‐molecular‐weight poly[oxy(2,6‐dimethyl‐1,4‐phenylene)]

A series of poly[oxy(2,6‐dimethyl‐1,4‐phenylene)]s (PPE) (trivial names: polyphenylenether, polyoxyxylene, polyphenyleneoxide) with narrow molecular weight distribution were prepared by polymerization of 4‐bromo‐2,6‐dimethylphenol and subsequent fractionation. The molecular weight dependence of the glass transition temperature obeys the Fox‐Flory equation. Polystyrene (PS)/PPE blends (PS: number‐average molecular weight M̄ n = 144 000, ratio of weight‐ to number‐average molecular weight M̄ w / M̄ n = 1,05) were prepared using PPE samples with molecular weights below the entanglement spacing of PPE, in order to obtain information about the influence of specific interactions on the linear viscoelastic properties in the plateau and terminal region. The iso‐free‐volume state turned out to be the most appropriate reference state to compare samples of various compositions. Low‐molecular‐weight PPE essentially acts as a solvent for polystyrene. The concentration dependence of the zero‐shear viscosity η 0 is proportional to ϕ 3,6 PS , ϕ PS being the volume fraction of PS, and the temperature dependence of the logarithmic shift factor log a T indicates that interactions, which are responsible for the thermodynamic miscibility in this system, do not alter the linear viscoelastic properties of PS. The concentration dependence of the plateau modulus (G (0) N ∝ ϕ 1,2 for PS/PPE‐1500) blends is explained by an additional small elastic contribution of the short PPE chains to the plateau modulus at higher frequencies.