Viscoelastic properties of sulfonated styrene ionomers

Abstract

AbstractThe solid‐state viscoelastic properties of polystyrene containing randomly distributed groups of styrene‐p‐sodium sulfonate are studied and compared with the corresponding properties of copolymers of styrene and sodium methacrylate (S‐NaMA). The viscoelastic behavior in the primary transition region of these two ionomers is very similar. As for the S‐NaMA copolymers, it is proposed that sulfonated polystyrene is composed of ion‐rich regions (clusters) immersed in a matrix of low ion concentration. Two peaks are observed in the plot of mechanical loss tangent versus temperature for the sulfonated material. The lower peak is assigned to the glass transition of the ion‐poor matrix and the upper to the glass transition of the clustered regions. As for some other ionomers, the presence of ions is found to slow down the stress relaxation rate, giving a broad distribution of relaxation times. Above a certain ion concentration, the sulfonated polystyrenes are thermorheologically complex owing to the onset of a secondary relaxation mechanism associated with the ion‐rich regions.