Glass transition in partially sulfonated polystyrene

Abstract The glass transition temperature Tg of partially sulfonated polystyrene has been measured dilatometrically as a function of degree of sulfonation. A semitheoretical relationship between Tg and degree of sulfonation has been derived by treating the strong‐acid polymer as a highly polar copolymer of styrene and styrenesulfonic acid. The Tg of copolymer has been found to increase linearly up to 0.15 weight fraction of styrene‐sulfonic acid wA as given by: where TgB is the glass transition temperature of loosely crosslined (1%) polystyrene matrix. Our experimental results agree well with theoretical relations developed on the basis of the iso‐free‐volume state of glass transition applied to sulfonated polystyrene. The marked linear increase in copolymer Tg with the styrenesulfonic acid is accounted for by the effect of progressively higher intermolecular forces due to the highly polar sulfonic acid substituents.