Dynamic mechanical properties of sulphonated polystyrene ionomers

Abstract

Measurements have been made of the dynamic mechanical properties of a series of partially sulphonated polystyrene ionomers. Results obtained indicate that two glass transition temperatures are present, with the lower temperature transition arising from a phase containing only ionic multiplets and the higher temperature transition arising from a phase containing ionic clusters. The loss peak height associated with the multiplet containing phase decreases with increasing ionic content while that associated with the cluster phase rises. The cluster phase appears to become the dominant phase at ion contents of about 6 mol%. The T g of PS increased linearly with ionic content at the rate of about 3°C per mol%. For each ion content, the average molecular weight between ionic crosslinks was determined from values of the rubbery plateau modulus and compared with calculated values, assuming all ion pairs participate in forming crosslinks. It was also observed that the rubbery plateau region extended over a considerably wider temperature range when samples were prepared with a divalent metal ion, such as Ca, instead of a monovalent ion.