VISCOELASTIC BEHAVIOR OF LIGHTLY SULFONATED POLYSTYRENE IONOMERS

Ionomers prepared by lightly sulfonating polystyrene exhibit a pseudorubbery plateau above the glass transition and a second mechanical loss process at elevated temperatures. The origin of these features in the linear viscoelastic properties is due to the formation of a second, microphase-separated phase, i.e., ionic clusters, that increases the longer time relaxation processes of the ionomer. For relatively low sulfonation levels (< 6 mol %) the terminal region of linear viscoelastic behavior shifts to at least several decades longer in time or lower in frequency. These longer relaxation times are responsible for the higher viscosities and network-type mechanical behavior of the ionomer compared with the unfunctionalized parent material. The major effect of changing the counterion used is on the long-time processes.