SIZES AND STABILITIES OF MULTIPLETS AND CLUSTERS IN CARBOXYLATED AND SULFONATED STYRENE IONOMERS

The mechanical properties of some random styrene ionomers are investigated in order to determine the effects of the type of the ionic groups and their position relative to the polymer backbone. Previous studies have shown that increasing the distance of the ion pairs from the polymer backbone leads to larger multiplets and greater intermultiplet spacings in random styrene ionomers. In this study, the position of the ion pairs relative to the polymer backbone is shown to have a profound influence on the mechanical properties of the material. This is attributed to differences in morphology resulting from different extents of steric hindrance to ion-pair aggregation in each ionomer. The strength of the electrostatic interactions between ionic groups is governed by the type of the ionic species. Strong electrostatic interactions between ion pairs tend to give rise to relatively stable multiplets which act as cross-links even at relatively high temperatures. The modulus of the material in the rubbery region remains constant while the multiplets are stable but decreases with the onset of ion hopping. This provides some insight into ion-hopping kinetics.