EXTENDED X-RAY ABSORPTION FINE-STRUCTURE SPECTROSCOPIC ANALYSIS OF CATION LOCAL ENVIRONMENT IN MODEL POLYURETHANE IONOMERS

The local environment of the neutralizing cation was examined by extended X-ray absorption fine structure spectroscopy in a series of model polyurethane ionomers. Polyol type, polyol molecular weight and pendant anion type had small effects on cation local environment. Sample preparation conditions had a noticeable effect in one case. The type of cation was the dominant factor in determining local ordering. The degree of local order decreased with cation type in the order Ni2+ > Sr2+ > Cd2+, in agreement with the trend of decreasing tensile properties with cation type. Hydration of Ni2+-neutralized ionomers induced no change in the Ni2+ local environment for a sulphonated ionomer, but hydration caused a rapid change in the local structure of the analogous carboxylated ionomer. The changes were in accord with water molecules coordinating to the Ni2+ cation.