X-ray absorption spectroscopy studies of zinc-neutralized ethylene-methacrylic acid ionomers

A series of zinc-neutralized ethylene-methacrylic acid ionomers was studied using X-ray absorption spectroscopy. Neutralization methodology, neutralization level and methacrylic acid content were varied to test whether any of these factors affected the local environment of the zinc cations. Three different neutralization methods were tested: melt neutralization with zinc oxide, melt neutralization with zinc acetate and solution neutralization with zinc acetate. Neutralization levels varied between 25 and 100% of stoichiometric, and methacrylic acid contents varied between 10 and 20% by weight. Samples were prepared and handled to rigorously exclude water. Despite the substantial differences in sample preparation procedures, the local environments around the zinc atoms were identical in all materials, resembling the arrangement of atoms in the crystal structure of monoclinic anhydrous zinc acetate. In this compound, four oxygen atoms surround the zinc atom with distances ranging from 1.950 to 1.965 Å.