A poly(ethy1ene-co-methacrylic acid) polymer containing 3.8 mol 9' 0 methacrylic acid and it's 64% neutralized cesium salt were subjected to a small-and wide-angle X-ray scattering study. The radial distribution functions (RDF's) were obtained by carrying out the Fourier transforms of the angular dependences of the scattered X-ray intensities. The RDF of the acid form was subtracted from the RDF of the salt form to approximately cancel the light atom contributions leaving only cesium atom contributions. The results of these analyses indicate that electron density fluctuations having spatial extents of the order of 20 A are present in the salt but absent in the acid copolymer. One model consistent with these results is an ionic cluster model in which the metal atoms tend to segregate in regions of 20-A diameter. An attempt was made to fit a hard sphere cluster model to the experimental RDF but this was found to be inadequate to account for the data.
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