Effects of water sorption on the structure and properties of poly(ethylene-co-methacrylic acid)based ionomers were investigated by various physicochemical techniques (FTIR, differential scanning calorimetry (DSC), thermogravimetry, X-ray scattering, and dilatometry). It is revealed that water molecules are absorbed preferentially at the COONa ion pairs in both the amorphous and ionic cluster regions, and that three water molecules per one sodium ion form the primary hydration shell. In the more hydrated samples, the excess water molecules are found to locate just around the primary hydration shell. It was found by DSC that both the transition temperature and enthalphy change for the transition near 330 K decrease with increasing hydration. However, this transition was observed even in the fully hydrated samples. These results are well explained by the order-disorder transition model of ionic clusters proposed previously. It is concluded that the ionic clusters consist of the COONa ion pairs and a small portion of the polyethylene backbones.

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Dielectric relaxation studies were performed for the alkali (Na, K), alkaline earth (Mg, Ca), and transition [Cu(II), Mn(II), Co(II)] metal salts of the ethylene-methacrylic acid (5.4 mol%) copolymer (EMAA), and for the transition metal complexes with l,3-bis(aminomethyl)cyclohexane (BAC) of EMAA. It was pointed out that the dielectric relaxations of the ethylene ionomers are sensitive to the formation of ionic clusters. When the ionic clusters are formed, the ß' relaxation related to a glass-rubber transition above Tg was depressed and there appeared two relaxations, the a relaxation above T" due to a micro-Brownian molecular motion of long segments containing the salt groups incorporated into the ionic clusters, and the ß relaxation below T" due to a molecular motion of short segments containing the isolated salt groups. From this relationship between dielectric relaxations and the formation of ionic clusters, it was concluded that the Na, K, Ca, Mg, and Co(II) salts of EMAA form the ionic clusters at higher neutralization above about 30%, but the Cu(II) and Mn(II) salts do not form clusters even at 60% neutralization. In the transition-metal complexes with BAC, the formation of ionic clusters was drastically promoted by the addition of BAC.