The microphase structure of noncrystalline poly(ethylene-co-13.3 mol % methacrylic acid) (E-0.133MAA) ionomers was investigated by using infrared (IR) spectroscopic, X-ray scattering, differential scanning calorimetric (DSC), and dielectric measurements. The noncrystallinity was confirmed by small-angle X-ray scattering (SAXS) and DSC studies, which has enabled a quantitative analysis of the SAXS ionic peak associated with ionic aggregates without being perturbed by the polyethylene lamellae peak. In 60% neutralized Na ionomer, it was revealed that almost 100% of MAA side groups including unneutralized COOH are incorporated into the ionic aggregates with an average ionic core radius (R 1) of ∼6 Å. The dielectric relaxation studies showed that the ionic aggregates form a microphase-separated ionic cluster. Analysis of dielectric strengths indicated the most (∼90%) of the COONa groups are present in the ionic cluster. On the other hand, in the 60% neutralized Zn ionomer, both SAXS and dielectric studies indicated that the ionic aggregates with R 1 ∼ 4 Å are almost isolated and dispersed in the matrix; the formation of ionic cluster was not recognized. Similarly to partly crystalline E-MAA ionomers, all noncrystalline E-0.133MAA ionomers exhibited an endothermic peak at 320−330 K (labeled T i) on the first heating, depending on the aging time at room temperature. Several factors that would be critical for the DSC T i peak were discussed. It was concluded that the DSC T i peak is certainly associated with changes of the state of ionic aggregate region.

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.

Dynamic mechanical properties were measured for metal salts (Li, Mg, Na, and Zn) of poly-(ethylene-co-methacrylic acid) (EMAA) using a dynamic viscoelastometer. The study reproduced the previous observation that the mechanical relaxation behavior clearly responded to ionic cluster formation and its phase separation from the hydrocarbon matrix-the Li, Mg, and Na ionomers formed ionic clusters at a neutralization of ~35% or higher, and the Zn ionomer did not form ionic clusters at neutralization up to 60 %. However, this work has revealed clear evidence that even the Zn ionomer forms regions of microphaseseparated ionic clusters at a neutralization of 80% or higher. A peak, designated as the o' peak, appeared at ~325 K on the loss modulus curve of all EMAA ionomers that form ionic clusters, and the temperature exhibiting this peak proved to be independent of frequency. The order-disorder transition temperature (T¡) of the ionic clusters of EMAA ionomers, measured by differential scanning calorimetry, agreed with the a' peak temperature. From the frequency independence of this o' peak temperature, it is proposed that the o' peak is regarded as a first-order transition at T¡ and represents the existence of the order-disorder transition in the ionic clusters.

No abstract