Investigation of microphase separation and thermal properties of noncrystalline ethylene ionomers. 2. IR, DSC, and dielectric characterization

The microphase structure of noncrystalline poly(ethylene-co-13.3 mol % meth acrylic 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-a ngle X-ray scattering (SAXS) and DSC studies, which has enabled a quantitat ive analysis of the SAXS ionic peak associated with ionic aggregates withou t being perturbed by the polyethylene lamellae peak. In 60% neutralized Na ionomer, it was revealed that almost 100% of MAA side groups including unne utralized COOH are incorporated into the ionic aggregates with an average i onic core radius (R-1) of similar to6 Angstrom . The dielectric relaxation studies showed that the ionic aggregates form a microphase-separated ionic cluster. Analysis of dielectric strengths indicated the most (similar to 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 indica ted that the ionic aggregates with R-1 similar to 4 Angstrom are almost iso lated and dispersed in the matrix; the formation of ionic cluster was not r ecognized. Similarly to partly crystalline E-MAA ionomers, all noncrystalli ne 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 chang es of the state of ionic aggregate region.