SUMMARYA spin-probing technique was first applied to a study of a non-magnetic ionomer, polyethylene/methacrylic acid copolymer neutralized with Zn2+ (E-MAA-Zn); 2 mol-Vo Cu2+ ions were incorporated in replacement of Zn2+, and its ESR spectra were observed in detail at various temperatures in order to obtain physico-chemical properties of E-MAA-Zn, especially its structural changes. We found no significant influence of the 2 mol-Vo Cu2+-incorporation upon the properties of the Zn2+ ionomer by differential scanning calorimetry (DSC), which showed two endothermic peaks, 1) an irreversible one at lower temperature which is associated with the ionic aggregate phase in the ionomer, 2) a reversible one at higher temperature with considerable thermal hysteresis which is due to melting of the polymer main chains. ESR hyperfine coupling constants (A and A I) of Cu2+ showed no sign of structural changes of the polymer around the phase-transition temperatures, whereas ESR g-values (sll and g I) of Cu2+ proved the onset of the softening of the polymers to be attributable to polymer melting. The latter slope-changes in the temperature dependences were reversible, although with considerable thermal hysteresis. These findings are compatible with the DSC data. As for the irreversibility regarding the endotherm at lower temperature, broad ESR hyperfine components recovered gradually, indicating an order-disorder nature of the ionic aggregate phase transition.

SUMMARY:Temperature-dependent ESR spectra of Cu2+-Cu2+ pairs in ethylene/methacrylic acid copolymer neutralized with Cu(I1) were reexamined in detail. The resonance positions and the linewidths of one of the ESR fine-structure lines showed thermal distension of the Cu2+-Cu2+ distance, and the slopes in the temperature variations changed at the temperature associated with melting of the polymer crystallites. No meaningful anomalies were observed around the temperature at which the preceding endothermic transition takes place. In this transition, the Cu2+-Cu2+ pairs seems to enter a disordered state, keeping almost the same paired structure. In contrast to this irreversible order-disorder transition, the melting process in the most part of the polyethylene crystallite phases starts to impose stress upon the Cu2+-Cu2+ pairs, accompanying the slope changes of the ESR parameters. These reversible variations with remarkable thermal hysteresis are compatible with the DSC analyses.