DC CONDUCTION PROPERTIES OF A MODEL ETHYLENE METHACRYLIC-ACID IONOMER

dc conductivity (sigma) in the temperature range from room temperature to 400 K was examined for a zinc(II) complex salt of a poly(ethylene-co-5.4 mol % methacrylic acid) (EMAA) ionomer with 1,3-bis(aminomethyl)cyclohexane (BAC), where the neutralization degree by zinc(II) was 60% and the equivalent ratio of BAC to COOH was 0.4. In sigma vs the reciprocal of temperature (1/T) plots measured in the heating process, a sample aged at room temperature exhibited a bend near 366 K and an anomalous peak near 325 K. The bend corresponds to the melting point of polyethylene crystallites(T(m)). Interestingly, the temperature exhibiting the anomalous peak coincided with an order-disorder transition temperature of the ionic clusters (T(i)) observed by differential scanning calorimetry (DSC). This peak was not observed in the cooling process from a temperature above T(m), but in the subsequent heating, the peak reappeared; the peak area became larger, and its position shifted to higher temperatures during aging at room temperature. This thermal hysteresis is phenomenologically analogous to that of the T(i) peak observed on DSC. From DSC, X-ray scattering, and thermally stimulated depolarization current results, it was concluded that the de conduction mainly comes from ionic conduction and that the 325 K peak originates from the ionic cluster transition at T(i).