Dynamic Viscoelasticity of Ionomers Based on Ethylene-co-Methacrylic Acid Copolymer in the Melt State.

Dynamic viscoelasticity of ethylene-co-methacrylic acid copolymer (EMAA) and its ionomers (EMAA-Zn and EMAA-Na) has been measured in the melt state. The time-temperature superposition principle is applicable to data of angular frequency dependences of storage modulus (G') and loss modulus (G") for EMAA very well from 140°C to 200°C. On the other hand, data for ionomers give two separated master curves with different temperature dependences of shift factor, one from the data obtained in the range of 140°C-170°C and the other in the range of 180°C-200°C. Even at 200°C, the moduli G' and G" are still much higher than those of EMAA. These results indicate that a structure change in EMAA ionomers occurs between 170°C and 180°C. The free volume fraction (fr) and the thermal expansion coefficient (αf) in the range of 180°C-200°C are larger than those in the range of 140°C-170°C for EMAA ionomers. This implies that in higher temperature range, some hydrocarbon chains depart from cross-links of ion aggregates and move much more freely.