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 degrees C to 200 degrees 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 degrees C-170 degrees C and the other in the range of 180 degrees C-200 degrees C. Even at 200 degrees 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 degrees C and 180 degrees C. The free volume fraction (f(r)) and the thermal expansion coefficient (alpha(f)) in the range of 180 degrees C-200 degrees C are larger than those in the range of 140 degrees C-170 degrees 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.