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 (f r ) and the thermal expansion coefficient (α f ) 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.

Fourier-transform infrared spectra (FTIR) measurement was made on zinc and sodium ionomers (EMAA-Zn and EMAA-Na) of ethylene-co-methacrylic acid copolymer. It was found that the asymmetry stretching vibration peak of CO bond of COO-group in ion aggregates of EMAA-Na appeared at lower wavenumber, compared with EMAA-Zn. This means that complete and stable ion aggregates exist in EMAA-Na. Differential scanning calorimetry (DSC) measurement showed that endotherm peak (T1) in lower temperature range resulted from melting of subcrystallites of crystalline ethylene in EMAA and EMAA ionomers. Tensile properties and dynamic viscoelasticity of EMAA greatly changed with the introduction of ionic groups.

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Stress relaxation behavior under large step shear strain γ for ethylene-co-methacrylic acid copolymer (EMAA) and its ionomers (EMAA-Zn and EMAA-Na) was studied in the melt state. EMAA ionomers show higher relaxation modulus G (t,γ ) and slower relaxation rate than EMAA. At 140°C the strain dependence of G (t,γ ) for EMAA ionomers is very strong. The corresponding damping function h (γ ) decreases with γ in two steps around γ =0.6 and γ =4. This suggests that the ion aggregates become small in two steps. However, at 200°C h (γ ) monotonically decreases with γ , indicating that the ion aggregates are already small and become smaller monotonically with increasing γ . Compared with EMAA-Na, EMAA-Zn has higher stress relaxation modulus because of strong interactions due to cooperation between the carboxyl acid group and Zn 2+ .