Effect of hydrogen bonding and ionic aggregation on the melt rheology of an ethylene–methacrylic acid copolymer and its sodium salt

Abstract

AbstractA study has been made of the dynamic and steady shear melt theology of an ethylene‐methacrylic acid copolymer, its methyl ester, and 70% neutralized sodium salt. Measurements were made with a Rheometrics mechanical spectrometer using the eccentric rotating disks and cone‐and‐plate geometries over a temperature range of 120–180°C and frequency range of 10−3 to 102 rad/sec. Correspondence was found between steady shear viscosity and the complex dynamic viscosity for the ester and acid materials. Over the temperature and frequency range studied the time‐temperature superposition principle was applicable to G′ data for each of the derivatives and a supermaster curve could be constructed from the three individual master curves. Time‐temperature superposition was found not applicable to G″ data for the sodium salt. Differences in rheological response between the ester and acid copolymers are explained by differences in Tg. It is suggested that differences in temperature shifts ΔT required to produce G′ superposition between the three derivatives reflect differences in ΔH for interchain interactions. A mechanism for flow of clustered ionomers is consisting of an initiation and a propagation step.