Influence of Sodium Ion Content on the Structure and Mechanical Properties of Polyethylene Methacrylic Acid Ionomers

Abstract

Ionomers, such as neutralized ethylene-methacrylic acid (EMAA) copolymers, are widely used materials whose mechanical properties are governed by the interplay between crystalline domains and ionic aggregates. In this study, we systematically investigate how varying the degree of neutralization affects the crystallization kinetics and mechanical performance of EMAA ionomers. Our results show that increasing neutralization reduces the mobility of ionic associations, leading to suppressed crystallization. Notably, the tradeoff between physical crosslinking and crystallization determines the material’s creep and tensile resistances, and an optimal degree of neutralization has been identified where the highest creep resistance, yield resistance, and toughness have been achieved. In particular, the flow-induced breakup of ionic associations appears to be responsible for the sample toughening before the slip of the crystalline lamellae. These findings provide insights into the design of ionomer materials with tailored mechanical performance.