Effects of the Degree of Neutralization and Type of Cations on the Water Absorption Behavior of Styrene-co-Methacrylate Ionomers

In this study, the effects of the degree of neutralization and cation type on water absorption of poly(styrene-co-methacrylate) ionomers were investigated. It was found that the water absorption of the ionomer increased as the degree of neutralization increased. It was also observed that for the same ion content, fully neutralized ionomers had less water absorption than partially neutralized ionomers. In the case of ionomers neutralized with various cations, water absorption increased when the type of cation was changed from Li+ to Na+, whereas the water absorption decreased when the type of cation was changed from Na+ to Cs+. Ba2+-neutralized ionomers absorbed less water than K+-neutralized ionomers with a cation size similar to Ba2+. Based on the above findings, it was concluded that the water absorption of ionomers could be understood only by simultaneously considering the number and size of multiplets, the plasticization of multiplets, and the contact surface area occupied by the polymer chains emanating from the multiplets.