Relationship between the chemical structure, morphology, and water absorption of styrene-co-itaconate ionomers

Abstract

In this study, the water absorption of poly(styrene-co-itaconate) PSITNa ionomers, having two ion pairs in an ionic repeat unit, was investigated. Plotting the water absorption data as a function of the ionic repeat unit content revealed that the PSITNa ionomer exhibited more water uptake than the poly(styrene-co-methacrylate) PSMANa ionomer, having one Na-carboxylate ion pair per ionic repeat unit. On the other hand, when the water absorption data were simply expressed as a function of the ion content, it was found that the PSMANa ionomer showed more water absorption than the PSITNa ionomer. These results and the SAXS results suggested that to increase the degree of water absorption of the ionomer, it would be better for the ion pairs of the ionomer to form aggregates with other ion pairs rather than to exist alone in the matrix. In addition, it was observed that the degree of water absorption of the ionomer gradually improved as the size of the cation used for neutralization of the ionomer increased. These results and morphological results indicated that when the strength of interaction between ion pairs was weakened, the number of ionic aggregates decreased, and, at the same time, the ionic aggregates readily absorbed water due to weak interaction between ion pairs in the aggregates. (GRAPHICS)