Local structure and composition of the ionic aggregates in Cu(II)-neutralized poly(styrene-co-methacrylic acid) ionomers depend on acid content and neutralization level

The morphologies of poly(styrene-ran-methacrylic acid) (SMAA) copolymers neutralized with Cu(II), including the local structure and composition of the ionic aggregates, were investigated as a function of acid content and level of neutralization. X-ray scattering and scanning transmission electron microscopy (STEM) results suggested that the sizes of the ionic aggregates in Cu(II)-neutralized SMAA are independent of the acid content and neutralization level. The number density of ionic aggregates increased slightly with acid content and neutralization level, but the increase was significantly less than expected for aggregates of fixed composition. Electron spin resonance (ESR) spectra of Cu(II) detected three distinct cation sites whose relative amounts changed with acid content. These results combined to indicate that the ionic aggregates contain non-ionic species and that the aggregate compositions become more ionic with increasing acid content and neutralization level.