Mechanical Properties of Poly(methyl methacrylate-co-3-sulfopropyl methacrylate) Ionomers Acting as a Filled System

The dynamic mechanical properties of newly-made poly(methyl methacrylate-co-3-sulfopropyl sodium methacrylate) (M-SPMA) ionomers were measured and compared with those of methyl methacrylate ionomers having sodium methacrylate units (M-MA) and styrene ionomers having SPMA or MA units (S-SPMA or SMA). It was observed that the position of the matrix loss tangent peak of M-SPMA ionomers was not changed by the ion content, but the size of the peak was decreased. At high ion contents, however, the ionomers showed a cluster loss tangent peak and a very weak SAXS peak. These results were quite different from those obtained from the styrene ionomers. Thus, it was concluded that this dissimilarity was due to the differences in the polarity and persistence length of PS and PMMA. When the mechanical data of M-SPMA ionomers were compared with those of M-MA ionomers, M-SPMA and M-MA ionomers were found to behave like a filled system and a cross-linked system, respectively. This was due to the fact that M-SPMA ionomers had propyl groups and sodium sulfonate ion pairs, and thus the ionic groups formed fewer and larger ionic aggregates than M-MA ionomers.