왕관형 에터를 첨가한 스타이렌 아이오노머의 기계적인 성질과 형태학

Abstract

In the present work, the effects of the degree of neutralization, the addition of crown ether (CE) or pentaethylene glycol (EG) on the dynamic mechanical properties and morphology of the styrene-based ionomers were investigated. It was found that the decrease in the neutralization degree reduced the clustering degree of MA5.9Na ionomers. This was owing to the fact that the acid groups of methacrylic acid resided in the multiplets together with the ionic groups of the ionomers, leading to a H+↔Na+ exchange mechanism. This type of exchange mechanism made the acid groups act as multiplet plasticizer, which affected the multiplet formation and lowered the clustering degree. On the other hand, It was observed that the addition of CE affected the ionomer's clustering more strongly than the neutralization degree. This might be owing to the fact that the CE formed complexes with Na+, enlarged the cation size and reduced effective charge density of the cation, which weakened the strength of interactions between ion pairs in the multiplet. In addition, the complexes resided in the multiplets acted also as multiplet plasticizer. These two factors influenced the mechanical properties and morphology of MA5.9Na ionomers simultaneously. In the case of EG, we found a more significant plasticization effect, compared to that of CE. This was reasonable because the mobility of linear EG would be higher than that of ring-type CE. The activation energies (Ea) for the glass transitions of ionomers also supported the interpretation mentioned above. That is, the Ea for the matrix Tg of ionomer decreased more significantly with adding EG to the ionomer, compared to CE, indicating that the EG made the ionomer need smaller Ea for the matrix Tg, compared to the CE.

For SA5.6Na ionomers, it was found that the addition of CE affected the matrix Tg more strongly, than the neutralization degree. In addition, the curve deconvolution of the loss tangent peaks revealed that the size of cluster tan δ peak decreased with decreasing neutralization degree, but it remained more or less constant with the addition of CE. This indicated that the addition of CE did not affected the size of the cluster regions.

Thus, it was proposed that the difference in the effects of the addition of CE was caused by the differences in the strength of interactions between the anionic groups and cationic groups of MA5.9Na and SA5.6Na ionomers and 3-dimensional packings of ion pairs in the multiplets. That is, in the case of SA5.6Na ionomers having stronger interactions between ion pairs, Na+ cation that formed a complex with CE could interacted, probably very weakly, with sulfonate anionic group of the ionomer, forming “multiplets”. This, in turn, made the ionomer showed ionomeric characteristics. This interpretation was also evidenced by the morphological data. When CE was added to the MA5.9 Na ionomer, the average size of multiplets decreased, and the average distance between multiplets also decreased. On the other hand, when CE was added to the SA5.6 Na ionomer, the average size of the multiplets increased, but the average distance between multiplets increased. This SAXS data were in accordance with the interpretation mentioned above. Upon the Soxhlet extraction, the CE-Na+ complex-extracted SA6.0Na-CE and MA6.7Na-CE ionomers showed different dynamic mechanical data. This was probably owing to the difference in the strength of interactions between CE-Na+ cations and carboxylate or sulfonate anionic groups of MA6.7Na and SA6.0Na ionomers, respectively.