A Study on Higher-order Structures and Dynamics of Ionic Aggregates in Ionomers

点击翻译按钮获取中文摘要

The ionomers are defined as polymers with non-polar backbones containing up to about 10 mol% salt groups of carboxyl or sulfonic acids. It can be, therefore, said that the ionomers is one of the hybrid materials. The ionomers can form the ionic aggregates, which improve the mechanical properties of them. In cadmium salt ethylene ionomers, it is confirmed that the ionic aggregates are also formed, from SAXS analysis. The size of the ionic aggregates of this ionomer becomes larger with the degree of neutralization. This is a different point in comparing with the other ethylene ionomers using divalent metal cations such as zinc cation. The ^<113>Cd MAS spectra with and without CP experiment for cadmium salt ethylene ionomer at various temperatures were observed. In CP/MAS spectra, a very broad peak is only observed at low temperatures. It can be seen that these spectra consists of several peaks appeared at about 120 to -50 ppm. Consequently, the broadening of this peak may be mainly caused by the very wide distribution of micro structures at surroundings of^<113>Cd nuclei in the ionic aggregates. At higher temperatures, this CP/MAS peak disappears, indicating that the mobility of ^<113>Cd nuclei close to the dipolar decoupling frequency and/or the CP efficiency becomes too low to detect the CP signals because of the high mobility of 1H nuclei at surroundings of ^<113>Cd. That is, the ionic aggregates in cadmium salt ethylene ionomers leads to mobile state from immobile one by heating. On the contrary, the ^<113>Cd MAS NMR spectra without CP experiment are observed only at high temperatures, and the width of observed peaks are relatively narrow compared with CP/MAS. In addition, the ^<113>Cd NMR chemical shift changes by temperature. These findings indicate that the mobility of the ionic aggregates is high at higher temperatures.