고체 상태의 무정형 랜덤 아이오노머의 기계적 성질과 형태학

Abstract

Ionomers are ion-containing polymers that have a relatively small amount of ionic groups along relatively non-polar polymer backbone chains. Since their first appearance ca. 40 years ago, ionomers have been studied extensively because they exhibit unique physical properties owing to the ionic interaction. It has been well known that ionic groups of ionomers tend to aggregates since they are in a matrix of low dielectric constant, thus forming ionic aggregates (so-called multiplets). The rigidity of the multiplets depends on the strength of the ionic interactions between ionic groups, and the mobility of chains surrounding the multiplets is reduced. When the multiplets are sufficiently dense so that the regions of restricted mobility surrounding each multiplet overlap, thereby larger regions of restricted mobility (so-called clusters) form. The cluster regions show their own Tg, i.e. cluster Tg, that is higher than the Tg of ion-poor matrix phase. In the present study, we investigated the dynamic mechanical properties and morphology of amorphous random ionomers in a solid state using dynamic mechanical thermal analysis (DMTA) and small-angle x-ray scattering (SAXS) techniques. This thesis consists of five chapters. In the first chapter as an introduction section, the history and general characteristics of ionomers are presented. The second chapter deals with the morphology of poly(ethyl acrylate-co-itaonate) ionomers neutralized with various cations as a function of ion contents, degree of neutralization, and the type of cations. In addition, the glass transition temperatures of poly(ethyl acrylate) ionomers neutralized with various cations were explored, as well. The change of the cation from Li+ to either Na+ or Zn2+ resulted in the increase in the Bragg distance between ionomers, i.e. the Bragg spacing increased from ca. 2.7 to 3.0 nm for the 5.8 mol% ionomers. For the 11.9 mol% ionomers, the Bragg spacing increased from ca. 2.4 to 2.7 nm, when the cation was changed from Li+ to either Na+ or Zn2+. These results indicated that the presence of the two ionic groups in the repeat unit probably affected the formation of multiplets. In that study, the SAXS data and the density values of the ionomers, the number of ionic groups per multiplet and the size of the multiplet of the ionomers were calculated. The multiplet radii were also calculated with the information of the estimated size of atoms in the multiplets. In the third chapter, the mechanical properties and morphology of homoblends of poly(ethyl acrylate-co- itaconate) (PEAITA) and poly(ethyl acrylate-coacrylate) (PEAA) ionomers were discussed. It was found that the compositional variation of the ionomer blends did not affect the matrix and cluster Tgs of the ionomer blends. However, the ionomer blends showed two ionic plateaus, and the changes in the two ionic moduli of the blends were directly related with the relative amounts of the two ionomers in the blends. In addition, it was observed that the calculated ionic moduli using the model dealing with hard filler dispersed soft matrix (and soft filler dispersed hard matrix) materials were close to the experimental ionic modulus values. Therefore, it was suggested that the PEAITA/PEAA ionomer blends acted not as miscible blend but as phase-separated composite materials. The fourth chapter describes the mechanical properties of poly(styrene-co-methacrylate-co-styrenesulfonate) ionic terpolymers. To prepare the terpolymers, the poly(styrene-co-methacrylic acid) copolymers were sulfonated. The dynamic mechanical data revealed that the ionic terpolymers showed mainly the properties of sulfonated ionomers. This implied that the strength of ionic interaction was more important than the ion content for determining the ionomer properties. In addition, the results obtained from SAXS experiments indicated that the morphology of the ionic terpolymers was mainly affected by Na-sulfonate ionic groups. Thus, it was speculated that when the neutralizing agents were added to the acid form terpolymers, the Na-sulfonated ionic groups, ionic interaction of which was stronger than that of the Na-carboxylate ionic groups, formed ionic aggregates with another Na-sulfonate ion pairs at their preferred distances. Then, the Na-carboxylate ion pair would reside in multiplets with Na-sulfonate ionic groups or in a matrix singly. Therefore, the morphology and mechanical properties of the ionic terpolymers depended mainly on the sulfonation level, not on the carboxylation degree. In the fifth chapter, the mechanical properties of the mesogen unit-containing poly(styrene-co-styrenesulfonate) ionomers were discussed. It was observed that the mesogen unist in the ionomer formed a nematic phase. It was also found that above 6 mol% of ions the ionic modulus changed significantly. The SAXS profiles showed that the size of the multiplets of these liquid crystalline ionomers was larger than that of the multiplets of the ionomers neutralized with Na.