랜덤 스타이렌 아이오노머의 물 흡수

Abstract

Ionomers are the polymers containing a small amount of ionic groups in the relatively non-polar polymer backbone chains. Because of the nature of the ionomers, if water molecules meet the ionomer, the water molecules reside in the ionic aggregates and act as polar plasticizer. When the ion content of ionomers is sufficiently high, the plasticization by water becomes a major drawback for the ionomer applications. Thus, naturally the contact of water with the ionomers of high ion contents has been avoided as much as possible. In this study, we investigated the effects of the type of neutralizing cations on the water uptake of poly(styrene-co-methacrylate) ionomers of varying degrees of ion contents to understand the water uptake behavior of ionomers more quantitatively. Firstly, we prepared poly(styrene-co-methacrylic acid) copolymer containing 6.1, 12.2 and 21.3 mol% of acidic units. Then, the acid groups of the copolymers were neutralized with various cations including Li(I), Na(I), K(I), Cs(I), and Ba(II). Subsequently, we molded the coin-type samples using a hot press and a mould. Then, the polymer specimens were immersed in water. After certain periods of time, the weights of specimens were measured, and compared with those of the samples containing no water. It was found that the acid copolymer did not absorb the water noticeably. In the cases of the ionomers, the initial rates of the water uptake were very high and the amounts of water in the ionomers reached maximum within two to three days, and then leveled off with further increasing absorption time. For 6.1 mol% ionomers, it was observed that the initial rates of water absorption were not dependent on the type of cations. This indicates that the size of the cations matters for the initial rate of water uptake. However, the maximum amounts of water were relatively low for the Li- and Ba-ionomers. On the other hand, the amounts of absorbed water were relatively large for the Cs- and K-ionomers. This suggests that the strength of the interactions between ion pairs of the ionomers affects the water absorption behavior of the ionomers. In the cases of 12.2 mol % and 21.3 mol% ionomers, the initial rates of water uptake seemed to depend on the type of cations. The trend of the maximum amounts of water for the 12.2 mol% ionomers was similar to that for the 6.1 mol% ionomers. However, the trend was found to be opposite for the 21.3 mol% ionomers. This indicates the ion content also plays an important role in the water absorption behavior of the ionomers.