Monolayers of Poly(methyl acrylate) Saponified Partially in Homogeneous and Heterogeneous Systems

Abstract
Poly (methyl acrylate) prepared by radical polymerization of methyl acrylate was saponified partially in acetone-water mixtures (5 : 2 and 100 : 1 by volume), using sodium hydroxide as the catalyst. Saponification in an acetone-water mixture of a 5 : 2 ratio by volume proceeded in a homogeneous state, but the reaction solution of a 100 :1 ratio by volume was in a white-turbid state, in which saponification proceeded in a heterogeneous state. The properties of the monolayers of polymers saponified in different states were studied at the air/water interface by measuring the surface pressure. The limiting areas obtained on distilled water for each polymer saponified in these two systems decreased linearly with an increase in the degree of saponification. However, the monolayers of polymer saponified in a homogeneous system were more stable on sodium chloride solution than those obtained in a heterogeneous system, and gave the limiting areas on solutions above 5% corresponding with the theoretical values calculated from the areas per methyl acrylate and acrylic acid residue and the degree of saponification. This can be explained by the fact that some of the hydrophilic parts of the saponified polymers submerged into the water phase were squeezed out onto the water surface by the salting out effect. On the other hand, those values obtained in a heterogeneous system neither corresponded to the theoretical values nor gave reproducible areas at high concentrations. These facts may be due to the differences in the states of the saponified polymers.

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