The solubility and swelling of latex particles

Abstract

A vapor pressure method has been used to determine the solubility of vinyl acetate, styrene, and vinyl hexanoate in both the aqueous phase and in the polymer particles. All the systems have been measured at 30° or 60°C. or both. The vapor pressure measurement permits an estimation of the partial molar free energy of the monomer-polymer system. A thermodynamic treatment of the latex system, modified from that of Morton, yields a relationship from which the monomer-polymer interaction parameter, μ, and the interfacial tension, γ, may be obtained. Several tests of the thermodynamic relationship involving variations of the interfacial tension proved successful. Reasonable values are obtained for both the interaction parameter and the interfacial tension, although checks of two interaction parameters with literature values show some differences due to dissimilarities in the conditions of measurement. The solubility figures for the systems studied are high compared to most literature values at other temperatures; however, the difference is readily explained by consideration of the dependence of solubility on the temperature. Increased solvency of the monomers at polymerization temperatures tends to swell the particles more than at ambient temperatures. The increased solubility of monomer in the polymer is reflected in a lowering of the interaction parameter. The values determined at polymerization temperatures are obviously more representative of the polymerizing system.