Mixed Polyelectrolyte/Ionomer Behavior of Poly(methacrylic acid) Gel upon Titration

Abstract

The titration of poly(methacrylic acid) gel with sodium methoxide was studied in water, methanol, dioxane, and their mixtures. There are three main regimes of the swelling behavior of the gels depending on the dielectric constant ε of the medium. In polar media with ε larger than a critical value ε1, the gel swells monotonically with the increase of the degree of ionization, α, due to the osmotic pressure of counterions. In media with ε smaller than a critical value ε2, the gel always shrinks with increasing α due to ion-pair formation with their aggregation to multiplets. In media with dielectric constants ranging from ε1 to ε2, the gel swells at α up to ca. 0.1 and then collapses. The collapse induced by ionization is in agreement with recent theoretical findings.