Oe. Philippova et al., MIXED POLYELECTROLYTE IONOMER BEHAVIOR OF POLY(METHACRYLIC ACID) GEL UPON TITRATION/, Macromolecules, 29(13), 1996, pp. 4642-4645
The titration of poly(methacrylic acid) gel with sodium methoxide was
studied in water, methanol, dioxane, and their mixtures. There are thr
ee main regimes of the swelling behavior of the gels depending on the
dielectric constant epsilon of the medium. In polar media with epsilon
larger than a critical value epsilon 1, the gel swells monotonically
with the increase of the degree of ionization, alpha, due to the osmot
ic pressure of counterions. In media with epsilon smaller than a criti
cal value epsilon(2), the gel always shrinks with increasing a due to
ion-pair formation with their aggregation to multiplets. In media with
dielectric constants ranging from epsilon(1) to epsilon(2), the gel s
wells at alpha up to ca. 0.1 and then collapses. The collapse induced
by ionization is in agreement with recent theoretical findings.