Preferential Adsorption Determined by Specific Interactions. Poly(dialkyl itaconates) /1,4-Dioxane/Methanol

The variation of the preferential adsorption coefficient, λ, with the solvent composition, for a series of poly(dialkyl itaconates) is studied in the mixed solvent 1,4-dioxane/methanol. In these systems specific hydrogen bonding of methanol to 1,4-dioxane and to the polymer take place. Methanol is preferentially adsorbed at low methanol composition, but 1,4-dioxane is preferentially adsorbed at high compositions. All systems here studied show inverstion in λ. The variation of λ with solvent composition depends on the size of the side group of the polymer. In order to interpret the influence of hydrogen bonding on these systems, the recent theory of the association equilibria has been applied. According to the results of this theory, the inversion and extrema of λ come from a balance of effects: the high quality of 1,4-dioxane as solvent and the length of the chains of self-associated methanol, which are complexed with the polymer. It is possible to find a quantitative agreement between this theory and experimental results by using reasonable values for the association constants and interaction parameters of the theory.