Conformational transition in poly(methacrylic acid)

The potentiometric behaviour of poly(methacrylic acid) was examined in water/1,4‐dioxane mixtures at 25°C. Conformational transitions were observed in about the same range of apparent ionization in the 1,4‐dioxane concentration range 0 to 15 vol.‐%. Transitions were not observed in the 1,4‐dioxane concentration range 20 to 35% and the corresponding Henderson‐Hasselbalch plots were found to be linear. Phase separations were observed to occur beyond 40 vol.‐% 1,4‐dioxane. The free energy of the conformational transition decreased very rapidly with the initial incorporation of 1,4‐dioxane but slowly at higher concentrations. Van der Waals methyl‐methyl interactions as the cause of the compact form has been inferred. The large increase in intrinsic viscosity observed for the unneutralized poly(methacrylic acid) in a relatively narrow range of composition of the 1,4‐dioxane/water mixtures has been ascribed to a solvent induced conformational transition.