Poly(diphenylenesulfophthalide) and the related alkali-metal salts

Poly(diphenylenesulfophthalide) in which a sulfophthalide cycle functions as a hidden electrolyte group was synthesized, and its properties were studied. The treatment of poly(diphenylenesulfophthalide) with aqueous solutions of univalent metal hydroxides (LiOH, NaOH, KOH) leads to the quantitative opening of the sulfophthalide cycle to form the corresponding salts. The effect of concentration on the reduced viscosity of poly(diphenylenesulfophthalide) and its salts in various solvents were determined, and it was established that water plays an important role in the polyelectrolyte properties of solutions. It was shown that all salts absorb a great amount of water and that the lithium salt completely dissolves in water. In dilute solutions of the salts, an association of macromolecules takes place which subsequently transforms into the formation of physical gels (in water and glycerol) as the polymer concentration in solution grows. The incorporation of metal ions into poly(diphenylenesulfophthalide) increases its thermal stability and glass transition temperature. In both solution and the condensed state, polymer salts exhibit a bright color, which changes with both time and the amount of water contained in the polymer.