Modification of sulfonated polyphenylquinoxaline by alkali and alkaline earth metal cations

Abstract

Salts of sulfonated polyphenylquinoxaline (SPPQ) containing alkaline earth metal ions—Mg²⁺, Ca²⁺, and Ba²⁺—were synthesized. The paper considers their solubilities, the properties of solutions, and thermal stability in comparison with analogous characteristics of SPPQ salts with alkali metals. The introduction of alkaline earth metal cations into SPPQ affords soluble polymeric salts having high thermal stability. Solutions of SPPQ salts in N-methylpyrrolidone (N-MP) containing Mg²⁺, Ca²⁺, and Ba²⁺ ions do not exhibit polyelectrolyte properties, unlike solutions of SPPQ salts in which the counterions are Li⁺, Na⁺, and K⁺. Solutions of SPPQ and its salts in N-MP can be converted to water-soluble form by dialysis. This opens up new prospects for using the polymeric salts.