Synthesis of a New Polyanion Possessing Dense 1,2,3-Triazole Backbone

Polyanions are an important class of water-soluble polymers because polyanions are utilized in a wide range of industrial fields. It is thus a great challenge to develop polyanions with novel structures to make their applications broader. In this study, a new polyanion with a dense 1,2,3-triazole backbone, poly(4-azido-5-hexanoic acid) (poly(AH)), was synthesized by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization of t-butyl 4-azido-5-hexanoate followed by hydrolysis of the t-butyl ester groups. Turbidimetric and potentiometric titration data indicated that poly(AH) was well soluble in water under basic conditions (pH < 7) and a weaker polyanion (apparent pK_a = 5.4) than polyacrylic acid (apparent pK_a = 4.5). Adsorption tests exhibited that sodium salt of poly(AH) (poly(AH)Na) adsorbed most preferably Fe³⁺ among the four metal ions examined, i.e., Cu²⁺, Pb²⁺, Li⁺, and Fe³⁺. ¹H spin-lattice relaxation time measurements indicated that Fe³⁺ ions were adsorbed favorably onto the 1,2,3-triazole residues.