Eco-friendly Synthesis of Ionic Helical Polymers and Their Chemical Properties and Reactivity

Reaction of -(2,4-dinitrophenyl)pyridinium chloride (salt(Cl)) with sodium dicyanamide (Na(CN)N) resulted in anion exchange between Cl and (CN)N to yield a new Zincke salt, salt((CN)N). Reactions of salt((CN)N) with piperazine, specifically ()-(-)- or ()-(+)-2-methylpiperazine under eco-friendly conditions, such as in aqueous solution, in the absence of a catalyst, and at room temperature, resulted in pyridinium ring opening to yield ionic high-molecular-weight polymers with 5-2,4-dienylideneammonium dicyanamide units or chiral 5-(2-methylpiperazinium)-2,4-dienylideneammonium dicyanamide units, namely, polymer(H;(CN)N), polymer(-Me;(CN)N), and polymer(-Me;(CN)N). UV-Vis measurements revealed that the π-conjugation system expanded along the polymer chain due to the orbital interaction between the electrons on the two nitrogen atoms of the piperazinium ring. Circular dichroism (CD) measurements revealed a helical conformation of the main chain in polymer(-Me;(CN)N) and polymer(-Me;(CN)N). The reaction of polymer(H;(CN)N) with -phenylenediamine (PDA) caused recyclization of the 2,4-dienylideneammonium unit and resulted in depolymerization to yield -(4-aminophenyl)pyridinium dicyanamide. Cyclic voltammetry analysis suggested that the polymers obtained in this study undergo electrochemical oxidation and reduction.