Dye-incorporated water-soluble polymer via click triazole formation

A click triazole-polymerization is proposed for the synthesis of a water-soluble polymer dye. 4,4′-Diazidostilbene-2,2′-disulfonate (DASS) sodium salt reacted with a diacetylenic derivative of para-methyl red (PMR) in water, which was catalyzed by copper (I) ion or accelerated under ultrasound irradiation. DASS formed a soluble polymer with a carboxylate salt of PMR showing a water solubility of 120 g/100 mL but it generated an insoluble polymer with an alkyl ammonium salt. The prepared polymeric dye underwent color transition at pH 5–6, which is higher than that of PMR and similar to that of ortho-methyl red (OMR). The quinonoid canonical structure of PMR generated a purple water solution and was dominant in the polymer solution at pH below 5. Intra-molecular hydrogen bonding between the triazoles and azo nitrogens was presumed to have induced the formation of the quinonoid structure. The color change of the polymer was reproducible during successive up/down pH cycles.

Para-methyl red was incorporated into a polymer where it was combined with water-soluble 4,4′-diazidostilbene-2,2′-disulfonate (DASS) sodium salt via click triazole formation. Clear color transition of the polymer was observed at pH 5–6 due to intra-molecular hydrogen bond of adjacent triazole group and reproducible during successive pH change.Figure optionsDownload as PowerPoint slideHighlights
► Water-soluble polymer dye was prepared by click polymerization.
► Para-methyl red incorporated polymer revealed reproducible color transition at pH 5–6, unlike para-methyl red at pH 2–3.
► Intra molecular H-bonding by triazole was suggested for the color transition.