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. (C) 2012 Elsevier Ltd. All rights reserved.