Synthesis of anionic water‐borne polyurethane with the covalent bond of a reactive dye

We successfully synthesized an anionic water‐borne polyurethane (PU) capable of reacting with a reactive dye to form a covalent bond with the dye molecule. The anionic water‐borne PU was synthesized and grafted with the reactive dye to form a dyed PU. First, the PU prepolymer was synthesized from 4,4′‐methylene bis(isocyanatocyclohexane), poly(tetramethylene glycol), 2,2′‐bis(hydroxymethyl) propionic acid (as an anionic center), and triethyleneamide (as a neutralizer). Then, pure water was added to emulsify and disperse the prepolymer to form an anionic water‐borne PU prepolymer. Finally, the extender N ‐(2‐hydroxyethyl) ethylene diamine was used to extend the anionic water‐borne prepolymer to form a PU polymer with hydroxyl groups that could further react with the reactive dye molecule. With respect to the heating properties, the dyed PU polymers exhibited higher glass‐transition temperatures of the hard segment than those without dye molecules. However, neither the glass‐transition temperature of the soft segment nor the melting temperature of the soft segment varied in the presence of dye molecules, but they were changed with various chain lengths of the soft segment. As for the mechanical properties, the modulus and strength of the dyed PU polymers decreased because of the bulkiness of their dye molecules, but the breaking elongation increased. Moreover, the inherent viscosity decreased in the presence of the dye molecules. As for the dyeing properties, the percentage of dye grafting was greater than 90%. The dye‐grafted PU exhibited a lower percentage of migration than PU extended with ethylene diamine (without hydroxy groups) and also showed a higher grade of colorfastness to light. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 797–805, 2002; DOI 10.1002/app.10336