Post‐modification of azo dyes using an α‐phenyl diazo ester for improving the colour fixation properties of polyurethane fibre

Colour fastness of polyurethane fibre dyed with conventional disperse dyes is always poor owing to the insufficient affinity between fibres and dyes. Thus, three novel azo dyes containing an α‐phenyl diazo ester moiety were designed in this study. The dyes were synthesised through two‐step post‐modification of a hydroxylated azo benzene chromophore. All three dyes were characterised using proton and carbon nuclear magnetic resonance, high‐resolution mass spectrometry and infrared spectrometry. The ultraviolet‐visible absorption and thermal properties of the dyes were also studied. Fixation properties of these dyes on polyurethane fibre were examined using samples dyed using a non‐aqueous dyeing method. Practicality of these dyes, that is colour depth, fixation value, colour fastness and dye migration degree, was further verified on fibre dyed via an aqueous dyeing method. Finally, the mechanical properties of the dyed polyurethane fibre were explored.