Reactive dyes containing a sulphonylazide group can undergo fixation on nylon substrates by two different mechanisms. Under aqueous dyeing conditions, at or below 120d̀ C, the free amino end‐groups of the polymer attack the sulphonylazide group with displacement of azide ion, and results in attachment of the dye to the substrate by a sulphonamide linkage. In contrast, if the dyed substrate is subjected to dry heat fixation at 170d̀ C, the azide group decomposes to a sulphonylnitrene species which undergoes insertion into C‐H bonds of the polymer. The dye is again attached by a sulphonamide bridge, but in this case the amount of dye that can be fixed is independent of the amino end‐group content of the polymer.

e d s LS2 9JTThe transfer-printing properties of dyes containing the sulphonylazide (-SO2 N3) and arylazide (ArN3) groups have been examined for nylon 6.6 substrates. After sublimation at 200°C the azide group decomposes rapidly to a nitrene species which reacts with the polymer. Dye fixation occurs by insertion of the nitrene into the carbon-hydrogen bonds of the polymer, thus forming a nitrogen bridge. A competing reaction involves hydrogen abstraction from the substrate to give an amino derivative of the dye which is not covalently bound to the polymer. Fibre-grafting occurs to the extent of about 60-75% for both series of dyes. Unlike the sulphonylazides, the arylazide dyes show a pronounced colour change after transfer, as the thermallv-generated amino group is directly conjugated with the dye chromogen.