Insight into structure-property relationship of diazo-based carbene-type dyes towards high fixing performance on synthetic fiber

This paper investigated the reaction performance of diazo based carbene dyes with synthetic fibers, particularly the substituent effect of reactive group on fixation property of dyed fibers. Thus, a series of six azo dyes containing one diazo ester group were designed and synthesized. Their structures, absorption and thermal properties were firstly characterized. Four typical synthetic fibers, including polyurethane (PU), polyamide (PA), polyethylene terephthalate (PET), and polypropylene (PP) fibers, were dyed using the diazo type dyes in organic solvent followed by fixing the dyed fibers under high temperature. Substituent at alpha-position to diazo group was found to significantly affect the thermal stability of dye molecules and chemical reactivity of dyes with fibers. In donor-acceptor system, electron-withdrawing group on phenyl substituent increased the thermal stability of diazo moiety, and also largely improved the reactivity of dyes with various types of fibers. As comparison, diazo dyes having acceptor-acceptor system exhibited high thermal stability and needed more energy to initiate the reaction. However, these dyes, once initiated, presented higher reactivity with fibers, especially with PET fiber. The reaction mechanisms between dyes and synthetic fibers were reasonably speculated through small molecule simulation reactions and theoretical calculations, combined with the dye fixation results on fibers. All the aliphatic C-H or N-H bonds, as well as aromatic structures existed in fibers were possible sites for carbene reactions. These reactions included at least insertion reaction, addition reaction, and Wolff rearrangement reaction. N-H bond insertion reaction underwent much more easily than C-H bond insertion reaction, while addition reaction with phenyl group appeared the most difficult. Besides, carbonyl group lied in alpha-position to diazo group would induce a Wolff rearrangement reaction, which was also an efficient pathway for combining dyes with fibers containing N-H bonds.