The FT-IR spectrum of PAZ-NT-PAZ also shows the absorption peak of the symmetrical stretching vibration of the azo group (-N=N-, 1384 [cm.sup.-1]) which confirms the existence of azo chromophores in PAZ-NT-PAZ.
In addition to that they are highly resistant to aerobic biodegradation due to the strong electron-withdrawing characteristics of the azo group. Under anaerobic conditions the degradation takes place slowly by decolorization.
RNIP promotes the cleavage of azo group in basic conditions : with particularly active (polymer protected) RNIP samples, the 1A2N given rise partially further oxidizes to o-naphthoquinone, which condenses back with SA to yield a molecule close in structure to AO7, so mimicking a partial reversal of the degradation reaction.
An environment with low oxygen content facilitates the breakdown of the azo group links due to a reduction mechanism, which can result in the formation of colorless solutions, as demonstrated in the study by Chen et al.
In the prior works attempt insertion of azo group in phenol novolac resin at a molecular level has recently been shown to impart improvements in thermal properties, mechanical properties, flame retardance, and char yields in cured epoxy resins [23, 24].