Bis(1-propyloxy-2,2,6,6-tetramethylpiperidin-4-yl)-diazene – An innovative multifunctional radical generator providing flame retardancy to polypropylene even after extended artificial weathering

Abstract In this work, we report the synthesis and use of an innovative multifunctional radical generator, i.e., bis(1-propyloxy-2,2,6,6-tetramethylpiperidyl)-4-diazene (AZONOR) that alone can effectively provide flame retardancy and self-extinguishing properties to both polypropylene films and plaques. Polypropylene samples containing very low concentrations of 0.25–1 wt% of this additive can successfully pass not only the fire standard tests of DIN 4102 B2 and NF P92-505 but also the more challenging UL94 VTM-2 standard. Besides relative low levels of addition and having no detrimental effect on polypropylene appearance or its mechanical and processing properties another great advantage offered by this flame retardant is its multifunctionality, i.e., high flame retardant durability after artificial weathering. Thus, even after 2000 h of artificial weathering no significant decrease in flame retardant efficacy could be observed.