Design and Utilization of Nitrogen Containing Flame Retardants Based on N-Alkoxyamines, Azoalkanes and Related Compounds

The desire to reduce the load on the ecosystem has in recent years driven flame retardant research toward halogen-free systems or at least toward combinations that permit a substantial reduction in the percentage of halogenated substances. This review provides a comprehensive and chronological insight into some novel developments within the family of nitrogen-based flame retardants and their structure–property relationships. It focuses on a series of different N-alkoxy hindered amines (NOR), azoalkanes (AZO) of the general formula R′–NN–R, and related compounds such as azoxy, hydrazone, azine, triazene, tetrapotassium azo diphosphonate (INAZO), and bis(1-alkoxy-2,2,6,6-tetramethylpiperidyl)-4-diazene compounds. These nitrogen-containing flame retardants mainly exhibit self-extinguishing properties for polypropylene and polyethylene films or even in some cases for polypropylene moldings, polyurethane adhesives, and polystyrene. In addition, their performance in combination with various conventional flame retardant classes is discussed. Contrary to other nitrogen-containing flame retardants, such as melamines, the presented nitrogen-based flame retardants are effective at very low additive levels (<1 wt%), they do not weaken the mechanical or physical properties of the host polymer, and after structural optimization, they are likely to meet the criteria for sustainable production and development.