Versatile bis(1-alkoxy-2,2,6,6-tetramethylpiperidin-4-yl)-diazenes (AZONORs) and related structures and their utilization as flame retardants in polypropylene, low density polyethylene and high-impact polystyrene

Various analogs of (1-alkoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (AZONOR), symmetric and asymmetric (1,2,2,6,6 pentamethylpiperidin-4-yl)diazene flame retardants such as (N-t-butyl-N′-1,2,2,6,6 pentamethylpiperidin-4-yl)diazene (1), (N-cyclohexyl-N′-1,2,2,6,6 pentamethylpiperidin-4-yl)diazene (2), bis(1,2,2,6,6 pentamethylpiperidin-4-yl)diazene (3), bis(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (4), bis(1-ethoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (5), bis(1-propoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (6), bis(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (7), bis(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (8), bis(1-methoxy-2,2,6,6-tetramethyl-4-piperidone)azine (9) have been prepared and tested as either flame retardants alone or as flame retardant synergists in different polyolefin formulations. The flame retardant efficacy increased in the following order in polypropylene films DIN 4102 B2 test standard 4, 5 > 7, 6, 8> FLAMESTAB NOR116, 9, 2 > 1, 3. Only AZONOR flame retardants were capable of preventing burning dripping. Whereas in polyethylene films the best performance was recorded for 6 followed by FLAMESTAB NOR116 and 9 had clearly the lowest performance in this test series. The long term flame retardant efficacy in polypropylene plaques after accelerated weathering (WOM Ci 65 A, BPT 63 °C, 60% relative humidity. water spray) was also studied and the results showed that all AZONOR compounds exhibited excellent and unchanged flame retardant performance even after extended weathering for 2000 h. In polypropylene plaques a strong synergistic effect between 6 and brominated flame retardants and alumina trihydrate (ATH) were observed. Thus, the addition of AZONOR allowed for a significant reduction of the commercial flame retardants while still achieving a UL94 V-2 rating for 1.6 mm polypropylene plaques. The synergistic effect in high-impact polystyrene films was also evident, although it was much weaker than in polypropylene plaques.