Dithiocyanurates and thiocyamelurates: Thermal thiyl radical generators as flame retardants in polypropylene

A series of aliphatic and aromatic dithioethers of s-triazine and thioethers of s-heptazines were incorporated into polypropylene and their effectivity as flame retardants was analyzed using a limiting oxygen index (LOI) test, a DIN 4102-1 B2 test, thermogravimetric analyses coupled with mass spectrometry (TGA-MS) and FTIR coupled gas phase analysis (EGA-FTIR). Four symmetric s-triazine disulfides of the type (RSS)3C3N3 - namely 2,4,6-tris(phenyldithio)- (2), 2,4,6-tris(para-tolyldithio)- (4), 2,4,6-tris(octyldithio)- (8) and 2,4,6-tris(dodecyldithio)-1,3,5-triazine (10) - as well as five symmetric s-heptazine sulfides of the type (RS)3C6N7 - namely 2,5,8-tris(phenylthio)- (3), 2,5,8-tris(para-tolylthio)- (5), 2,5,8-tris(1,3-benzothioazol-2-yl)- (6), 2,5,8-tris(iso-propylthio)- (7) and 2,5,8-tris(octylthio)-s-heptazine (9) - were studied. The syntheses of 6, 7, 8 and 9 are reported for the first time. All compounds were analyzed by 1H and 13C NMR spectroscopy, FTIR and elemental analysis. The molecular structure of 7 was determined by single crystal XRD. Beside the flame retardant tests, the fluorescence of 3, 5 and 6 in powder form and when incorporated into polypropylene was measured. In the LOI test, the disulfides of s-triazine are more effective flame retardants than previously known organic disulfides studied in polypropylene.