The impact of sulfur oxidation level on flame retardancy

Compounds containing sulfur in various forms may be used as flame retardants or as adjuvants to promote the activity of other flame-retarding elements, most notably phosphorus. To gain a better understanding of the nature of the sulfur moiety in a flame retardant on performance, a series of phosphorus esters derived from isosorbide containing sulfur at various levels of oxygenation (sulfide, sulfoxide, sulfone) have been prepared and evaluated for flame-retardant impact in diglycidyl ether of bis-phenol A epoxy. In all cases, the presence of sulfur positively impacts flame retardancy. In general, the impact on flame retardancy increases as the level of oxygenation at sulfur increases (sulfone > sulfoxide > sulfide).