Polymers vary widely in their resistance to burning. Some, such as the polyolefins, polystyrene, polyalkyl acrylates and methacrylates, and the like, burn readily. Polytetrafluoroethylene, polyvinylidene chloride and polyvinyl chloride, on the other hand, have a rather high resistance to burning. In any event, it obviously is highly desirable that, for certain applications, a polymer should have a high degree of flame retardance so that it will meet the requirements of various building codes or that it will meet safety standards imposed on toys, carpeting, drapery materials, automotive applications, etc.
The treatment of these more flammable polymers to increase their resistance to burning is well known; such treatment generally has involved the incorporation in the polymer composition of substantial proportions of antimony oxide, halogenated hydrocarbons and low molecular weight phosphate esters. Ordinarily, though, the effective use of these and other additives has required their presence in such high concentrations as to adversely affect the desirable properties of the polymer. Thus, such desirable properties as hardness, clarity, strength, elasticity, etc., are diminished significantly by the presence of large amounts of a flame-retardant chemical.
The formulator's goal, in preparing a flame-retardant polymer composition, is to add just enough of the flame retardant compound so as to provide the desired degree of flame retardance, but no more than this minimum amount, so as to preserve as much as possible the advantageous properties of the polymer. Frequently, it is not possible to select a flame-retardant which will meet these requirements satisfactorily.
U.S. Pat. No. 3,877,655 (Shim) shows the use of phosphoramidate esters of dibromoneopentlyglycol as flame-retardant additives in a wide variety of polymer compositions. The phosphoramidate for which flame-retardant test data is shown is the N,N'-dimethylamide.
U.S. Pat. No. 4,041,012 (Albright et al.) shows the use of acrylate esters of dihaloneopentylglycol phosphates as flame-retardant additives in acrylic polymer compositions. The esters are incorporated in polyacrylate compositions by copolymerization with methyl methacrylate, for example, although at column 7, lines 15-59, it is stated that they may be used in combination with known synergists in other types of polymers "such as polystyrene" (see line 37).
The preparation of the calcium salt of pentaerythritoldiiodohydrin phosphoric acid is shown in "Iodine-Containing Aliphatic Phosphoric Acid Esters," Eidenbenz et al., Arch. Pharm. 280, 227-31 (1942).