Flame retardant spandex type polyurethanes

A flame retardant spandex type polyurethane resin suitable for forming into fibers and which is formed from a mixture comprising:

• a. a diisocyanate selected from the group consisting of arylene diisocyanates, 4,4' diphenylmethane diisocyanate and mixtures thereof,
• b. a halogen containing difunctional polyol selected from the group consisting of dibromoneopentyl glycol, polyesters of dibromoneopentyl glycol, esters of the product obtained from the reaction of ethylene oxide and tetrabromophthalic anhydride, esters of the product obtained from the reaction of propylene oxide and tetrabromophthalic anhydride and esters of the product obtained from the reaction of ethylene oxide, propylene oxide and tetrabromophthalic anhydride, said polyol being substantially free of corresponding monofunctional and trifunctional impurities, and
• c. a urea producing compound selected from the class consisting of diamines and water,
• wherein the composition defined in (b) is first reacted with a stoichiometric excess of the composition defined in (a) to form an isocyanate terminated prepolymer, said halogen containing polyol being present in an amount sufficient to render said prepolymer substantially non-flammable in ambient environments and wherein said prepolymer is then extended by reacting said prepolymer with the composition defined in (c).