Abstract: The fire retardancy of polyesters is enhanced with halophenoxyphosphazenes that contain a P--O--P bond. Preferred materials are reaction products of a halogenated phenol and a phosphonitrilic halide. Brominated phenols are preferred although chlorophenols can be used. Of the brominated phenols, preferred starting materials are p-bromophenol, 2,4-dibromophenol and mixtures thereof. Phosphonitrilic chlorides are preferred starting materials. Pure phosphonitrilic halides can be used; however, phosphonitrilic halide mixtures are preferred because of their availability. Cyclic and linear phosphonitrilic halides are useful as well as mixtures thereof. Saturated and unsaturated polyesters can be made fire retardant by this invention, as can thermoplastic and thermosetting materials. Linear and crosslinked polyesters can be treated. Preferred polyesters are fiber-forming polyesters of a diol and dibasic acid, such as poly(ethylene terephthalate) and poly(1,4-cyclohexylenedimethyleneterephthalate).

Abstract: The fire retardancy of polyesters is enhanced with halophenoxyphosphazenes that contain a P--O--P bond. Preferred materials are reaction products of a halogenated phenol and a phosphonitrilic halide. Brominated phenols are preferred although chlorophenols can be used. Of the brominated phenols, preferred starting materials are p-bromophenol, 2,4-dibromophenol and mixtures thereof. Phosphonitrilic chlorides are preferred starting materials. Pure phosphonitrilic halides can be used; however, phosphonitrilic halide mixtures are preferred because of their availability. Cyclic and linear phosphonitrilic halides are useful as well as mixtures thereof. Saturated and unsaturated polyesters can be made fire retardant by this invention, as can thermoplastic and thermosetting materials. Linear and crosslinked polyesters can be treated. Preferred polyesters are fiber-forming polyesters of a diol and dibasic acid, such as poly(ethylene terephthalate) and poly(1,4-cyclohexylenedimethyleneterephthalate).