This article describes the synthesis and characterization of a polymer-bound nonhalogen fire retardant (NHFR). The reactive fire retardant used in this study is 2-carboxyethyl(phenylphosphinic) acid (CEPP); the polymer is poly(ethylene terephthalate) (PET). Fire-retardant and other modifiers of polymer properties must be bound to the polymer for use in fiber, medical, and food contact applications. Copolymers containing very high levels of CEPP have been prepared. Although fire retardancy in PET is achieved at relatively low levels of CEPP, our ability to produce copolymers with high levels of phosphorous makes them very attractive as polymeric nonfugitive fire retardants for other polymers, such as polycarbonate, nylon, acrylonitrile-butadiene-styrene (ABS), poly(butylene terephthalate) (PBT), and various polymer blends. This article also describes NHFR polyester compositions containing 4,4'-biphenyl dicarboxylic acid and CEPP. It is shown that an increase in aromaticity gained by incorporating the 4,4'-biphenyl dicarboxylic acid leads to higher limiting oxygen index values.