fluoropolymers , specifically polyvinylidene fluoride polymers stabilized against color degradation due to high thermal exposure . the fluoropolymers are produced with free - radical initiators in the presence of surfactants containing acid end groups . the fluoropolymer resins are melt processed into final articles at high temperatures , above the melting point of the polymer . while the fluoropolymer is stable , residual acid surfactant causes discoloration during thermal processing . stabilization is achieved by the addition of small amounts of ammonium or phosphonium cations to the fluoropolymer composition . it is believed the cations react with any residual acid to form a less reactive salt . these salts do not adversely affect the color of a melt processed product . the phosphonium or ammonium ions can be added to the fluoropolymer at any point from the polymerization step up to the thermal processing step . a preferred family of salts are quaternary alkyl ammonium halides .