A study of thermal stability of polyester containing phenyl phosphonate unit for flame retardant fiber

Abstract

Phenyl phosphonic acid (PPA) was chosen as a comonomer to manufacture flame retardant polyester fiber. The yield based on PPA is less than 55% by a conventional polyester formation process. Different factors which might affect the yield of the copolymerization were investigated. The phosphorus residues in the reactor during the process of polymerization were monitored. It is found that the phosphorus residues decrease sharply in the high vacuum stage. This indicates that factors which increase the molecular weight of the prepolymer containing phenyl phosphonate unit will promote the yield of the copolymerization. In order to get an insight into the low yield of the copolymerization, the compounds containing phenyl phosphonate unit, bis(2-naphtholyloxyethyl) phosphonate (BNEP) and bis( p-methoxycarbonyl phenyl) phosphonate (BMPP) were synthesized for model studies. The preliminary results showed that these compounds decompose significantly above 240 °C. This suggests that the low yield of the PPA polymerization process may be attributed to the thermal instability of the OP bond in the phenyl phosphonate unit at the polymerization temperature.