Preparation of phosphorus-containing polymers. XXVIII. Synthesis and flame resistance of phenoxaphosphine-containing copolyesters

Copolyesters containing phenoxaphosphine rings were prepared from 2,8-dichloroformyl-10-phenylphenoxaphosphine 10-oxide and isophthaloyl chloride and three bisphenols (bisphenol A, tetrabromobisphenol A, and tetrachlorobisphenol A) by interfacial polycondensation, and the flame resistance of the resulting copolyesters was investigated by measuring limiting oxygen index (LOI) values. Most of the copolyesters had good solubilities in N-methyl-2-pyrrolidone and chloroform and gave the films from the chloroform solutions. The relationship between the melting temperature of copolyesters and phenoxaphosphine content held for the Flory's equation for random copolymers over 20–30% of phenoxaphosphine content. The halogen-free copolyesters with phenoxaphosphine rings showed not only good thermostability but also good flame resistance. In contrast with these copolymers the halogen-containing copolyesters with phenoxaphosphine rings had very high LOI values and exhibited excellent flame-retardant property, but their thermostability was poor and the copolymers began to decompose at lower temperatures in comparison with the halogen-free copolyesters. The mode of action of the halogen-free copolyesters containing phenoxaphosphine rings was based on the effect of phosphorus in the solid phase, whereas the action of the copolyesters with both halogen and phenoxaphosphine ring was due to the additive effect of the solid-phase and the gas-phase mechanisms.