Patent ID: 7399799

Claim:
A method of producing a flame-retardant polyester polymer, which is dyeable with a cationic dye, comprising: synthesizing bis(hydroxyethyl terephthalate) containing a metal sulfonate of Formula 3; feeding bis(hydroxyethyl terephthalate) so that a content of bis(hydroxyethyl terephthalate) is 0.01-5 mol % based on a diacid component in a polymer in a course of producing polyester; feeding a phosphorus-based flame retardant of Formula 1 so that a content of a phosphorus atom is 500-40000 ppm based on the polymer; and copolymerizing a mixture, wherein, a material of Formula 3 is produced by reacting a material of Formula 2 with ethylene glycol in an extent of reaction of 95% or more (R 1 and R 2 are radicals, which each have a reactive group capable of forming an ester group and 2-4 carbons, and p is an integer ranging from 1 to 5) (wherein, M is an alkaline metal, including Na, Li, or K) (wherein, M is an alkaline metal, including Na, Li, or K).