Abstract: Thermal stability and thermal degradation kinetics of poly(ethylene terephthalate)(PET) and flame retardant copolyester(FR-PET) containing phosphorus linked pendant groups were investigated by a conventional dynamic thermogravimetric analysis(TG) under highly purity N₂ atmosphere at different heating rates between 10 and 40 K/min and the flame retardant of PET and FR-PET were studied by limiting oxygen index(LOI) method. The thermal degradation activation energy of PET and FR-PET were determined by using Flynn-Wall-Ozawa method. The thermal degradation kinetic mechanism and models of PET and FR-PET were determined by the selection of different mechanical models, by which the isothermal kinetic equations and thermal degradation velocity curves of the main degradation process were obtained. The flame retardant of PET by incorporation of phosphorus unit linked pendant groups was improved. The degradation of FR-PET was determined by the breaking of P—C and P—O bonds, and thermal stability of FR-PET was lower than that of PET. Thermal degradation activation energies of PET and FR-PET were in the range of 194—227 kJ/mol and 184—209 kJ/mol(0.1≤α≤0.85), respectively. The solid-state decomposition mechanism of PET and FR-PET corresponded to the controlled decelerating α-t curve, a reaction order mechanism and the mechanism functions f(α) were 3(1-α)^2/3(0.1≤α≤0.85).The thermal degradation velocity of the main degradation process of PET and FR-PET were near. Flame retardant mechanism of novel copolyester phosphorus containing linked pendant groups was most likely through the gas phase rather than the condensed phase.

Key words: Poly(ethylene terephthalate), Phosphorus-containing copolyester, Thermal degradation, Kinetics, Flame retardant mechanism