Abstract: The flame retarding mechanism of a sulfur-containing polyphosphonate, poly (9, 10-dihydro-9-oxa-10- (2, 5-dihyroxyphenyl) phosphaphenanthrene-10-oxide) thiophenylphosphonate (PDPTP) in PET was studied through the analysis on the products of thermal degradation using PY-GC-MS, TG/FT-IR and XPS. It showed that the presence of PDPTP promoted the formation of char and delayed its decomposition. Most sulfur species in PDPTP volatized at lower temperature in the form of SOx, which diluted the flammable gases and thus retarded the fire. However, the volatization of phosphorus species mainly occurred in the second stage of decomposition, which generated small molecular compounds containing P=O and P-H bonds. Besides, PY-GC-MS showed that PDPTP strongly retarded the deep pyrolysis of PET, hence reduced the yield of small molecular flammable compounds. According to XPS, the phosphorus species of PDPTP accumulated on the carbonaceous polymer surface in the form of phosphoric acid or metaphosphoric acid, which acted as an efficient dehydrator and promoted the charring of polymer surface.

Key words: Flame retardancy, PET, PY-GC-MS, TG-FTIR, XPS, Sulfur-containing polyphosphonate