A novel non-dripping oligomeric flame retardant for polyethylene terephthalate

An oligomer or low polymer, polysulfonyldiphenylene thiophenylphosphonate (PSTPP), was synthesized from phenylphosphonothioic dichloride (PPTD) and 4,4′-sulfonyldiphenol (SDP) by polycondensation reaction. Its structures and thermal behaviors were studied using infrared spectrophotometer and thermal gravimetric analysis, respectively. This novel oligomer can be used as the flame retardant for poly(ethylene terephthalate) (PET). PET samples containing PSTPP can reach an oxygen index (OI) of 29 and a UL-94 V-0 rating when the phosphorus content of the sample is 2.5 wt%. No melting dripping was observed during the UL-94 flame test.