Syntheses And Applications Of Sulfur-Containing Aryl Polyphosphonates As Flame Retardants For Poly (Ethylene Terephthalate)

Three kinds of aryl polyphosphonates (APPs), polysulfonyldiphenylene thiophenylphosphonate (PSTPP), poly(9,10-dihydro-9-oxa-10-(2,5- dihyroxyphenyl) phosphaphenanthrene-10-oxide) phenylphosphonate (PDPPP), and poly(9,10-dihydro-9-oxa-10-(2,5-dihyroxyphenyl) phosphaphenanthrene-10-oxide) thiophenylphosphonate (PDPTP) were synthesized from the melting polycondensations of thiophenyl- phosphnoic dichloride with 4,4'-dihydroxyphenyl sulphone, phenyl- phosphnoic dichloride with 2-(6-oxide-6H-dibenz <1,2>oxa phosphorin-6-yl) -1,4-dihydroxyphenylene, and thiophenylphosphnoic dichloride with 2-(6-oxide-6H-dibenz <1,2>oxa phosphorin-6- yl)-1,4-dihydroxy-phenylene, respectively. Their structures were characterized by elemental analysis, FT-IR, NMR and MS. Their thermal behaviors were investigated by differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The existence of sulfur in the structures of aryl polyphosphonates resulted in the variety of their thermal stabilities, which followed the descending order: TODOP, PSTPP and OODOP. All those aryl polyphosphonates are stable under 300℃, and their melting points are around 200℃. Their onset temperatures of decomposition were between 300 and 350℃. The most rapid decomposing temperatures of those APPs were between 428 and 460℃. At 600℃ they have the residues of at least 25wt%. Those three kinds of aryl polyphosphonates (APPs) have been used as flame retardants (FRs) for polyethylene terephthalate (PET). The flame retardancy, thermal behaviors, morphology, crystallinity and flame retardant mechanism of PET/APPs systems have been investigated. At the loading of 10% in PET, all the PET/APPs systems can achieve a V0 rate of UL94, and have an oxygen index (LOI) of 47, 42 and 26 for PET/PDPTP, PET/PDPPP and PET/PSTPP systems, respectively. APPs improved remarkably the flame retardancy of PET by decreasing the rate of heat release, postponing the ignition time, and increasing the char residues of the systems. DSC and wide-angle X-ray diffractometry (WAXD) measurements showed that APPs acted as nucleating agents and accelerated the crystallization rate of PET. The scan electronic microscope showed that the sizes of APPs distributed in PET matrix were about 0.05μm.The study on the flame-retardant mechanism of PET/APPs systems revealed that the effect of phosphorus-containing FRs on the flame retardancy of PET depended not only on their loading in PET, but also the specific structures of FRs; the sulfur in the structures of aryl polyphosphonates can improve the flame retardant effectiveness of aryl polyphosphonates on PET; The integrated results from various flame-retardant factors contribute the fame retardancy of PET/APPs systems.