Synthesis Of Hyperbranched Liquid Poly-phosphonate And Study On Properties Of Its Flame-retardant Epoxy Resin

With high specific strength,resistance to chemical corrosion and high bonding strength,epoxy resin(EP)has been widely used in construction,aerospace,electrical and electronic fields.But the inherent flammability imposes restrictions on its application,so it is necessary to improve the fire safety of epoxy resin.Currently,most of flame retardants are small molecular,which is easy to migrate,leading to reduction in flame retardant efficiency service life.Due to the high molecular weight and character of hard-to-migrate,hyperbranched flame polymers have become the focus of research in the field of flame retardants.In order to improve the flame retardancy of EP,three kinds of hyperbranched polyphosphonates have been synthesized and characterized by FTIR?¹H NMR?³¹P NMR and GPC.The effects of the three hyperbranched polymers on the thermal degradation and combustion behavior of epoxy resin were studied by UL-94,LOI,TGA,and Cone.The flame retardant mechanism of the three hyperbranched polymers was investigated by SEM,Raman,TG-IR and FTIR.It was found that three kinds of hyperbranched polymers can greatly increase the limiting oxygen index of epoxy resin,and made it pass UL-94 V0 grade at 4%of addition.Obvious"blowing out"phenomenon was observed in the vertical combustion test.The decomposition temperature and maximum mass loss rate of the three flame retardant epoxy resins decreased,but the carbon residue rate increased significantly.The Cone results showed that the peak heat release rate(p-HRR)and total heat release(THR)of the three flame retardant epoxy resins decreased,with a maximum reduction of 51.8%and 30.5%,respectively.However,the peak smoke release rate(p-SPR)of the three flame retardant epoxy resins decreased first and then increased due to the strong vapor-phase flame retardant effect.TG-IR results showed that various kinds of toxic and flammable gases generated in the pyrolytic process of the three flame retardant epoxy resins were significantly reduced,and phosphorous free radicals were found in the gas phase.By capturing hydrogen free radicals or hydroxyl free radicals that are necessary for combustion reaction,phosphorous free radicals can extinguish flame effectively.Microstructure,Raman and FTIR spectra of carbon residues showed that three kinds of flame retardant epoxy resin formed carbon layers that were bonded by P-O-C during the combustion,which leads to the higher degree of graphitization,thermal stability and strength.In conclusion,the three kinds of hyperbranched polyphosphonates both have gas phase and condensed phase flame retardant mechanisms,thus leading to excellent flame retardancy at low addition.Besides,HPNFR would not significantly damage the transparence of EP thermosets,consequently reserved its application value in some special fields.