Investigation On The Molecular Design, Synthesis Of Phosphorus-containing Polybenzoxazines And Its Application On The Flame-retardant Epoxy

As a novel phenolic resin polymerized through ring opening, polybenzoxazines (PBZs)have excellent characteristic such as various raw materials, easy synthesis, molecular designflexibility, low shrinkage in curing and good thermal stability. PBZs have wide applicationdue to the high mechanical properties, insulating property, shape stability, flame retardant andlow smoke, been applied to a wide area. However, the performances of the PBZs are still notgood enough to be applied in some harsh conditions, many works have been carried out toimprove the performances of PBZs. One effective way is to synthesize the specially designedbenzoxazines. In the present work, three kinds of benzoxazines containing phosphorus havebeen synthesized using different amine source and phenol source as starting materials. Byincorporating these functional groups and the special elements to the molecular structure ofPBZs, the thermal properties of PBZs were improved obviously.Intermediate phenol containing phosphorus, Bis (phenoxy) phenyl-phosphine (BPPP),was synthesized from dichlorophenylphosphine and resorcinol. Two kind of benzoxazineswere synthesized based on BPPP, formaldehyde solution and phenylamine/allylamine asstarting materials. The chemical structures of the monomers are characterized by1H nuclearmagnetic spectroscopies (1H-NMR) and Fourier transform infrared spectroscopy (FTIR). Itdemonstrates that the benzoxazines were synthesized successfully, and the influence of theloading sequence, reaction time, stirring speed and solvent type on the benzoxazine productsis investigated. The curing behaviors are studied by differential scanning calorimetry (DSC).The curing temperature, onset exotherm temperatures, maximum exotherm temperatures andthe reaction enthalpy of the polymerization for the phenylamine-based benzoxazine monomercontaining phenylphosphine are226.5oC,135oC,261oC and213J/g, respectively. Thecorresponding values for the allylamine-based benzocazine are216oC,158oC,281oC and139.8J/g, respectively. The thermal properties of the benzoxazines have been studied by thermogravimetric analysis (TGA). The5%and10%weight loss temperatures forphenylamine-based polybenzoxazine were267oC and293oC, respectively, and the char yieldat800oC is up to53%. The corresponding values for the allylamine-based benzocazine are269oC,315oC and51%, respectively.A benzoxazine monomer containing DOPO has been synthesized using BPA (bisphenolA), formaldehyde, allylamine and DOPO as starting materials by two approaches. Anapproach is based on the reaction between DOPO and a benzoxazine monomer containingallyl group which is synthesized using BPA, formaldehyde and allylamine as startingmaterials. The other approach is used BPA, formaldehyde and amine containing DOPO asstarting materials. The FTIR spectra show that benzoxazine monomers containing DOPO canbe successfully synthesized through the above two approaches.The Epoxy/PBZs sheets are casted by mixing Bisphenol-A based benzoxazine containingDOPO and phenolic based epoxy resin (E-51) in different mass ratios, the thernmal stabilityand flame retardancy of the sheets are investigated. The incorporation of PBAs containingDOPO results in the reduction of the maximum weight loss rate and the improvement o f thechar yield. The cured epoxy resins with benzoxazine containing DOPO loading of30wt%showed LOI values of30.5%and achieved UL94V-O ratings．The heat release rate and massloss rate of epoxy resin have been significantly reduced in the process of combustion. Thethermal stability and the improved flame retardant properties can be contributed to thesynergistic effect between phosphorus and nitrogen．...