Preparation Of Phosphorus-containing Bismaleimides And Their Applications On Flame-retardanted Epoxy Resin

Because of its excellent comprehensive properties,epoxy resin?EP?has been widely used in various fields of national economy.However,the epoxy resin is flammable and is accompanied by heavy smoke and droplets,which greatly limits its application in the field of high flame retardant requirements such as construction,transportation and electronic.Therefore,it is essential to study the epoxy resin flame retardant.Based on the good compatibility between maleimide group and epoxy resin,two phosphorus-containing Bismaleimides were synthesized and used for flame retardant epoxy resin in this paper,aiming at improving the flame retardancy of composites while maintaining their mechanical properties.The main work are as follows:1.Two kinds of flame retardants,Phenyl di-?4-maleimido-phenoxyl?phosphate?PDMP?and Phenyl phosphonic di-phenoxyl maleimide?PPDPM?,were prepared by nucleophilic substitution reaction from phenyl dichlorophosphate?PDCP?,benzene phosphorous oxydichloride?BPOD?and N-?4-hydroxyphenyl?maleimide?4-HPM?,respectively.The structures of target products were characterized by Fourier transform infrared?FTIR?,¹H Nuclear magnetic resonance spectroscopy?¹H NMR?,³¹P Nuclear magnetic resonance spectroscopy(³¹P NMR),Elemental analysis?EA?and Ion Chromatography?IC?.Furthermore,the thermal decomposition behavior of the two flame retardants was studied by Thermogravimetric analysis?TGA?.The results showed that the two flame retardants exhibited excellent thermal stability due to the presence of rigid groups,and the amount of carbon residue at 700°C was 62.4 and 54.9 wt%respectively.2.The PDMP and PPDPM were separately added to the diglycidyl ether of bisphenol A?DGEBA?/4,4'-diaminodiphenylmethane?DDM?system to prepare the flame-retardant composites by heat curing.Then the effects of two kinds of flame retardants on the properties of epoxy resin were studied and their flame retardant mechanism was deduced.The results of transparency and cross-section morphology of flame retardant EP showed that the EP/PDMP and EP/PPDPM exhibited certain transparency due to the good compatibility between maleimide and EP,with the cross-linking density increased.Differential scanning calorimetry?DSC?and TGA tests showed that EP composites have excellent thermal performance.The flame retardancy of flame retardant epoxy resin composites were investigated using the Limit oxygen index?LOI?,vertical burning tests?UL-94?and Cone calorimeter measurements?Cone?.The results showed that both flame retardants increased the LOI value of EP,in which the LOI values of EP/3PDMP and EP/3PPDPM were 29.7%and 30.3%respectively,and both passed the UL-94 V-0.In Cone test,the peak heat release rate?PHRR?and total heat release rate?THR?of EP/2PDMP and EP/3PPDPM were significantly reduced;the smoke release rate?SRR?and total smoke release rate?TSP?of EP/2PDMP were reduced;the CO release rate?COPR?of EP/3PDPM was increased and the CO₂ release rate?CO₂PR?was decreased,which indicated that both flame retardants played an effective role in flame retardant.The residue after Cone test was analyzed by scanning electron microscopy?SEM?and Raman spectroscopy?Raman?,showed that the two flame-retardant EP composites have formed a dense and complete protective carbon layer.In the pyrolysis-gas chromatography/mass spectrometry?Py-GC/MS?test,the flame retardants PDMP and PPDPM all have various cracking products,which can effectively quench the free radicals and exert the flame retarding effect.In the thermogravimetry-infrared combination?TG-IR?test,the volatilization time of gas in EP/2PDMP was earlier than that of pure EP,and the gas intensity was greatly reduced,which indicated that PDMP promoted the decomposition of EP,effectively inhibited the formation of gas products and played a role of gas flame retardant.The tensile test results showed that the addition of the two flame retardants did not significantly reduce the mechanical properties of EP.3.The flame retardant EP composites were prepared by adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide?DOPO?and two kinds of phosphorus-containing bismaleimide.The effect of DOPO combined with flame retardant on the properties of epoxy resin was studied,and the flame retardant mechanism was analyzed.It can be seen from the transparency test results that the transparency of the EP/PDMP/DOPO composites is slightly lower than that of the EP/PDMP samples,but it still maintains a high visible light transmittance.However,due to the relatively poor dispersion of PPDPM and DOPO in EP,EP/PPDPM/DOPO is almost opaque.Analysis of DSC and TGA test results showed that the composite flame retardant EP composites have excellent thermal properties.In the flame retardancy test,the compound flame retardant EP all passed V-1 and above,and the LOI of EP/0.5PDMP/1.5DOPO and EP/2PPDPM/1DOPO were as high as 34.1%,which is a significant improvement compared to the EP/PDMP and EP/PPDPM systems.Analysis of Cone test results showed that the PHRR and THR of EP/1.5PDMP/0.5DOPO decrease,the COPR increases,the CO₂PR decreases,and the incomplete combustion degree of the materials increases,indicating that the addition of flame retardant played a role in gas phase flame retardant effect.However,when PPDPM was added together with DOPO,the PHRR and THR of the composites were lower than EP,but higher than EP/3PPDPM and EP/3DOPO,indicating that.although it can exert a certain flame retarding effect,the effect is not satisfactory.The SEM and Raman results of residue showed that PDMP and PPDPM can form dense and complete protective carbon layer when combined with DOPO,and released the non-combustible gases at the same time,thus realizing the synergistic flame retardancy of gas-solid phases.The tensile test results showed that EP still maintained good mechanical properties when phosphorus-containing bismaleimide and DOPO were added.