Synthesis And Characterization Of DOPO-based Bifunctional Benzoxazine

The DOPO-based bifunctional benzoxazines (3a~3c) were synthesized by salicylaldehy-de,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), aromatic diamines(4,4’-diaminodiphenyl methane,4,4’-diaminodiphenyl ether,4,4’-diaminodiphenyl sulfone).The first step is the condensation reaction of2-hydroxybenzaldehyde with aromatic diamines,forming intermediates(1a~1c) with an imine linkage. The second step is the nucleophilicaddition reaction of DOPO with an imine linkage, resulting in intermediates(2a~2c) with asecondary amine linkage.The last step is the ring closure condensation of2a~2c, leading tobenzoxazine3a~3c. It was demonstrated by experiments that the reaction can be finished justin5hours with strong acid being catalyst. The structure of benzoxazines and intermediatewere confirmed by FTIR and1H NMR and31P NMR. The thermal stability of2a~2c and3a~3c was confirmed by TG(DTG). It was demonstrated that the char yield of2a~2c were18.31%,27.24%,30.51%at700℃, respectively. The temperature of maximum weight lossrate of3a~3c were484.98℃,464.98℃,372.48℃, respectively. the char yield of2a~2c were36.93%,34.59%,38.70%at700℃, respectively.It was researched thermosetting reaction of the epoxy resin and2a~2c as curing agent.FTIR analysis showed that the mass ratio of epoxy resin:2a~2c=1:1,1:2,1:3, respectively,the curing reaction can be completed at160℃for2h, It can be said that DOPO-basedsecondary amine of2a~2c can be prepared epoxy curing agents, making migration-resistanc-e’s composite material of flame retardant epoxy resin.It can be calculated the dynamic thermal degradation kinetics process of3a-3b byFlynn-Wall-Ozawa and Friedman. The results indicated that the activation energy of3b waslowest and3c was highest, when the conversion ratio is less than0.25. Therefore, when theconversion rate is lower,3a was decomposed easier than3b and3c. The two methods wereindicated the order of the average activation energy was3b＞3c＞3a.It was studied thermosetting reaction of the epoxy resinwith3a~3c as curing agent.FTIR analysis was showed that the curing reaction can be fully cured at160℃for2h, whenepoxy resin:3a=1:1. FTIR analysis was showed that the curing reaction can be fully cured at160-180℃for4h, when epoxy resin:3b(and3c)=1:1.