Preparation And Properties Of Imide-functional Benzoxazine Resins With Self-catalytic Curing Characteristic

In the past few decades,benzoxazine resin has gradually become a substitute for traditional phenolic resins.Different from phenolic resin,there are a large number of intermolecular and intramolecular hydrogen bonds in polybenzoxazine networks due to the existence of large amount of tertiary amine groups in polybenzoxazine structure.Therefore,polybenzoxazines possess high mechanical strength,good acid and alkali resistance,high char yield,high glass transition temperature and high thermal stability.In addition,polybenzoxazine also has the characteristics of low water absorption and very low polymerization-shrinkage.Based on the above advantages,benzoxazine resin has been widely applied in aerospace and electronicareas.Moreover,benzoxazine resin exhibits very flexible structural controllability,so it can be given various properties by introduction of different functionalities.In this paper,the heat resistance and flame retardancy properties of polybenzoxazines are significantly improved by introducing o-imide group and nitrile group,the effect of isomerization on the performance of polybenzoxazines has been studied,and the self-catalytic effect amongst the groups in benzoxazine has also been investigated.The research content is as follows:?1?Two benzoxazine monomers containing both nitrile and3-methyltetrahydrophthalimide groups,pHMTI-pan and oHMTI-oan were synthesized.In pHMTI-pan structure,the imide and nitrile groups are in the para position of the oxygen and nitrogen atoms in the oxazine ring.Meanwhile,both functional groups are in the ortho position in oHMTI-oan.The molecular structures of the two benzoxazine monomers were confirmed by ¹H NMR,¹³C NMR and FT-IR,and the curing behaviors of the two benzoxazines were studied by DSC and in situ FT-IR.The curing peak temperature of pHMTI-pan is 287.5 ?,while the curing peak temperature of oHMTI-oan is 269.9 ?.Besides,the dynamic thermomechanical analysis of polybenzoxazine was performed by DMA,and the Tg temperature of poly?pHMTI-pan?is 201 ? and the Tg of poly?oHMTI-oan?is 260 ?.The thermal stability and flame retardancy of the obtained polybenzoxazine were studied by TGA and MCC.The Td₅ and Td₁₀ of poly?pHMTI-pan?are 323 ? and 373 ?,respectively.In addition,the char yiled value at 800 ? is 26.7%,and the HRC value is251 J/?g K?and the THR value is 27.2 KJ/g.Morevoer,the measured Td₅ and Td₁₀ of poly?oHMTI-oan?are 333 ? and 378 ?,respectively.The char yield value at 800 ? is 40.1%.The HRC value is 180 J/?g K?and the THR value is 21.2 KJ/g.By analyzing the effect of isomerization on the curing and performance of benzoxazines and the corresponding polybenzoxazines,it is concluded that the fully ortho-functionalized benzoxazine resin has lower curing temperature,higher thermal stability and flame retardancy.?2?An ortho-imide-functionalized benzoxazine,oHMTI-a,was synthesized by incoperating a more active carbon-carbon double bond.The structural of the newly obtained benzoxazine monomer was confirmed by ¹H NMR,¹³C NMR and FT-IR,and the curing behavior of the benzoxazine was studied by DSC and in situ FT-IR.The curing peak temperature was found to be 242.6 ?,and the carbon-carbon double bond was observed to polymerize after the ring-opening polymerization of oxazine ring.DMA,TGA and MCC tests were carried out to study the mechanical,thermal stability and flame retardancy of the obtained polybenzoxazine.The Tg of poly?oHMTI-a?was measured to be 194 ?.The Td₅ and Td₁₀ values of the polybenzoxazine is 301 ? and 323 ?,respectively,and the residual carbon yield at800 ? is 41.2%.The HRC value is 147.1 J?g K?,and the THR value of polybenzoxazine is 20.0 KJ g.?3?A benzoxazine monomer bearing both ortho-imide functionality containing carbon-carbon double bond and phthalonitrile groups,oHMTI-pn,has been synthesized.Meanwhile,a counterpart,PH-pn,which only phthalonitrile group in benzoxazine,has also been obtained.It has been found that there is a synergistic curing effect of groups in oHMTI-pn.The molecular structure of the synthesized benzoxazines were proved by ¹H NMR,¹³C NMR and FT-IR.The curing behaviors of benzoxazine monomers were studied by DSC and in situ FT-IR.The curing peak temperature of oHMTI-pn was found to be 282.4 ?,and the curing peak temperature of PH-pn is 288.8 and 297.2 ?.The cured product was tested by DMA,TGA and MCC.The mechanical properties,thermal stability and flame retardancy of the obtained polybenzoxazine were studied,and the Tg of poly?oHMTI-pn?was measured as high as 330 ?.The Td₅ and Td₁₀ values of polybenzoxazine are 387 ? and 417 ?,respectively.In addition,the char yiled value at 800 ? is 64.8%.Morevoer,theHRC value was found to be 35.2 J/?g K?,and THR value was measured as 7.9 KJ/g.It is determined that there is a synergistic curing effect between the carbon-carbon double bond and phthalonitrile during the curing of oHMTI-pn,and the excellent thermal stability and flame retardancy of the cured thermoset has been achieved.