Research On The Propertues And Mechanism Of Benzoxazine Modified Cyanate Ester/bismaleimide System

It would have great significance to study the high performance polymers composites,which are applied widely in high-tech areas and national defense areas.At present,the high performance polymers composites are widely using in modern national defense areas and hence increasing the effective load,flying-range and flexibility of carrying weapons.Cyanate ester/bismaleimide?BMI/BADCy?based composites have wide application in the field of national defense science and technology due to the excellent performance.With advances in technology,the strength,mechanical properties,processing requirements of the BMI/BADCy have more demanding,such as high temperature,high strength,machinability.The structure of BMI/BADCy resin contains more rigid group,which leads to poor toughnessand excellent heat resistance.By introducing reactive groups,a branched structure,a flexible group,etc.in the BMI/BADCy copolymer,it can without sacrificing thermal performance of the BMI/BADCy copolymer.The BMI/BADCy copolymer also have excellent mechanical properties.In this paper,we synthesized a series of novel benzoxazine monomers?Boz?,2,2'-bis?8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl?propane?Bz-allyl-1?and 2,2'-bis?8-allyl-3-allyl-3,4-dihydro-2H-1,3-benzoxazinyl?propane?Bz-allyl-2?,by molecular structure design.Then BMI/BADCy resin was modified by Bz-a,Bz-allyl-1 and Bz-allyl-2,respectively.The effects of Boz content on the properties of resin system such as mechanical properties,thermal stability,dielectric properties were investigated.The organo-modified montmorillonite?OMMt?/Bz-a/BT nanocomposites were prepared by OMMt as reinforcing materials and the properties of nanocomposites were investigated.Two novel benzoxazine monomers with allyl groups?Bz-allyl?viz:Bz-allyl-1and Bz-allyl-2 have been synthesized from allylamine and amine with 2,2'diallyl bisphenol-A,and paraformaldehyde.The chemical structures of each benzoxazine monomers were confirmed by FT-IR and ¹H-NMR.FT-IR was applied to monitor the curing reactions of the reactive blends.Three reactions were observed in the curing reactions:the first was the polymerization reaction of parts allyl groups;the second was the ring-opening polymerization of benzoxazine;and the third was polymerization reaction of remian allyl groups.Compared to the typical polybenzoxazine,the higher crosslinking density of PBz-allyl-2 led to the higher glass transition temperature?T_g?,as well as the 5%weight loss temperatures(Td_5%),indicating the better thermal stability of PBz-allyl-2.And the data for the dielectric properties also showed that the PBz-allyl-2 performs better than the typical polybenzoxazine.Thermosetting terpolymer composed of Bz-a,BADCy and BMI was prepared via co-curing reactions.The curing reaction of Bz-a with BMI/BADCy resin and the thermal,mechanical and dielectric properties of the terpolymer were studied.The FT-IR was applied to monitor the curing reactions of the reactive blends.Three reactions were observed in the curing reactions:the first was firstly the cyclotrimerisation of BADCy and BMI resin after oxazine ring opening,producing the triazine structure;the second was the coreaction between the triazine structure and Bz-a,forming alkyl isocyanurate and diphenyl ether linkages,followed by the further reaction of the isocyanurate linkage;and the third was the self-polymerization of BMI and Bz-a,and coreaction with each other.Compared to the PBz-a,the higher crosslinking density of the terpolymer led to the higher T_g,as well as Td_5%,indicating the better thermal stability of the terpolymer at service temperature.And the data for the mechanical and dielectric properties also showed that the terpolymer performs better than polybenzoxazine and the copolymer.The impact strength of the PBOZ10was 17.3kJ/m².Functionalized Boz with allyl groups was blended with BMI/BADCy to improve the properties of BMI/BADCy.Effect of functionalized Boz with allyl groups on dielectric,mechanical and thermal properties of BMI/BADCy composites were systematically investigated.The results show that formation of mannich bridge networks and interpenetrating polymer network in the polymerizations of Bz-allyl and BMI/BADCy increased the cross-linking densities and thermal stability.Allyl-based polymers also exhibited high T_g above 265°C,high char yields.The dielectric constant values and the dielectric loss factor of BBz8-2 reached minimum value of3.17 and 0.083 at 10⁶ Hz.The mechanical properties?high flexural modulus of4.18GPa and flexural strength of 120 MPa?of the BBz8-2 were superior.The impact strength of the BBz6-2 was 18.5kJ/m².Introducing Bz-a,Bz-allyl would have a large influence on the curing process of BMI/BADCy.The introduction of Bz-a and Bz-allyl in to BMI/BADCy resin will change the thermal curing process of BMI/BADCy.Each BMI/BADCy system will follow different kinetic models.The addition of Bz-a into the copolymer decrease the apparent activation energy at heat curing process.It indicated that the introduction of Bz-a into the copolymer would make it easier to curing for theinitial stage.The addition of Bz-allyl would increass the apparent activation energy of BMI/BADCy reain at the thermal curing process.The result showed that the introduction of Bz-allyl into BMI/BADCy would make it harder to curing for the later stage.The content and structure of Bz-a,Bz-allyl would have a large influence on the properties of modified BMI/BADCy adhesive.And the result show that the maximum tensile shear strength of the adhesive modified by Ba-10,Bz-allyl-1,Bz-allyl-2 were21.11 MPa and 17.31MPa,21.28 MPa and 17.94MPa,24.01 MPa and 17.45MPa,respectively.The test results of the composite material show that,the bending strength and interlaminar shear strength of Bz-a/QFs/BADCy,Bz-allyl-1/QFs/BADCy,Bz-allyl-2/QFs/BADCy were 587.9 MPa and 51.1 MPa,643.8 MPa and 57.5 MPa,647.2 MPa and 56.9 MPa at room temperature,respectively.The bending strength retention rate is above 59%,and the interlaminar shear strength retention rate is about64%at 250°C.In the heat and humidity and boiling conditions,the three composites could maintain high mechanical properties.A high-performance OMMt/Bz-a/BT nanocomposites was prepared by OMMt,Bz-a,BADCy,BMI.Effect of OMMt on dielectric,mechanical and thermal properties of Bz-a/BT composites was studied.The impact strength and flexural strength of MMt4 were 20.2 kJ/m² and 119 MPa,respectively.The addition of OMMt can effectively improve the composites'dielectric properties.In this paper,several series of Boz were prepared.The effects of Boz,allyl structures on the mechanical properties,thermal stability,dielectric properties and thermal curing processes of BMI/BADCy were studied comprehensive.