Synthesis Of Bismaleimides Containing Cardo And Cyano Groups And Properties Of Their Composites

Aerospace is an important manifestation of defence force,and advanced polymer composite(APC)is an important part of aerospace industries.Matrix resins with high performance are the key of the development and applications of polymeric composite materials.Bismaleimides(BMI)are an important type of thermoset polymeric materials,which meet the fiber-composite processing requirements for various processing techniques,characterized by excellent processability and balance of thermal,electrical and mechanical properties.However,the common BMI monomers generally suffered poor solubility in common organic solvents and high melting temperature because of its rigid and symmetrical structure,and the cured resins have high inherent brittleness because of their high crosslink density and rigid molecular networks.These shortcomings have considerably restricted their application in advanced technology fields.In order to meet the needs of new generation of ultra-high-speed fighters,three kinds of novel BMIs containing Cardo and cyano groups were designed and synthesized in this paper;the novel BMIs were modified through the copolymerization with 4,4’-bismaleimidodi-phenylmethane(BDM)and o,o’-diallyl bisphenol A(DABPA);the novel BMIs were prepared polymer matrix composites;and thermal oxygen aging experiments on composites,with the aim of obtain a matrix resin used in the aerospace field.Two novel n≈1 oligomeric BMI monomers containing phthalide cardo and cyano groups(PPCBMI and MPCBMI)were designed and synthesized based on phenolphthalein,o-cresolphthalein and dichlorobenzonitrile.The chemical structures of the monomers were confirmed from 1H NMR spectroscopy and FTIR.PPCBMI and MPCBMI exhibit good solubility in common organic solvents.Through the DSC curves,Ea is calculated to be 83.94 KJ/mol and 96.69 KJ/mol,respectively,and n is 1.21.The FTIR spectroscopy of cured BMI resins showed the participation of cyano group during the polymerization.TGA investigations showed that the maleimide groups of the two BMIs undergo thermal radical polymerization at first.Cyano groups are involved in the cross-linking reaction at higher temperatures,which can improve thermal stability and the overall char yield.Furthermore,the cross-linking reaction of cyano groups improves the interfacial properties of the resulting composites significantly.The copolymerizations of PPCBMI/DABPA with three different molar ratios were prepared.The curing behavior investigated by DSC,the kinetics and curing process were also calculated and determined by DSC.The TGA investigations showed that the thermostability of cured resins was improved with the increase of PPCBMI.The DMA and mechanical investigations indicated that the composites based on PPCBMI/DABPA gained best combination property with a little much PPCBMI.When the molar ratio of maleimide to allyl groups wasl:0.87,the copolymerizations of PPCBMI/BDM/DABPA were prepared.The effects of mass concentration of PPCBMI on their curing behavior,heat resistance,dynamic thermo-mechanical properties and mechanical properties investigated.The results indicated that with the increase of PPCBMI,the thermal decomposition rate decreased,the thermal decomposition temperature increased firstly and then decreased,the char yield increased,the glass transition temperature increased,the flexural strength and impact strength increased firstly and then decreased,but the flexural modulus kept increasing.In addition,we chose the coposites which gained the best combination property and evaluated the thermal ageing effects on the interlaminar shear strength(ILSS).We used scanning electron microscopy(SEM)and scanning acoustic microscope(SAM)for interface morphology,FTIR for chemical structures,and DMA for glass transition temperature.The results indicated that composites based on PPCBMI/DABPA had good interface bonding capacity and aging resistance.One novel n≈1 oligomeric BMI monomer containing fluorene cardo and cyano groups(PFCBMI)was synthesized based on 9,9’-bis[4-(4-maleimidophenoxy)phenyl]fluorine and dichlorobenzonitrile.The chemical structures of the monomers were confirmed from 1H NMR spectroscopy and Fourier transform infrared spectroscopy(FTIR).PFCBMI exhibits good solubility in common organic solvents.The curing behavior and the thermal stability of the BMIs were characterized using dynamic differential scanning calorimeter(DSC)and thermogravimetric analysis(TGA).The DSC result of PFCBMI/BDM indicated that the characterstic datas of DSC curves for PFCBMI/BDM resin system increased with the increase of PFCBMI.The TGA result of PFCBMI/BDM indicated that the increase of PFCBMI lead to the decrease of the crosslink density,with the decrease of the characterstic datas.The thermal mechanical properties of their composites were characterized using dynamic mechanical analysis(DMA),the result indicated they have excellent heat resistance with the storage modulus about 10 GPa and the glass transition temperature above 470℃.A series of chain-extended phthalide-containing BMIs(PM)were prepared via Michael-type addition based on 3,3’-bis[4-(4-aminophenoxy)phenyl]phthalide(PPDA)and BDM.The chemical structures of the monomers were confirmed from 1H NMR spectroscopy and FTIR.The curing behavior investigated by DMA,and we calculated the degree of the curing reaction.The TGA of cured resins showed high thermal stability and high thermo-oxidative stability of PM.The DMA results showed a high "operating temperature range"(>320℃)and Tg(>340℃).The relationship among mole concentration of PMs and curing process,mechanical properties,fracture toughness and heat resistance of PM2/BDM/DABPA blends were also investigated.The investigations of the mechanical properties showed a complicated trend with the increase of PM2.When the proportion of PM2 is 0.05,the impact strength of modified resins was increased by 121.3%.In addition,the moisture resistance of cured resins was improved with the increase of prepolymer contents.