Synthesis And Properties Of New Aromatic Heterocyclic Inner Chain-extended Bismaleimides

Bismaleimide(BMI)resin is a kind of high performance thermosetting resin,which has been widely used in aerospace,electronics and other fields.However,the BMI resin still has some shortcomings,such as intractable processing and poor impact resistance,so that its application is limited.In order to overcome these defects,a new type of high performance BMI resins were prepared from molecular structure design by introducing some specific structures in the BMI molecular chain.Firstly,three kinds of chain-extended bismaleimide resins(MPEIBMI-1.25 、MPEIBMI-1.5 、 MPEIBMI-2.0)were synthesized in three steps by etherification condensation 、 nitroreduction and amidation-imide cyclation while o-cresolphthalein as its initial raw material.The molecular structure of the products was characterized and analyzed by means of FTIR,NMR and elemental analysis.The results show that the three resins all belong to non crystalline polymers,which have good solubility and the intrinsic viscosity increase with the increase of the molecular chain.A melting transition and a curing exothermic peak are displayed during the curing process,and all the cured products have good thermal stability.Moreover,the cured films of three kinds of resins have excellent heat resistance and high temperature mechanical properties.MPEIBMI/BDM/DABPA resin systems were prepared by copolymerization of MPEIBMI-2.0 and commercialized two benzyl methane bismaleimide(BDM)and allyl bisphenol A(DABPA),and carbon fiber reinforced composites were prepared by solution wet prepreg.On the basis of the molar ratio of 0.87 to BDM and DABPA,the effects of the addition of MPEIBMI-2.0 on the properties of the modified resins and its composites were investigated.The results show that the modified resins have a low softening point,and there are two curing exothermic peaks in the curing process.The addition of MPEIBMI-2.0 decrease the strength of the low temperature exothermic peak and the high temperature exothermic peak move to the high temperature direction.With the increase of MPEIBMI-2.0 content,the thermal stability of the copolymerization systems increase gradually,and the moisture and heat aging and mechanical properties of the cured and its composites also increase.Especially,the impact strength of the cured products increase significantly.The moisture resistance of the composites increase with the increase of MPEIBMI-2.0.