Structures And Properties Of Bismaleimide/Poly(Phthalazinone Ether Ketone) Blends

Bismaleimide(BMI) resins,as high performance composite matrices,have been widely used in the aerospace field and electronic industry because of their good thermal stability,low water absorption and good retention of mechanical properties at high temperatures.However, their wide spread use was unfortunately limited in many applications by their inherent brittle behavior.In the past two decades,various attempts have been made to improve the fracture toughness of BMI resins without scarificing their desirable attributes.Poly(phthalazinone ether ketone)(PPEK) is an amorphous high-performance thermoplastic with excellent thermal resistance and mechanical properties,as well as good solubility.Thus,the present study reported the modification of bismaleimide resin by PPEK based on the early works of thermoset/thermoplastic blends.A series of BMI/PPEK blends were prepared by using solvent or melting method.The effects of PPEK content,molecular weight and reactive end-cap on structures and properties were investigated in order to produce a new matrix possessing good thermal and mechanical properties.First,dynamic differential scanning calorimetry(DSC) was carried out to calculate cure kinetics parameters.Furthermore,the curing cycle was determined on the study of cure kinetics.Second,the effects of PPEK molecular weight and content on phase behavior and property were investigated.Optical microscopy(OM) was used to investigate the phase evolution process of BMI/PPEK blends cured at 160℃.The reaction-induced phase separation of the blends origined from a micro-cocontinuous structure and were fixed at different stage.It was the characteristic of spinodal decomposition,and the secondary phase separation indicated that the phase separation was affected by viscoelastic effect.With varying PPEK content and molecular weight,the phase separation mehcanism didn't change, while the phase separation procedures were different.Scanning electronic microscopy(SEM) graphs showed that the morphology of the cured blends changed from a dispersed structure to a phase-inverted structure with the increase of PPEK concentration.And the phase domain sizes were different when PPEKs with varying molecular weight were incorporated.The impact strength and critical stress intensity factor(K_IC) values got a maximum when 10-phr PPEK was added and it decreased with further increase of PPEK concentration.Several toughening mechanisms,such as local plastic deformation,crack deflection,and branches, presumably took part in improving the toughness of BMI/PPEK blends.The modified BMI blends had good thermal resistance.However,the solvent resistance showed a sharply decrease when cocontinuous or phase-inverted structure was obtained.Unfortunately,a poor toughening effect was observed when cocontinuous structure or phase-inverted structure was obtained because of the poor interfacial adhension between BMI and PPEK.Thus,reactive PPEKs containning amino or maleimido end groups(PPEK-DA & PPEK-BMI) were synthesized to toughen BMI resin.The PPEK-DA reacted with 4,4'-bismaleimidodiphenyl methane via Michael addition reaction and PPEK-BMI reacted with O,O'-diallyl bisphenyl A via ene addition reaction to participate in the formation of crossliked networks.Opitical microscopy graphs showed that the phase separation was hindered when reactive PPEKs were incorporated.As a result,the phase structure was fixed at the early stage of phase separation and a single phase structure was obtained.Compared to the neat BMI resin,the impact strength and critical stress intensity factor values of the blends revealed a remarkable increase when PPEK-DA or PPEK-BMI was added.The main factor that attributed to improve touheness was the incorporation of flexible chains to the crosslinked networks except crack deflection and branches.The new blend also possessed good thermal and solvent resitance properties and it's a potential candidate used as advanced composite matrix resin.