Study On The Epoxy/Cyanate Resin Blends Modified By Soluble Poly (Aryl Ether)

Both epoxy resins(EP) and cyanate ester resins(CE) are the important thermosetting resins.However,they are usually brittle because of high crosslink density.Phenolphthalein poly(ether ketone)(PEK-C) and Poly(phthalazione ether sulfone ketone)(PPESK) are two classes of soluble high-performance poly(aryl ether) resins with different temperatureresistant grades.Blending the thermosetts with thermoplastics is an attractive method to improve the fracture toughness without the sacrifice of the thermal and mechanical properties. Thus,in this paper,the relationships between structure and properties in PEK-C/EP/CE and PPESK/CE resin systems were studied in order to obtain the high-temperature resistant and toughened resin matrix for advanced composites.The effect of PEK-C on the co-curing reactivity and reaction mechanism for the stoichiometric EP/CE blend was first studied by DSC and FTIR.The results show that PEK-C accelerated the curing rates between epoxy and cyanate.But the mechanism in the EP/CE blends was hardly changed by the addition of PEK-C.According to dynamic DSC curves,the curing process was chosen,and the subtracted FTIR spectra indicate that the curing reaction in all the studied PEK-C/EP/CE systems was complete.Subsequently the relationship between structure and properties in the PEK-C/EP/CE blends was studied.The initial thermal decomposition temperature was reduced and the flexural properties,Tg and the thermal distortion temperature for the EP/CE blends were elevated with increasing the CE content.However,the fracture toughness had a greatest value in the stoichiometric EP/CE blend.In all EP/CE systems cases,the addition of PEK-C effectively increased the fracture toughness,without the sacrifice of the flexural properties,Tg and thermal stability.But higher fracture toughness was obtained in the blend with the excess of cyanate groups.DMA and SEM results indicate that the blend with the lack of cyanate groups was homogeneous,while the blend with the excess of cyanate groups was phase-separated. Hence higher fracture toughness may be due to the formation of phase-separated structure.In addition,the dielectic properties of the co-curing systems were slightly reduced with the modification of PEK-C.The effect of CE content on the phase structure of epoxy resins with PEK-C was further analyzed from the kinetic and thermodynamic factors.DSC results show that the cure temperature and the activation energy E of the co-curing resin systems increased with the increase of CE content,while the reaction order of the blends and the reaction rate constant at 150℃(K_150℃) were basically constant.On the other hand,the solubility parameters of the uncured EP,CE and PEK-C calculated by the group contribution methods were 20.29 MPa^1/2, 22.32 MPa^1/2,19.09 MPa^1/2,respectively.Thus,the miscibility between the epoxy and PEK-C was higher than that between the cyanate ester and PEK-C.Thus,the thermodynamic factor of phase separation is dominant in the process of phase separation.Finally,the structure and properties of the PPESK/CE systems were studied.The results indicate that the PPESK/CE blends exhibited superior fracture toughness and flexural properties compared to pure CE system.And the molecular weight of the used PPESK used was higher,and higher fracture toughness was obtained.Furthermore,the heat distortion temperature and the moisture uptake of the PPESK/CE blends were close to those of pure CE resin.But the dielectric properties and the initial decomposition temperature decreased with the incorporation of PPESK.