Preparation And Properties Of Cyanate/Benzoxazine And Cyanate/Hyperbranched Benzoxazine Blends

As a high-performance resin,cyanate ester resin(CE)is widely used in aerospace composite structural materials.However,the curing temperature of cyanate resin is high and the brittleness is large.Therefore,how to reduce the curing temperature and improve the toughness has always been a concern in this field.In this paper,phenol-furfuryl benzoxazine(K-a),phenol-aniline benzoxazine(P-a)and hyperbranched benzoxazine were used as modifiers to modify the cyanate resin by copolymerization.Differential scanning calorimetry(DSC)and Fourier transform infrared spectroscopy(FT-IR)were used to study the curing behavior and curing reaction kinetics of cyanate/benzoxazine,cyanate/hyperbranched benzoxazine resin systems The thermal stability,mechanical properties and fracture morphology of the above resin systems were studied by DSC,thermogravimetric analyzer(TGA),universal material testing machine,impact testing machine and scanning electron microscope(SEM).In the cyanate ester/benzoxazine resin system,K-a and P-a can undergo ring-opening cross-linking at lower temperatures,resulting in a large number of phenolic hydroxyl groups,thereby promoting cross-linking of cyanate resins at low temperatures.When the amount of K-a added is 7%(mass fraction,the same applies hereinafter),the curing temperature decreases by 68°C.The apparent activation energy of each system was calculated by three kinetic models.The apparent activation energy of the K-a system was lower,which was 63.88 k J/mol.With the increase of K-a and P-a content,the glass transition temperature(T_g)and thermal stability of the resin system gradually decreased,but the mechanical properties improved.Among them,T_g decreased by7?68°C,thermal decomposition temperature(T₅)at a weight loss of 5%decreased by12?52°C,and the carbon residue ratio(Y_c)at 800°C decreased by 0.7?2.6%.However,the addition of K-a and P-a can improve the bending and impact properties of the resin system.When the amount of K-a is 5%,the bending strength is increased from 91 MPa to 124 MPa of pure cyanate resin;when the content of P-a is 7%Compared with pure cyanate resin,the impact strength is improved by 1.4 times.4,4',4'-trihydroxytrimethylbenzene-polyetheramine hyperbranched benzoxazine(HJB),1,1,1-tri-p-hydroxyphenylethane-polyetheramine hyperbranched benzoxazine(HYB)and hydroquinone-polyetheramine hyperbranched benzoxazine(HDB)as modifiers.The effects of hyperbranched benzoxazine polymers on the curing behavior,curing reaction kinetics and properties of cyanate resins were studied.With the help of hyperbranched benzoxazine having a large number of terminal reactive groups,the cyanate resin can be cured at a lower temperature.When the addition amount of hyperbranched benzoxazine is 7%,the curing peak temperature is reduced.It was43?93?.HYB hyperbranched benzoxazine molecules have relatively many phenolic hydroxyl groups at the ends,so the apparent activation energy of the HYB system is the lowest,followed by HJB,and the apparent activation energy of the HDB system is the highest.Because the hyperbranched benzoxazine contains more long-chain alkoxy groups,the thermal properties of the copolymer are reduced to a certain extent.The values of T_g,T₅and Y_c have decreased by 2?46°C,11?51°C and 0.6?2.7%.Based on the hyper-branched benzoxazine rich in nano-cavities,the mechanical properties of the copolymer have been greatly improved.Among them,when the amount of HYB is 5%and 7%,the bending and impact strength of the material are 135 MPa and 50.8 k J/m²,which are 48.3%and 1.7 times higher than pure cyanate.And comprehensive performance is better than benzoxazine monomer copolymerization system.