Study Of The Benzoxazine Resins Modified By Copoly(Aryl Ether Nitrile)Containing Phthalazinone And Biphenyl Moieties

As a new type of thermosetting resin, polybenzoxazine has been widely used in many fields such as the aerospace and rail systems owing to its high performance mechanical and physical property, thermal property and molecular design flexibility. However,the defects, such as the excessive internal stress, poor impact strength, have affected the application and the popularization of the polybenzoxazine. How to overcome the drawbacks of polybenoxazine on the basis of its original properties hits research area. On the basis of the comprehensive study, herein, a series of novel soluble copoly(aryl ether nitrile) containing phthalazinone moieties (PPBEN-Ps) were synthesized to modify the benzoxazine resin, and then its carbon fiber reinforced resin matrix composites (PBOZ/PPBEN-P/T700) were also prepared.A series of PPBEN-Ps were synthesized by the solution polycondensation reaction based on 4-(4-hydroxylphenyl)-(2H)-phthalazin-l-one (DHPZ),4,4'-dihydroxybiphenyl (BP) and 2,6-difluorobenzonitrile (DFBN). FT-IR,1H-NMR, GPC were used to characterize the structures and molecular weight of the resulting polymers. The curing kinetics of the PPBEN-P/PBOZ blend systems were measured by differential scanning calorimetry(DSC). The results indicate that with the increase of the content of PPBEN-P, the curing characteristic temperatures of the blend systems shows a trend from decrease to increase, and the same trend as the activation energy. Finally, on the basis of the results of curing kinetics and actual experiments, the optimal curing process was chosen as 160 ?/2 h+180 ?/2 h+200 ?/2 h+postcured 200?/2 h.The PPBEN-P/PBOZ systems were prepared by solution blending and cast molding. Then the influence of dosage, monomer ratio and molecular weight of the PPBEN-P on the polybenzoxazine were studied. The results indicate that the addition of PPBEN-Ps obviously improve impact strength and thermal stability of the PPBEN-P/PBOZ blend systems compared with pure PBOZ. Meanwhile, the obvious changes of the strength, modulus and heat resistance in the blend systems were not observed. Among them, the addition of 10phr PPBEN-P, whose number average molecular weight is 12000 and the molar ratio of the comonomer DHPZ and BP is 7 to 3, into the blend system displays the best comprehensive properties. Its unnotched impact strength reaches up to 14.5 KJ/m2, increased by 237%, char yield in nitrogen atmosphere at 800? increased nearly by 10%, Tg increased by 7?, respectively, compared with pure PBOZ.We employed the optimal toughened blend system to produce T700 carbon fiber reinforced resin matrix composites. The molding process was investigated via the DSC and the AR rheometer.And the best molding process was chosen as:140?/1h,0 MPa+170?/5-10 min (starting elevating the pressure to 1.0 MPa)+180?/2 h,1.0 MPa+200?/2 h,1.0 MPa(the heating rate was 2 ?/min.Then the PBOZ/T700 and PBOZ/PPBEN-P/T700 composite laminates were prepared by the method of solution impregnation and compression molding. The mechanical properties and thermal performance tests were carried out. The results reveal that the addition of PPBEN-P has a remarkbale increase on the interlaminar shear strength, approximately by 30%, and has a little influence on the flexural property and heat resistance, compared with PBOZ/T700 composites.