Synthesis and characterization of bismaleimide containing benzimidazole structure
Aiming at the application requirements of high temperature resistance of structural composites,in order to improve the properties of bismaleimide(BMI)resin matrix,the rigid benzimidazole ring structure was introduced into the main chain of the monomer by molecular design method,and the bismaleimide monomer containing single benzimidazole structure(BZ-BMI)and bismaleimide monomer containing o-benzimidazole structure(OBZ-BMI)were synthesized by azeotropic toluene method.The structure of the intermediate product and the target product was characterized by nuclear magnetic resonance spectroscopy(1H-NMR)and Fourier transform infrared spectroscopy(FTIR).The curing behavior of the monomer and the thermal stability of the cured product were studied by differential scanning calorimetry(DSC)and thermogravimetric(TG)analysis.The results of DSC curves show that BZ-BMI and OBZ-BMI are crosslinked and cured in the temperature range of 210-370℃,and the curing behavior is greatly affected by the length of the segment,the regularity of the molecular structure and the interaction force.At the same time,combined with the DSC curve,the curing process of the monomer is determined to be 200℃/2 h + 250℃/2 h + 330℃/6 h.FTIR analysis shows that this process can be completely cured.The results of TGA shows that the thermal decomposition temperature of P(BZ-BMI)and P(OBZ-BMI)are comparable to that of diphenylmethane bismaleimide(BDM),while the residual carbon rates of P(BZ-BMI)and P(OBZ-BMI)at 800℃are 74.7%and 70.4%,respectively,which are much higher than the test value of P(BDM)(48.3%),indicating that the introduction of benzimidazole structure effectively improves the thermal flame retardancy.The OBZ-BMI copolymerization modification system maintains excellent mechanical properties,and the impact strength is 20%higher than that of the traditional diallyl bisphenol A modified BMI system,which broadens the application range of bismaleimide in the field of high temperature resistant resin-based structural composites.
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