The Synthesis And Modification Of A New Type Of Bismaleimide Resin

Bismaleimide resins?BMI?,a kind of high-performance thermosetting resin that widely used in aerospace,electronics,as well as many other fields,is considered to be one of the most promising thermosetting materials due to its excellent thermal properties caused by the large crosslinking density.However,the rigid structure and large cross-linked density also make BMI bear poor toughness.Another drawback associated with BMI is the demand of high boiling point solvent during its molding process because of the crystal structure of BMI monomers.So,it is of particular importance to obtain BMI resins with excellent comprehensive properties,including processability,mechanical behavior and thermal properties,through modification.A similar modification also exist in BT resins,and the preparation of BMI monomers possessed good processibility and thermal behavior,can yet be regarded as one effective modification methods.Based on the processable and tough BMI systems containing phthalein pedant group and extended molecular chain,which is synthesized by Xiong^[111]in our group,we further introduced a strong polar cyanotype into the BMI monomer to enhance the interaction between molecular chains and eventually gain a new kind of BMI resins having good adhesive properties,thermal behaviors,processability,and mechanical performances.In addition,as the potential crosslinks,cyano group can react slowly during its use in high temperature,thus,the heat resistance of the system can be further improved.Based on above ideas,two modified resin systems,which were MCBMI/BDM/DABPA and MCBMI/BADCy/DABPA,were prepared by newly synthesized MCBMI monomer.The research of the effect to curing process,curing mechanism,thermal performance and mechanical properties caused by the composition and component content of the two systems were also conducted.The solubility test confirmed that MCBMI was soluble in the conventional solvents such as acetone,dichloromethane and chloroform.The study of MCBMI/BDM/DABPA showed that with the increase of the MCBMI,the thermal decomposition temperature maintained,the char yield at 800°C increased,while the Tg decreased,but its minimum value can still up to288°C.It also indicated that with the increase of the MCBMI,the bending modulus of modified resins raised to 4.69 GPa,which increased by 23.4%compared with unmodified system.While,the bending strength and impact strength all increased first and then decreased,their peak values were 175.7 MPa and 20.1 kJ/m²,which increased by 27.7%and 125.8%respectively,compared with unmodified system.As for the MCBMI/BADCy/DABPA systems,we found that,in the unmodified resin systems:BDM/BADCy/DABPA,two networks react independently of one another,so,it has two Tg.While,in the MCBMI/BADCy system,the co-reaction occurred.And after the addition of DABPA,MBD0.8?MBD1.0?MBD1.2 resin systems formed an IPN homogeneous system consisting the networks formed by copolymerization of cyanate and the other networks formed by reaction between BADCy and DABPA.The study of thermal properties of BT resins showed that the modified resin system has good heat resistance,and their Tgs are superior to the unmodified resin systems.The study of mechanical properties indicated that,the maximum value of bending modulus,bending strength and impact strength were 3.50 GPa,99.2 MPa and 8.35 kJ/m²,which increased by 9.4%,26,89%,and 133.9%,respectively.