Research On Modified Resin Systems Containing Oxadiazole Diamine And Bismaleimides

Bismaleimides resin (BMI) is a high performance themoset. Its molding temperature and pressure are lower than polyimide resin, and its thermo stability is higher than epoxy resin. So it can be used as insulating varnish, adhesive and resin matrix of advanced composite in machinery, electronics and aerospace fields. However, BMI resin still has disadvantages of high melting point, poor solubility and high brittleness. Therefore, it is usually used after modification.A diamine(DA) containing both ether linkage and 1,3,4-oxadiazole structure was synthesized through molecular design in this paper. It was used to modify diallylbisphenol A(DABPA)/dephenylmethane bismaleimides(BMDM) resin after prepolymerization with BMDM(DAB) to improve its impact toughness and processability without sacrificing its thermo stability.Firstly, the diamine was synthesized through Williamson etherification, methyl oxidation, carboxyl hydrazidation, hydrazide cyclization and nitro reduction, FTTR and NMR tests were used to confirm the chemical structure of intermediates and target product.Then it was used to prepare the prepolymer with BMDM, compared with bis(4-aminophenyl)sulfone(DDS)/BMDM. Their curing mechanism and thermostability at different molar ratios between diamine and BMDM were studied through DSC, FTIR and TGA tests. The results showed that Michael addition reaction was happened between amino and double bond in the prepolymer, which made the melting point of BMI decrease. The curing temperature of two prepolymers both decreased, of which DAB systems was lower than that of DSB systems, so DA had a better modification effect. When the molar ratio between diamine and BMDM was 1:2, the extent of prepolymerization was the highest, and it was best for Michael addition reaction.Finally, two prepolymers were used to modify DABPA/BMDM system, and their curing behavior, thermostability, mechanical properties and moisture absorption with different prepolymer contents were investigated. The results showed that the curing temperature (Tp) of two systems both decreased because of the addition of prepolymers, Tp of system containing 3% DAB(DAB3) was 20℃ lower than that of DSB3. The 5% and 10% weight loss temperature(T5% and T10%) of two systems both increased a little compared to that of unmodified system, meaning their thermos tab ility both improved. The T5% of DAB3 system had increased by 10℃, while 14℃ of DSB3. Moreover, the bending strength, modulus and impact strength of two systems all had a considerable improvement. The impact strength of DSB7 and DAB7 systems were 15.7 kJ/m2 and 17.3kJ/m2, had improved 88% and 107% compared to unmodified system.