Synthesis and Characterization of 4,4'-Bis(maleimido)diphenylmethane Resin and Evaluation of Its Curing Behavior in Blending with Epoxy

Hypothesis: 

Bismaleimide resin, due to its favorable mechanical and thermal properties, can improve the properties of epoxy resin. 4,4'- Bis(maleimido)diphenylmethane resin (BMI) is one of bismaleimide resins that can be cured simultaneously with epoxy resin by amine curing agents and both resins can be cured with the same curing cycle. This improves the physical-mechanical properties of epoxy-based composites.

BMI resin was synthesized using the reaction between maleic anhydride and 4,4'-diaminodiphenyl methane in acetone to form an intermediate of amic acid. The dehydration of the amic acid was carried out to form an imide using acetic anhydride, triethylamine and sodium acetate. The product was characterized by FTIR and 1H NMR spectroscopy techniques. The synthesized resin was blended with DGEBA epoxy resins in different amounts of 10, 20, 30 and 40 phr. Next, the blends were cured by 4,4'-diaminodiphenyl methane as a curing agent, and the composites were prepared from the blends and glass fibers. The interlaminar shear strength (ILSS) of the prepared composites was measured as a key parameter of composites. The curing behavior of epoxy/bismaleimide blend was investigated using isothermal differential scanning calorimetry (DSC) and FTIR spectroscopy.

4,4'-Bis(maleimido)diphenylmethane resin was used to improve ILSS properties of the composite prepared based on DGEBA epoxy resin and glass fibers. The value of 52.50 MPa was obtained as the optimum value of ILSS at 78°C for the mixture with 30 phr of bismaleimide. DGEBA and BMI resins have the ability to simultaneously cure by 73% and 78% using MDA curing agent at 160°C. Full curing of the epoxy and bismaleimide mixture requires a temperature higher than 160°C, such as 220°C.