Cure mechanism and thermal properties of the phthalide-containing bismaleimide/epoxy system

• The cure temperature of BMIP is reduced in the presence of epoxy group.
• The Michael addition of BMIP and DDS is of higher reactivity than BMIP homopolymerization.
• The blends contain three different cure regimes in the temperature range of 150–350 °C.
• The Tgs of the cured resins are decreased with the DGEBA content.
• The cured resins containing higher DGEBA content possess lower thermal stability.

A series of novel resin systems were prepared using a novel thermosetting bismaleimide containing phthalide cardo structure (BMIP), diglycidyl ether of bisphenol A epoxy resin (DGEBA) and 4,4′-diamino diphenyl sulfone (DDS). The cure mechanism of the mixture was studied by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The FTIR results demonstrated the cure temperature of BMIP was reduced in the presence of epoxy group. The DSC thermogram of the blends showed three different cure regimes in the temperature range of 150–350 °C and the intensity and position of the exothermic peaks were varied with the blend formulation. The cause of their formation was analyzed in detail. Thermal properties of the cured network were characterized by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Experimental results exhibited that the heat resistance and thermal stability were decreased with the epoxy content and the molar ratio of the BMIP and DDS exhibited little effect on them.