Bismaleimide-diamine copolymers containing phthalide cardo structure and their modified BMI resins

3,3-Bis[4-(4-aminophenoxy)phenyl]phthalide (PPDA) and 4,4′-bimaleimidodiphenyl-methane (BDM) were prepared via a Michael-type addition using molar ratio 1:2(PM₂), 1:3(PM₃) and 1:4(PM₄) in acetone as solvent and acetic acid as a catalyst. The chemical structures of prepolymers were characterized by hydrogen-1 nuclear magnetic resonance (¹H NMR) spectroscopy and Fourier transform infrared spectroscopy. These prepolymers exhibit good solubility in common organic solvents. The thermal properties of the prepolymers were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Composites composed of carbon cloth and the phthalide-containing Michael addition-type prepolymers (0.5% triphenylphosphine) were also prepared. The DMA results demonstrated that the resulting composites have excellent thermal stability. Besides, N,N-4,4′-bismaleimidodiphenylmethylene (BDM) and O,O′-diallyl bisphenol A (DABPA) resin blends were modified by PM₂. We investigated the effects of mole concentration of prepolymers on the curing process, mechanical properties, fracture toughness, and heat resistance of the modified resins. The investigations of the mechanical properties showed a complicated trend with an increase in prepolymer contents. When the proportion of PM₂ is 0.05, the impact strength of modified resins was increased by 121.3%. In addition, the moisture resistance of cured resins was improved with the increase in prepolymer contents.