Polyetherimide‐modified bismaleimide resins. II. Effect of polyetherimide content

Abstract A novel polyetherimide was prepared and used to improve the toughness of bismaleimide resin composed of bis(4‐maleimidediphenyl) methane and O,O′‐diallyl bisphenol A. The morphologies of the modified resins change from spherical particles to an inverted phase structure, depending on the modifier's content based on the scanning electronic microscopy results. Dynamic mechanical analysis is also used to characterize morphologies of the modified resins. The phase‐separation process of the modified system is traced by time‐resolved light scattering. The change in the light‐scattering profile with curing time showed that the phase separation mechanism depended on the modifier concentration. Phase separation took place via the spinodal decomposition mechanism in the PEI 15‐phr‐ and 20‐phr‐modified system. The fracture energy ( G IC ) increased with PEI content in the modified system; in the PEI 15‐phr‐modified system, the G IC value was three times greater than that of the unmodified BMI resin. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 350–358, 2001