Upgrading of unsaturated polyesters by reactive blending with bismaleimide resins

An unsaturated polyester resin has been modified by adding a thermosetting bismaleimide (BMI) as second co-reactive monomer. The bismaleimide resin teas readily dissolved in the uncured polyester matrix up to a concentration of about 20%. Fourier transform infrared spectroscopy was employed to monitor the cure kinetics of this complex system. The available spectroscopic evidence indicated that both the mechanism and the kinetics of the crosslinking process were strongly affected by the presence of the bismaleimide in the system. The molecular structure of this intercrosslinked network is discussed. The dynamic-mechanical behavior of a typical blend composition was found to be in agreement with the proposed molecular structure. The yield stress and Young's modulus were found to increase by increasing the BMI content in the blend, while the fracture parameter K-c was not affected by the presence of BMI.