A POLYMER NETWORK OF UNSATURATED POLYESTER AND BISMALEIMIDE RESINS - YIELDING AND FRACTURE-BEHAVIOR

The yielding and the fracture behaviour of an intercrosslinked polymer network obtained by the simultaneous curing of an unsaturated polyest er (UP) and a thermosetting bismaleimide resin (BMI) was investigated in a wide range of temperatures and testing rates. The yield stress si gma(y) and the Young's modulus E increase by increasing the testing ra te and decreasing temperature. Moreover, under the same testing condit ions, sigma(y) and E increased as the BMI content in the blend was enh anced. On the other hand, it was found that the fracture parameter K-c was not affected by the presence of BMI. The yielding process was ana lyzed using the theories both of Argon and Bowden and the molecular pa rameters derived there were related to the molecular structure of the network developed upon curing.