ABSTRACT
Crazing, although not as effective as shear banding, is a major source of toughening in polymers. For thermosetting polymers, however, crazing is thought to be unsuitable because of the inability of the crosslinked molecules to undergo significant molecular stretching and disentanglement, which are among the essential mechanisms for crazing to take place. Benefiting from the preceding technological achievements, focuses on the toughening mechanisms of the newly developed thermoset resins, which are intrinsically tough despite high glass transition temperature. The synthesis and the physical and mechanical properties of a number of AB-BCB-MI resins have been discussed by others. For AB-BCB-MI polymers, given the large differences in fracture toughness among these samples, one expects corresponding differences in the size of the damage zone and perhaps also in the operative fracture mechanism. AB-BCB-MI-2B has a higher rubbery modulus than AB-BCB-M1-2A, which indicates that it is more highly crosslinked.
