Deformation behavior of weakly segregated block copolymers. 2. Correlationbetween phase behavior and deformation mechanisms of diblock copolymers

The deformation behavior of poly(styrene-b-butyl methacrylate) diblock copo lymers, PS-b-PBMA, is studied by high-voltage electron microscopy (HVEM) wi th an in-situ tensile device. While in the first part the phase behavior of PS-b-PBMA diblock copolymers is investigated via small-angle neutron scatt ering (SANS), in the second part the deformation behavior depending on comp osition and molecular weight is discussed. Disordered block copolymers have the same deformation mechanism as the corresponding homopolymers, while mi crophase-separated block copolymers undergo a cavitation mechanism. At the order-disorder transition, ODT, a transition from crazing to cavitation mec hanism is found via HVEM. Moreover, a sharp increase of the diameter of cra ze fibrils occurs at the ODT, demonstrating that the craze microstructure i s strongly influenced by phase behavior. As the incompatibility increases w ith increasing molecular weight, deformation mechanisms such as diversion a nd termination of crazes are observed for intermediately segregated block c opolymers. The discussed correlation between phase behavior and deformation mechanisms indicates the existence of a unified scheme for deformation beh avior of diblock copolymers depending on the strength of segregation,;CN.