chapter  8
36 Pages

Correlation Between Phase Behavior, Mechanical Properties, and Deformation Mechanisms in Weakly Segregated Block Copolymers

ByRoland Weidisch, Goerg H. Michler

The development of materials with improved property profiles is one of the im­ portant fields of materials science. The use of block copolymers aiming at specific mechanical properties opens up a wide field of possibilities due to different avail­ able highly ordered structures. It is well known that enhancement of toughness of polymers is possible in high-impact polymers via the incorporation of a dispersed elastomeric phase. This effect is caused by multiple crazing or multiple cavitation with shear yielding, which is macroscopically often shown by the phenomenon of stress-whitening (1,2). Whereas polymer blends show macrophase-separated structures, which often leads to a deterioration of mechanical properties due to the immiscibility of the components, in block copolymers microphase-separated mor­ phologies at the typical size scale 10-100 nm are observed (3). Many authors re­ port the existence of different ordered structures, including BCC spheres, hexagonally packed cylinders (HEX), ordered bicontinuous double diamonds

(OBDDs), cubic bicontinous (“gyroid”) structures, and lamellar and perforated lamellar structures (HPL) (4-7).