IMPACT OF MORPHOLOGICAL ORIENTATION IN DETERMINING MECHANICAL-PROPERTIES IN TRIBLOCK COPOLYMER SYSTEMS

In contrast to other types of segmented multiblock thermoplastic elast omers, simple ABA block copolymers represent a class of well-defined n anostructured materials. Due to the inherent block lengths built in du ring the polymerization, the microdomain structure of block copolymers exhibits a size scale of typically 10-100 nm. The ability to control the individual chemistry of each block as well as the size and the sha pe of the domains in a block copolymer affords enormous advantages to tailor physical properties. By globally orienting the microdomains, a well-defined initial morphological state aids greatly in the interpret ation and modeling of mechanical deformation and allows for exploitati on of the inherent anisotropy of the cylindrical and lamellar structur es. Several types of orientation techniques are reviewed. Experiments investigating structure-mechanical properties in styrene-diene tribloc k copolymers with spherical, cylindrical, and lamellar morphologies ar e discussed, with emphasis on the clarifying role of global morphologi cal orientation in data interpretation Composite theory which treats e ach microphase as a continuum describes small str ain behavior of cyli nders and lamellae quite well. Molecular variables such as the number of effective bridge vs loop conformations in the rubber midblock becom e more important at large strains. With controlled chemistry and morph ology as well as with improved dynamic probes, further understanding b etween the interplay of molecular and morphological structure in influ encing the deformation process is expected.