| Abstract: | Dynamic viscoelastic properties of S—B—S block copolymers were measured in the tensile and shear deformation modes. Between the glass transitions of the polybutadiene and polystyrene domains the ratio of storage moduli E'/G' in tension and in shear for the same polymer varied from 3 to more than 30, depending on sample preparation. For films cast from good solvents this ratio was near 3; large ratios resulted from deposition from poor polybutadiene solvents or from compression molding. Above the polystyrene glass transition, E'/G' approached 3 for all samples. The effect is ascribed to various degrees of polystyrene domain connectivity. Electron micrographs confirm this interpretation. For morphologies of high polystyrene domain connectivity, the loss tangent in tension is heavily weighted by mechanical losses in the polystyrene phase; the loss tangent in shear is affected only moderately by differences in domain morphology. |
