Temperature-composition phase diagrams for binary blends consisting of chemically dissimilar diblock copolymers

Temperature-composition phase diagrams for binary blends of chemically diss imilar diblock copolymers, (A-block-B) and (A-bloch-C) copolymers, were con structed experimentally. For the study, two polystyrene-block-polyisoprene (SI diblock) copolymers (SI-7/8 and SI-10/53) and three polystyrene-block-p olybutadiene (SB diblock) copolymers (SB-9/8, SB-5/36, and SE-10/10) were u sed. Three binary blend systems were prepared: (i) (SI-7/8)/(SB-9/8) blends consisting of two nearly symmetric lamella-forming diblock copolymers havi ng different chemical structures, (ii) (SI-10/53)/(SB-5/36) blends consisti ng of two highly asymmetric sphere-forming diblock copolymers having differ ent chemical structures, and (iii) (SB-10/10)/(SB-9/8) blends consisting of two nearly symmetric lamella-forming diblock copolymers having different m icrostructures in the polybutene block. It has been found, via transmission electron microscopy (TEM), that no macrophase separation took place in eac h binary blend system over the entire range of blend compositions investiga ted. The order-disorder transition temperature of each binary blend was det ermined using oscillatory shear rheometry, enabling us to construct a tempe rature-composition phase diagram for each blend system. It has been found t hat the temperature-composition phase diagrams for the (SB-9/8)/(SI-7/8) an d (SB-10/10)/(SB-9/8) blend systems follow nearly a Linear relationship, wh ereas the temperature-composition phase diagrams for the (SI-10/53)/(SB-5/3 6) blend system show positive deviation from linearity. The experimentally determined temperature-composition phase diagrams are found to be consisten t with the predictions from random phase approximation calculations. It has been found that the microdomain structure, as determined by TEM, of each b inary blend was the same as that of the constituent block copolymers.