Small-Angle X-Ray Scattering Study of Microand Macro-Phase Separations in Blends of Block Copolymer with Homopolymer

The order-disorder phase transition behavior exhibited by blends of a styrene-butadiene diblock copolymer (76% styrene) with a polystyrene of various molecular weight (from 2,200 to 50,000) is studied by means of small-angle X-ray scattering. With a polystyrene of a relatively short chain length the blend, on lowering the temperature, undergoes a microphase separation, and the scattering curve shows a peak at a finite scattering angle. With a polystyrene of relatively long chain length, the scattered intensity curve shows additional low angle component with intensity increasing rapidly as q→0, and this is interpreted in terms of the macrophase separation accompanying the transition from the disordered to ordered phase.