Phase Behavior of the Blend of Rod–Coil Diblock Copolymer and the Corresponding Coil Homopolymer

Blending with a homopolymer is an effective approach to tailor the microphase-separated morphology of block copolymers. It has been established for the blends of coil–coil diblock copolymer (A-b-B) with the corresponding homopolymer (h-A) that h-A can be solubilized uniformly into A mcirodomain to induce structure transformation when its molecular weight is smaller than that of the A block, i.e., α = Mh-A/Mb-A < 1. Here we examine if the microdomain structure of a rod–coil diblock copolymer, poly(2,5-diethylhexyloxy-1,4-phenylenevinylene)-block-poly(methyl methacrylate) (DEH-PPV-b-PMMA), may be systematically tuned by blending with PMMA hompolymer (h-PMMA). The blends over the major composition window were found to undergo macrophase separation even when the value of α was as low as 0.3. The phase separation led to the formation of a copolymer-rich phase and a homopolymer-rich phase, in which microphase separation occurred, yielding a well-ordered lamellar structure and a sponge structure, respectively. T...