ARCHITECTURE-INDUCED PHASE IMMISCIBILITY IN A DIBLOCK MULTIBLOCK COPOLYMER BLEND/

Ordered diblock copolymer blends have recently become the subject of t remendous research interest since they can be used to elucidate the in tramicrodomain segregation of blocks differing in length, as well as t o identify the molecular and blend parameters yielding phase immiscibi lity. In this work, we explore the influence of molecular architecture on block copolymer blend miscibility by examining an equimolar mixtur e of two symmetric styrene (S)/isoprene (I) block copolymers, one an S I diblock and the other an (SI)(4) octablock. Their molecular weights are identical, so that the ratio of block lengths is 4:1 SI:(SI)(4). W hile this ratio is expected to yield a single phase in diblock copolym er blends, transmission electron microscopy reveals here that the dibl ock/multiblock blend is macrophase-separated due to the Linear multibl ock architecture and midblock conformations of the (SI)(4) copolymer. Electron tomography (3D imaging) permits direct visualization of conne cted SI and (SI)(4) microdomains at the SI/(SI)(4) interface at relati vely high spatial resolution (ca. 3 nm). In addition, the presence of SI molecules in the (SI)(4) phase or (SI)(4) molecules in the SI phase frustrates SI lamellae, resulting in curved microphase boundaries.