Morphologies of binary ABAC diblock copolymer blends

The self-assembled structures of the mixtures of AB and AC diblock copolymers were investigated using transmission electron microscopy (TEM). For this purpose, two kinds of asymmetric polystyrene-block-polyisoprene (SI30 and SI87) and one symmetric polystyrene-block-poly(2-vinylpyridine) (SVP) were anionically polymerized. Both macro- and microphase separations occur in all binary mixtures examined in this work, yielding various morphologies. The morphologies of the phase-separated macro-domains are found to be the same as those of pure diblock copolymers. However, at the phase boundary where two diblock copolymers with different microphase-separated structures are in contact with each other, the morphological transition is observed due to the preferential location of the common polystyrene (PS) blocks in two copolymers at the interface. From TEM observations and random phase approximation (RPA)-based prediction, it is identified that the macrophase transition takes place prior to the microphase transition, leading to the interface-induced ordering.