Structure and Phase Behavior of Bottlebrush Diblock Copolymer-Linear Homopolymer Ternary Blends

In this work, we systematically investigated the structure and phase behavior of ternary mixtures containing an AB bottlebrush diblock copolymer and A and B linear homopolymers, where A is polystyrene and B is poly(ethylene oxide), using a combination of small-angle X-ray scattering and cloud point measurements. We found that the overall phase behavior of such mixtures closely resembles the linear counterparts, with lamellae occurring in the copolymer-rich region, macrophase separation in the homopolymer-rich region, and a bicontinuous microemulsion in between. However, the increase in lamellar and microemulsion domain spacing with increasing homopolymer content is significantly weaker than that found with ternary mixtures containing linear diblock copolymers and depends on the relative size of the homopolymers and bottlebrush side chains. We attribute this behavior to an unconventional spatial distribution of the homopolymer within the bottlebrush architecture of the diblock copolymer. These ternary mixtures offer a promising platform for the design of cocontinuous materials with an expanded parameter space made possible by the application of bottlebrush polymers.