Controlling the morphology of immiscible polymer blends using bottlebrush random copolymers

Bottlebrush polymers are highly branched macromolecules with polymeric side-chains attached to a linear backbone. The functionality and properties of the bottlebrush is controlled by the side-chain composition, side-chain length, and backbone length. In this study, we investigate the thin film phase behavior of a ternary blend system consisting of polystyrene (PS) and poly (methyl methacrylate) with 20 wt{\%} of a bottlebrush poly (styrene-r-methyl methacrylate) additive. The blend morphologies were characterized using atomic force microscopy and optical microscopy. We find that bottlebrush poly (styrene-r-methyl methacrylate) additives having 50-60 mol{\%} styrene are soluble in the PS phase, reaching a concentration of 20 vol{\%}, but limited miscibility with PMMA can drive the formation of a PMMA/bottlebrush interphase. This interphase inhibits the coarsening of microstructures while forming a co-continuous network.