Analysis of Surface Segregation of Bottlebrush Polymer Additives in Thin Film Blends with Attractive Intermolecular Interactions

The surface chemistry of polymer films and coatings is relevant to a wide range of applications, and recent work has shown that bottlebrush polymers can be used as additives to modify film interfaces and surfaces. In blends with linear polymers of a sufficient molecular weight, bottlebrush polymers will enrich interfaces driven, in part, by entropic effects. However, prior work has only studied a limited set of systems with either neutral or repulsive interactions between the bottlebrush and linear polymers. Herein, we investigated surface segregation in blends of bottlebrush and linear polymers with attractive intermolecular interactions. Specifically, we studied blends of bottlebrush poly(cyclohexyl methacrylate) (BBPCHMA) and linear polystyrene (PS) over a range of BBPCHMA backbone and linear PS lengths. Time-of-flight secondary ion mass spectroscopy measurements of the blends showed that bottlebrush additives strongly segregated to the film surface when the bottlebrush side chain was shorter than matrix linear PS, and the surface remained enriched with bottlebrush after 2 days of thermal annealing. In comparison to studies with bottlebrushes having neutral or repulsive interactions with linear PS, the surface segregation of BBPCHMA was weaker in the as-cast films but more significant after thermal annealing. This comparison suggests that architectural effects can drive segregation during casting and the interaction of the polymers with the air interface is more significant during thermal annealing. Finally, we demonstrated that these bottlebrush additives could self-heal a damaged surface by diffusing to a damaged region during thermal annealing. This work provides new insight into the segregation behavior of bottlebrush polymer additives and factors that drive segregation during casting and thermal annealing.