Bottlebrush polymer additives in linear polymer matrices spontaneously segregate to surfaces and interfaces driven in part by the branched architecture and high density of side-chains. Prior work has primarily focused on athermal blends, where the composition of the bottlebrush side-chains matches that of the linear matrix. Here, we investigate segregation of bottlebrush polymers with mixed and random copolymer side-chains in a linear polymer matrix and utilize time-of-flight secondary ion mass spectroscopy (ToF-SIMS) to elucidate the distribution of bottlebrush polymers as a function of thermal annealing time, linear polymer molecular weight, and side-chain composition. Specifically, bottlebrush polymers with mixed polystyrene (PS) and polymethyl methacrylate (PMMA) side-chains were synthesized and analyzed in blends with both linear PS and PMMA. For comparison, bottlebrush polymers with styrene-<i>co</i>-methyl methacrylate side-chains were synthesized and analyzed in blends with both linear PS and linear PMMA. Bottlebrush additive segregate to film interfaces (film-air and film-substrate) as additives (10 wt %) in both linear PS and linear PMMA matrices. Bottlebrush polymers segregate to film interfaces more strongly with increasing linear matrix molecular weight, and segregation is strongest after casting and prior to thermal annealing. With thermal annealing, the surface segregation of bottlebrush polymers with random copolymer side-chains disappears while that of bottlebrushes with mixed side-chains is stable. We hypothesize that this is driven by the stronger repulsive enthalpic interactions between the bottlebrush side-chains and linear polymer matrices. This study provides insight into the phase behavior of mixed bottlebrush polymers with and linear polymers and demonstrates that bottlebrush polymers with mixed composition side-chains can be used to tailor properties of film interfaces.

Enthalpy and entropy-driven segregation of mixed bottlebrush polymers in linear polymer matrices

2019 Spring National Meeting

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