Functional Surfaces Using Bottlebrush Copolymer Additives

Bottlebrush polymers are macromolecules with polymeric side chains grafted onto a linear backbone. The highly branched architecture leads to unusual physics in polymer blends, such as limited miscibility with long linear polymers and a strong entropic attraction to surfaces and interfaces. The tendency for bottlebrush accumulation at the interfaces can be used to design functional coatings. We examine the thin film phase behavior of bottlebrush poly(styrene-r-deuterated styrene) (PS-r-dPS) in linear PS. The bottlebrush side chain length (Nsc) and linear PS length (Nm) were varied to examine their impacts on film structure. Thin films were prepared by flow coating, and the through-film structure was measured with time-of-flight secondary ion mass spectrometry (TOF-SIMS). The as-cast films exhibited a strong surface and weak substrate excess for nearly all bottlebrush architectures. After thermal annealing, the equilibrated film structures strongly depend on bottlebrush architecture: At fixed Nsc, the segregation of bottlebrush polymers at the surface and substrate interfaces increases with increasing Nm. At fixed Nm, the enrichment of bottlebrush polymers at the free surface increases with decreasing Nsc. These studies provide guidelines for the design of surface-active additives.