Bottlebrush Polymers: A Pathway to Engineering Surfaces and Interfaces

Bottlebrush polymers are macromolecules with a linear backbone and densely-grafted polymeric side-chains. Steric repulsion between the side chains forces the backbone to extend, leading to a rod or wormlike conformation. Therefore, bottlebrush polymers resemble both comb polymers and polymer-grafted particles. Our goal is to develop an in-depth understanding on the thermodynamics of bottlebrush polymer additives for linear hosts, with an emphasis on understanding interface and surface attraction for the design of compatibilizers and functional coatings. First, we studied the phase behavior of bottlebrush polymers with random copolymer poly (styrene-r-methyl methacrylate) side-chains in a blend of two immiscible homopolymers, polystyrene and polymethyl methacrylate. We determined that bottlebrush composition and architecture will control the morphology of the blends and identified the conditions that lead to the formation of a bottlebrush-rich interphase that suppresses coarsening of the blend microstructures. Second, we studied the segregation behavior of bottlebrush polystyrene in a blend with linear polystyrene by systematically changing the bottlebrush side-chain length, bottlebrush backbone length, and length of the linear host. We developed a scaling law and generated a phase diagram that describes the segregation behaviors of bottlebrush polymers in a thin film. Finally, we investigated the stability and swelling response of bottlebrush networks that were crosslinked using atom beam lithography. We found that swelling declines as the number of side-chains is increased, which is consistent with a simple Flory model for equilibrium swelling of networks.