Dilute Solution Structure of Bottlebrush Polymers

Bottlebrush polymers are a class of macromolecules that has recently found usein a wide variety of materials, ranging from lubricating brushes andnanostructured coatings to elastomeric gels that exhibit structural color. Thesepolymers are characterized by dense branches extending from a central backbone,and thus have properties distinct from linear polymers. It remains a challengeto specifically understand conformational properties of these molecules, due tothe wide range of architectural parameters that can be present in a system, andthus there is a need to accurately characterize and model these molecules. Inthis paper, we use a combination of viscometry, light scattering, and computersimulations to gain insight into the conformational properties of dilutebottlebrush polymers. We focus on a series of model bottlebrushes consisting ofa poly(norbornene) (PNB) backbone with poly(lactic acid) (PLA) side chains. Wedemonstrate that intrinsic viscosity and hydrodynamic radius are experimentalobservations \emph{sensitive} to molecular architecture, exhibiting distinctdifferences with different choices of branch and backbone lengths. Informed bythe atomistic structure of this PNB-PLA system, we rationalize a coarse-grainedsimulation model that we evaluate using a combination of Brownian Dynamics andMonte Carlo simulations. We show that this exhibits quantitative matching toexperimental results, enabling us to characterize the overall shape of thebottlebrush via a number of metrics that can be extended to more generalbottlebrush architectures.