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Abstract
Bottlebrush polymers are a class of macromolecules that has recently found use
in a wide variety of materials, ranging from lubricating brushes and
nanostructured coatings to elastomeric gels that exhibit structural color. These
polymers are characterized by dense branches extending from a central backbone,
and thus have properties distinct from linear polymers. It remains a challenge
to specifically understand conformational properties of these molecules, due to
the wide range of architectural parameters that can be present in a system, and
thus there is a need to accurately characterize and model these molecules. In
this paper, we use a combination of viscometry, light scattering, and computer
simulations to gain insight into the conformational properties of dilute
bottlebrush polymers. We focus on a series of model bottlebrushes consisting of
a poly(norbornene) (PNB) backbone with poly(lactic acid) (PLA) side chains. We
demonstrate that intrinsic viscosity and hydrodynamic radius are experimental
observations \emph{sensitive} to molecular architecture, exhibiting distinct
differences with different choices of branch and backbone lengths. Informed by
the atomistic structure of this PNB-PLA system, we rationalize a coarse-grained
simulation model that we evaluate using a combination of Brownian Dynamics and
Monte Carlo simulations. We show that this exhibits quantitative matching to
experimental results, enabling us to characterize the overall shape of the
bottlebrush via a number of metrics that can be extended to more general
bottlebrush architectures.
