Concentration Dependence of the Size and Symmetry of a Bottlebrush Polymer in a Good Solvent

DF Sunday and A Chremos and TB Martin and AB Chang and AB Burns and RH Grubbs, MACROMOLECULES, 53, 7132-7140 (2020).

DOI: 10.1021/acs.macromol.0c01181

Bottlebrush polymers consist of a linear backbone with densely grafted side chains which impact the rigidity of the molecule. The persistence length of the bottlebrush backbone in solution is influenced by both the intrinsic structure of the polymer and the local environment, such as the solvent quality and concentration. Increasing the concentration reduces the overall size of the molecule because of the reduction in backbone stiffness. In this study, we map out the size of a bottlebrush polymer as a function of concentration for a single backbone length. Small-angle neutron scattering measurements are conducted on a polynorbornene-based bottlebrush with polystyrene side chains in a good solvent. The data are fit using a model which provides both the long and short axis radius of gyration (R(g,2 )and R-g,R-1/respectively), providing a measure for how the conformation changes as a function of concentration. At low concentrations, a highly anisotropic structure is observed (R-g,R-2/R-g,R-1 approximate to 4), becoming more isotropic at higher concentrations (R-g,R-2/Rg,1 approximate to 1.5). The concentration scaling for both R-g,R-2 and the overall R-g is evaluated and compared with predictions in the literature. Coarse-grained molecular dynamics simulations were also conducted to probe the impact of concentration on bottlebrush conformation, showing qualitative agreement with the experimental results.

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