From Fully Stretched to Collapsed: Bottlebrush Polymer Chain Dimensions when Grafted to Nanoparticles

Polymer composites are used abundantly in daily life for their unique ability to improve material properties and diversify applications. Polymer grafted nanoparticles (PGNs) have been key to controlling targeted filler dispersion, which is essential for material performance. Thus far, studies on PGNs have been limited by the narrow scope of polymer chemistry and architecture, focusing on linear glassy chains. Macromolecular architecture plays a significant role in controlling material properties, but surprisingly, there are few examples of non-linear polymer chains grafted to nanoparticle surfaces. Here, the presentation will discuss drastic changes in polymer chain dimensions for bottlebrush polymer grafted nanoparticles synthesized via surface-initiated ring-opening metathesis polymerization (SI-ROMP). Bottlebrush PGNs display a substantial change in brush height, which is dependent on environmental conditions. In solvent, the brush heights are consistent with fully extended bottlebrushes, seen in dynamic light scattering (DLS) and cryo-transmission electron microscopy (TEM). In the melt, the brushes collapse on the particle surface, seen in TEM and ultra-small angle X-ray scattering (USAXS). These extreme polymer chain conformational differences with respect to condition have not been observed in linear architectures and is expected to influence self-assembly and the properties of the materials.