Molecular Bottlebrushes: Crowdedness of Side Chains Matters

Abstract

Molecular bottlebrushes (MBBs) represent a class of densely grafted macromolecules where polymeric side chains are covalently and compactly tethered to a polymeric backbone. These highly grafted chain architectures create a confined microenvironment induced by steric congestion of the side chains, offering an exceptional platform for investigating polymer behaviors under molecular confinement. The unique topological structure alters the conformation of backbones and side chains from an entangled coil to an extended chain and endows the MBBs with a unimolecular nanoobject structure with a defined length/diameter ratio and an intrinsically ordered intra- and intermolecular structure. The correlation between chain crowdedness, governed by grafting density and side chain structures, and physical properties, e.g., crystallization, glass transition temperature, and viscoelastic behavior, may direct the development of unique polymer materials through reorganization of known polymer chains. In this Perspective, we focus on the relationship between the crowded structure and the physical properties of MBBs, highlighting the crowdedness-derived material properties. We first introduce the unique nanostructure of MBBs, followed by chemistry and physical properties. Finally, we highlight the functions that differ from those of non-topological polymers and discuss their potential application.