Cylindrical molecular brushes: Synthesis, characterization, and properties

Brush-like macromolecules are unique polymer molecules whose conformation and physical properties are controlled by steric repulsion of densely grafted side chains. Molecules can be either flexible or stiff, depending on the grafting density and the length of the side chains. Molecules can switch their conformation in response to alterations in the surrounding environment, e.g. changes of temperature, solvent quality, pH, and ionic strength. Furthermore, one can control molecular conformation and related properties using external stimuli such as light and electro-magnetic fields. Molecular brushes are also very informative model systems for experimental studies of polymer properties. Molecules are readily visualized by atomic force microscopy, opening unique opportunities to observe single polymer molecules as they move, order, and react on surfaces. Brush-like molecular architectures are well-known in biology where they are responsible for various functions including mucociliary clearance of lung airways and mechanical performance of articular cartilage. Polymer chemistry is currently making the first steps in controlling molecular architecture and understanding the distinctive properties of molecular brushers. This article reviews the characteristic physical properties of well-defined molecular brushes and the different strategies employed for their preparation, with particular focus on synthesis via controlled radical polymerization techniques.