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Polymers are commonly chain-like in structure but new polymeric materials that more resemble chains from which hang tiny "bottle brushes" can form gigantic spherical micelles in solution, according to a German team. The researchers have used NMR to study the structure of these materials and suggest new intriguing transport properties. Michael Neiser, Sandra Muth, Ute Kolb, and Manfred Schmidt of the Johannes Gutenberg University in Mainz, working with Robin Harris and Jun Okuda of RWTH Aachen were aware of numerous studies into the synthesis and properties of so-called rod-block coil copolymers. These materials have been investigated in detail for their potential liquid crystal and other applications. However, as the team points out, these materials contain short, rigid rods whereas giant rod materials might have more sophisticated behaviour. Researchers are keenly investigating micelles as potential carriers of smaller molecules, such as pharmaceuticals. Their ability to transport such molecules from one solvent type to another making them potentially valuable in, for instance, carrying a polar drug across the hydrophobic surface of the skin or across a membrane that would otherwise exclude it. Schmidt and his colleagues have now synthesised for the first time giant rod-coil amphiphiles that consist of stiff cylindrical brush-like groups attached to a polymer backbone. These materials form microscopic "bubbles" known as micelles in solution as the hydrophobic, or water repelling, portion of the amphiphilic group attempts to avoid polar molecules, while the polar, hydrophilic, portion of the amphiphile attempts to seek out water and other polar molecules. The researchers have investigated the chemical and physical nature of their micelles using NMR spectroscopy, gel-permeation chromatography (GPC), light scattering, atomic force microscopy (AFM), and transmission electron microscopy (TEM). Such techniques revealed the micelles to have the predicted structure based on the polymer synthetic procedures although the team is yet to look in detail at the mechanism of micelle formation. Indeed, the use of a samarium-containing metallocene catalyst allowed them to build up relatively long brush polymers bristle by bristle with fine definition, something that has not been possible for such materials until now. Related links: |
 TEM image of a micelle formed from a giant brush-coil block copolymer. (Credit: Schmidt et al./Wiley)  More than blue-skies research, bottle-brush polymers could help build micelles for molecular transport (Credit: David Bradley) |
