Control over the Self-Assembly and Dynamics of Metallacarborane Nanorotors by the Nature of the Polymer Matrix: A Solid-State NMR Study

• Published in: Macromolecules 2014-09, Vol.47 (18), p.6343-6354
• Main Authors: Brus, Jiri, Zhigunov, Alexander, Czernek, Jiří, Kobera, Libor, Uchman, Mariusz, Matějíček, Pavel
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma501117a

Solids that combine long-range order with rapid molecular reorientation offer a promising approach for the development of a novel class of functional materials with potential applications in materials science and nanotechnology. In this contribution, the capability of dicarbollide ions to undergo self-assembly processes with suitable macromolecules is demonstrated, and a strategy leading to the formation of structurally and dynamically well-defined amphidynamic polymeric composites is introduced. For this purpose, three amphidynamic nanocomposites were synthesized via the self-assembly of cobalt bis(dicarbollide) anions (CoD–), with neutral poly(ethylene oxide) (PEO), and two isomers of poly(vinylpyridine), P2VP and P4VP, in protonated form. All of the systems were characterized by a combined study employing WAXS, advanced solid-state NMR, and quantum chemical calculations. It was found out that the interaction of neutral PEO with CoD– ions driven by weak dihydrogen bonding resulted in the formation of a uniquely organized periodic structure. In contrast, the self-assembly of the systems based on the electrostatic interactions (charge-transfer-assisted hydrogen bonding) of P2(4)VP was controlled by the position of the positive charge in pyridine ring and resulted in unique well-defined orientations of the CoD– ions (parallel and perpendicular) with respect to the polymer chains. In addition, the CoD– ions exhibited uniaxial relatively large-amplitude rotational motions in all of the nanocomposites over the broad range of T g. The motional amplitudes executed by the CoD– ions are significantly more extensive than those of the polymer segments in all of the systems. Macromolecules thus represent a rigid support (stator) for the more mobile CoD– ions (rotators). The obtained findings revealed that a relatively simple self-assembly procedure could be used for the preparation of well-defined amphidynamic nanocomposites, thereby opening a route to construct sophisticated supramolecular systems.