Anion To Radical To Polyarene

Researchers in Germany have taken advantage of the synergy between organic synthesis and polymer chemistry to develop a method for making structurally uniform polyphenylenes (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201206096). These polymers have a growing number of applications in materials science, such as thin films for organic light-emitting diodes. Sandip Murarka and Armido Studer of the University of Münster used either the tetramethylpiperidine-based nitroxide radical called TEMPO or O₂ from air to initiate oxidation of alkyl- or alkoxy-substituted iodoarene Grignard reagents. The subsequent polymerization proceeds via a “crossover” mechanism in which the active end of the growing polymer chain alternates between anionic and radical intermediates as each new monomer unit is added. In the past, researchers have been able to chemically control anion-to-radical crossover or vice versa, but the ability to regularly alternate between the two processes is unprecedented. The Münster method avoids transition-metal catalysts, which can be expensive and require sophisticated purification procedures to prevent residual metal from disrupting the polymer structure. Murarka and Studer used the approach to make poly(m-phenylene), poly(p-phenylene), and polynaphthalene, as well as styrene block copolymers, all end-capped with reactive functional groups.