Facile synthesis of cyclic polyphenylene oxide as an electroactive supramolecule

Abstract

Heteroatom containing polymers such as polyphenylene sulfides, polyanilines, and polyphenyl ethers are known to have high chemical and thermal stability. Polyphenyl ether is one of the most important engineering plastics and their structures contribute to the toughness, strength, and thermal performance. Although various substituted polyphenyl ethers are studied for their enhanced polymer properties, supramolecular polyphenyl ethers are largely unexplored. Therefore, the objective of this research is to synthesize and study a cyclic polyphenylene oxide. In this study a supramolecular ether structure, cyclic polyphenylene oxide with six phenoxy units was successfully synthesized by using N,Ndimethylglycine prompted Ullmann coupling, characterized by 1H/13C NMR spectroscopy, and the redox properties were evaluated by cyclic voltammetry. The cation radical was generated by using NOSbCl6 and studied using NIR spectroscopy. The cyclic voltammogram of cyclic polyphenylene oxide shows three oxidations (1.53, 1.78, 1.83 V vs SCE). The first oxidation is reversible, and the others are quasi reversible. The reversibility of the first oxidation at 1.53 V vs SCE predicts the potent use of the cyclic polyphenylene oxide in secured repeated redox processes in molecular electronics. The absorption band around 1600 nm in the cation radical spectrum suggests the coupling between aryl groups. The availability of reversible oxidations and interactions between aryl groups suggest that the cyclic polyphenylene oxide is a promising candidate for applications in emerging areas of molecular technology.