Polymerization of 4-ethynylbiphenyl by transition metal catalysts

Abstract

Abstract The polymerization of 4-ethynylbiphenyl (4-EBP) was performed by various transition metal catalysts. The polymerization of 4-EPB proceeded well to give a high yield of polymer. The W-based catalysts were found to be more effective for this polymerization than the Mo-based catalysts. The EtAlCl2 showed high cocatalytic activity for the polymerization of 4-EPB by WCl6 or MoCl5. The [Rh(nbd)Cl]2/Et3N catalyst showed high catalytic activities, whereas the poly(4-EBP)s obtained by Rh catalyst were mostly insoluble in organic solvents. The analytical results for the polymer structure revealed that the resulting polymer have a conjugated polymer backbone system with the biphenyl substituents. The poly(4-EPB)s prepared by W- and Mo-based catalysts were completely soluble in such organic solvents such as benzene, carbon tetrachloride, chloroform, 1,4-dioxane, methylene chloride, THF, and toluene. The maximum peak of photoluminescence spectrum of polymer was located at 474 nm corresponding to the photon energy of 2.62 eV, which is sky blue region. The cyclic voltammograms of poly(4-EBP) exhibited not only irreversible oxidation and reduction peaks but also the electrochemically stable window in the range of −1.3 to 1.3 V. HOMO and LUMO levels and band gap of poly(4-EBP) were 5.43, 2.72 eV and 2.71 eV, respectively.