Synthesis and Properties of Hyperbranched Poly(triphenylamine)s Prepared by Palladium Catalyzed C–N Coupling Reaction

Abstract

ABSTRACT:Hyperbranched poly(triphenylamine)s with various end functional groups were prepared starting from 4,4 -diamino-4 -bromotriphenylamine through palladium catalyzed C-N coupling reaction. The self-polycondensation of the monomer afforded secondary amino groups predominantly. End-capped polymers were isolated by the chemical modification of unreacted amino groups by acid chlorides. The properties of the hyperbranched poly(triphenylamine)s, such as solubility, thermal stability and ionization potential, were dependent on the end functional groups. The hyperbranched poly(triphenylamine)s were examined as a hole transporting material for organic light emitting diodes. The multi-layered device composed of ITO/hyperbranched poly(triphenylamine)/Alq 3 /Mg-Ag showed yellow-green emission derived from Alq 3 . The device performance was improved when the polymer end-capped with alkyl chlorides were used as a hole transporting material. Since the ionization potentials of the hyperbranched polymer with alkyl amide end groups were higher than that with aromatic amide end groups, efficient hole injection from ITO/hyperbranched poly(triphenylamine)/Alq 3 might be achieved to improve the device performance.KEY WORDS Hyperbranched Polymer / Triphenylamine / C-N Coupling / Palladium Catalyst / EL Device / Dendritic macromolecules, such as dendrimers and hyperbranched polymers deserve much attention from both synthetic and application viewpoints, and are characterized by low viscosity, good solubility and amorphous nature in solid state. [1][2][3][4][5][6][7][8][9][10][11] It is also well-known that the properties of the dendritic macromolecules are dependent on terminal functional groups in addition to backbone structure. 12, 13 Therefore, the properties of dendritic macromolecules can be tuned in some extent by the chemical modification of end functional groups. Although multi-step procedures required for the preparation of dendrimers allow the precise control of molecular architecture, one-step process to prepare hyperbranched polymers seems to be attractive for mass production and industrial applications.Palladium catalyzed condensations are one of the useful propagation reactions for polycondensation. We have previously reported the palladium catalyzed polycondensations to form linear polyamides, 14 polycinnamamides, 15, 16 and hyperbranched polyesters. 17 Recently, Buchard and Hartwig have been independently reported palladium catalyzed C-N coupling reactions. [18][19][20][21][22] The reaction conditions required for the palladium catalyzed C-N coupling are apparently much milder in comparison with conventional Ullmann type coupling reactions.Polycondensa- † To whom correspondence should be addressed.tions through the amination were also reported by Kanbara, [23][24][25][26][27] Hartwig, 28, 29 and Meyer. 30 Among them, Meyer reported linear and hyperbranched mpolyanilines through the amination in the presence of BINAP ligand and sodium t-butoxide. According to the model reaction for the polymerization, triphenylamine...

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