Synthesis and hole-transporting properties of vinyl-type polynorbornenes with ethyl ester linked triarylamine side groups

Palladium(II)-catalyzed polymerization of norbornene monomers bearing triarylamine side groups was investigated to prepare the vinyl-type polynorbornenes having hole-transporting properties. Norbornene monomers (M1–M3) with the ethyl ester linked aryldiphenylamines where the aryl group is phenyl, m-tolyl, and 1-naphthyl, respectively, were employed. The combined use of the Pd(II) catalyst supported by N-heterocyclic carbene ligand and AgSbF6 leads to the production of soluble polynorbornenes (P1–P3). While the cyclic voltammetry measurements show the relatively low oxidational stability of polymers, the polymers exhibit the high glass transition temperature of 305–333 °C. The atomic force microscopy images of the thin film of P1 reveal the very smooth film surface with a roughness of 0.29 nm, indicating the good film-forming capability of polymer. When incorporated as a hole-transporting layer in Alq3-based electroluminescent devices, the spin-coated polymer films display hole-transporting property suitable for the proper green emission of Alq3. Among the devices studied, the one based on 1-naphthylamine-containing P3 exhibits the highest performance in terms of luminance and external quantum efficiency.