Synthesis, Electrochemical Behavior, and Electronic Properties of Hyperbranched Poly(p-methylenetriphenylamine): An Unexpected Condensation Polymerization from N-[4-(Tosyloxybutyloxymethyl)phenyl]-N,N-diphenylamine

N-[4-Tosyloxybutyloxymethyl]phenyl]-N,N-diphenylamine showed unexpected chemical reactivity and polymerized to form hyperbranched poly(p-methylenetriphenylamine) (PMTPA) under neat conditions. The hyperbranched PMTPA was electrochemically active and could be deposited on electrode surface when oxidized. The SEM study revealed that electropolymerization of PMTPA would form uniform coating on ITO surface. Polymeric light-emitting diodes (PLEDs) employing the electroactive hyperbranched PMTPA as hole-transport layer in ITO/electrochemically polymerized HTL/EML(PVK-PBD-Ir(ppy)3)/Mg/Ag demonstrated the brightness over 20 000 cd/m2 and low turn-on voltage. In particular, the device performance was very steady regardless of the thickness of the PMTPA layer, ranging from 4 to 10 nm.