Grafted polytriphenylamines synthesized by atom transfer radical polymerization in tandem with oxidative polycondensation

Abstract

Arylamine polymers are among the most studied conducting polymers due to a whole range of interesting properties and applications. In this paper, we describe the synthesis of soluble and processable electroactive poly(triphenylamine-g-oligostyrene) by two polymerization methods in tandem. In the first step, oligostyrene macromonomers with well-defined molecular weight, polydispersity and chain-end functionality were obtained by radical-controlled polymerization (i.e., atom transfer radical polymerization, ATRP) of styrene. The styrene oligomerization was carried out using a new triphenylamine-based initiator, [4-(diphenylamino)benzyl 2-bromo-2-methylpropanoate], cuprous bromide as co-initiator and bipyridine as ligand, at 100 °C, in bulk. Using two feed molar ratios of components: [styrene]0:[initiator]0:[CuBr]0:[bipyridine]0, two macromonomers with M n = 9,900; M w/M n = 1.25 and M n = 3,460; M w/M n = 1.22, respectively, were synthesized. The presence of triphenylamine moiety at one end of the macromonomer allowed the chemical and electrochemical polymerization of macromonomers to polytriphenylamine brushes having short oligostyrene grafts in every structural unit. The oligostyrene substituents confer processability and good solubility in common organic solvent characteristics for polystyrene while preserving the optoelectronic properties of arylamine-conjugated main chain. The chemical oxidative polymerization of macromonomer was carried out using iron (III) chloride dissolved in nitrobenzene. The redox behavior of the initiator, macromonomer and graft polymer was investigated by cyclic voltammetry. In all cases, it was observed that the reversible oxido-reduction of arylamine sites was accompanied by irreversible oxidative electropolymerization by free-para positions of triphenylamine substituents and deposition of thin films on working electrode. The structures of the initiator, macromonomers and graft copolymers were determined by Fourier transform infrared, 1H and 13C NMR spectroscopy. The absorption and fluorescence spectroscopy have revealed absorption and emission maxima characteristics for triphenylamine group. DSC studies have confirmed glass transitions characteristics for styrene oligomers.