Synthesis of electroactive tetraaniline-PEO-tetraaniline triblock copolymer and its self-assembled vesicle with acidity response.

A novel ABA triblock copolymer containing electroactive tetraaniline [(ANI)(4)] and poly(ethylene oxide) (PEO600, M(n) = 600), (ANI)(4)-b-PEO600-b-(ANI)(4), was synthesized by coupling tetraaniline and PEO600 with tolylene 2,4-diisocyanate. FTIR, NMR, and UV-vis spectroscopy were combined to characterize the chemical structure of (ANI)(4)-b-PEO600-b-(ANI)(4). The electrochemical properties, self-assembly, and acidity response of copolymer in aqueous solution were investigated by cyclic voltammetry, electron microscopy, and dynamic light scattering. Different from pure tetraaniline and polyaniline, the triblock copolymer in 1.0 M sulfuric acid solution only exhibits one oxidation peak in cyclic voltammetry. In a neutral aqueous solution, the triblock copolymer self-assembled into vesicles with diameter of about 258 nm. Upon acidification with HCl, the size of the vesicles increases to 471 nm and 1.19 microm when the concentration of HCl changes to 10(-3) and 10(-1) M, respectively. With addition of aqueous 1.0 M HCl to the triblock copolymer solution in THF, hollow spheres and bowl-like aggregates were obtained. A bilayer model was proposed for the vesicle formation, and the mechanism of acidity response was discussed.