Star-like polyaniline prepared from octa(aminophenyl) silsesquioxane: Enhanced electrochromic contrast and electrochemical stability

We report the structures, electrochemical and electrochromic properties of organic-inorganic hybrid polymers prepared via copolymerization of octa(aminophenyl) silsesquioxane and aniline. Compared with homopolyaniline (PANI), this class of novel materials exhibits much greater thermodynamic penetrability in solution, as detected using static and dynamic light scattering, suggesting that they have a star-like molecular geometry. Due to their star-like geometry, in solid state the copolymers (POSS-PANI) exhibit a loosely packed structure with relatively low crystallinity, as evidenced by X-ray and TEM characterization, and hence relatively high ionic conductivity. Cyclic voltammetric studies show that POSS-PANI undergoes similar electrochemical reactions to that of PANI but its loosely packed structure allows slightly faster cation diffusion. Spectro-electrochemical studies show a ∼40% enhancement in electrochromic contrast brought by tethering PANI onto POSS, which can be attributed to more accessible doping sites in POSS-PANI. Furthermore, the electrochemical stability of POSS-PANI is also significantly improved over that of PANI. Infrared spectroscopic measurements indicate that the formation of electrochemically inactive quinonediimine is retarded in POSS-PANI possibly due to the increased conformation freedom of the dopant anions.