PACKING IN AMORPHOUS REGIONS OF HYDROFLUORIC-ACID-DOPED POLYANILINE POWDER BY N-15-F-19 REDOR NMR

Anhydrous N-15-labeled polyaniline powders have been examined by C-13, N-15, and F-19 solid-state NMR as a function of HF doping. Chemical s hifts in the F-19 NMR spectra of doped polyaniline reveal three distin ct types of charged environments. Carbon, nitrogen, and fluorine spin counts show that only about one-third of all the chains in fully HF-do ped polyaniline are detected. This observation is consistent with the assumption that the entire crystalline region, and amorphous regions w ithin 50 Angstrom of the crystalline border, is rendered unobservable by paramagnetic delocalized electrons in the crystalline region. Rotat ional-echo double-resonance N-15 NMR (with F-19 dephasing) indicates t hat in the observable amorphous regions the polyaniline chains are tig htly packed with an in-plane interchain separation of 10 Angstrom and that fully charged main-chain nitrogens have, on average, one nearest- neighbor fluorine 4 Angstrom away and three next-nearest-neighbor fluo rines with an average N-15-F-19 distance of just over 5 Angstrom.