Polyimides derived from condensation of pyromellitic dianhydride with various diamines have been shown to be electrochemically active. Films of these materials coated on the surface of solid electrodes, immersed in electrolyte solutions of dipolar aprotie solvents undergo two distinct reversible redox processes, involving addition of one or two electrons per repeat unit. These processes can be carried out completely and stoichiometrically for films as thick as 20 ~m. Spectrophotometric studies and comparison with model compounds lead to the following conclusions: (i) ion permeability, which is a necessary component of the electrochemical charging and discharging processes, is related to solvent swelling and is, in turn, strongly influenced by the physical history of the polymer, (ii) redox activity involves localized molecular electronic states of the pyromellitic diimide group, (iii) there is no evidence for electronic interactions between pyromellitimide groups along a given polymer chain, and (iv) spectroscopic evidence indicates that weak interactions within the bulk of the polymer give rise to detectable inhomogeneities in optical or electrochemical properties of individual functional groups as a function of the charge on groups in their environment.
Commercially available, thermally cyclized, poly(4,4′‐oxydiphenylenepyromellitimide) displays ohmic charge transport when suitably doped through an aqueous interfacial electron transfer reaction. The normally highly insulating polymer increases in conductivity by approximately 11 to 13 orders of magnitude becoming an air‐sensitive semiconductor with bulk conductivities ranging from 10−5 to 10−7 Ω−1 cm−1. The mechanism of conduction appears to be based upon interchain electron hopping.
served relaxation behavior involves considerable motional anisotropy and strongly hindered methyl rotation, the latter being only marginally a' dependent.By use of the expressions for rotational friction of a prolate ellipsoid of resolution it has been possible to calculate hydrodynamical particle dimensions, which, considering the crudeness of the method, yielded surprisingly realistic values in view of the chain diameter, interchain distance, and persistence length. Clearly, for PMA such dimensions, and accordingly rotational-diffusion coefficients, do not relate to motions of the whole polymer molecule, but rather relate to motions of limited parts of the single backbone chain.electrodes which were surface modified by the deposition of an iron-containing plasma polymer or iron-containing plasma deposit followed by the electrochemical deposition of iron hexacyanoferrate. These results support the formation of surface-bound Prussian brown, Berlin green, Prussian blue, and Everitt's salt depending on the potential of the electrode and the identity of the cation of the bulk electrolyte. The electrode-surface-bound iron hexacyanoferrate acts as a zeolite in which hydrated K+ and Na+ may enter into the lattice. Hydrated Li+, which possesses a larger hydration shell, cannot enter the countercation sites associated with the low-spin iron redox couple and, having entered those sites associated with the high-spin iron redox couple, is unable to exit. The naked or unsolvated cations K+, Na+, or Li+ can enter these countercation lattice sites when the solvent is propylene carbonate. Results presented here suggest that the countercation lattice sites associated with the high-spin Fe(3+/2+) redox couple are distinguishable from the countercation cavities associated with the low-spin Fe(III/II) redox couple.
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