Production of a Polymer with Highly Anisotropic Conductivity and Structure by Co-Electroprecipitation of an Imide Anion Radical and Polycation

Abstract

Polymer films were grown by electroreduction on solid electrodes or a mercury surface from an aqueous solution containing disodium N,N-bis(p-sulfonatophenyl)naphthalenedicarboximide (1) and the cationic polymer poly- (diallyldimethylammonium) (2+). Electrochemical studies of the film formation are reported. The films (50–300 µm thick) were removed from the electrode and characterized by XPS, ESR, UV, VIS, NIR, and IR spectroscopy. The films were stable in dry air for months. They contain 2+ and anion radicals (1−) in the form of π-dimers and π-stacks. IR spectra showed the optical conduction band at 4 µm and three vibronic bands assigned to π-stacks. Polarized transmission NIR spectra of thin films taken at various incidence angles and ESR spectra on free standing films, which were oriented in the cavity, showed that the stacks were oriented preferentially in the film plane, with a tilt angle of 5° up from the surface. The electrical conductivity was electronic and highly anisotropic. Measured at ca. 90% relative humidity at room temperature with four probes, in the film plane, σ = 10−1 S cm−1; across the film plane, σ = 5 × 10−8 S cm−1. Measured in dry nitrogen, the in-plane σ = 10−4 S cm−1. Variable-temperature in-plane conductivity measurements on humidified films showed a linear dependence of σ on T−1 over the range 220–300 K and an activation energy of 0.3 eV. There was an unusual minimum in the conductivity at about 180 K. The in-plane conductivity of humidified films also showed unusual temporal dependence, in that, depending on the size of the current step applied, the conductivity improved substantially during the first few minutes of current passage. © 1993, American Chemical Society. All rights reserved.