Characterization of cobalt‐modified polyimides

Modified polyimide films containing cobalt have been prepared by the addition of cobalt(II) chloride to a solution containing one of the diamines 4,4′‐oxydianiline (ODA) or 4,4′‐diaminodiphenylsulfide (DDS) and one of the dianhydrides 3.3′, 4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) or 4,4′‐bis(3,4‐dicarboxyphenoxy)diphenylsulfide dianhydride (BDSDA) and characterized by thermal methods, UV‐visible spectra, room‐temperature direct‐current electrical resistivity measurements, and X‐ray photoelectron and Auger electron spectroscopy. A principal goal of this work was to establish if there was coordination of the potential donor atoms of the polymide to cobalt. UV‐visible spectra of the modified polyamic acid solutions and polyimide films and a titration study of a model system do not show any appreciable coordination with either the polyamic acid or the polyimide; rather, the cobalt(II) appears to be coordinated to the solvent, N,N ‐dimethylacetamide (DMAc), as [Co(DMAc) 4 ] 2+ , until the temperature is raised above 200°C. X‐ray photoelectron spectra of films cured only to 200°C also do not show significant shifts in the binding energies of the potential donor atoms from those binding energies of the undoped polymers, confirming little direct coordination of the cobalt to atoms of the polyimide. Heating the films to 300°C in a forced‐air oven causes the formation of a cobalt oxide layer on the air side of the polymer. Direct‐current electrical resistivity measurements on this surface show a 10 4 –10 6 reduction in resistivity due to this layer.