ELECTROPOLYMERIZATION OF THIOPHENE ON OXIDIZABLE METALS IN ORGANIC MEDIA

The electropolymerization of thiophene on oxidizable metals (Fe, Zn, A l) has been investigated in different organic media (acidic, neutral o r basic) with a view to obtaining adherent and homogeneous polythiophe ne (PT) films. In propylene carbonate (PC), considered as a neutral me dium (DN = 15) and a good solvent for the electropolymerization of thi ophene on noble metals, it was found that, of several salts, PF6- alon e could hinder the anodic dissolution of iron and allow the galvanosta tic electropolymerization of thiophene on this metal. In a basic solve nt, such as THF (DN = 20), electropolymerization of PT could not be ac hieved, due to passivation of the metal making the electrode surface h ighly insulating. The best results were obtained in dichloromethane (D CM), considered as acidic (DN = 4), which allowed the deposition of ho mogeneous PT films on Fe and Al in potentiodynamic or galvanostatic mo des easily, and on Zn in the galvanostatic mode only. Polymer films ob tained on these metals in PC and DCM were analysed by LR spectroscopy and XPS; their structure appeared quite similar to those obtained on P t with, in particular, strictly alpha,alpha' coupling of thiophene uni ts. However, the conductivities of these PT films, related to their do ping level, are much lower than on Pt(10 S cm(-1)), and seem to be cor related with the redox potential of the metal: 10(-3) S cm(-1) with Fe and Zn, 10(-4) S cm(-1) with Al. The adherence of PT films synthesize d in DCM on Fe and Zn is not very good (maximum adherence about 35% fo r iron and 0% for Zn). In the case of iron it was found to decrease wh en the current density increased from 4 to 10 mA cm(-2). With Al, the adherence is excellent (100%) and is due to the formation of S-Al and C-Al bonds, as confirmed by XPS analysis. (C) 1997 Elsevier Science S. A.