INFLUENCE OF OXYGEN ON THE PARAMAGNETIC PROPERTIES OF POLYPYRROLE LAYERS

Different polypyrrole films with a defined one- and two-dimensional mi crostructure are prepared by electrochemical polymerization. In as pre pared films paramagnetic species are formed which have been investigat ed by paramagnetic electron spin resonance (ESR) spectroscopy. Single line ESR spectra with a line width of Delta B = 0.022 mT in vacuum, a spin concentration of N = 3 x 10(19) spins/g and a g-factor of g = 2.0 026 were measured. In the presence of oxygen the ESR linewidth of poly pyrrole increases almost linearily with increasing oxygen pressure by a factor of more than 10, resulting in a line width of Delta B = 0.28 mT at atmospheric conditions. There is also a time dependence of the i ncreasing ESR line width influenced by the oxygen diffusion processes in the different polypyrrole structures. The ESR line width varies hig hly reversibly upon evacuation. Successive repetitions of oxygen expos ure/pump off procedures show an excellent reproducibility. This revers ible reaction of the paramagnetic centres in polypyrrole films upon in teraction with oxygen opens the possibility for an application of thes e polymer films as oxygen sensors.