Spectroscopic study of thermo-oxidative degradation of polypyrrole powder by FT-IR

Thermal ageing of compressed polypyrrole powder, with FeCl4− as a dopant, at 90 °C has been monitored by IR spectra and evolved gas analysis (EGA). The thermo-oxidative degradation results in a decrease in the absorption of the electronic transition band, reduction in intensity and slight shift in position of most of the IR absorptions, the loss of the 870 cm−1 absorption shoulder, and the formation of hydroxyl, nitrile and carbonyl species. In both air and nitrogen ageing environment, the evolution of carbon monoxide (CO), carbon dioxide (CO2), water (H2O) and ammonium chloride (NH4Cl) is detected. The dopant decomposes to form ferric oxide and to produce chlorine and/or hydrogen chloride, which in turn reacts with the pyrrole moiety in both air and nitrogen atmosphere. The source of oxygen for the thermal oxidation in nitrogen is the oxygen present in the polymer, probably as a dopant, O2−. Thermal degradation results in ring-opening reactions and the formation of oxidation species, which shorten the conjugation length leading to a rapid loss of conductivity. The loss of conductivity does not correspond exactly with the loss or formation of any individual species, but is best matched by the production of water and the decrease in the 870 cm−1 shoulder. This indicates that the mechanisms of thermo-oxidative degradation are complex and the conductivity decay is likely to be caused by a number of different mechanisms.