A study of the degradation and stability of polypyrrole by inverse gas chromatography, X-ray photoelectron spectroscopy, and conductivity measurements

Chloride- and p-toluene sulphonate-doped polypyrrole powders (PPyCl and PPyTS, respectively) were characterized by inverse gas chromatography (IGC) and X-ray photoelectron spectroscopy (XPS) in order to study their degradation and stability. Freshly synthesized PPys appear as a high energy materials as judged from the dispersive contribution to the surface energy (gamma(s)(d)) values in the 80-225 mJ/m(2) range determined by IGC. An IGC investigation of the effect of temperature and ageing on the degradation and stability of doped PPy showed that gamma(s)(d) is only slightly affected by ageing at room temperature (RT) although conductivity (sigma) of PPyCl decreases by 80% (for sigma(o) = 4 S/cm). PPyTS was found to be very stable since it retained nearly the same gamma(s)(d) and conductivity values over a period of 3 months. In-situ heat treatment (at 150degreesC for up to 15 h) of the PPy powders packed in the GC columns induced a significant decrease of gamma(S)(d) of PPyCl from 227 to 175 mJ/m(2) and the conductivity by two orders of magnitude at RT. XPS indicates an increase of the C=N imine defects due to deprotonation of the pyrrole repeat units of PPyCl. In contrast, PPyTS became slightly more activated (gamma(s)(d) = 95 mJ/m(2)) after 15 h of heat treatment although conductivity decreased (i.e. sigma = 9 S/cm and sigma/sigma(0) = 24%) and the fraction of C=N bonds (defects in the chemical structure of polypyrrole backbone) increased. (C) 2004 Elsevier B.V. All rights reserved.