Doped polyacetylene (PA) samples stored under vacuum at room temperature in
ESR sample tubes reach after three months nearly a steady state in the tem
perature dependent intensity and linewidth behaviour. The ESR spectra show
two lines with an equal g-factor. In particular the linewidth of the small
line demonstrates a remarkable property. The temperature dependence of the
linewidth indicates a maximum at 30 K, and has a value of about 0.17 mT abo
ve this temperature in the whole investigated region up to 300 K. The ESR d
ata are dicussed in a two spin model of delocalized states at the PA chain
and fixed spins in the dopants. The interpretation underlines the metallic
behaviour of the doped PA at low temperatures.