The tetrabutylammonium bromide catalysed sulfonation of cis-1,4-polybutadiene in the presence of alkaline sodium bisulfite was successfully carried out without crosslinking. The sulfur content was analysed by XPS and the Schoniger method. The sulfonated polybutadiene was characterised by IR,H-1 and C-13 NMR spectroscopy The probable reaction mechanism of a radical anion transfer is proposed. Conclusions regarding the ionomer formation are drawn by interpreting the glass transition (T-g) and reduced viscosity (eta(red)) data.