Fluorescence spectroscopy using an intramolecular excimer-forming probe has been used to investigate chain mobility in various polybutadienes and copolymers of styrene and butadiene. The temperature dependence of the correlation time of the probe motion can be fitted to a Williams-Landel-Ferry equation which shows that the probe mobility reflects the glass transition phenomenon of the host matrix. However, it is obtained that the probe presents an additional mobility which depends on the polymer structure, on the existence and the nature of lateral chains.