Carbon-carbon torsional barriers driving the fast dynamics in glass-forming polymers

By considering neutron-scattering data of 17 glass-forming polymers, an experimental correlation is found between the temperature range $T_f,$ at which the fast dynamics sets in, and the carbon-carbon torsional barrier in the polymer chain. This model-independent result, which suggests an intramolecular interpretation of the fast dynamics in glass-forming polymers, is easily explained in the framework of a model which relates the fast dynamics to the short-time regime of the segmental dynamics (α relaxation).