Local dynamics of atactic polypropylene across the glass transition

We report a dynamic investigation of the molecular processes in atactic polypropylene using quasi-elastic neutron scattering (QENS). This polymer was investigated over a wide temperature range across the glass transition temperature, T-g, using various QENS spectrometers with different energy resolutions. Below T-g, methyl side group reorientations take place. We have characterized this motion using a model that accounts for a distribution of activation energies. In the melt, where the polymer chain backbone is no longer frozen in, segmental motion occurs. QENS data analysis allows us to identify three distinct molecular processes and we present evidences for the existence of slow dynamics in the melt. (C) 2001 Elsevier Science B.V. All rights reserved.