Local dynamics of atactic polypropylene across the glass transition

We report a dynamic investigation of the molecular processes in atactic pol ypropylene using quasi-elastic neutron scattering (QENS). This polymer was investigated over a wide temperature range across the glass transition temp erature, T-g, using various QENS spectrometers with different energy resolu tions. Below T-g, methyl side group reorientations take place. We have char acterized this motion using a model that accounts for a distribution of act ivation energies. In the melt, where the polymer chain backbone is no longe r frozen in, segmental motion occurs. QENS data analysis allows us to ident ify three distinct molecular processes and we present evidences for the exi stence of slow dynamics in the melt. (C) 2001 Elsevier Science B.V. All rig hts reserved.