NEUTRON-SCATTERING STUDY OF SEGMENTAL DYNAMICS IN THE DISORDERED REGIONS OF PARTIALLY CRYSTALLINE POLYETHYLENE

Segmental dynamics in the disordered regions of partially crystalline polyethylene was investigated by quasielastic incoherent neutron scattering. Experiments provide evidence for the peculiar nature of the disorderd regions, where the motion is restricted due to the chain fixing in the crystallites and the unresolvable entanglements. There are strong variations in the mobility between different samples. Partial melting results in a release of the constraints, which is reflected in an increase in the mobility. Conclusions are based on a determination of the mean-squared displacements [u2]r in all the disordered regions. Values for [u2]r were derived from T- and q-dependent elastic window scans and measured dynamic structure factors. In the frequency range of the experiment motion is made up of two components, the fast local mode generally found in glass-forming liquids and a slow diffusive mode which corresponds to the beta- and gamma-process. Up to the onset of partial melting they contribute with similar weights to [u2]r. Partial melting then mainly affects the slow diffusive mode and leads to a further increase of its amplitude.