LOCAL MOTION IN THE BETA-TRANSITION RANGE OF PARTIALLY CRYSTALLINE POLYETHYLENE STUDIED BY NEUTRON-SCATTERING

We have performed inelastic neutron scattering experiments on protonat ed and fully deuterated partially crystalline polyethylene. Using a hi gh-resolution, three-axes spectrometer with an energy resolution of 80 mu eV, it was possible to detect a quasielastic process in the dynami c structure factor with a FWHM of 0.3meV. This process was shown to be active above T-0 = 260 K and its FWHM was nearly independent of tempe rature and scattering vector. The spatial extent of the underlying mot ional process was determined from the corresponding Debye-Waller facto r. The mean squared displacement increases strongly with T above T-0 u p to 4 Angstrom(2) at T = 380 K. Comparison with results from similar work on fully amorphous polymers suggests to relate T-0 to the glass t ransition of the amorphous phase in partially crystalline polyethylene . The coherent structure factor shows no evidence for a significant co ntribution of correlated motion to the process. A speculative explanat ion of the observed phenomenon as a non-equilibrium soft-mode is propo sed.