MOLECULAR MOTIONS IN POLYISOBUTYLENE - A NEUTRON SPIN-ECHO AND DIELECTRIC INVESTIGATION

We present neutron spin-echo and dielectric results on the local dynam ics of polyisobutylene. The dielectric spectra reveal the existence of a so far unknown secondary relaxation process being distinctly differ ent to previous theoretical predictions. Neutron spectra have been tak en over a large range in momentum transfer Q and temperature. At the Q value of the first structure factor maximum the dynamic pair correlat ion function is selective for interchain motions. There the neutron sp ectra display the same temperature dependence and shape as the classic al rheological data taken in the terminal zone and do not follow the t emperature laws based on spectroscopic results. A quantitative evaluat ion combining the information content of the dielectric and neutron re sults reveals a small stepwidth of 0.5-0.9 Angstrom involved in the se condary process. The alpha process is diffusive and follows the Gaussi an approximation resulting in a sublinear time development of associat ed mean squared displacements.