| Abstract
| - Recently by dielectric spectroscopy a new secondary relaxation process in polyisobutylene(PIB) was detected showing all the signatures of a Johari−Goldstein relaxation [Richter, D; Arbe, A.;Colmenero, J.; Monkenbusch, M.; Farago, B.; Faust, R. Macromolecules1998, 31, 1133]. Using highresolution neutron backscattering, we investigated the quasielastic neutron spectra from protonated PIBwhich are related to this process as a function of momentum transfer and temperature. In addition westudied the elastically scattered intensity over a wide temperature range. After multiple scatteringcorrections all results can be described consistently in terms of a local jump process with the distributionparameters from the dielectric β-relaxation. The spatial extent of the associated protonic motion wasdetermined to be d = 2.7 Å. A comparison with the existing body of data for PIB leads to the conclusionthat the dielectric β-process and the earlier found δ-process must be identical, thereby revising theassignment of the δ-process as due to methyl group rotation. Finally, we remark on aspects of the relationbetween quasielastic coherent and incoherent scattering and address the seemingly contradictory resultof different length scales revealed for the same process with the two techniques.
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