Secondary Relaxation Processes in Polybutadiene Studied by 2H Nuclear Magnetic Resonance and High-Precision Dielectric Spectroscopy

Using 2H NMR and high-precision dielectric spectroscopy, we identified in polybutadiene (PB) at low temperatures (20−100 K) a third relaxation process (γ-process) in addition to the α- and β-processes. PB samples with different molecular weights (Mw) exhibit a strongly varying relaxation strength (Δeγ) though no clear-cut relationship is observed between Δeγ and Mw. Concerning the temperature dependence of the γ-process, the set of samples can be divided into two subsets characterized by different activation energies, where one subset of time constants agrees well with those obtained recently from quasi-elastic light scattering in the melt. From our NMR experiments we conclude that at T < Tg a highly hindered motion (<8°) is responsible for the γ-process, which is difficult to explain by typical conformational changes.