Thermal Neutron Spin–Echo Studies on Dynamics of a Glass-Forming Polymer in a High Q Range

We performed thermal neutron spin echo measurements on a glass-forming polymer, deuterated polybutadiene (–[CD 2 –CD=CD–CD 2 ] n –; PB- d 6 ), in a high Q range up to 3.5 Å -1 covering the first and second peaks of the structure factor S ( Q ), and evaluated the decay rate Γ( Q ) of the coherent intermediate scattering function as a function of Q . In contrast to the previous experimental findings on the first peak of S ( Q ) at Q =1.5 Å -1 , no `de Gennes' type narrowing was observed on the second peak at Q =2.9 Å -1 . This novel finding indicates that the narrowing is hidden by the distinct motions of the soft –CD 2 –CD 2 – and =CD–CD 2 – units and the self-motions of the rigid and soft units in the Q range around the second peak. The temperature dependence of the relaxation rate Γ( Q ) suggests that in the high Q range beyond the first peak of S ( Q ) the conformational changes in a deutrated PB chain are mainly observed.