2D-Deuteron NMR Studies of Ultraslow Motions in Solid Polymers Phenylflips in the Glassy State and Chain Motions at the Glass Transition

Abstract

Ultraslow reorientation can be monitored by two-dimensional (2D) exchange NMR on the time scale of milliseconds to seconds /l/. Molecular reorientation during the mixing time results in 2D cross-signals, which correlate initial and final orientations. The singularities of these exchange signals form characteristic geometrical ridge patterns. Molecular reorientation by discrete jumps and by angular diffusion can be discriminated simply by inspection. The 2D absorption mode spectrum is identical to a two-time distribution function /2/, which describes the joint probability density of finding a frequency w ₁ at the beginning of the experiment and a frequency w ₂ at the end. Thus a 2D spectrum for a fixed mixing time is an image of the state of the dynamic process. It directly provides the distribution of reorientational angles in that state.