ABSTRACT
Because some chemical and physical properties of solids, particularly polymeric systems or porous materials containing organic or inorganic fragments, depend on the mobility of molecules or molecular groups, the characterization of molecular dynamics is an important aspect of solid-state NMR studies. Generally, they are aimed at identifying motions to determine the type (motional model), frequencies, and activation energies of reorientations. It should be added that, in contrast to solutions, molecular motions in solids can be cooperative and give signicant contributions to the mechanical properties of systems. Initially, studies of the dynamics in polymers, both crystalline and amorphous, considered rotational motions to be simple jumps about well-established axes, such as phenyl ips. However, later solid-state NMR and other methods have shown that the mechanism of the rotational motions is complex, such that large-angle uctuations of polymers over rotational jumps play the important role. In other words, in reality, motions are cooperative, particularly in supramolecular systems. It is now generally accepted that conformational transitions in polymers involve rotations of individual groups through typically large bond angles (e.g., 120°) that occur via chain dynamics for angle uctuations with small angular displacements, followed by large angle jumps due to conformational transitions of the chains.1
