Molecular Interpretation of Relaxation Processes in Amorphous Polymers Based on Data Far-Infrared and Raman Spectroscopy

The properties of polymers are largely controlled by molecular mobility-torsional-vibrational and high-amplitude motion of atomic groups of macromolecules, which manifests itself in the form of , , -relaxation transitions at temperatures below Tc and -glass transition at Tc. The stepwise "defrosting" of molecular motion is directly reflected in the temperature changes in the properties of polymers. Despite a large number of studies of transitions, their general molecular mechanisms remained unexplained until recently. A series of experimental works performed by the methods of low-frequency Far-infrared and Raman spectroscopy and generalizations made with the use of published data also made it possible to solve named task. The starting points for the molecular interpretation of transitions were estimates of potential barriers and units of motion, their comparison with the characteristics of molecules and parameters of relaxation transitions. The experiments were carried out in the spectral range 8-420 cm-1 ( 0.24-12.5 THz), including at temperature variation from 85 to 400K, on a wide range of organic linear and cross-linked polymers, as well as oligomers and low molecular weight substances. All the results presented in this work show that low-frequency Infrared and Raman spectroscopy allows clarifying molecular mechanisms of the relaxation transitions in amorphous polymers and establishing the relations of these processes with molecular characteristics of polymers, such as the structure of a monomer unit, the cohesion energy, the potential barrier to internal rotation and thermodynamic chain rigidity.