Dielectric relaxation of high polymers in the solid state

Dielectric relaxation processes observed in solid polar polymers seem to be generally classified into three kinds. Amorphous polymers with flexible polar side groups usually show two kinds of relaxation process. The high‐temperature process is attributed to the large scale conformational rearrangements of the main chains, while the low‐temperature one results from the motion of side groups. We shall call the former αa relaxation and the latter β relaxation, where the subscript refers to the amorphous phase. Even in amorphous polymers without flexible side groups, two processes are observed. The molecular mechanism of high temperature one is the same as the αa relaxation. The low‐temperature one is due to the “local relaxation mode” of the main chains. We shall call it also β relaxation because of the similarity of the observed characteristics. Semicrystalline polymers show two relaxation processes classified as αa and β, although their behavior is modified by crystallization. When the crystallinity is greatly increased, a third relaxation process with associated with crystalline phase appears. We shall call it αc relaxation, where the subscript means the crystalline phase. The effects of chemical structure, stereoregularity, pressure, and crystallization on the dielectric behavior can be explained consistently based on the above molecular mechanisms.