Molecular Mobility in Comb-Shaped Polymers

The nature of the molecular mobility in polymers is determined by the presence of long-chain molecules and the possibility of internal rotation of the atoms in the main and side chains. At temperatures below the glass transition temperature, movement of the kinetic units located in small volumes (short segment or unit of the main chain, side sub-stituent or part of the side substituent) is possible. This type of motion, related to the mobility of only a few groups of atoms, is usually called group motion, and is indicated by the Greek letters β, γ, δ, etc., as a function of the character of the relaxing groups. At temperatures close to Tg and higher, a second type of motion begins to appear: segmental motion, related to the cooperative movement of the kinetic segments of the main chain, called α-relaxation [1–6]. This division is arbitrary to a significant degree, since the different types of motion which frequently take place simultaneously in a similar region of frequencies and temperatures, thereby impeding their determination and unambiguous interpretation, cannot be distinguished for all polymers.