Molecular relaxations in poly(ethylene adipate) and block urethane elastomers as studied by the spin probe method

The spin‐probe method is used to study the rotational mobility of two different probes in poly(ethylene adipate) and a block urethane elastomer synthetized using poly(ethylene adipate), 4,4′‐methylenebis(phenyl isocyanate) and 1,4‐butanediol. The observed ESR spectra correspond to slow and rapid rotations of spin probe molecules. They are interpreted using both the isotropic and anisotropic models for the spin probe motion. It is found that at low temperatures the behaviour of spin probes is related to the β‐relaxation, whereas at higher temperatures to the α + β‐relaxation. Differences in mobilities are probably connected with different sizes of spin probes used.