A Double-Modulation ESR Study of Internal Dynamics in the Glassy Polymer Matrix Detected by a Nitroxide Spin Probe

The double-modulation ESR spin-probe technique was employed to study slow-motional dynamics in amorphous polymer matrices of polybutadiene, polyisobutylene, poly(methyl methacrylate), and paraffin. It was shown that the low-lying excitation levels of the polymer matrix, found in the range from 77 to 190 K below the internal spin-probe transition, affect the effective relaxation rate of a perdeuterated nitroxide probe. The interrelationship between the effective relaxation rates and the local molecular dynamics of side-chain groups attached to the polymer backbone was observed. Possible relaxation mechanisms are discussed within the electron-nuclear dipolar interaction.