Electron‐electron double resonance study of polymer chain motions

The technique of frequency-swept electron–electron double resonance (ELDOR) has been used to study polymer chain motions in dilute solutions. ELDOR effects have been measured at different temperatures and pump powers. The maximum de-enhancements obtained by extrapolating the data to infinite pump powers were used to interpret molecular motions. Amorphous polystyrene with nitroxides spin-labeled at both chain ends was employed in this study. The result agrees excellently well with the result obtained from electron spin resonance (ESR) line-width analysis. Both the activation energy (12 kJ/mole) and the correlation times of the motion, were found to be significantly smaller than the values obtained from other ESR and nuclear magnetic resonance (NMR) studies on aromatic substituted polystyrene. Explanations were given as due to the smaller steric hindrance and less backbone coupling among neighboring bonds for the local motions of polymer chain ends.