Electron spin resonance studies rotational motions

Functional groups attached to solvent-swollen polymer chains exhibit free rotational motion as indicated by electron spin resonance rotational correlation times 132-134) These studies using nitroxide spin labels covalently bound to polystyrene matrices indicated that the mobility of the substituent is a function of the cross-link density and degree of swelling. The rotational correlation time of nitroxide within 2% cross-linked beads was about 100 times shorter in dichloromethane or benzene than in ethanol, and 2-3 times longer than nitroxide bound to non-cross-linked polystyrene. The latter observation shows that the heterogeneous reaction involving 2% cross-linked polystyrene is 2-3 times slower than the same reaction in solution. 

Special techniques in surface science to study molecular motion in adsorbed layers are a problem that has found little attention in surface science, even though it is of utmost importance. Electron spin resonance is one such method. We discuss diffusion of NO2, rotational motion of ((CH3)3C)2NO and melting of self-assembled layers of spin-labeled fatty acids adsorbed on Al203(0001). 

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