CHARACTERIZATION OF THE MOTION OF SPIN PROBES AND SPIN LABELS IN AMORPHOUS POLYMERS WITH 2-DIMENSIONAL FIELD-STEP ELDOR

The motion of nitroxide spin probes and spin labels in amorphous polym ers is studied below the glass transition temperature with a two-dimen sional pulsed electron double-resonance experiment. Polystyrene and a liquid crystalline side group polymer are studied using both spin prob es and spin labels covalently bound to specific sites along the polyme r chain. Two methyl acrylic polymers differing only in their side grou p structure and polyvinylacetate are compared and large differences in the molecular dynamics deduced from both the nuclear and the electron spin relaxation rates are observed as the glass transition is approac hed. The results demonstrate the complexity of small amplitude motion in simple polymers below the glass transition temperature and show tha t it is very sensitive to the packing in the polymer. (C) 1996 John Wi ley & Sons, Inc.