STUDIES OF MAGNETIC-RESONANCE PHENOMENA IN POLYMERS .1. THE EFFECTS OF FREE-VOLUME AND SEGMENTAL MOBILITY ON THE MOTION OF NITROXIDE SPIN PROBES AND LABELS IN POLY(METHYL METHACRYLATE)

In the reported experiments, thin films of spin-probed and spin-labeled poly(methyl methacrylate) (PMMA) have been examined by electron spin resonance (ESR) at X-band frequency (9. 2 GHz) and at various temperatures. Direct spectral evidence is presented to indicate that the composite ESR spectra observed in a certain temperature range originate from two states of distinctly different mobility, one with slow motions corresponding to a glassy state and the other with fast motions corresponding to a liquidlike state. The coexistence of these two states at temperatures considerably below the glass transition temperature can be explained as a result of the effect of free volume in a solid polymeric glass.