A PARAMAGNETIC-RESONANCE STUDY OF THE MOLECULAR MOTIONS OF SPIN PROBES DISSOLVED IN POLY(VINYL ACETATE)

The molecular motions of two spin nitroxide probes of vastly different geometries dissolved in poly(vinyl acetate) have been studied over a large temperature range. The smaller spherical probe's motion follows the main glass relaxation at higher temperatures and the gamma-transition at lower temperatures. Its small size allows it to occupy multiple sites as indicated by the observed spectra. The larger probe appears to occupy a single type of site. Its motion follows the main relaxation at higher temperatures and appears to abruptly jump to the beta-relaxation at approximately 330 K.