Xenon self-diffusion in organic polymers by pulsed field gradient NMR spectroscopy

Xenon self-diffusion coefficients of commercially available organic polymers have been determined by application of pulsed field gradient (PFG) NMR spectroscopy. Xenon diffusion in the elastomeric terpolymer ethylene-propylene-diene (EPDM) was found to be about 20 times faster than in the more rigid semi-crystalline poly(propylene) (PP). In a polymer blend of both materials consisting of 80% PP and 20% EPDM both diffusion coefficients are in the same range and between the values of the pure materials. As SEM pictures show, this incompatible blend consists of small EPDM domains (1-3 mu m) within the PP matrix. The root mean square displacement of xenon within the time interval of the PFG NMR experiment is greater than the domain sizes of EPDM. These results also evidence that xenon in this blend is mainly absorbed in EPDM domains and in the PP matrix near the PP/EPDM interface.