Continuous Flow Hyperpolarized129Xe NMR for Studying Porous Polymers and Blends

Abstract

Hyperpolarized (HP) 129Xe NMR spectroscopy has been applied to high-impact porous polymers and copolymers obtained by the latest generation supported Ziegler−Natta catalysts. Hyperpolarized xenon gas rapidly flows into the open cavities and then penetrates the amorphous phases of polypropylene (PP) and ethylene−propylene copolymer (EPR) millimeter particles. Variable temperature HP 129Xe NMR demonstrated that xenon uptake is largely modulated by the motional state of the phases and is considerably reduced if glass transition is approached because the polymeric matrix becomes impermeable to the gas phase. This is an alternative method to detect the occurrence of the glass transition even in polymeric complex systems. The competitive absorption of xenon in PP and EPR microphases shows the morphology of the particles and the phase architecture. The intermixing of the phases at micrometer level was established on the basis of the xenon diffusion rates. 2D 129Xe EXSY experiments disclose the freshly polarized xenon exchange pathways from the free gas to the EPR phase and, later on, between the polymeric phases.