LAUSR

Abstract The aging behavior of a series of polypropylene random copolymer (PP-RCP) reactor powder samples was studied by NMR relaxometry, a.k.a. Industrial Magnetic Resonance (IMR). The samples, which had been stored for two years since polymerization, were heated for 20 min at 120 °C to mimic the morphology of freshly polymerized samples, then cooled down and stored at ambient temperature for one month during which NMR experiments were conducted to observe the morphological changes. Sixteen PP-RCP samples with a wide range of compositions were found to follow a rather consistent trend. For most samples, crystallinity increased during aging, at the expense of the amorphous population, while the interfacial population remained mostly unchanged. In the meantime, the segmental mobility of the interfacial phase steadily decreased. A strong correlation was found between the population of the amorphous component and the T2 relaxation time of the interfacial component, the precise mechanism of which is unknown. The likely mechanism of the morphological change during ambient temperature aging is secondary crystallization of the γ form on the lateral surface of the scaffold crystallites.