Morphological and structural changes of commercial-brand low-density polyethylene induced by thermal aging for different times at different temperatures are studied by compact 1 H NMR relaxation, FTIR spectroscopy, and SEC including the impact of wax content. Two regimes were observed. The changes in phase composition and relaxation time suggest that thermally induced crystallization is predominant during aging and oxidation of LDPE below 100 8C while, after 28 d aging at 100 8C, oxidative degradation is predominant. This is in good agreement with carbonyl index and molecular weight variations evaluated by FTIR and SEC, respectively, which indicate multi-stage oxidation during aging.

The properties of plasticized poly(vinyl chloride) (PVC) , one of the most important polymers today, are strongly dictated by the concentration of plasticizer. Yet, it has been impossible to quantify this concentration at different positions inside a PVC product without its destruction because of a lack of suitable analytical methods. Thus, this paper introduces a simple, fast, and efficient way to determine truly nondestructively the concentration of plasticizer in PVC by single-sided nuclear magnetic resonance (NMR). With the help of correlation curves between the concentration of plasticizer inside nonaged PVC samples and the corresponding volume-averaged NMR parameters, single-sided NMR allows the quantification of the local concentration of plasticizer in aged PVC plates at different depths by spatially resolved relaxation measurements. The presented approach represents a fundamental step toward in situ characterization of plasticized PVC.

A simple and fast way to measure proton self-diffusion coefficients of small penetrant molecules in semicrystalline polymers is introduced. The approach takes advantage of the strong static gradient of a mobile single-sided NMR sensor and it is demonstrated on PE samples with varying degrees of crystallinity fully saturated in either toluene or n-hexane. The self-diffusion coefficients were measured using the gradient stimulated echo sequence appended with a CPMG. It is also shown for the first time, with demonstration on PE plates several millimeter thick with different aging histories, that one-dimensional profiles of self-diffusion coefficients as a function of depth can be easily obtained.

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