The effect of degassing on the measurement of transverse relaxation times in molten polymers
β Scribed by Tim Bremner; Alfred Rudin
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 825 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0887-6266
No coin nor oath required. For personal study only.
β¦ Synopsis
Three commercially produced polymer samples (polyethylene, polypropylene, and polystyrene) have been analyzed in the melt state using proton nuclear magnetic resonance (NMR) T2 relaxation methods using the Carr-Purcell-Meiboom-Gill (CPMG) spin-echo pulse sequence. Samples were run with exposure to air and again after extensive degassing a t a vacuum of mmHg for periods of not less than 96 h. The comparison is made by initially considering the presence of microscopic voids in the samples as a source of local field inhomogeneity and how they affect the T2 relaxation behavior. For PP and PS samples, degassing caused a decrease in all T, time constants associated with the multicomponent decays. The component intensities each of the time constants was also significantly altered. For the P E sample, degassing caused a decrease in the time constants associated with the amorphous material in the molten polymer. Examination of the fastest relaxing component of the three component decay showed approximate invariance in the T2 decay constant. This result supports our previously reported model in which that fast relaxing component is attributable to regions of local order or high segmental density within the molten polyethylene, a remnant of the crystalline material which exists in the premelting bulk polymer. The results of this research are of particular significance to those who wish to use this NMR technique as a quantitative method of determination of NMR distinct morphological regions within heterogeneous polymers.
π SIMILAR VOLUMES
The effect of fructose loading on high-energy phosphates in the jejunum, ileum, and large intestine ofrats was studied using "P NMR. Following fructose loading, an increase in the intensity of the PME resonance was observed in the jejunum, indicating an accumulation of fructose-I-phosphate. There we
## Abstract Previous modeling studies have predicted that a significant fraction of the signal in arterial spin labeling (ASL) experiments originates from labeled water in the capillaries. Provided that the relaxation times in blood and tissue are similar, ASL data can still be analyzed with the co
Various strategies are described and compared for measurement of one-bond J(NH) and J(NC') splittings in larger proteins. In order to evaluate the inherent resolution obtainable in the various experiments, relaxation rates of (15)N-(1)H(N) coupled and heteronuclear decoupled resonances were measured
## Abstract The addition of iodine to pyridine not only causes appreciable changes in the ^13^C chemical shifts but also a marked reduction in spinβlattice relaxation times. The effect at the Ξ³βcarbon is larger than at the Ξ±β and Ξ²βcarbons. This is consistent with the formation of a pyridineβiodine