| Abstract: | 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 at a vacuum of 10−4 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 T2 time constants associated with the multicomponent decays. The component intensities each of the time constants was also significantly altered. For the PE 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. © 1996 John Wiley & Sons, Inc. |
