ISSN:
0887-6266
Keywords:
polyethylene
;
crystalline
;
intermediate
;
amorphous
;
proton NMR
;
rotating frame
;
2D time-domain analysis
;
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
With two-dimensional time-domain NMR analysis in the proton spin rotating frame, three phases are identifiable in the solid polyethylene. The major proton magnetization fraction is due to the polymer's crystalline region, where the motion is least isotropic and slowest. A magnetization fraction with intermediate relaxation rate is also intermediate in magnitude. This component is proposed to comprise chain loops on the surfaces of crystallites and effectively entangled chain segments. The most mobile fraction, which is most liquid-like with a T2 of near 1 ms at 120°C, is also the smallest. It is proposed that it is due to polymer chains in the amorphous phase. In the crystalline phase the chain motion is an unexpectedly effective relaxation mechanism at ∼50 KHz. This process, which involves propagation of a twisted region along the crystallite, as has been suggested before, is either not present in the other two phases of the HDPE or is less efficient because of the lower polymer density. The activation energies for the crystalline, intermediate and amorphous phases are estimated to be 34 ± 3, 13 ± 3, and 8 ± 2 Kcal/mol, respectively. The frequencies of the relaxation process at 120°C are 43 KHz, 350 KHz, and 1.5 MHz, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2551-2558, 1997
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
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