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Crystallinity in ethylene-1-hexene copolymers determined by 1H- and 13C NMR in a comparative study

Crystallinity in ethylene-1-hexene copolymers determined by 1H- and 13C NMR in a comparative study

Kategori
Vitenskapelig artikkel
Sammendrag
The 13C DD-MAS spectra of six ethene/1-hexene (E/H) copolymers were fitted simultaneously to a sum of four pseudo Voigt functions in which two were assigned to the alltrans crystalline region. These two peaks possessed the same chemical shift but differed in both line width and line shape. Regarding the amorphous region, it was found to be represented by a sum of a Lorenzian function and a Gaussian function possessing different chemical shifts. The latter simply reflects the asymmetry of the spatial distribution of transgauche conformations. The crystallinity of the samples, as determined by DSC, was found to be in excellent agreement with the crystallinity determined from 13C DD-MAS spectra. Moreover, the crystalline part of the 1H-FID (acquired at 0.5 T and 4.7 T) was fitted by using a Pake function and Abragamian function, respectively. The latter was found to give a crystallinity in quantitative agreement with the 13C DD-MAS and DSC. In contrast, the replacement of the Abragamian function with a Pake function (to represent the crystalline part of the FID) resulted often in unstable and poor model fits with rather unreliable estimate of the crystallinity. The inherent problem related to the necessary blanking of the receiver during the initial part of the FID (dead-time) is discussed.
Språk
Engelsk
Institusjon(er)
  • SINTEF Industri / Materialer og nanoteknologi
År
2009
Publisert i
Macromolecules
ISSN
0024-9297
Årgang
42