Crystallinity in Ethene−1-Hexene Copolymers Determined by 1H and 13C NMR. A Comparative Study

The 13 C 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 all-trans 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 trans-gauche conformations. The crystallinity of the samples, as determined by DSC, was found to be in excellent agreement with the crystallinity determined from 13 C DD-MAS spectra. Moreover, the crystalline part of the 1 H-FID (acquired at 0.5 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 13 C 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.